Tuesday.
1406.7431
Luminous blue variables are antisocial: their isolation implies that they are kicked mass gainers in binary evolution
Smith, Tombleson
Based on their relatively isolated environments, argue that LBVs must be primarily the product of binary evolution, challenging the traditional single-star view wherein LBVs mark a brief transition between massive O stars and WR stars. If the latter were true, then LBVs should be concentrated in young clusters and found alongside MS stars with similarly high inferred initial mass. This is decidedly not the case. Examining locations of LBVs compared to O stars in our Galaxy and the Magellanic Clouds reveals that LBVs systematically avoid clusters of O stars, and many reside over 100 pc from any O star. In the LMC, LBVs are statistically much more isolated than O-type stars, and (perhaps most surprisingly) even more isolated than most WR stars. This makes it impossible for LBVs to be massive stars in transition to WR stars. Instead, propose that massive stars and SN subtypes are dominated by bifurcated evolutionary paths in interacting binaries, wherein most WR stars and SNeIbc correspond to the mass donors, while LBVs ( and their lower-mass analogs like B[e] supergiants, which is shown to be even more isolated) are the mass gainers. LBVs are essentially the late evolutionary stage of massive blue stragglers. Through binary mass transfer, rejuvenated mass gainers get enriched, spun up, and sometimes kicked far from their clustered birth sites by their companion's SN. This scenario agrees better with LBVs exploding as SNeIIn and the observed isolation of SNe~IIn and SN impostors. Argue that environmental trends of various SN subtypes are influenced more by binary and SN kicks, rather than tracing initial mass as is generally assumed. Mergers of Throne-Zykow objects also give rise to LBVs, but these scenarios may have a harder time explaining why LBVs avoid clusters.
1406.7536
Estimating the distribution of galaxy morphologies on a continuous space
Vinci, Freeman, Neewman, Wasserman, Genovese
The incredible variety of galaxy shapes cannot be summarized by human defined discrete classes of shapes without causing a possibly large loss of information. Dictionary learning and sparse coding allow reduction of the high dimensional space of shapes into a manageable low dimensional continuous vector space. Statistical inference can be done in the reduced space via probability distribution estimation and manifold estimation.
1406.7714
The origin of galactic cosmic rays
Amato
Initial discovery of CRs dates back to a century ago (1912). Their identification as particles rather than radiation dates to about 20 years later and in 20 more years also the first suggestion that they were associated with SNRs was in place. The basic mechanism behind their acceleration was suggested almost 40 years ago. Much work has been done wince then to the aim of proving that both the acceleration mechanism and site are well understood, but no definite proof has been obtained: in spite of impressive progress of both theory and observations, the evidence in support of the commonly accepted interpretation is only circumstantial. In this paper, make the point on where we stand in terms of how the theories confront with data: review recent progress on the subject and try to point to avenues to pursue in order to farther new proofs, if not smoking gun evidence of the origin of Galactic Cosmic Rays.
Monday, June 30, 2014
Sunday, June 29, 2014
Day 688
Monday.
1406.7003
The most metal-poor damped Lyman alpha systems: an insight into dwarf galaxies at high redshift
Cooke, Pettini, Jorgenson
Analyze the kinematics, chemistry, and physical properties of a sample of the most metal-poor damped Lyman alpha systems (DLAs), to uncover their links to modern-day galaxies. Present evidence that the DLA population as a whole exhibits a 'knee' in the relative abundances of the alpha-capture and Fe-peakelements when the metallicity is [Fe/H]~-2.0. In this respect, the chemical evolution of DLAs is clearly different form that experienced by MW halo stars, but resembles that of dwarf spheroidal galaxies in the Local Group. Also find a close correspondence between the kinematics of LG dwarf galaxies and of high z metal-poor DLAs, which further strengthens this connection. On the basis of such similarities, propose that the most metal-poor DLAs provide the unique opportunity to directly study the dwarf galaxy population more than 10B years in the past, at a time when many dwarf galaxies were forming the bulk of their stars. To this end, measure some f the key physical properties of the DLA gas, including their neutral gas mass, size, kinetic temperature, density, and turbulence. Find that metal-poor DLAs mostly consist of a warm neutral medium with T_gas~9600K predominantly held up by thermal pressure. All of the DLAs in the sample exhibit a subsonic turbulent Mach number, implying that the gas distribution is largely smooth. These results are among the first empirical descriptions of the environments where the first few generation of stars may have formed in the universe.
1406.7284
Exploring the diffuse interstellar bands with the Sloan Digital Sky Survey
Lan, Ménard, Zhu
Use star, galaxy, and quasar spectra in SDSS to map out the distribution of diffuse interstellar bands (DIBs) induced by the MW. Show that, after carefully removing the intrinsic SED of each source, it is possible to measure statistical flux fluctuations at the 1e-3 level, detect about thirty DIBs and measure their strength as a function of position on the sky. Create a map of DIB absorption covering about 5000 sq deg and measure correlations with various tracers of the ISM: atomic & molecular H, dust and PAHs. After recovering known correlations, show that each DIB has a different dependence on atomic and molecular H: while they are all positively correlated with N(HI), they exhibit a range of behaviors with N(H2) showing positive, negative or no correlation. Show that a simple parameterization involving only N(HI) and N(H2) applied to all the DIBs is sufficient to reproduce a large collection of observational results reported in the literature: it allows a natural description of the relations between DIB strength and dust reddening (including the so-called skin effect), the related scatter, DIB pair-wise correlations & families, the affinity for a sigma/zeta-type environments and other correlations related to molecules. This approach allows characterization of DIB dependencies in a simple manner and provides a metric to characterize the similarities between different DIBs.
1406.7003
The most metal-poor damped Lyman alpha systems: an insight into dwarf galaxies at high redshift
Cooke, Pettini, Jorgenson
Analyze the kinematics, chemistry, and physical properties of a sample of the most metal-poor damped Lyman alpha systems (DLAs), to uncover their links to modern-day galaxies. Present evidence that the DLA population as a whole exhibits a 'knee' in the relative abundances of the alpha-capture and Fe-peakelements when the metallicity is [Fe/H]~-2.0. In this respect, the chemical evolution of DLAs is clearly different form that experienced by MW halo stars, but resembles that of dwarf spheroidal galaxies in the Local Group. Also find a close correspondence between the kinematics of LG dwarf galaxies and of high z metal-poor DLAs, which further strengthens this connection. On the basis of such similarities, propose that the most metal-poor DLAs provide the unique opportunity to directly study the dwarf galaxy population more than 10B years in the past, at a time when many dwarf galaxies were forming the bulk of their stars. To this end, measure some f the key physical properties of the DLA gas, including their neutral gas mass, size, kinetic temperature, density, and turbulence. Find that metal-poor DLAs mostly consist of a warm neutral medium with T_gas~9600K predominantly held up by thermal pressure. All of the DLAs in the sample exhibit a subsonic turbulent Mach number, implying that the gas distribution is largely smooth. These results are among the first empirical descriptions of the environments where the first few generation of stars may have formed in the universe.
1406.7284
Exploring the diffuse interstellar bands with the Sloan Digital Sky Survey
Lan, Ménard, Zhu
Use star, galaxy, and quasar spectra in SDSS to map out the distribution of diffuse interstellar bands (DIBs) induced by the MW. Show that, after carefully removing the intrinsic SED of each source, it is possible to measure statistical flux fluctuations at the 1e-3 level, detect about thirty DIBs and measure their strength as a function of position on the sky. Create a map of DIB absorption covering about 5000 sq deg and measure correlations with various tracers of the ISM: atomic & molecular H, dust and PAHs. After recovering known correlations, show that each DIB has a different dependence on atomic and molecular H: while they are all positively correlated with N(HI), they exhibit a range of behaviors with N(H2) showing positive, negative or no correlation. Show that a simple parameterization involving only N(HI) and N(H2) applied to all the DIBs is sufficient to reproduce a large collection of observational results reported in the literature: it allows a natural description of the relations between DIB strength and dust reddening (including the so-called skin effect), the related scatter, DIB pair-wise correlations & families, the affinity for a sigma/zeta-type environments and other correlations related to molecules. This approach allows characterization of DIB dependencies in a simple manner and provides a metric to characterize the similarities between different DIBs.
Thursday, June 26, 2014
Day 687
Friday.
1406.6692
The VIMOS public extragalactic redshift survey (VIPERS). Measuring nonlinear galaxy bias at z~0.8
Di Porto, Branchini, ... et al
Use the first release of VIPERS of ~50k objects to measure the biasing relation between galaxies and mass in 0.5<z<1.1. Estimate the PDF of VIPERS galaxies from counts in cells and, assuming a model for the mass PDF, infer their mean bias relation. The reconstruction of the bias relation from PDFs is performed through a novel method that accounts for Poisson noise, redshift distortions, inhomogeneous sky coverage and other selection effects. With this procedure, constrain galaxy bias and its deviations from linearity down to scales as small as 4 Mpc/h and out to z=1.1. Detect small (~3%) but significant deviations from linear bias. The mean biasing function is close to linear in regions above the mean density. The mean slope of the biasing relation is a proxy to the linear bias parameter. It increases both with luminosity, in agreement with results of previous analyses, and with redshift. However, detect a strong bias evolution only for z>0.9 in agreement with some, but not all, previous studies. Also detected a significant increase of the bias with the scale, from 4 to 8 Mpc/h, now seen for the first time out to z=1. The amplitude of NL depends on redshift, luminosity and on scales but no clear tree is detected. Thanks to the large cosmic volume probed by VIPERS, find that the mismatch between the previous estimates of bias at z~1 from zCOSMOS and VVDS-Deep samples is fully accounted for by cosmic variance. The results of the work confirm the importance of going beyond the over-simplistic linear bias hypothesis showing that NLs can be accurately measured through the applications of the appropriate statistical tools to existing datasets like VIPERS.
1406.6762
Constraining dust formation in high-redshift young galaxies
Hirashita, Ferrara, Dayal, Ouchi
Core-collapse SNe are believed to be the first significant source of dust in the Universe. Such SNe are expected to be the main dust producers in young high-z LAEs given their young ages, providing an excellent testbed of SN dust formation models during the early stages of galaxy evolution. Focus on the dust enrichment of a specific, luminous LAE (Himiko, z~6.6) for which a stringent upper limit of 52.1 uJy (3sigma) has recently been obtained from ALMA continuum observations at 1.2 mm. Predict its sub millimeter dust emission using detailed models that follow SN dust enrichment and destruction and the equilibrium dust temperature, and obtain a plausible upper limit to the dust mass produced by a single SN: m_d,SN<0.15-0.45 Msun, depending on the adopted dust optical properties. These upper limits are smaller than the dust mass deduced for SN1987A and that predicted by dust condensation theories, implying that dust produced in SNe are likely to be subject to reverse shock destruction before being injected into the ISM. Finally, provide a recipe for deriving m_d,SN from sub millimeter observations of young, metal poor objects wherein condensation in SN ejecta is the dominant dust formation channel.
1406.6692
The VIMOS public extragalactic redshift survey (VIPERS). Measuring nonlinear galaxy bias at z~0.8
Di Porto, Branchini, ... et al
Use the first release of VIPERS of ~50k objects to measure the biasing relation between galaxies and mass in 0.5<z<1.1. Estimate the PDF of VIPERS galaxies from counts in cells and, assuming a model for the mass PDF, infer their mean bias relation. The reconstruction of the bias relation from PDFs is performed through a novel method that accounts for Poisson noise, redshift distortions, inhomogeneous sky coverage and other selection effects. With this procedure, constrain galaxy bias and its deviations from linearity down to scales as small as 4 Mpc/h and out to z=1.1. Detect small (~3%) but significant deviations from linear bias. The mean biasing function is close to linear in regions above the mean density. The mean slope of the biasing relation is a proxy to the linear bias parameter. It increases both with luminosity, in agreement with results of previous analyses, and with redshift. However, detect a strong bias evolution only for z>0.9 in agreement with some, but not all, previous studies. Also detected a significant increase of the bias with the scale, from 4 to 8 Mpc/h, now seen for the first time out to z=1. The amplitude of NL depends on redshift, luminosity and on scales but no clear tree is detected. Thanks to the large cosmic volume probed by VIPERS, find that the mismatch between the previous estimates of bias at z~1 from zCOSMOS and VVDS-Deep samples is fully accounted for by cosmic variance. The results of the work confirm the importance of going beyond the over-simplistic linear bias hypothesis showing that NLs can be accurately measured through the applications of the appropriate statistical tools to existing datasets like VIPERS.
1406.6762
Constraining dust formation in high-redshift young galaxies
Hirashita, Ferrara, Dayal, Ouchi
Core-collapse SNe are believed to be the first significant source of dust in the Universe. Such SNe are expected to be the main dust producers in young high-z LAEs given their young ages, providing an excellent testbed of SN dust formation models during the early stages of galaxy evolution. Focus on the dust enrichment of a specific, luminous LAE (Himiko, z~6.6) for which a stringent upper limit of 52.1 uJy (3sigma) has recently been obtained from ALMA continuum observations at 1.2 mm. Predict its sub millimeter dust emission using detailed models that follow SN dust enrichment and destruction and the equilibrium dust temperature, and obtain a plausible upper limit to the dust mass produced by a single SN: m_d,SN<0.15-0.45 Msun, depending on the adopted dust optical properties. These upper limits are smaller than the dust mass deduced for SN1987A and that predicted by dust condensation theories, implying that dust produced in SNe are likely to be subject to reverse shock destruction before being injected into the ISM. Finally, provide a recipe for deriving m_d,SN from sub millimeter observations of young, metal poor objects wherein condensation in SN ejecta is the dominant dust formation channel.
Day 686
Thursday.
1406.6361
The Lyman-$\alpha$ forest in optically-thin hydrodynamical simulations
Lukic, Stark, Nugent, White, Meiksin, Almgren
Study the statistics of the Lya forest in flat LCDM cosmology with N-body+Eulerian hydrodynamics code Nyx. Produce a suite of simulations, covering the observationally relevant redshift range 2<z<4. Find that a grid resolution of 20 kpc/h is required to produce 1% convergence of Lya flux statistics, up to k=10 h/Mpc. In addition to establishing resolution requirements, study the effects of missing modes in these simulations, and find that box sizes of L>40 Mpc/h are needed to suppress numerical errors to a sub-percent level. This optically-thin simulations with the ionizing background prescription of Haardt&Madau(2012) reproduce an IGM equation of state with T0~1e4K and gamma~1.55 at z=2, with a mean transmitted flux close to the observed values. When using the ionizing background prescription of Faucher-Giguere+(2009), the mean flux is 10-15% below observed values at z=2, and a factor of 2 too small at z=4. Show the effects of the common practice of rescaling optical depths to the observed mean flux and how it affects convergence rates. Also investigate the common practice of 'splicing' results from a number of different simulations to estimate the 1d flux PS and show it is accurate at the 10% level. Finally, find that collisional heating of the gas from DM particles is negligible in modern cosmo sims.
1406.6362
The chosen few: the low mass halos that host faint galaxies
Sawala, Frenk, Fattahi, Navarro, Theuns, Bower, .. et al
Since reionization prevents SF in most haloes below 3e9 Msun, dwarf galaxies only populate a fraction of existing DM haloes. Use hydro cosmo sims on the Local Group to study the discriminating factors for galaxy formation in the early Universe and connect them to the present-day properties of galaxies and haloes. A combination of selection effects related to reionization, and the subsequent evolution of haloes in different environments, introduces strong biases between the population of haloes that host dwarf galaxies, and the total halo population. Haloes that host galaxies formed earlier and are more concentrated. In addition, haloes more affected by tidal stripping are more likely to host a galaxy for a given mass or maximum circular velocity, vmax, today. Consequently, satellite haloes are populated more frequently than field halos, and satellite haloes of 1e8-9 Msun or vmax of 12-20 km/s, similar to the LG dwarf spheroidals, have experienced a greater than average reduction in both mass and vmax after infall. They are on closer, more radial orbits with higher infall velocities and earlier infall times. Together, these effects make dwarf galaxies highly biased tracers of the underlying DM distribution.
1406.6361
The Lyman-$\alpha$ forest in optically-thin hydrodynamical simulations
Lukic, Stark, Nugent, White, Meiksin, Almgren
Study the statistics of the Lya forest in flat LCDM cosmology with N-body+Eulerian hydrodynamics code Nyx. Produce a suite of simulations, covering the observationally relevant redshift range 2<z<4. Find that a grid resolution of 20 kpc/h is required to produce 1% convergence of Lya flux statistics, up to k=10 h/Mpc. In addition to establishing resolution requirements, study the effects of missing modes in these simulations, and find that box sizes of L>40 Mpc/h are needed to suppress numerical errors to a sub-percent level. This optically-thin simulations with the ionizing background prescription of Haardt&Madau(2012) reproduce an IGM equation of state with T0~1e4K and gamma~1.55 at z=2, with a mean transmitted flux close to the observed values. When using the ionizing background prescription of Faucher-Giguere+(2009), the mean flux is 10-15% below observed values at z=2, and a factor of 2 too small at z=4. Show the effects of the common practice of rescaling optical depths to the observed mean flux and how it affects convergence rates. Also investigate the common practice of 'splicing' results from a number of different simulations to estimate the 1d flux PS and show it is accurate at the 10% level. Finally, find that collisional heating of the gas from DM particles is negligible in modern cosmo sims.
1406.6362
The chosen few: the low mass halos that host faint galaxies
Sawala, Frenk, Fattahi, Navarro, Theuns, Bower, .. et al
Since reionization prevents SF in most haloes below 3e9 Msun, dwarf galaxies only populate a fraction of existing DM haloes. Use hydro cosmo sims on the Local Group to study the discriminating factors for galaxy formation in the early Universe and connect them to the present-day properties of galaxies and haloes. A combination of selection effects related to reionization, and the subsequent evolution of haloes in different environments, introduces strong biases between the population of haloes that host dwarf galaxies, and the total halo population. Haloes that host galaxies formed earlier and are more concentrated. In addition, haloes more affected by tidal stripping are more likely to host a galaxy for a given mass or maximum circular velocity, vmax, today. Consequently, satellite haloes are populated more frequently than field halos, and satellite haloes of 1e8-9 Msun or vmax of 12-20 km/s, similar to the LG dwarf spheroidals, have experienced a greater than average reduction in both mass and vmax after infall. They are on closer, more radial orbits with higher infall velocities and earlier infall times. Together, these effects make dwarf galaxies highly biased tracers of the underlying DM distribution.
Tuesday, June 24, 2014
Day 685
Wednesday.
1406.6056
The distribution of satellites around massive galaxies at 1<z<3 in ZFOURGE/CANDELS: dependence on star formation activity
Kawinwanichakij, et al
Deep NIR data select satellites down to log(M/Msun)>9 at z<3. The radial satellite distribution around centrals is consistent with a projected NFW profiles. Massive quiescent centrals have ~2x the number of satellites compared to SF centrals with a significance of 2.7 sigma even after accounting for differences in the centrals' stellar-mass distributions. Find no statistical difference in the satellite distributions of intermediate-mass quiescent and SF centrals (10.48-10.78 for log(M/Msun)). Comparing to the Guo2011 SAM, the excess number of satellites indicates that quiescent centrals have halo masses 0.3 dex larger than SF centrals, even when the stellar-mass distributions are fixed. Use a simple toy model that relates halo mass and quenching, which roughly reproduces the observed quenched fractions and the differences in halo mass between SF and quenched galaxies only if galaxies have a quenching probability that increases with halo mass from ~0 for log (Mh/Msun)~11 to ~1 for log(Mh/Msun)~13.5. A single halo-mass quenching threshold is unable to reproduce the quiescent fraction and satellite distribution of centrals. Therefore, while halo quenching may be an important mechanism, it is unlikely to be the only factor driving quenching. It remains unclear why a high fraction of centrals remain star-forming even in relatively massive haloes.
1406.6062
Co-orbiting planes of sub-aloes are similarly unlikely around paired and isolated hosts
Pawlowski, McGaugh
Sub-haloes in DM cosmo sims tend to be distributed approximately isotropically around their host; the observed VPOS (vast polar structure) of satellites around MW and M31 is a possible problem for cosmo models. Perhaps the pair is an environmental consideration. Search for VPOS analogs in the ELVIS suite of cosmo sims, which consists of 24 paired and 24 isolated host halos. Do not find significant differences between the properties of sub-halo distributions around paired and isolated hosts. The observed flattening and the observed orbital alignment are each reproduced by only 0.2 to 2% of paired and isolated systems incorporating the obscuration of satellites by randomly oriented galactic discs. Only one of all 4800 analyzed realizations (0.02%) reproduces both parameters simultaneously, but the average orbital pole of this sub-halo system does not align as well with the normal to the plane fit as observed. That the MW is part of a galaxy pair thus does not help in explaining the existence of the VPOS if the satellite galaxies are identified with sub-haloes found in dissipationless simulations.
1406.6152
Can one determine cosmological parameters from multi-plane strong lens systems?
Schneider
Strong gravitational lensing of sources with different redshifts has been used to determine cosmological distance ratios, which in turn depend on the expansion history. Hence, such systems are viewed as potential tools for constraining cosmological parameters. Show that in lens systems with two distance source redshifts, of which the nearest one contributes to the light deflection towards the more distant one, there exists and invariance transformation which leaves all SL observables unchanged (except the product of time delay and H0), generalizing the well-known mass-sheet transformation in single plane lens systems. The transformation preserves the relative distribution of mass and light, so that a 'mass-follows-light' assumption does not fix the MST [?]. All time delays (from sources on both planes) scale with the same factor -- time-delay ratios are therefore invariant under the MST. Changing cosmological parameters, and thus distance ratios, is essentially equivalent to such a mass-sheet transformation. As an example, discuss the double source plane system DSSSJ0946+1006, which has been recently studied gy Colett and Auger, and show that variations of cosmo params within reasonable ranges lead to only a small mass-sheet transformation in both lens planes. Hence the ability to extract cosmo information from such systems depends heavily on the ability to break the mass-sheet degeneracy.
1406.6056
The distribution of satellites around massive galaxies at 1<z<3 in ZFOURGE/CANDELS: dependence on star formation activity
Kawinwanichakij, et al
Deep NIR data select satellites down to log(M/Msun)>9 at z<3. The radial satellite distribution around centrals is consistent with a projected NFW profiles. Massive quiescent centrals have ~2x the number of satellites compared to SF centrals with a significance of 2.7 sigma even after accounting for differences in the centrals' stellar-mass distributions. Find no statistical difference in the satellite distributions of intermediate-mass quiescent and SF centrals (10.48-10.78 for log(M/Msun)). Comparing to the Guo2011 SAM, the excess number of satellites indicates that quiescent centrals have halo masses 0.3 dex larger than SF centrals, even when the stellar-mass distributions are fixed. Use a simple toy model that relates halo mass and quenching, which roughly reproduces the observed quenched fractions and the differences in halo mass between SF and quenched galaxies only if galaxies have a quenching probability that increases with halo mass from ~0 for log (Mh/Msun)~11 to ~1 for log(Mh/Msun)~13.5. A single halo-mass quenching threshold is unable to reproduce the quiescent fraction and satellite distribution of centrals. Therefore, while halo quenching may be an important mechanism, it is unlikely to be the only factor driving quenching. It remains unclear why a high fraction of centrals remain star-forming even in relatively massive haloes.
1406.6062
Co-orbiting planes of sub-aloes are similarly unlikely around paired and isolated hosts
Pawlowski, McGaugh
Sub-haloes in DM cosmo sims tend to be distributed approximately isotropically around their host; the observed VPOS (vast polar structure) of satellites around MW and M31 is a possible problem for cosmo models. Perhaps the pair is an environmental consideration. Search for VPOS analogs in the ELVIS suite of cosmo sims, which consists of 24 paired and 24 isolated host halos. Do not find significant differences between the properties of sub-halo distributions around paired and isolated hosts. The observed flattening and the observed orbital alignment are each reproduced by only 0.2 to 2% of paired and isolated systems incorporating the obscuration of satellites by randomly oriented galactic discs. Only one of all 4800 analyzed realizations (0.02%) reproduces both parameters simultaneously, but the average orbital pole of this sub-halo system does not align as well with the normal to the plane fit as observed. That the MW is part of a galaxy pair thus does not help in explaining the existence of the VPOS if the satellite galaxies are identified with sub-haloes found in dissipationless simulations.
1406.6152
Can one determine cosmological parameters from multi-plane strong lens systems?
Schneider
Strong gravitational lensing of sources with different redshifts has been used to determine cosmological distance ratios, which in turn depend on the expansion history. Hence, such systems are viewed as potential tools for constraining cosmological parameters. Show that in lens systems with two distance source redshifts, of which the nearest one contributes to the light deflection towards the more distant one, there exists and invariance transformation which leaves all SL observables unchanged (except the product of time delay and H0), generalizing the well-known mass-sheet transformation in single plane lens systems. The transformation preserves the relative distribution of mass and light, so that a 'mass-follows-light' assumption does not fix the MST [?]. All time delays (from sources on both planes) scale with the same factor -- time-delay ratios are therefore invariant under the MST. Changing cosmological parameters, and thus distance ratios, is essentially equivalent to such a mass-sheet transformation. As an example, discuss the double source plane system DSSSJ0946+1006, which has been recently studied gy Colett and Auger, and show that variations of cosmo params within reasonable ranges lead to only a small mass-sheet transformation in both lens planes. Hence the ability to extract cosmo information from such systems depends heavily on the ability to break the mass-sheet degeneracy.
Monday, June 23, 2014
Day 684
Tuesday.
1406.4908
Background sky observation by cluster galaxies as a a source of systematic error for weak lensing
Simet, Mandelbaum
Lensing magnification and stacked shear measurements of galaxy clusters rely on measuring the density of background galaxies behind the clusters. The most common ways of measuring this quantity ignore the fact that some fraction of the sky is obscured by the cluster galaxies themselves, reducing the area in which background galaxies can be observed. Discuss the size of this effecting the SDSS and CFHTLenS, finding a minimum 1 % effect at 0.1 Mpc/h from the centers of clusters in SDSS; the effect is an order of magnitude higher in CFHTLenS. The resulting biases on cluster mass and concentration measurements are of the same order as the size of the obscuration effect, which is below the statistical errors for cluster lensing in SDSS but likely exceeds them for CFHTLenS. Also forecast the impact of this systematic error on cluster mass and magnification measurements in several upcoming surveys, and find that it typically exceeds the statistical errors. Conclude that future surveys must account for this effect in stacked lensing and magnification measurements in order to avoid being dominated by systematic error.
1406.5509
Some stars are totally metal: a new mechanism driving dust across star-forming clouds, and consequences for planets, stars, and galaxies
Hopkins
Dust grains in neutral gas behave as aerodynamic particles, so the y can develop large local density fluctuations entirely independent of gas density fluctuations. Specifically, gas turbulence can drive order-of-magnitude 'resonant' fluctuations in the dust density on scales where the gas stopping/drag timescale is comparable to the turbulent eddy turnover time. Show that for large grains (>0.1 micron, containing most grain mass) in sufficiently large molecular clouds (>1-10pc, >1e4 Msun), this scale becomes longer than the characteristic sizes of pre-stellar cores (the sonic length), so large fluctuations in the dust-to-gas ratio are imprinted on cores. As a result, star clusters and protostellar disks formed in large clouds should exhibit substantial abundance spreads in the elements preferentially found in large grains (C, O, Si). This naturally predicts populations of carbon-enhanced stars, certain highly unusual stellar populations observed in nearby open clusters, and may explain the 'UV upturn' in early-type galaxies. It will also dramatically change planet formation in the resulting protostellar disks, by preferentially seeding disks with an enhancement in large carbonaceous or silicate grains. The relevant threshold for this behavior scales simply with cloud densities and temperatures, making straightforward predictions for clusters in starbursts and high-redshift galaxies. Because of the selected sorting by size, this process is not visible in extinction mapping. Also predict the shape of the abundance distribution. When these fluctuations occur, a small fraction of the cores are actually seeded with abundances Z~100 Z_mean, such that they are almost 'totally metal' (Z~1)! Assuming the cores collapse, these to ally metal stars would be rare (1 in 1e4 in clusters where this occurs), but represent a fundamentally new staler evolution channel.
1406.4908
Background sky observation by cluster galaxies as a a source of systematic error for weak lensing
Simet, Mandelbaum
Lensing magnification and stacked shear measurements of galaxy clusters rely on measuring the density of background galaxies behind the clusters. The most common ways of measuring this quantity ignore the fact that some fraction of the sky is obscured by the cluster galaxies themselves, reducing the area in which background galaxies can be observed. Discuss the size of this effecting the SDSS and CFHTLenS, finding a minimum 1 % effect at 0.1 Mpc/h from the centers of clusters in SDSS; the effect is an order of magnitude higher in CFHTLenS. The resulting biases on cluster mass and concentration measurements are of the same order as the size of the obscuration effect, which is below the statistical errors for cluster lensing in SDSS but likely exceeds them for CFHTLenS. Also forecast the impact of this systematic error on cluster mass and magnification measurements in several upcoming surveys, and find that it typically exceeds the statistical errors. Conclude that future surveys must account for this effect in stacked lensing and magnification measurements in order to avoid being dominated by systematic error.
1406.5509
Some stars are totally metal: a new mechanism driving dust across star-forming clouds, and consequences for planets, stars, and galaxies
Hopkins
Dust grains in neutral gas behave as aerodynamic particles, so the y can develop large local density fluctuations entirely independent of gas density fluctuations. Specifically, gas turbulence can drive order-of-magnitude 'resonant' fluctuations in the dust density on scales where the gas stopping/drag timescale is comparable to the turbulent eddy turnover time. Show that for large grains (>0.1 micron, containing most grain mass) in sufficiently large molecular clouds (>1-10pc, >1e4 Msun), this scale becomes longer than the characteristic sizes of pre-stellar cores (the sonic length), so large fluctuations in the dust-to-gas ratio are imprinted on cores. As a result, star clusters and protostellar disks formed in large clouds should exhibit substantial abundance spreads in the elements preferentially found in large grains (C, O, Si). This naturally predicts populations of carbon-enhanced stars, certain highly unusual stellar populations observed in nearby open clusters, and may explain the 'UV upturn' in early-type galaxies. It will also dramatically change planet formation in the resulting protostellar disks, by preferentially seeding disks with an enhancement in large carbonaceous or silicate grains. The relevant threshold for this behavior scales simply with cloud densities and temperatures, making straightforward predictions for clusters in starbursts and high-redshift galaxies. Because of the selected sorting by size, this process is not visible in extinction mapping. Also predict the shape of the abundance distribution. When these fluctuations occur, a small fraction of the cores are actually seeded with abundances Z~100 Z_mean, such that they are almost 'totally metal' (Z~1)! Assuming the cores collapse, these to ally metal stars would be rare (1 in 1e4 in clusters where this occurs), but represent a fundamentally new staler evolution channel.
Sunday, June 22, 2014
Day 683
Monday.
1406.5183
On the correlation between metallicity and the X-shaped morphology of the Milky Way bulge
Nataf et al
The trend of the X-shape being more pronounced among the more metal-rich stars may have been overestimated, as it is relatively easier to detect a bimodality in the distance distribution function at higher metallicities.
1406.5187
Kinematic evolution of simulated star-forming galaxies
Kassin et al
Recent observations have shown that SF galaxies like MW evolve kinematically into ordered thin disks over the last ~8B yrs since z=1.2, undergoing a process of "disk settling". For the first time, study the kinematic evolution of a suite of four state of the art "zoom in" hydro sims of galaxy formation and evolution n a fully cosmological context and compare with these observations. Until now, robust measurements of the internal kinematics of simulated galaxies were lacking as the simulations suffered from low resolution, overproduction of stars, and overly massive bulges. The current generation of simulations has made great progress in overcoming these difficulties and is ready for a kinematic analysis. Show that simulated galaxies follow the same kinematic trends as read galaxies: they progressively decrease in disordered motions (sigma_g) and increase in ordered rotation (Vrot) with time. The slopes of the relations between both sigma_g and Vrot with redshift are consistent between the simulations and the observations. In addition, the morphologies of the simulated galaxies become less disturbed with time, also consistent with observations, and they both have similarly large scatter. This match between the simulated and observed trends is a significant success for the current generation of simulations, and a first step in determining the physical processes behind disk settling.
1406.5196
Constraints on the alignment of galaxies in galaxy clusters from $\sim$15,000 spectroscopic members
Sifón, Hoekstra, Cacciato, Viola, et al
Torques acting on galaxies lead to physical alignments, but the resulting ellipticity correlations are difficult to predict. As they constitute a major contaminant for cosmic shear studies, it is important to constrain the IA signal observationally. Measure the alignments of satellite galaxies within 91 massive galaxy clusters in 0.05<z<0.55 and quantify their impact on the cosmic shear signal. Combine a sample of 38k galaxies with spec-z with ihg-quality data from CFHT. Use phase information to select 15k cluster members, 14k of which have shape measurements, and measure 3 different types of alignment: the radial alignment of satellite galaxies towards the BCGs, the common orientations of satellite galaxies and BCGs, and the radial alignments of satellites with each other. Residual systematic effects are much smaller than the statistical uncertainties. Detect no galaxy alignment of any kind out to at least 3r200. The signal is consistent with zero for both blue and red galaxies, bright and faint, and also for subsamples of clusters based on redshift, dynamical mass, and dynamical state. These conclusions are unchanged if the sample is increased with bright clusters members from the red sequence. Augment constraints with those from the literature to estimate the importance of the IA of satellites compared to that of central galaxies, for which the alignments are described by the linear alignment model. Find that the additional contribution from satellite can be ignored for current cosmic shear surveys such as KiDS, and that the linear alignment model is accurate enough to model IA for these surveys.
1406.5250
Alignments of the galaxies in and around the Virgo cluster with the local velocity shear
Lee, Rey, Kim
Observational evidence presented for the alignment between the cosmic sheet and the principal axis of the velocity shear field at the position of the Virgo cluster. The galaxies in and around the Virgo cluster from the Extended Virgo Cluster Catalog recently constructed by Kim+ are used to determine the direction of the local sheet. The peculiar velocity field reconstructed from the SDSS DR7 is analyzed to estimate the local velocity shear tensor at the Virgo center. Showing first that the minor principal axis of the local velocity shear tensor is almost parallel to the line of sight direction, detect a clear signal of alignment between the positions of the Virgo satellite and the intermediate principal axis of the local velocity shear projected onto the plane of the sky. Furthermore, the dwarf satellites are found to appear more strongly aligned than the normal counterparts, which is interpreted as indication of the following: (i) the normal and the dwarf satellites fall in the Virgo cluster preferentially along the local filament and the local sheet, respectively. (ii) the local filament is aligned with the minor principal axis of the local velocity shear while the local sheet is in parallel to the plane spanned by the minor and they intermediate principal axes. Result is consistent with the recent numerical claim that the velocity shear is a good tracer of the cosmic web.
1406.5459
Dependence of the cosmic microwave background lensing power spectrum on the matter density
Pan, Knox, White
Provide an analytic explanation of the matter in which the lensing of CMB anisotropies deneds on the matter density, finding that the dominant effete comes from the shape of the matter PS set by the decay of small-scale potentials between horizon crossing and matter-radiation equality.
1406.5183
On the correlation between metallicity and the X-shaped morphology of the Milky Way bulge
Nataf et al
The trend of the X-shape being more pronounced among the more metal-rich stars may have been overestimated, as it is relatively easier to detect a bimodality in the distance distribution function at higher metallicities.
1406.5187
Kinematic evolution of simulated star-forming galaxies
Kassin et al
Recent observations have shown that SF galaxies like MW evolve kinematically into ordered thin disks over the last ~8B yrs since z=1.2, undergoing a process of "disk settling". For the first time, study the kinematic evolution of a suite of four state of the art "zoom in" hydro sims of galaxy formation and evolution n a fully cosmological context and compare with these observations. Until now, robust measurements of the internal kinematics of simulated galaxies were lacking as the simulations suffered from low resolution, overproduction of stars, and overly massive bulges. The current generation of simulations has made great progress in overcoming these difficulties and is ready for a kinematic analysis. Show that simulated galaxies follow the same kinematic trends as read galaxies: they progressively decrease in disordered motions (sigma_g) and increase in ordered rotation (Vrot) with time. The slopes of the relations between both sigma_g and Vrot with redshift are consistent between the simulations and the observations. In addition, the morphologies of the simulated galaxies become less disturbed with time, also consistent with observations, and they both have similarly large scatter. This match between the simulated and observed trends is a significant success for the current generation of simulations, and a first step in determining the physical processes behind disk settling.
1406.5196
Constraints on the alignment of galaxies in galaxy clusters from $\sim$15,000 spectroscopic members
Sifón, Hoekstra, Cacciato, Viola, et al
Torques acting on galaxies lead to physical alignments, but the resulting ellipticity correlations are difficult to predict. As they constitute a major contaminant for cosmic shear studies, it is important to constrain the IA signal observationally. Measure the alignments of satellite galaxies within 91 massive galaxy clusters in 0.05<z<0.55 and quantify their impact on the cosmic shear signal. Combine a sample of 38k galaxies with spec-z with ihg-quality data from CFHT. Use phase information to select 15k cluster members, 14k of which have shape measurements, and measure 3 different types of alignment: the radial alignment of satellite galaxies towards the BCGs, the common orientations of satellite galaxies and BCGs, and the radial alignments of satellites with each other. Residual systematic effects are much smaller than the statistical uncertainties. Detect no galaxy alignment of any kind out to at least 3r200. The signal is consistent with zero for both blue and red galaxies, bright and faint, and also for subsamples of clusters based on redshift, dynamical mass, and dynamical state. These conclusions are unchanged if the sample is increased with bright clusters members from the red sequence. Augment constraints with those from the literature to estimate the importance of the IA of satellites compared to that of central galaxies, for which the alignments are described by the linear alignment model. Find that the additional contribution from satellite can be ignored for current cosmic shear surveys such as KiDS, and that the linear alignment model is accurate enough to model IA for these surveys.
1406.5250
Alignments of the galaxies in and around the Virgo cluster with the local velocity shear
Lee, Rey, Kim
Observational evidence presented for the alignment between the cosmic sheet and the principal axis of the velocity shear field at the position of the Virgo cluster. The galaxies in and around the Virgo cluster from the Extended Virgo Cluster Catalog recently constructed by Kim+ are used to determine the direction of the local sheet. The peculiar velocity field reconstructed from the SDSS DR7 is analyzed to estimate the local velocity shear tensor at the Virgo center. Showing first that the minor principal axis of the local velocity shear tensor is almost parallel to the line of sight direction, detect a clear signal of alignment between the positions of the Virgo satellite and the intermediate principal axis of the local velocity shear projected onto the plane of the sky. Furthermore, the dwarf satellites are found to appear more strongly aligned than the normal counterparts, which is interpreted as indication of the following: (i) the normal and the dwarf satellites fall in the Virgo cluster preferentially along the local filament and the local sheet, respectively. (ii) the local filament is aligned with the minor principal axis of the local velocity shear while the local sheet is in parallel to the plane spanned by the minor and they intermediate principal axes. Result is consistent with the recent numerical claim that the velocity shear is a good tracer of the cosmic web.
1406.5459
Dependence of the cosmic microwave background lensing power spectrum on the matter density
Pan, Knox, White
Provide an analytic explanation of the matter in which the lensing of CMB anisotropies deneds on the matter density, finding that the dominant effete comes from the shape of the matter PS set by the decay of small-scale potentials between horizon crossing and matter-radiation equality.
Thursday, June 19, 2014
Day 682
Thursday, Friday.
1406.4668
Intrinsic alignment of simulated galaxies in the cosmic web: implications for weak lensing surveys
Codis et al
The IA of galaxy shapes and their cross-correlation with the surrounding DM tidal field are investigated using the 1600k, z=1.2 synthetic galaxies extracted from the high-res cosmo hydro sim Horizon-AGN. One- and two-point statistics of the spin of the stellar component are measured as a function of mass and color. For the low-mass galaxies, this spin is locally aligned with the tidal field 'filamentary' direction while, for the high-mass galaxies, it is perpendicular to both filaments and walls. The bluest galaxies of the synthetic catalog are more strongly correlated with the surrounding tidal field than the reddest galaxies, and this correlation extends up to 10 Mpc/h comoving distance. Also report a correlation of the projected ellipticities of blue, intermediate mass galaxies on a similar scale at a level of 1e-4 which could be a concern for cosmic shear measurements. Do not report any measurable intrinsic alignments of the reddest galaxies in the sample. This work is a first step toward the use of very realistic catalog of synthetic galaxies to evaluate the contamination of WL measurement by IA.
1406.4728
Damping of glacial-interglacial cycles from anthropogenic forcing
Haqq-Misra
Climate variability over the past million years shows a strong glacial-interglacial cycle of ~100k years as a combined result of Milankovitch orbital forcing and climatic resonance. It has been suggested that anthropogenic contributions to radiative forcing may extend the length of the present interglacial, but the effects of anthropogenic forcing on the periodicity of glacial-interglacial cycles has received little attention. Demonstrate the moderate anthropogenic forcing can act to damp this 100k year cycle and reduce climate variability from orbital forcing. Future changes in solar insolation alone will continue to drive a 100k year climate cycle over the next million years, but the presence of anthropogenic warming can force the climate into an ice-free state that only weakly responds to orbital forcing. Sufficiently strong anthropogenic forcing that eliminate the glacial-interglacial cycle may serve as an indication of an epoch transition from the Pleistocene to the Anthropocene.
1406.4542
Computing and using metrics in the ADS
Henneken et al
"Discuss how the ADS can be used to quench the first for impact measures."
1406.4859
Herschel-Atlas and ALMA: HATLAS J142935.3-002836, a lensed major merger at redshift 1.027
Messias et al
A system comprising of a foreground edge-on disk galaxy (at z=0.218) with an almost complete Einstein ring around it. The background source (z=1.027) is magnified by a factor of ~8-10 depending on wavelength. It is comprised of two components and a tens of kpc long tidal tail resembling the Antennae merger. Utilized multi wavelength data.
1406.4871
Can weak lensing surveys confirm BICEP2?
Chisari, Dvorkin, Schmidt
The detection of B_modes in the CMB polarization by BICEP2, if interpreted as evidence for a primordial gravitational wave background, has enormous ramifications for cosmology and physics. It is crucial to test this hypothesis with independent measurements. A gravitational wave background leads to B-modes in galaxy shape correlations (shear) both through lensing and tidal alignment effects. Since the systematics and foregrounds of galaxy shapes and CMB polarization are entirely different, a detection of a cross-correlation between the two observables would provide conclusive proof for the existence of a primordial gravitational wave background. Find that upcoming weak lensing surveys will be able to detect the cross-correlation between B-modes of the CMB and galaxy shapes. However, this detection is not sufficient to confirm or falsify the hypothesis of a primordial origin for CMB B-mode polarization.
1406.4668
Intrinsic alignment of simulated galaxies in the cosmic web: implications for weak lensing surveys
Codis et al
The IA of galaxy shapes and their cross-correlation with the surrounding DM tidal field are investigated using the 1600k, z=1.2 synthetic galaxies extracted from the high-res cosmo hydro sim Horizon-AGN. One- and two-point statistics of the spin of the stellar component are measured as a function of mass and color. For the low-mass galaxies, this spin is locally aligned with the tidal field 'filamentary' direction while, for the high-mass galaxies, it is perpendicular to both filaments and walls. The bluest galaxies of the synthetic catalog are more strongly correlated with the surrounding tidal field than the reddest galaxies, and this correlation extends up to 10 Mpc/h comoving distance. Also report a correlation of the projected ellipticities of blue, intermediate mass galaxies on a similar scale at a level of 1e-4 which could be a concern for cosmic shear measurements. Do not report any measurable intrinsic alignments of the reddest galaxies in the sample. This work is a first step toward the use of very realistic catalog of synthetic galaxies to evaluate the contamination of WL measurement by IA.
1406.4728
Damping of glacial-interglacial cycles from anthropogenic forcing
Haqq-Misra
Climate variability over the past million years shows a strong glacial-interglacial cycle of ~100k years as a combined result of Milankovitch orbital forcing and climatic resonance. It has been suggested that anthropogenic contributions to radiative forcing may extend the length of the present interglacial, but the effects of anthropogenic forcing on the periodicity of glacial-interglacial cycles has received little attention. Demonstrate the moderate anthropogenic forcing can act to damp this 100k year cycle and reduce climate variability from orbital forcing. Future changes in solar insolation alone will continue to drive a 100k year climate cycle over the next million years, but the presence of anthropogenic warming can force the climate into an ice-free state that only weakly responds to orbital forcing. Sufficiently strong anthropogenic forcing that eliminate the glacial-interglacial cycle may serve as an indication of an epoch transition from the Pleistocene to the Anthropocene.
1406.4542
Computing and using metrics in the ADS
Henneken et al
"Discuss how the ADS can be used to quench the first for impact measures."
1406.4859
Herschel-Atlas and ALMA: HATLAS J142935.3-002836, a lensed major merger at redshift 1.027
Messias et al
A system comprising of a foreground edge-on disk galaxy (at z=0.218) with an almost complete Einstein ring around it. The background source (z=1.027) is magnified by a factor of ~8-10 depending on wavelength. It is comprised of two components and a tens of kpc long tidal tail resembling the Antennae merger. Utilized multi wavelength data.
1406.4871
Can weak lensing surveys confirm BICEP2?
Chisari, Dvorkin, Schmidt
The detection of B_modes in the CMB polarization by BICEP2, if interpreted as evidence for a primordial gravitational wave background, has enormous ramifications for cosmology and physics. It is crucial to test this hypothesis with independent measurements. A gravitational wave background leads to B-modes in galaxy shape correlations (shear) both through lensing and tidal alignment effects. Since the systematics and foregrounds of galaxy shapes and CMB polarization are entirely different, a detection of a cross-correlation between the two observables would provide conclusive proof for the existence of a primordial gravitational wave background. Find that upcoming weak lensing surveys will be able to detect the cross-correlation between B-modes of the CMB and galaxy shapes. However, this detection is not sufficient to confirm or falsify the hypothesis of a primordial origin for CMB B-mode polarization.
Wednesday, June 18, 2014
Day 681
Wednesday.
1406.4130
Constraining the galaxy's dark halo with RAVE stars
Piffl et al
Use the kinematics of ~200k giant stars that lie within ~1.5kpc of the plane to measure the vertical profile of mass density near the Sun. Find that the dark mass constrained within the isodensity surface of the dark halo that passes through the Sun (6pm0.9e10Msun) and the surface density within 0.9 kpc of the plane (69pm10Msun/pc^2) are almost independent of the (oblate) halo's axis ratio q. If the halo is spherical, 45% of the radial force on the Sun is provided by baryons, and only 4.3 % of the Galaxy's mass is baryonic. If the halo is flattened, the baryons contribute even less strongly to the local radial force and to the Galaxy's mass. The dark-matter density at the location of the Sun is 0.0126q^-0.89 Msun/pc^3=0.48 q^-0.89 GeV/cm^3. When combined with other literature results, find hints for a mildly oblate dark halo with q~0.8. Value for the dark mass within the solar radius is larger than that predicted by cosmological DM-only simulations but in good agreement with simulations once the effects of baryonic infall are taken into account. The mass models consist of 3 double-exponential discs, an oblate bulge and a NFW DM halo, and model the dynamics of the RAVE stars in the corresponding gravitational fields by finding distribution functions f(J) that depend on three action integrals. Statistical errors are completely swamped by systematic uncertainties, the most important of which is the distance to the stars in the photometric and spectroscopic samples. Systematics other than the flattening of the dark halo yield overall uncertainties ~10%.
1406.4135
The bispectrum in the effective field theory of large scale structure
Baldauf, Mercolli, Mirbabayi, Pajer
Study the bispectrum in the EFT of LSS, consistently accounting for the effects of short-scale dynamics. Begin by proving that, as long as the theory is perturbative, it can be formulated to arbitrary order using only operations that are local in time. Then derive all the new operators required to cancel the UV-divergences and obtain a physically meaningful prediction for the one-loop bispectrum. In addition to new, subleading stochastic noises and the viscosity term needed for the one-loop power spectrum, find 3 new effective operators. The three new parameters can be constrained by comparing with N-body simulations. The best fit is precisely what is suggested by the structure of UV-divergences, hence justifying a formula for the EFTofLSS bispectrum whose only fitting parameter is already fixed by the PS. This result predicts the bispectrum of N-body simulations up to k~0.22 h/Mpc at z=0, an improvement by nearly a factor of two as compared to one-loop standard perturbation theory.
1406.4140
Beyond the linear-order relativistic effect in galaxy clustering: second-order gauge-invariant formalism
Yoo, Zaldarriaga
Present the second-order general relativistic description of the observed galaxy number density in a cosmological framework. The observed galaxy number density is affected by the volume and the source effects, both of which arise due to the mismatch between physical and observationally inferred quantitates such as the redshift, the angular position, the volume, and the luminosity of the observed galaxies. These effects are computed to the second order in metric perturbations without choosing a gauge condition or adopting any restrictions on vector and tensor perturbations, extending the previous linear-order calculations. Paying particular attention to the second-order gauge transformation, explicitly isolate unphysical gauge modes and construct second-order gauge-invariant variables. Moreover, by constructing second-order tetrads in the observer's rest frame, clarify the relate between the physical and parameterized photon wave vectors. The second-order relativistic description will provide an essential tool for going beyond the PS in the era of precision measurements of galaxy clustering. Discuss potential applications and extensions of the second-order relativistic description of galaxy clustering.
1406.4143
The one-loop matter bispectrum in the effective field theory of large scale structures
Angulo, Foreman, Schmittfull, Senatore
It is crucial to reliably predict the LSS survey observables. The EFTofLSS provides a manifestly convergent perturbative scheme to compute the clustering of DM in the weakly NL regime in an expansion in k/k_NL, where k is the wavenumber and k_NL is the wavenumber associated to the NL scale. It has been recently shown that the EFTofLSS matches to 1% level the DM PS at z=0 up to k~0.3 h/Mpc and k~0.6 h/Mpc at one and two loops respectively, using only one counter term that is fit to data. Similar realists have been obtained for the momentum power spectrum at one loop. This is a remarkable improvement with respect to former analytical techniques. Study the prediction for the equal-time DM bispectrum at one loop. Find that at this order, it is sufficient to consider the same counter term that was measured in the PS. Without any remaining free parameter, and in a cosmology for which k_NL is smaller than in the previously considered cases, find that the prediction from the EFTofLSS agrees well with N-body sims up to k~0.3 h/Mpc, given the accuracy of the measurements, which is of order a few% at the highest k's of interest. While the fit is very good on average up to k~0.3 h/Mpc, the fit performs slightly worse on equilateral configurations, failing approximately at k~0.23 h/Mpc, in agreement with expectations that for a given maximum k, equilateral triangles are the most nonlinear.
1406.4149
The inside-out growth of the most massive galaxies at 0.3<z<0.9
Bai, Yee, ... Gladders, et al
Study the surface brightness profiles of a sample of BCGs with 0.3<z<0.9. The BCGs are selected from the RCS and X-ray cluster survey. The surface brightness profiles of the BCGs are measured using HST ACS images, and most of them can be all modeled by a Sersic profile with index ~6 and half-light radius ~30 kpc. Although the single Sersic model fits the profiles well, argue that the systematics in the sky background measurement and the coupling between the model parameters make the comparison of the model parameters ambiguous. Direct comparison of the BCG profiles, on the other hand, has revealed an inside-out growth for these most massive galaxies: as the mass of a BCG increases, the central mass density of the galaxy increase slowly (rho_1kpc ~ M*^0.39), while the slope of the outer profile grows continuously shallower (alpha~M*^-2.5). Such a fashion of growth continues down to the less massive ETGs, without apparent distinction between BCGs and non-BCGs. For the very massive ETGs and BCGs, the slope of the Kormendy relation starts to trace the slope of the surface brightness profiles and becomes insensitive to subtle profile evolution. These results are generally consistent with dry mergers being the major driver of the mass growth for BCGs and massive ETGs. Also find strong correlations between the richness of clusters and the properties of BCGs: the more massive the clusters are, the more massive the BCGs (M*_bcg ~ M^0.6_clusters) and the shallower their surface brightness profiles. After taking into account the bias in the cluster samples, find the masses of the BCGs have grown by at least a factor of 1.5 from z=0.5 to z=0, in contrast to the previous findings of no evolution. Such an evolution validates the expectation from the LCDM model.
1406.4159
Halo abundances within the cosmic web
Alonso, Eardley, Peacock
Investigate the dependence of the MF of DM haloes on their environment within the cosmic web of LSS. A dependence of the halo MF on large-scale mean density is a standard element of cosmo theory, allowing mass-dependent biasing to be understood via the peak-background split. On the assumption of a Gaussian density field, this analysis can be extended to ask how the MF depends on the geometrical environment: clusters, filaments, sheets and voids, as classified via the tidal tensors (the Hessian matrix of the gravitational potential). In linear theory, the problem can be solved exactly, and the result is attractively simple: the conditional MF has no explicit dependence on the local tidal field, and is a function only of the local density on the filtering scale used to define the tidal tensor. There is nevertheless a strong implicit predicted dependence on geometrical environment, because the local density couples statistically to the derivatives of the potential. Compute the predictions of this model and study the limits of their validity by comparing them to results deduced empirically from N-body simulations. For sufficiently large filtering sizes, the agreement is good, but there are deviations from the Gaussian prediction at high nonlinearities. Discuss how to obtain improved predictions in the regime, using the `effective-universe` approach.
1406.4357
Galaxy filaments are pearl necklaces
Tempel, Kpper, Saar, Bussov, Pelt
The characteristic length of galaxy (pearl) placement in a filament (necklace) is 7 Mpc/h, although they are not spaced uniformly.
1406.4369
Why are the magnetic field directions measured by Voyager 1 on both sides of the heliopause so similar?
Grygorczuk, Czechowski, Grzedzielski
The solar wind carves in the interstellar plasma a cavity bounded by a surface, called the heliopause (HP), that separates the plasma and B-field of solar origin from the interstellar ones. It is now generally accepted that in August 2012 Voyager 1 (V1) crossed that boundary. Unexpectedly, the B-fields on both its sides, although theoretically independent of each other, were found to be similar in direction. This delayed the identification of the boundary as the HP and led to many alternative explanations. Show that the V1 observations can be readily explained and, after the Interstellar Boundary Explorer (IBEX) discovery of the ribbon, could even have been predicted. The explanation relies on the fact that V1 and the undisturbed interstellar field directions (which is assumed to be given by the IBEX ribbon center) share the same heliolatitude (~34.5 deg) and are not far separated in longitude (~27 degrees). Result confirmed that V1 has indeed crossed the HP and offers the first independent confirmation that the IBEX ribbon center is in fact the direction of the undisturbed interstellar magnetic field. For V2 predict that the difference between the inner and outer magnetic field directions at the HP will be significantly larger that the one observed by V1 (~30 degs instead of 20 degs), and that the outer field direction will be close to the ribbon center.
1406.4407
Photometric redshift analysis in the Dark Energy Survey Science Verification data
Sánchez, et al
Present results form a study of photo-z performance of DES, using the early data from a Science Verification (SV) period of observations in late 2012 and early 2013 that provided science-quality images for almost 200 sq deg at the nominal depth of the survey. Assess the photo-z performance using about 15k galaxies with spectra-z available from other surveys. These galaxies are used, in different configurations, as a calibration sample, and photo-z's are obtained and studied using most of the existing photo-z codes. A weighting method in a multi-dimensional color-magnitude space is applied to the spectra sample in order to evaluate the photo-z performance with sets that mimic the full DES photo sample, which is on average significantly deeper that the calibration sample due to the limited depth of spectra surveys. Empirical photo-z methods using, for instance, ANN or Random Forests, yield the best performance in the tests, achieving core photo-z resolutions sigma_68~0.08. Moreover, the results from most of the codes, including template fitting methods, comfortably meet the DES requirements on photo-z performance, therefore, providing an excellent precedent for future DES data sets.
1406.4130
Constraining the galaxy's dark halo with RAVE stars
Piffl et al
Use the kinematics of ~200k giant stars that lie within ~1.5kpc of the plane to measure the vertical profile of mass density near the Sun. Find that the dark mass constrained within the isodensity surface of the dark halo that passes through the Sun (6pm0.9e10Msun) and the surface density within 0.9 kpc of the plane (69pm10Msun/pc^2) are almost independent of the (oblate) halo's axis ratio q. If the halo is spherical, 45% of the radial force on the Sun is provided by baryons, and only 4.3 % of the Galaxy's mass is baryonic. If the halo is flattened, the baryons contribute even less strongly to the local radial force and to the Galaxy's mass. The dark-matter density at the location of the Sun is 0.0126q^-0.89 Msun/pc^3=0.48 q^-0.89 GeV/cm^3. When combined with other literature results, find hints for a mildly oblate dark halo with q~0.8. Value for the dark mass within the solar radius is larger than that predicted by cosmological DM-only simulations but in good agreement with simulations once the effects of baryonic infall are taken into account. The mass models consist of 3 double-exponential discs, an oblate bulge and a NFW DM halo, and model the dynamics of the RAVE stars in the corresponding gravitational fields by finding distribution functions f(J) that depend on three action integrals. Statistical errors are completely swamped by systematic uncertainties, the most important of which is the distance to the stars in the photometric and spectroscopic samples. Systematics other than the flattening of the dark halo yield overall uncertainties ~10%.
1406.4135
The bispectrum in the effective field theory of large scale structure
Baldauf, Mercolli, Mirbabayi, Pajer
Study the bispectrum in the EFT of LSS, consistently accounting for the effects of short-scale dynamics. Begin by proving that, as long as the theory is perturbative, it can be formulated to arbitrary order using only operations that are local in time. Then derive all the new operators required to cancel the UV-divergences and obtain a physically meaningful prediction for the one-loop bispectrum. In addition to new, subleading stochastic noises and the viscosity term needed for the one-loop power spectrum, find 3 new effective operators. The three new parameters can be constrained by comparing with N-body simulations. The best fit is precisely what is suggested by the structure of UV-divergences, hence justifying a formula for the EFTofLSS bispectrum whose only fitting parameter is already fixed by the PS. This result predicts the bispectrum of N-body simulations up to k~0.22 h/Mpc at z=0, an improvement by nearly a factor of two as compared to one-loop standard perturbation theory.
1406.4140
Beyond the linear-order relativistic effect in galaxy clustering: second-order gauge-invariant formalism
Yoo, Zaldarriaga
Present the second-order general relativistic description of the observed galaxy number density in a cosmological framework. The observed galaxy number density is affected by the volume and the source effects, both of which arise due to the mismatch between physical and observationally inferred quantitates such as the redshift, the angular position, the volume, and the luminosity of the observed galaxies. These effects are computed to the second order in metric perturbations without choosing a gauge condition or adopting any restrictions on vector and tensor perturbations, extending the previous linear-order calculations. Paying particular attention to the second-order gauge transformation, explicitly isolate unphysical gauge modes and construct second-order gauge-invariant variables. Moreover, by constructing second-order tetrads in the observer's rest frame, clarify the relate between the physical and parameterized photon wave vectors. The second-order relativistic description will provide an essential tool for going beyond the PS in the era of precision measurements of galaxy clustering. Discuss potential applications and extensions of the second-order relativistic description of galaxy clustering.
1406.4143
The one-loop matter bispectrum in the effective field theory of large scale structures
Angulo, Foreman, Schmittfull, Senatore
It is crucial to reliably predict the LSS survey observables. The EFTofLSS provides a manifestly convergent perturbative scheme to compute the clustering of DM in the weakly NL regime in an expansion in k/k_NL, where k is the wavenumber and k_NL is the wavenumber associated to the NL scale. It has been recently shown that the EFTofLSS matches to 1% level the DM PS at z=0 up to k~0.3 h/Mpc and k~0.6 h/Mpc at one and two loops respectively, using only one counter term that is fit to data. Similar realists have been obtained for the momentum power spectrum at one loop. This is a remarkable improvement with respect to former analytical techniques. Study the prediction for the equal-time DM bispectrum at one loop. Find that at this order, it is sufficient to consider the same counter term that was measured in the PS. Without any remaining free parameter, and in a cosmology for which k_NL is smaller than in the previously considered cases, find that the prediction from the EFTofLSS agrees well with N-body sims up to k~0.3 h/Mpc, given the accuracy of the measurements, which is of order a few% at the highest k's of interest. While the fit is very good on average up to k~0.3 h/Mpc, the fit performs slightly worse on equilateral configurations, failing approximately at k~0.23 h/Mpc, in agreement with expectations that for a given maximum k, equilateral triangles are the most nonlinear.
1406.4149
The inside-out growth of the most massive galaxies at 0.3<z<0.9
Bai, Yee, ... Gladders, et al
Study the surface brightness profiles of a sample of BCGs with 0.3<z<0.9. The BCGs are selected from the RCS and X-ray cluster survey. The surface brightness profiles of the BCGs are measured using HST ACS images, and most of them can be all modeled by a Sersic profile with index ~6 and half-light radius ~30 kpc. Although the single Sersic model fits the profiles well, argue that the systematics in the sky background measurement and the coupling between the model parameters make the comparison of the model parameters ambiguous. Direct comparison of the BCG profiles, on the other hand, has revealed an inside-out growth for these most massive galaxies: as the mass of a BCG increases, the central mass density of the galaxy increase slowly (rho_1kpc ~ M*^0.39), while the slope of the outer profile grows continuously shallower (alpha~M*^-2.5). Such a fashion of growth continues down to the less massive ETGs, without apparent distinction between BCGs and non-BCGs. For the very massive ETGs and BCGs, the slope of the Kormendy relation starts to trace the slope of the surface brightness profiles and becomes insensitive to subtle profile evolution. These results are generally consistent with dry mergers being the major driver of the mass growth for BCGs and massive ETGs. Also find strong correlations between the richness of clusters and the properties of BCGs: the more massive the clusters are, the more massive the BCGs (M*_bcg ~ M^0.6_clusters) and the shallower their surface brightness profiles. After taking into account the bias in the cluster samples, find the masses of the BCGs have grown by at least a factor of 1.5 from z=0.5 to z=0, in contrast to the previous findings of no evolution. Such an evolution validates the expectation from the LCDM model.
1406.4159
Halo abundances within the cosmic web
Alonso, Eardley, Peacock
Investigate the dependence of the MF of DM haloes on their environment within the cosmic web of LSS. A dependence of the halo MF on large-scale mean density is a standard element of cosmo theory, allowing mass-dependent biasing to be understood via the peak-background split. On the assumption of a Gaussian density field, this analysis can be extended to ask how the MF depends on the geometrical environment: clusters, filaments, sheets and voids, as classified via the tidal tensors (the Hessian matrix of the gravitational potential). In linear theory, the problem can be solved exactly, and the result is attractively simple: the conditional MF has no explicit dependence on the local tidal field, and is a function only of the local density on the filtering scale used to define the tidal tensor. There is nevertheless a strong implicit predicted dependence on geometrical environment, because the local density couples statistically to the derivatives of the potential. Compute the predictions of this model and study the limits of their validity by comparing them to results deduced empirically from N-body simulations. For sufficiently large filtering sizes, the agreement is good, but there are deviations from the Gaussian prediction at high nonlinearities. Discuss how to obtain improved predictions in the regime, using the `effective-universe` approach.
1406.4357
Galaxy filaments are pearl necklaces
Tempel, Kpper, Saar, Bussov, Pelt
The characteristic length of galaxy (pearl) placement in a filament (necklace) is 7 Mpc/h, although they are not spaced uniformly.
1406.4369
Why are the magnetic field directions measured by Voyager 1 on both sides of the heliopause so similar?
Grygorczuk, Czechowski, Grzedzielski
The solar wind carves in the interstellar plasma a cavity bounded by a surface, called the heliopause (HP), that separates the plasma and B-field of solar origin from the interstellar ones. It is now generally accepted that in August 2012 Voyager 1 (V1) crossed that boundary. Unexpectedly, the B-fields on both its sides, although theoretically independent of each other, were found to be similar in direction. This delayed the identification of the boundary as the HP and led to many alternative explanations. Show that the V1 observations can be readily explained and, after the Interstellar Boundary Explorer (IBEX) discovery of the ribbon, could even have been predicted. The explanation relies on the fact that V1 and the undisturbed interstellar field directions (which is assumed to be given by the IBEX ribbon center) share the same heliolatitude (~34.5 deg) and are not far separated in longitude (~27 degrees). Result confirmed that V1 has indeed crossed the HP and offers the first independent confirmation that the IBEX ribbon center is in fact the direction of the undisturbed interstellar magnetic field. For V2 predict that the difference between the inner and outer magnetic field directions at the HP will be significantly larger that the one observed by V1 (~30 degs instead of 20 degs), and that the outer field direction will be close to the ribbon center.
1406.4407
Photometric redshift analysis in the Dark Energy Survey Science Verification data
Sánchez, et al
Present results form a study of photo-z performance of DES, using the early data from a Science Verification (SV) period of observations in late 2012 and early 2013 that provided science-quality images for almost 200 sq deg at the nominal depth of the survey. Assess the photo-z performance using about 15k galaxies with spectra-z available from other surveys. These galaxies are used, in different configurations, as a calibration sample, and photo-z's are obtained and studied using most of the existing photo-z codes. A weighting method in a multi-dimensional color-magnitude space is applied to the spectra sample in order to evaluate the photo-z performance with sets that mimic the full DES photo sample, which is on average significantly deeper that the calibration sample due to the limited depth of spectra surveys. Empirical photo-z methods using, for instance, ANN or Random Forests, yield the best performance in the tests, achieving core photo-z resolutions sigma_68~0.08. Moreover, the results from most of the codes, including template fitting methods, comfortably meet the DES requirements on photo-z performance, therefore, providing an excellent precedent for future DES data sets.
Tuesday, June 17, 2014
Day 680
Tuesday.
1406.3622
The cold spot in the cosmic microwave background: the shadow of a supervoid
Szapudi, ... Silk, ... et al
Standard inflationary hot big bang cosmology predicts small fluctuations in the CMB with isotropic Gaussian statistics. All measurements support the standard theory, except for a few anomalies discovered in WMAP maps and confirmed recently by Planck. The Cold Spot is one of the most significant of such anomalies, and the leading explanation of it posits a large void that imprints this extremely cold area via the linear ISW effect due to the decay of gravitational potentials over cosmic time, or via the RS effect due to late-time NL evolution. Despite several observational campaigns targeting the Cold Spot region, to date no suitable large void was found at higher z>0.3. Report the detection of an R=192pm15 Mpc/h size super void of depth delta=-0.13pm0.03, and centered at z=0.22. This super void, possibly the largest ever found, is large enough to significantly affect the CMB via the NL RS effect, as shown in the Lemaitre-Tolman-Bondi framework. This discovery presents the first plausible explanation for any of the physical CMB anomalies, and raises the possibility that local LSS could be responsible for other anomalies as well.
1406.3709
Evolution of the gas mass fraction in galaxy clusters
Dvorkin, Rephaeli
The mass fraction of hot gas in clusters is a basic quantity whose level and dependence on the cluster mass and redshift are intimately linked to all cluster X-ray and SZ measures. Modeling the evolution of the gas fraction is clearly a necessary ingredient in the description of the hierarchical growth of clusters through mergers of sub clumps and mass accretion on the one hand, and the dispersal of gas from the cluster galaxies by tidal interaction, galactic winds, and ram pressure stripping on the other hand. A reasonably complete description of this evolution can only be given by very detailed Hydro sims, which are, however, resource-intensive, and difficult to implement in the mapping of parameter space. A much more practical approach is the use of SAM that can be easily implemented to explore a wide range of parameters. Present first results from a simple model that describes the build up of the gas mass fraction in clusters by following the overall impact of the above processes during the merger and accretion history of each cluster in the ensemble. Acceptable ranges for model parameters are deduced through comparison with results of X-ray observations. Basic implications of the work for modeling cluster statistical properties, and the use of these properties in joint cosmological data analyses, are discussed.
1406.3710
Extremely flat haloes and the shape of the galaxy
Evans, Bowden
Present a set of highly flattened galaxy models with asymptotically constant rotation curves. The mass density in the equatorial plane falls like (distance)^-1 at large radii. Although the inner equidensity contours may be spherical, oblate or prolate, the outer parts are always severely flattened. The elongated shape is supported by rotation or tangential velocity anisotropy. The models are thickened Mestel discs, and form a previously undiscovered parti f the Miyamoto & Nagai sequence of flattened galaxies. The properties of the models -- axis ratios, velocity dispersions, streaming velocities and distribution functions -- are all discussed in some detail. Pose the question: are extremely flattened or disk-like haloes possible for the MW galaxy? This has never been examined before, as very flattened halo models were not available. Fit the rotation curve and the vertical kinematics of disc stars in the solar neighborhood to constrain the overall shape of the Galaxy. Denoting the ratio of polar axis to major axis by q, show that models with z<0.57 cannot simultaneously reproduce the in-plane and out-of-plane constraints. The kinematics of the Sagittarius galaxy also strongly disfavor models with high flattening, as the orbital plane precession is too great and the height reached above the Galactic plane is too small. At least for out Galaxy, the dark halo cannot be flatter than E4 (q~0.57) at the Solar circle. Models in which the DM is accounted for by a massive baryonic disc or by decaying neutrinos are therefore ruled out by constraints form the rotation curve and the vertical kinematics.
1406.3730
A very simple cusped halo model
Evans, Willams
A close relative of Hernuqist's model, being generated by the same transformation but this time applied to the logarithmic potential rather than the point mass. The density is proportional to (distance)^-1 at small radii, whilst the rotation curve is flat at large radii. Isotropic and radially anisotropic distributions functions are readily found, and the intrinsic and line of sight kinematical quantities are available as simple formulae. Also provide an analytical approximation to the Hamiltonian as a function of the actions. As an application, study the kinematic properties of stellar haloes and tracers in elliptical galaxies. Show that the radial velocity dispersion of a power-law population in a galaxy with a flat rotation curve always tends to the constant values. This holds true irrespective of the anisotropy of the length scales of the dark or luminous matter. An analogous result holds for the line of sight or projected velocity dispersion of a power-law surface brightness profile. The radial velocity dispersion of Pop II stars in the MW is a strongly declining function of Galactocentric radius. So, if the rotation curve is flat, conclude that the stellar halo density cannot follow a power-law at large radii, but must decrease more sharply (like an Einasto profile) or be abruptly truncated at large radii. Both the star count and kinematic data of the MW stellar halo are all-represented by an Einasto profile with index m~2 and effective radius ~20 kpc.
1406.3622
The cold spot in the cosmic microwave background: the shadow of a supervoid
Szapudi, ... Silk, ... et al
Standard inflationary hot big bang cosmology predicts small fluctuations in the CMB with isotropic Gaussian statistics. All measurements support the standard theory, except for a few anomalies discovered in WMAP maps and confirmed recently by Planck. The Cold Spot is one of the most significant of such anomalies, and the leading explanation of it posits a large void that imprints this extremely cold area via the linear ISW effect due to the decay of gravitational potentials over cosmic time, or via the RS effect due to late-time NL evolution. Despite several observational campaigns targeting the Cold Spot region, to date no suitable large void was found at higher z>0.3. Report the detection of an R=192pm15 Mpc/h size super void of depth delta=-0.13pm0.03, and centered at z=0.22. This super void, possibly the largest ever found, is large enough to significantly affect the CMB via the NL RS effect, as shown in the Lemaitre-Tolman-Bondi framework. This discovery presents the first plausible explanation for any of the physical CMB anomalies, and raises the possibility that local LSS could be responsible for other anomalies as well.
1406.3709
Evolution of the gas mass fraction in galaxy clusters
Dvorkin, Rephaeli
The mass fraction of hot gas in clusters is a basic quantity whose level and dependence on the cluster mass and redshift are intimately linked to all cluster X-ray and SZ measures. Modeling the evolution of the gas fraction is clearly a necessary ingredient in the description of the hierarchical growth of clusters through mergers of sub clumps and mass accretion on the one hand, and the dispersal of gas from the cluster galaxies by tidal interaction, galactic winds, and ram pressure stripping on the other hand. A reasonably complete description of this evolution can only be given by very detailed Hydro sims, which are, however, resource-intensive, and difficult to implement in the mapping of parameter space. A much more practical approach is the use of SAM that can be easily implemented to explore a wide range of parameters. Present first results from a simple model that describes the build up of the gas mass fraction in clusters by following the overall impact of the above processes during the merger and accretion history of each cluster in the ensemble. Acceptable ranges for model parameters are deduced through comparison with results of X-ray observations. Basic implications of the work for modeling cluster statistical properties, and the use of these properties in joint cosmological data analyses, are discussed.
1406.3710
Extremely flat haloes and the shape of the galaxy
Evans, Bowden
Present a set of highly flattened galaxy models with asymptotically constant rotation curves. The mass density in the equatorial plane falls like (distance)^-1 at large radii. Although the inner equidensity contours may be spherical, oblate or prolate, the outer parts are always severely flattened. The elongated shape is supported by rotation or tangential velocity anisotropy. The models are thickened Mestel discs, and form a previously undiscovered parti f the Miyamoto & Nagai sequence of flattened galaxies. The properties of the models -- axis ratios, velocity dispersions, streaming velocities and distribution functions -- are all discussed in some detail. Pose the question: are extremely flattened or disk-like haloes possible for the MW galaxy? This has never been examined before, as very flattened halo models were not available. Fit the rotation curve and the vertical kinematics of disc stars in the solar neighborhood to constrain the overall shape of the Galaxy. Denoting the ratio of polar axis to major axis by q, show that models with z<0.57 cannot simultaneously reproduce the in-plane and out-of-plane constraints. The kinematics of the Sagittarius galaxy also strongly disfavor models with high flattening, as the orbital plane precession is too great and the height reached above the Galactic plane is too small. At least for out Galaxy, the dark halo cannot be flatter than E4 (q~0.57) at the Solar circle. Models in which the DM is accounted for by a massive baryonic disc or by decaying neutrinos are therefore ruled out by constraints form the rotation curve and the vertical kinematics.
1406.3730
A very simple cusped halo model
Evans, Willams
A close relative of Hernuqist's model, being generated by the same transformation but this time applied to the logarithmic potential rather than the point mass. The density is proportional to (distance)^-1 at small radii, whilst the rotation curve is flat at large radii. Isotropic and radially anisotropic distributions functions are readily found, and the intrinsic and line of sight kinematical quantities are available as simple formulae. Also provide an analytical approximation to the Hamiltonian as a function of the actions. As an application, study the kinematic properties of stellar haloes and tracers in elliptical galaxies. Show that the radial velocity dispersion of a power-law population in a galaxy with a flat rotation curve always tends to the constant values. This holds true irrespective of the anisotropy of the length scales of the dark or luminous matter. An analogous result holds for the line of sight or projected velocity dispersion of a power-law surface brightness profile. The radial velocity dispersion of Pop II stars in the MW is a strongly declining function of Galactocentric radius. So, if the rotation curve is flat, conclude that the stellar halo density cannot follow a power-law at large radii, but must decrease more sharply (like an Einasto profile) or be abruptly truncated at large radii. Both the star count and kinematic data of the MW stellar halo are all-represented by an Einasto profile with index m~2 and effective radius ~20 kpc.
Sunday, June 15, 2014
Day 679
Saturday.
1406.3343
Saturn ring seismology: evidence for stable stratification in the deep interior of Saturn
Fuller
Seismology allows for direct observational constraints on the interior structures of stars and planets. Recent observations of Saturn's ring system have revealed the presence of density waves within the rings excited by oscillation modes within Saturn, allowing for precise measurements of a limited set of the planet's mode frequencies. Construct interior structure models of Saturn, compute the corresponding mode frequencies, and compare them with the observed mode frequencies. The fundamental mode frequencies of the models match the observed frequencies (of the largest amplitude waves) to an accuracy of ~1, confirming that these waves are indeed excited by Saturn's f-modes. [What's an f-mode?] The presence of the lower amplitude waves (finely split in frequency from the f-modes) can only be reproduced in models containing gravity modes that propagate in a stably stratified region of the planet. The stable stratification must exist deep within the planet near the large density gradients between the core and envelope. The models cannot easily reproduce the observed fine splitting of the m=-3 modes, suggesting that additional effects (e.g., significant latitudinal differential rotation) may be important.
1406.3344
Satellite dwarf galaxies in a hierarchical universe: the prevalence of dwarf-dwarf major mergers
Deason, Wetzel, Garrison-Kimmel
Mergers are a common phenomenon in hierarchical structure formation, especially for massive galaxies and clusters, but their importance for dwarf galaxies in the LG remains poorly understood. Investigate the frequency of major mergers between dwarf galaxies in the LG using the ELVIS suit of cosmo zoom-in dissipation less simulations of the MW- and M31-like host haloes. Find that ~10% of satellite dwarf galaxies with M_star>1e6 Msun that are within the host virial radius experienced a major merger of stellar mass ratio closer than 0.1 since z=1, with a lower fraction for lower mass dwarf galaxies. Recent merger remnants are biased towards larger radial distance and more recent virial infall times, because most recent mergers occurred shortly before crossing within the virial radius of the host halo. Satellite-satllite mergers also occur within the host halo after virial infall, catalyzed by the large fraction of dwarf galaxies that fell in as part of a group. The merger fraction doubles for dwarf galaxies outside of the host virial radius, so the most distant dwarf galaxies in the LG are the most likely to have experienced a recent major merger. Discuss the implications of these results on observable dwarf merger remnants, their star formation histories, the gas content of mergers, and massive BHs in dwarf galaxies.
1406.3362
Optically selected fossil groups; X-ray observations and galaxy properties
Khosroshahi et al
[In X-ray selected fossil groups, the X-ray emission is extended.] Combine X-ray and optical observations of 4 galaxy groups, find evidences for the presence of a diffuse extended X-ray emission beyond the optical size of the brightest group galaxy. Taking both the X-ray and the optical criteria, one of the groups is identified as a fossil group and one is ruled out because of the contamination in the earlier optical selection. For the two remaining systems, the X-ray luminosity threshold is close to the convention known for fossil groups. In all cases the X-ray luminosity is below the expected value from the X-ray selected fossils for a given optical luminosity of the group. A rough estimation for the comoving number density of fossil groups is obtained and found to be in broad agreement with the estimations from observations of X-ray selected fossils and predictions of cosmo sims.
1406.3451
Universal profiles of the intracluster medium from Suzaku X-ray and Subaru weak lensing observations
Okabe, Umetsu, ... et al
Conduct a join X-ray and WL study of 4 relaxed galaxy clusters observed out to virial radii, with an aim to understand recently-discovered unexpected feature of the ICM in cluster outskirts. Show that the average hydrostatic-to-lensing total mass ratio for the 4 clusters decreases from ~70% to ~40% as the overdensity contrast decreases from 500 to the virial value. The average gas mass fraction from lensing total mass estimates increases with cluster radius and agrees with the cosmic mean baryon fraction within the virial radius, whereas the X-ray based gas fraction considerably exceeds the cosmic values due to underestimation of the hydrostatic mass. Also develop a new advanced method for determining normalized cluster radial profiles for multiple X-ray observables by simultaneously taking into account both their radial dependence and multivariate scaling relations with WL masses. Although the 4 clusters span a range of halo mass, concentration, X-ray luminosity and redshift, find that the gas entropy, pressure, temperature and density profiles are all remarkably self-similar when scaled with the lensing M200 mass and r_200 radius. The entropy monotonically increases out to ~0.5 r200 following the accretion shock heating model K(r)~r^1.1, and flattens at >~ 0.5 r200. The universality of the scaled entropy profiles indicates that the thermalization mechanism over the entire cluster region (>0.1 r200) is controlled by gravitation a common to all clusters, although the heating efficiency in the outskirts needs to be modified from the standard law. The bivariate scaling functions of the gas density and temperature reveal that the flattening of the outskirts entry profile is caused by the steepening of the temperature, rather than the flattening of the gas density.
1406.3343
Saturn ring seismology: evidence for stable stratification in the deep interior of Saturn
Fuller
Seismology allows for direct observational constraints on the interior structures of stars and planets. Recent observations of Saturn's ring system have revealed the presence of density waves within the rings excited by oscillation modes within Saturn, allowing for precise measurements of a limited set of the planet's mode frequencies. Construct interior structure models of Saturn, compute the corresponding mode frequencies, and compare them with the observed mode frequencies. The fundamental mode frequencies of the models match the observed frequencies (of the largest amplitude waves) to an accuracy of ~1, confirming that these waves are indeed excited by Saturn's f-modes. [What's an f-mode?] The presence of the lower amplitude waves (finely split in frequency from the f-modes) can only be reproduced in models containing gravity modes that propagate in a stably stratified region of the planet. The stable stratification must exist deep within the planet near the large density gradients between the core and envelope. The models cannot easily reproduce the observed fine splitting of the m=-3 modes, suggesting that additional effects (e.g., significant latitudinal differential rotation) may be important.
1406.3344
Satellite dwarf galaxies in a hierarchical universe: the prevalence of dwarf-dwarf major mergers
Deason, Wetzel, Garrison-Kimmel
Mergers are a common phenomenon in hierarchical structure formation, especially for massive galaxies and clusters, but their importance for dwarf galaxies in the LG remains poorly understood. Investigate the frequency of major mergers between dwarf galaxies in the LG using the ELVIS suit of cosmo zoom-in dissipation less simulations of the MW- and M31-like host haloes. Find that ~10% of satellite dwarf galaxies with M_star>1e6 Msun that are within the host virial radius experienced a major merger of stellar mass ratio closer than 0.1 since z=1, with a lower fraction for lower mass dwarf galaxies. Recent merger remnants are biased towards larger radial distance and more recent virial infall times, because most recent mergers occurred shortly before crossing within the virial radius of the host halo. Satellite-satllite mergers also occur within the host halo after virial infall, catalyzed by the large fraction of dwarf galaxies that fell in as part of a group. The merger fraction doubles for dwarf galaxies outside of the host virial radius, so the most distant dwarf galaxies in the LG are the most likely to have experienced a recent major merger. Discuss the implications of these results on observable dwarf merger remnants, their star formation histories, the gas content of mergers, and massive BHs in dwarf galaxies.
1406.3362
Optically selected fossil groups; X-ray observations and galaxy properties
Khosroshahi et al
[In X-ray selected fossil groups, the X-ray emission is extended.] Combine X-ray and optical observations of 4 galaxy groups, find evidences for the presence of a diffuse extended X-ray emission beyond the optical size of the brightest group galaxy. Taking both the X-ray and the optical criteria, one of the groups is identified as a fossil group and one is ruled out because of the contamination in the earlier optical selection. For the two remaining systems, the X-ray luminosity threshold is close to the convention known for fossil groups. In all cases the X-ray luminosity is below the expected value from the X-ray selected fossils for a given optical luminosity of the group. A rough estimation for the comoving number density of fossil groups is obtained and found to be in broad agreement with the estimations from observations of X-ray selected fossils and predictions of cosmo sims.
1406.3451
Universal profiles of the intracluster medium from Suzaku X-ray and Subaru weak lensing observations
Okabe, Umetsu, ... et al
Conduct a join X-ray and WL study of 4 relaxed galaxy clusters observed out to virial radii, with an aim to understand recently-discovered unexpected feature of the ICM in cluster outskirts. Show that the average hydrostatic-to-lensing total mass ratio for the 4 clusters decreases from ~70% to ~40% as the overdensity contrast decreases from 500 to the virial value. The average gas mass fraction from lensing total mass estimates increases with cluster radius and agrees with the cosmic mean baryon fraction within the virial radius, whereas the X-ray based gas fraction considerably exceeds the cosmic values due to underestimation of the hydrostatic mass. Also develop a new advanced method for determining normalized cluster radial profiles for multiple X-ray observables by simultaneously taking into account both their radial dependence and multivariate scaling relations with WL masses. Although the 4 clusters span a range of halo mass, concentration, X-ray luminosity and redshift, find that the gas entropy, pressure, temperature and density profiles are all remarkably self-similar when scaled with the lensing M200 mass and r_200 radius. The entropy monotonically increases out to ~0.5 r200 following the accretion shock heating model K(r)~r^1.1, and flattens at >~ 0.5 r200. The universality of the scaled entropy profiles indicates that the thermalization mechanism over the entire cluster region (>0.1 r200) is controlled by gravitation a common to all clusters, although the heating efficiency in the outskirts needs to be modified from the standard law. The bivariate scaling functions of the gas density and temperature reveal that the flattening of the outskirts entry profile is caused by the steepening of the temperature, rather than the flattening of the gas density.
Friday, June 13, 2014
Day 678
Friday.
1406.3020
Exoplanet population inference and the abundance of Earth analogs from noisy, incomplete catalogs
Foreman-Mackey, Hogg, Morton
No true extrasolar Earth analog is known. Hundreds of planets have been found around Sun-like stars that are either Earth-sized by on shorter periods, or else on year-long orbits but somewhat larger. Under strong assumptions, exoplanet catalogs have been used to make an extrapolated estimate of the rate at which Sun-like stars host Earth analogs. These studies are complicated by the fact that every catalog is censored by non-trivial selection effects and detection efficiencies, and every property (period, radius, etc.) is measured nosily. Present a general hierarchical probabilistic framework for making justified inferences about the population of exoplanets, taking into account survey completeness and, for the first time, observational uncertainties. Able to make fewer assumptions about the distribution than previous studies; it only requires that the occurrence rate density be a smooth function of period and radius (employing a Gaussian process). By applying method to synthetic catalogs, demonstrate that it produces more accurate estimates of the whole population than standard procedures based on weighting by inverse detection efficiency. Apply the method to an existing catalog of small planet candidates around G dwarf stars (Petigura+2013). Confirm a previous result that the radius distribution changes slope near Earth's radius. Find that the rate density of Earth analogs is about 0.02 (per star per natural log bin in period and radius) with large uncertainty. This number is much smaller than previous estimates made with the same data but stronger assumptions.
1406.3023
Driving the growth of the earliest supermassive black holes with major mergers of host galaxies
Tanaka
The formation mechanism of SMBHs in general, and of ~1e9 Msun SMBHs observed as luminous quasars at z>6 in particular, remains an open fundamental question. The presence of such massive BHs at such early times, when the Universe was less than a billion years old, implies that they grew few either super-Eddington accretion, or nearly uninterrupted gas accretion near the Eddington limit; the latter, at first glance, is at odds with empirical trends at lower redshifts, where quasar episodes associated with rapid BH growth are rare and brief. In this work, examine whether and to what extend the growth of the z>6 quasar SMBHs can be explained within the standard quasar paradigm, in which major mergers of host galaxies trigger episodes of rapid gas accretion below or near the Eddington limit. Using a suite of Monte Carlo merger tree simulations of the assembly histories of the likely hosts of the z>6 quasars, investigate (i) their growth and major merger rates out to z~40, and (ii) how long the feeding episodes induced by host mergers must last in order to explain the observed z>6 quasar population without super-Eddington accretion. The halo major merger rate scales roughly as (1+z)^5/2, with quasar hosts typically experiencing >10 major mergers between 15>z>6 (~650 Myr), compared to ~1 for typical massive galaxies at 3>z>0 (~11Gyr). An example of a viable sub-Eddignton SMBH growth model is one where a host merger triggers feeding for a duration comparable to the halo dynamical time. These findings suggest that the growth mechanisms of the earliest quasar SMBHs need not have been drastically different from their counterparts at lower redshifts.
1406.3025
Detecting industrial pollution in the atmospheres of earth-like exoplanets
Lin, Abad, Loeb
Detecting biomarker, such as molecular oxygen, in the atmospheres of transiting exoplanets has been am nor focus in the search for alien life. Point out that in addition to these generic indicators, anthropogenic pollution could be used as a novel biomarker for intelligent life. To this end, identify pollutants in the Earth's atmosphere that have significant absorption features in the spectral range covered by JWST. Estimate that for an Earth-mass planet i the habitable zone of a white dwarf, methane (CH4) and nitrous oxide (N2O) can be detected at earth-like concentrations with an integration time of ~1.5 hrs and 12 hrs respectively. Detecting pollutants that are produced nearly exclusively by anthropogenic activities will be sugfniciantly more challenging. Of these pollutants, focus on tetrafluoromethane (CF4) and trichlorofluoromethane (CCl3F), which will be the easiest to detect. Estimate that ~1.5 days (~3 days) of total integration time will be sufficient to detect or constrain the concentration of CCl3F (CF4) to ~100 times the current terrestrial level.
1406.3026
Maintaining low star formation rates in early-type galaxies with AGB heating
Conroy, van Dokkum, Kravtsov
Revisit previous suggestions that the heating provided by the winds of dying low-mass stars is capable of suppressing SF in quiescent galaxies. At the end of the asymptotic giant branch, intermediate and low-mass stars eject their envelopes rapidly in a super-wind phase, usually giving rise to planetary nebular. In galaxies with high stellar velocity dispersions, the interaction of these ejected envelopes with the ambient diffuse gas can lead to significant, isotropic and steady-state heating that scales as M_* sigma^2_*. Show that cooling of the central regions of the hot diffuse halo gas can be delayed for a Hubble time for haloes more massive than ~1e12.5 Msun at 0<z<2. This mechanism provides a natural explanation for the strong trend of galaxy quiescence with stellar surface density and velocity dispersion [what trend?], and may obviate the need for other proposed mechanisms that maintain the low observed SFRs of quiescent galaxies.
1406.3036
LensExplorer, a tool for the visualization of the gravitational lensing effect n the Hubble Frontiers Fields clusters
Diego
LensExplorer is an IDL GUI code that can be used to visualize the lensing deflection field derived in the HFF clusters. The code can be used for both research and educational purposes as it offers an intuitive way to explore the solutions in the different clusters. LensExplorer can be used to predict the magnifications at different redshifts of background sources and for a given location. Present in this document a quick guide to get started with LensExplorer. The code and lens models for A2744 and MACSJ0416.1-2403 are publicly available from a website where the new solutions ( and new versions of the code) will be also uploaded as they become available.
1406.3057
In what sense is the early universe fine-tuned?
Carroll
It is commonplace in discussions of modern cosmology to assert that the early universe began in a special state. Conventionally, cosmologists characterize the fine-tuning in terms of the horizon and flatness problems. Argue that the fine-tuning is real, but these problems aren't the best way to think about it: causal disconnection of separated regions isn't the real problem, and flatness isn't a problem at all. Fine-tuning is better understood in terms of a measure on the space of trajectories: given reasonable conditions in the late universe, the fraction of cosmological histories that were smooth at early times is incredibly tiny. This discussion helps clarify what is required by a complete theory of cosmological initial conditions.
1406.3102
Search for strong gravitational lensing effect in the current GRB data of BATSE
Li, Li
Because GRBs trace high-z Universe, there is an appreciable probability for a GRB to be gravitationally lensed by galaxies in the universe. Consider the gravitational lensing effect of GRBs contributed by the DM haloes in galaxies. Assuming that all halos have the SIS mass profile in the mass range 1e10 Msun/h < M < 2e13 Msun/h and all GRB samples follow the intrinsic redshift distribution and luminosity function derived from the Swift LGRBs sample, calculated the gravitational lensing probability in BATSE, Swift/BAT and Fermi/GBM GRBs, respectively. With a derived probability result in BATSE GRBs, searched for lensed GRB pairs in the BATSE 5B GRB Spectral catalog. The search did not find any convincing gravitationally lensed events. Discuss result and future observations for GRB lensing observation.
1406.3330
Joint likelihood function of cluster counts and $n$-point correlation functions: improving their power through including halo sample variance
Schaan, Takada, Spergel
Naive estimates of the statistics of LSS and WL PS measurements that include only Gaussian errors exaggerate their scientific impact. NL evolution and finite volume effects are both significant sources of non-Gaussian covariance that reduce the ability of PS measurements to constrain cosmological parameters. Using a halo model formalism, derive an intuitive understanding of the various contributions to the covariance and show that the analytical treatment agrees with simulations. This approach enables an approximate derivation of a joint likelihood for the cluster number counts, the WL PS and the bispectrum. Show that this likelihood is a good description of the ray-tracing simulation. Since all of these observables are sensitive to the same finite volume effects and contain information about the NL evolution, a combined analysis recovers much of the "lost" information and obviates the non-Gaussian covariance. For upcoming WL surveys, estimate that a joint analysis of PS, number counts and bispectrum will produce an improvement of about 30-40% in determinations of the matter density and scalar amplitude. This improvement is equivalent to doubling the survey area.
1406.3044
Astronomy of two Indian tribes: Banjaras and Kolams
Vahia et al
As the title says. ...Show that apart from the absolute importance of the data on human perception of the sky, the data also reveal subtle aspects of interactions between physically co-located but otherwise isolated communities as well as their own lifestyles. Also show that there is a strong relationship between profession and perspective of the sky.
1406.3020
Exoplanet population inference and the abundance of Earth analogs from noisy, incomplete catalogs
Foreman-Mackey, Hogg, Morton
No true extrasolar Earth analog is known. Hundreds of planets have been found around Sun-like stars that are either Earth-sized by on shorter periods, or else on year-long orbits but somewhat larger. Under strong assumptions, exoplanet catalogs have been used to make an extrapolated estimate of the rate at which Sun-like stars host Earth analogs. These studies are complicated by the fact that every catalog is censored by non-trivial selection effects and detection efficiencies, and every property (period, radius, etc.) is measured nosily. Present a general hierarchical probabilistic framework for making justified inferences about the population of exoplanets, taking into account survey completeness and, for the first time, observational uncertainties. Able to make fewer assumptions about the distribution than previous studies; it only requires that the occurrence rate density be a smooth function of period and radius (employing a Gaussian process). By applying method to synthetic catalogs, demonstrate that it produces more accurate estimates of the whole population than standard procedures based on weighting by inverse detection efficiency. Apply the method to an existing catalog of small planet candidates around G dwarf stars (Petigura+2013). Confirm a previous result that the radius distribution changes slope near Earth's radius. Find that the rate density of Earth analogs is about 0.02 (per star per natural log bin in period and radius) with large uncertainty. This number is much smaller than previous estimates made with the same data but stronger assumptions.
1406.3023
Driving the growth of the earliest supermassive black holes with major mergers of host galaxies
Tanaka
The formation mechanism of SMBHs in general, and of ~1e9 Msun SMBHs observed as luminous quasars at z>6 in particular, remains an open fundamental question. The presence of such massive BHs at such early times, when the Universe was less than a billion years old, implies that they grew few either super-Eddington accretion, or nearly uninterrupted gas accretion near the Eddington limit; the latter, at first glance, is at odds with empirical trends at lower redshifts, where quasar episodes associated with rapid BH growth are rare and brief. In this work, examine whether and to what extend the growth of the z>6 quasar SMBHs can be explained within the standard quasar paradigm, in which major mergers of host galaxies trigger episodes of rapid gas accretion below or near the Eddington limit. Using a suite of Monte Carlo merger tree simulations of the assembly histories of the likely hosts of the z>6 quasars, investigate (i) their growth and major merger rates out to z~40, and (ii) how long the feeding episodes induced by host mergers must last in order to explain the observed z>6 quasar population without super-Eddington accretion. The halo major merger rate scales roughly as (1+z)^5/2, with quasar hosts typically experiencing >10 major mergers between 15>z>6 (~650 Myr), compared to ~1 for typical massive galaxies at 3>z>0 (~11Gyr). An example of a viable sub-Eddignton SMBH growth model is one where a host merger triggers feeding for a duration comparable to the halo dynamical time. These findings suggest that the growth mechanisms of the earliest quasar SMBHs need not have been drastically different from their counterparts at lower redshifts.
1406.3025
Detecting industrial pollution in the atmospheres of earth-like exoplanets
Lin, Abad, Loeb
Detecting biomarker, such as molecular oxygen, in the atmospheres of transiting exoplanets has been am nor focus in the search for alien life. Point out that in addition to these generic indicators, anthropogenic pollution could be used as a novel biomarker for intelligent life. To this end, identify pollutants in the Earth's atmosphere that have significant absorption features in the spectral range covered by JWST. Estimate that for an Earth-mass planet i the habitable zone of a white dwarf, methane (CH4) and nitrous oxide (N2O) can be detected at earth-like concentrations with an integration time of ~1.5 hrs and 12 hrs respectively. Detecting pollutants that are produced nearly exclusively by anthropogenic activities will be sugfniciantly more challenging. Of these pollutants, focus on tetrafluoromethane (CF4) and trichlorofluoromethane (CCl3F), which will be the easiest to detect. Estimate that ~1.5 days (~3 days) of total integration time will be sufficient to detect or constrain the concentration of CCl3F (CF4) to ~100 times the current terrestrial level.
1406.3026
Maintaining low star formation rates in early-type galaxies with AGB heating
Conroy, van Dokkum, Kravtsov
Revisit previous suggestions that the heating provided by the winds of dying low-mass stars is capable of suppressing SF in quiescent galaxies. At the end of the asymptotic giant branch, intermediate and low-mass stars eject their envelopes rapidly in a super-wind phase, usually giving rise to planetary nebular. In galaxies with high stellar velocity dispersions, the interaction of these ejected envelopes with the ambient diffuse gas can lead to significant, isotropic and steady-state heating that scales as M_* sigma^2_*. Show that cooling of the central regions of the hot diffuse halo gas can be delayed for a Hubble time for haloes more massive than ~1e12.5 Msun at 0<z<2. This mechanism provides a natural explanation for the strong trend of galaxy quiescence with stellar surface density and velocity dispersion [what trend?], and may obviate the need for other proposed mechanisms that maintain the low observed SFRs of quiescent galaxies.
1406.3036
LensExplorer, a tool for the visualization of the gravitational lensing effect n the Hubble Frontiers Fields clusters
Diego
LensExplorer is an IDL GUI code that can be used to visualize the lensing deflection field derived in the HFF clusters. The code can be used for both research and educational purposes as it offers an intuitive way to explore the solutions in the different clusters. LensExplorer can be used to predict the magnifications at different redshifts of background sources and for a given location. Present in this document a quick guide to get started with LensExplorer. The code and lens models for A2744 and MACSJ0416.1-2403 are publicly available from a website where the new solutions ( and new versions of the code) will be also uploaded as they become available.
1406.3057
In what sense is the early universe fine-tuned?
Carroll
It is commonplace in discussions of modern cosmology to assert that the early universe began in a special state. Conventionally, cosmologists characterize the fine-tuning in terms of the horizon and flatness problems. Argue that the fine-tuning is real, but these problems aren't the best way to think about it: causal disconnection of separated regions isn't the real problem, and flatness isn't a problem at all. Fine-tuning is better understood in terms of a measure on the space of trajectories: given reasonable conditions in the late universe, the fraction of cosmological histories that were smooth at early times is incredibly tiny. This discussion helps clarify what is required by a complete theory of cosmological initial conditions.
1406.3102
Search for strong gravitational lensing effect in the current GRB data of BATSE
Li, Li
Because GRBs trace high-z Universe, there is an appreciable probability for a GRB to be gravitationally lensed by galaxies in the universe. Consider the gravitational lensing effect of GRBs contributed by the DM haloes in galaxies. Assuming that all halos have the SIS mass profile in the mass range 1e10 Msun/h < M < 2e13 Msun/h and all GRB samples follow the intrinsic redshift distribution and luminosity function derived from the Swift LGRBs sample, calculated the gravitational lensing probability in BATSE, Swift/BAT and Fermi/GBM GRBs, respectively. With a derived probability result in BATSE GRBs, searched for lensed GRB pairs in the BATSE 5B GRB Spectral catalog. The search did not find any convincing gravitationally lensed events. Discuss result and future observations for GRB lensing observation.
1406.3330
Joint likelihood function of cluster counts and $n$-point correlation functions: improving their power through including halo sample variance
Schaan, Takada, Spergel
Naive estimates of the statistics of LSS and WL PS measurements that include only Gaussian errors exaggerate their scientific impact. NL evolution and finite volume effects are both significant sources of non-Gaussian covariance that reduce the ability of PS measurements to constrain cosmological parameters. Using a halo model formalism, derive an intuitive understanding of the various contributions to the covariance and show that the analytical treatment agrees with simulations. This approach enables an approximate derivation of a joint likelihood for the cluster number counts, the WL PS and the bispectrum. Show that this likelihood is a good description of the ray-tracing simulation. Since all of these observables are sensitive to the same finite volume effects and contain information about the NL evolution, a combined analysis recovers much of the "lost" information and obviates the non-Gaussian covariance. For upcoming WL surveys, estimate that a joint analysis of PS, number counts and bispectrum will produce an improvement of about 30-40% in determinations of the matter density and scalar amplitude. This improvement is equivalent to doubling the survey area.
1406.3044
Astronomy of two Indian tribes: Banjaras and Kolams
Vahia et al
As the title says. ...Show that apart from the absolute importance of the data on human perception of the sky, the data also reveal subtle aspects of interactions between physically co-located but otherwise isolated communities as well as their own lifestyles. Also show that there is a strong relationship between profession and perspective of the sky.
Wednesday, June 11, 2014
Day 677
Thursday.
1406.2702
A rigorous free-form lens model of Abell 2744 to meet the Hubble frontier fields challenge
Lam, Broadhurst, Diego, Lim, Coe, Ford, Zheng
Deep Hubble Frontier Fields (HFF) imaging of the most powerful lensing clusters provides access to the most magnified distant galaxies. It is a challenge to construct lens models capable of describing these complex massive, merging clusters so that the intrinsic source properties can be meaningfully derived. Apply the general free-form lensing method (WSLAP+) to A2744, providing a model independent map of the cluster magnification and geometric distance estimates to multiply-lensed sources. Solve simultaneously for a smooth cluster component on a pixel grid, together with local deflections by the observed member galaxies. Solution is sufficiently accurate to securely identify 18 multiply-lensed systems behind A2744 totally 56 images, spanning 1.0<z<7.5. Model corrects and completes several systems recently claimed using the same data. The reconstructed mass shows a small enhancement in the direction where significant amount of hot plasma can be seen in X-rays. Compare photometric redshift estimates with "geometric redshifts", derived from the relative angles between the multiple images, finding tight agreement and consistency with the standard cosmological parameters. Predicted and observed magnitudes were found to agree with each other in general, but further refinement in the lens model is required such that the magnification can be accurately corrected. Intriguingly, no multiply-lensed galaxy is detected beyond z=7.5, despite the high magnification and the limiting redshift of z=11.5 permitted by the HFF filters. With the additional HFF clusters, can better examine the plausibility of any pronounced high-z deficit, averaging over clustering noise, with potentially important implications for the epoch of deionization and the nature of dark matter.
1406.2872
3C 220.3: a radio galaxy lensing a submillimeter galaxy
Haas, ... et al
Herschel Space Observatory photometry and extensive multi wavelength followup have revealed that the powerful radio galaxy 3C 220.3 at z=0.685 acts as a gravitational lens for a background SMG at z=2.221. At an observed wavelength of 1mm, the SMG is lensed into 3 distinct images. In the observed near infrared, these images are connected by an arc of 1.8" radius forming an Einstein half-ring centered near the radio galaxy. In the visible light, only the arc is apparent. 3C 220.3 is the only known instance of strong galaxy-scale lensing by a powerful radio galaxy not located in a galaxy cluster and therefore it offers the potential to probe the DM content of the rail galaxy host. Lens modeling rejects a single lens, but two lenses centered on the radio galaxy host A and a companion B, separated by 1.5", provide a fit consistent with all data and reveal faint candidates for the predicted fourth and fifth images. The model does not require an extended common dark halo, consistent with the absence of extended bright X-ray emission on the Chandra image. The projected DM fractions within the Einstein radii of A(1.02") and B(0.61") are about 0.4pm0.3 and 0.55pm0.3. The mass to i-band light ratios of A and B, M/L~8pm4 Msun/Lsun, appear comparable to those of radio-quiet lensing galaxies at the same redshift in the CASTLES, LSD, and SL2S samples. The lensed SMG is extremely bright with observed f(250um)=440mJy owing to a magnification factor mu~10. The SMG spectrum shows luminous, narrow CIV 154.9nm emission, revealing that the SMG houses a hidden quasar in addition to a violent starburst. Multicolor image reconstruction of the SMG indicates a bipolar morphology of the emitted UV light suggestive of cones through which UV light escapes a dust-enshrouded nucleus.
1406.2967
Characterizing simulated galaxy stellar mass histories
Cohn, van de Voort
Galaxy formation simulations can now predict many galaxy properties and their evolution through time. Classify ensembles of simulated stellar mass histories, holding fixed their z=0 stellar mass. Applied PCA to stellar mass histories from the DM + SAM Millennium sim and the hydrodynamical OverWhelmingly Large Simulations (OWLS) project, finding that a large fraction of the total scatter around the average stellar mass history for each sample is due to only one PCA fluctuation. This fluctuation differs between some different models sharing the same z=0 stellar mass and between lower (<=3e10 Msun) and higher final stellar mass Millennium samples. Correlated the PCA characterization with several z=0 galaxy observables (in principle observable in a survey) and galaxy halo history properties. Also explored separating galaxy stellar mass histories into classes, using the largest PCA contribution, k-means clustering, and simple Gaussian mixture models. For three component models, these different methods often had significant overlap. Provide several classification quantities for the Millennium and OWLS stellar mass histories, which can be compared with other simulation histories as well. These history classification methods provide a succinct and often quick way to characterize changes in histories of a simulated population as physical assumptions are varied, to compare histories of different simulated populations to each other, and to assess the relation of simulated histories to fixed time observations.
1406.2702
A rigorous free-form lens model of Abell 2744 to meet the Hubble frontier fields challenge
Lam, Broadhurst, Diego, Lim, Coe, Ford, Zheng
Deep Hubble Frontier Fields (HFF) imaging of the most powerful lensing clusters provides access to the most magnified distant galaxies. It is a challenge to construct lens models capable of describing these complex massive, merging clusters so that the intrinsic source properties can be meaningfully derived. Apply the general free-form lensing method (WSLAP+) to A2744, providing a model independent map of the cluster magnification and geometric distance estimates to multiply-lensed sources. Solve simultaneously for a smooth cluster component on a pixel grid, together with local deflections by the observed member galaxies. Solution is sufficiently accurate to securely identify 18 multiply-lensed systems behind A2744 totally 56 images, spanning 1.0<z<7.5. Model corrects and completes several systems recently claimed using the same data. The reconstructed mass shows a small enhancement in the direction where significant amount of hot plasma can be seen in X-rays. Compare photometric redshift estimates with "geometric redshifts", derived from the relative angles between the multiple images, finding tight agreement and consistency with the standard cosmological parameters. Predicted and observed magnitudes were found to agree with each other in general, but further refinement in the lens model is required such that the magnification can be accurately corrected. Intriguingly, no multiply-lensed galaxy is detected beyond z=7.5, despite the high magnification and the limiting redshift of z=11.5 permitted by the HFF filters. With the additional HFF clusters, can better examine the plausibility of any pronounced high-z deficit, averaging over clustering noise, with potentially important implications for the epoch of deionization and the nature of dark matter.
1406.2872
3C 220.3: a radio galaxy lensing a submillimeter galaxy
Haas, ... et al
Herschel Space Observatory photometry and extensive multi wavelength followup have revealed that the powerful radio galaxy 3C 220.3 at z=0.685 acts as a gravitational lens for a background SMG at z=2.221. At an observed wavelength of 1mm, the SMG is lensed into 3 distinct images. In the observed near infrared, these images are connected by an arc of 1.8" radius forming an Einstein half-ring centered near the radio galaxy. In the visible light, only the arc is apparent. 3C 220.3 is the only known instance of strong galaxy-scale lensing by a powerful radio galaxy not located in a galaxy cluster and therefore it offers the potential to probe the DM content of the rail galaxy host. Lens modeling rejects a single lens, but two lenses centered on the radio galaxy host A and a companion B, separated by 1.5", provide a fit consistent with all data and reveal faint candidates for the predicted fourth and fifth images. The model does not require an extended common dark halo, consistent with the absence of extended bright X-ray emission on the Chandra image. The projected DM fractions within the Einstein radii of A(1.02") and B(0.61") are about 0.4pm0.3 and 0.55pm0.3. The mass to i-band light ratios of A and B, M/L~8pm4 Msun/Lsun, appear comparable to those of radio-quiet lensing galaxies at the same redshift in the CASTLES, LSD, and SL2S samples. The lensed SMG is extremely bright with observed f(250um)=440mJy owing to a magnification factor mu~10. The SMG spectrum shows luminous, narrow CIV 154.9nm emission, revealing that the SMG houses a hidden quasar in addition to a violent starburst. Multicolor image reconstruction of the SMG indicates a bipolar morphology of the emitted UV light suggestive of cones through which UV light escapes a dust-enshrouded nucleus.
1406.2967
Characterizing simulated galaxy stellar mass histories
Cohn, van de Voort
Galaxy formation simulations can now predict many galaxy properties and their evolution through time. Classify ensembles of simulated stellar mass histories, holding fixed their z=0 stellar mass. Applied PCA to stellar mass histories from the DM + SAM Millennium sim and the hydrodynamical OverWhelmingly Large Simulations (OWLS) project, finding that a large fraction of the total scatter around the average stellar mass history for each sample is due to only one PCA fluctuation. This fluctuation differs between some different models sharing the same z=0 stellar mass and between lower (<=3e10 Msun) and higher final stellar mass Millennium samples. Correlated the PCA characterization with several z=0 galaxy observables (in principle observable in a survey) and galaxy halo history properties. Also explored separating galaxy stellar mass histories into classes, using the largest PCA contribution, k-means clustering, and simple Gaussian mixture models. For three component models, these different methods often had significant overlap. Provide several classification quantities for the Millennium and OWLS stellar mass histories, which can be compared with other simulation histories as well. These history classification methods provide a succinct and often quick way to characterize changes in histories of a simulated population as physical assumptions are varied, to compare histories of different simulated populations to each other, and to assess the relation of simulated histories to fixed time observations.
Tuesday, June 10, 2014
Day 676
Wednesday.
1406.2314
Halo mass dependence of HI and OVI absorption: evidence for differential kinematics
Mathes et al
Study a sample of 14 galaxies (0.1<z<0.7) with HST/WFPC2 and COS or STIS quasar spectroscopy of Lya, Lyb, OVI1031, and OVI1037 absorption. The galaxies, having 1.8<log(M/Msun)<12.2, lie within D=300 kpc of quasar sight lines, probing out to D/R_vir=3. When the full range of galaxy virial masses and D/R_vir of the sample are examined, 40% of the HI absorbing clouds can be inferred to be escaping their host halo. The fraction of bound clouds decreases as D/R_vir increases such that the escaping fraction is around 15% for D/R_vir<1, around 45% for 1<D/R_vir<2, and around 90% for 2<D/R_vir<3. Adopting the median mass log(M/Msun)=11.5 to divide the sample into "higher" and "lower" mass galaxies, find mass dependence for the hot CGM kinematics. To the survey limits, OVI absorption is found in only 40% of the HI clouds in and around lower mass haloes as compared to 85% around higher mass haloes. For D/R<1, lower mass haloes have an escape fraction of 65%, whereas higher mass haloes have an escape fraction of 5%. For 1<D/R_vir<2, the escape fractions are 55% and 35% for lower mass and higher mass haloes, respectively, for 2<D/R_vir<3, the escape fraction for lower mass haloes is around 90%. Show that it is highly likely that the absorbing clouds reside within 4 virial radii of their host galaxies and that the kinematics are dominated by outflows. Finding of "differential kinematics" is consistent with the scenario of "differential wind recycling" proposed by Oppenheimer+. Discuss the implications for galaxy evolution, the stellar halo mass function, and the mass metallicity relationship of galaxies.
1406.2315
The discovery of seven extremely low surface brightness galaxies in the field of the nearby spiral galaxy M101
Merritt, van Dokkum, Abraham
Dwarf satellite galaxies are a key probe of DM and of galaxy formation on small scales and of the DM halo masses of their central galaxies. They have very low surface brightness, which makes it difficult to identify and study them outside of the Local Group. Used the Dragonfly Telephoto Array to search for dwarf galaxies in the field of the massive spiral galaxy M101. Identify 7 large, LSB objects in this field, with effective radii of 10-30 arc seconds and central surface brightness of mu_g~25.5-27.5 mag/arcsec^2. Given their large apparent sizes and low surface brightnesses, these objects would likely be missed by standard galaxy searches in deep fields. Assuming the galaxies are dwarf satellites of M101, their absolute magnitudes are in the range `11.6<M_V<-9.3 and their effective radii are 350pc-1.3kpc. Their radial surface brightness profiles are well fit by Sersic profiles with a very low Sersic index (n~0.3-0.7). The properties of the sample are similar to those of well-studied dwarf galaxies in the LG, such as Sextans I and Phoenix. Distance measurements are required to determine whether these galaxies are in fact associated with M101 or are in its foreground or BG.
1406.2320
Creating mock catalogues of stellar haloes from cosmological simulations
Lowing, ... Frenk, Cole et al
Present a new technique for creating mock catalogues of the individual stars that make up the accreted component of stellar haloes in cosmo sims and show how the catalogues can be used to test and interpret observational data. Catalogues are constructed from a combination of methods. A SAM is used to calculate the SFH in haloes in an H-body sim, and DM particles are tagged with this stellar mass. The tags are converted into individual stars using a stellar population synthesis model to obtain the number density and evolutionary stage of the stars, together with a phase-space sampling method that distributes the stars while ensuring that the phase-space structure of the original N-body simulation is maintained. A set of catalogues based on the Aquarius simulations of MW mass haloes have been created and made publicly available on a website. Two example applications are discussed that demonstrate the power and flexibility of the mock catalogues. Show how the rich stellar substructure that survives in the stellar halo precludes a simple measurement of its density profile and demonstrate explicitly how pencil-beam surveys can return almost any value for the slope of the profile. Also show that localized variations in the abundance of particular types of stars, a signature of differences in the composition of stelar populations, allow streams to be easily identified.
1406.2327
Late-stage galaxy mergers in COSMOS to z~1
Lackner, ... Capak, .. Ilbert, Koekemoer, Le Fevre, Scoville... et al
Develop an automated method to identify late-stage galaxy mergers before coalescence of the galactic cores. ... Correcting for incompleteness and contamination, the fractional merger rate increases strongly with (1+z)^3.8 pm 0.9, in agreement with earlier studies and with DM halo merger rates. Separating the sample into SF and quiescent galaxies shows that the merger rate for SF galaxies increases strongly, (1+z)^4.5, while the merger rate for quiescent galaxies is consistent with no evolution (1+z)^1.1. Limiting the sample to galaxies with spectroscopic redshifts from zCOSMOS, find that the SFRs and X-ray selected AGN activity in likely late-stage mergers are enhanced by factors of ~2 relative to a control sample. Combining the sample with more widely separated paris, find that 8pm5% of SF and 20pm8% of AGN activity is triggered by close encounters (<143kpc) or mergers, once more suggesting that major mergers are not the only channels for SF and BH growth.
1406.2314
Halo mass dependence of HI and OVI absorption: evidence for differential kinematics
Mathes et al
Study a sample of 14 galaxies (0.1<z<0.7) with HST/WFPC2 and COS or STIS quasar spectroscopy of Lya, Lyb, OVI1031, and OVI1037 absorption. The galaxies, having 1.8<log(M/Msun)<12.2, lie within D=300 kpc of quasar sight lines, probing out to D/R_vir=3. When the full range of galaxy virial masses and D/R_vir of the sample are examined, 40% of the HI absorbing clouds can be inferred to be escaping their host halo. The fraction of bound clouds decreases as D/R_vir increases such that the escaping fraction is around 15% for D/R_vir<1, around 45% for 1<D/R_vir<2, and around 90% for 2<D/R_vir<3. Adopting the median mass log(M/Msun)=11.5 to divide the sample into "higher" and "lower" mass galaxies, find mass dependence for the hot CGM kinematics. To the survey limits, OVI absorption is found in only 40% of the HI clouds in and around lower mass haloes as compared to 85% around higher mass haloes. For D/R<1, lower mass haloes have an escape fraction of 65%, whereas higher mass haloes have an escape fraction of 5%. For 1<D/R_vir<2, the escape fractions are 55% and 35% for lower mass and higher mass haloes, respectively, for 2<D/R_vir<3, the escape fraction for lower mass haloes is around 90%. Show that it is highly likely that the absorbing clouds reside within 4 virial radii of their host galaxies and that the kinematics are dominated by outflows. Finding of "differential kinematics" is consistent with the scenario of "differential wind recycling" proposed by Oppenheimer+. Discuss the implications for galaxy evolution, the stellar halo mass function, and the mass metallicity relationship of galaxies.
1406.2315
The discovery of seven extremely low surface brightness galaxies in the field of the nearby spiral galaxy M101
Merritt, van Dokkum, Abraham
Dwarf satellite galaxies are a key probe of DM and of galaxy formation on small scales and of the DM halo masses of their central galaxies. They have very low surface brightness, which makes it difficult to identify and study them outside of the Local Group. Used the Dragonfly Telephoto Array to search for dwarf galaxies in the field of the massive spiral galaxy M101. Identify 7 large, LSB objects in this field, with effective radii of 10-30 arc seconds and central surface brightness of mu_g~25.5-27.5 mag/arcsec^2. Given their large apparent sizes and low surface brightnesses, these objects would likely be missed by standard galaxy searches in deep fields. Assuming the galaxies are dwarf satellites of M101, their absolute magnitudes are in the range `11.6<M_V<-9.3 and their effective radii are 350pc-1.3kpc. Their radial surface brightness profiles are well fit by Sersic profiles with a very low Sersic index (n~0.3-0.7). The properties of the sample are similar to those of well-studied dwarf galaxies in the LG, such as Sextans I and Phoenix. Distance measurements are required to determine whether these galaxies are in fact associated with M101 or are in its foreground or BG.
1406.2320
Creating mock catalogues of stellar haloes from cosmological simulations
Lowing, ... Frenk, Cole et al
Present a new technique for creating mock catalogues of the individual stars that make up the accreted component of stellar haloes in cosmo sims and show how the catalogues can be used to test and interpret observational data. Catalogues are constructed from a combination of methods. A SAM is used to calculate the SFH in haloes in an H-body sim, and DM particles are tagged with this stellar mass. The tags are converted into individual stars using a stellar population synthesis model to obtain the number density and evolutionary stage of the stars, together with a phase-space sampling method that distributes the stars while ensuring that the phase-space structure of the original N-body simulation is maintained. A set of catalogues based on the Aquarius simulations of MW mass haloes have been created and made publicly available on a website. Two example applications are discussed that demonstrate the power and flexibility of the mock catalogues. Show how the rich stellar substructure that survives in the stellar halo precludes a simple measurement of its density profile and demonstrate explicitly how pencil-beam surveys can return almost any value for the slope of the profile. Also show that localized variations in the abundance of particular types of stars, a signature of differences in the composition of stelar populations, allow streams to be easily identified.
1406.2327
Late-stage galaxy mergers in COSMOS to z~1
Lackner, ... Capak, .. Ilbert, Koekemoer, Le Fevre, Scoville... et al
Develop an automated method to identify late-stage galaxy mergers before coalescence of the galactic cores. ... Correcting for incompleteness and contamination, the fractional merger rate increases strongly with (1+z)^3.8 pm 0.9, in agreement with earlier studies and with DM halo merger rates. Separating the sample into SF and quiescent galaxies shows that the merger rate for SF galaxies increases strongly, (1+z)^4.5, while the merger rate for quiescent galaxies is consistent with no evolution (1+z)^1.1. Limiting the sample to galaxies with spectroscopic redshifts from zCOSMOS, find that the SFRs and X-ray selected AGN activity in likely late-stage mergers are enhanced by factors of ~2 relative to a control sample. Combining the sample with more widely separated paris, find that 8pm5% of SF and 20pm8% of AGN activity is triggered by close encounters (<143kpc) or mergers, once more suggesting that major mergers are not the only channels for SF and BH growth.
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