Friday. Still a week behind.
1308.4683
Hot-dust (690K) luminosity density and its evolution in the last 7.5 Gyr
Messias, Mobasher, Alfonso
Study the contribution of hot-dust to the luminosity density of galaxies and its evolution with cosmic time. Using the Spitzer IRAC data in the COSMOS field, estimate the contribution from hot-dust at rest-frame 4.2 um (from ~0<z<~0.2 up to ~0.5<z<~0.9). This wavelength corresponds to BB temperature of ~690K. The contribution due to stellar emission is estimated from the rest-frame 1.6 um luminosity (assumed to result from stellar emission alone) and subtracted from the MIR luminosity of galaxies to measure hot-dust emission. In order to attempt the study of the 3.3um-PAH feature, use the rest-frame 4.2um to infer the hot-dust flux at 3.3um. This study is performed for different spectral types of galaxies: early-type, late-type, starburst, and IR-selected AGN. Find: (a) the decrease of the hot-dust luminosity density since ~0.5<z<~1 is steeper (by at least ~0.5 dex) compared to that of the cold-dust, giving support to the scenario where galaxy obscuration increases with redshift, as already proposed in the literature; (b) hot-dust and PAH emission evolution seems to be correlated with stellar mass, where rest-frame 1.6um luminous non-AGN galaxies (i.e., massive systems) show a stronger decrement (with decreasing redshift) in hot-dust and PAH emission than the less luminous (less massive) non-AGN galaxies; (c) despite comprising <~3% of the total sample, AGN contribute as much as a third to the hot-dust luminosity density at z<1 and clearly dominate the bright-end of the total hot-dust Luminosity Density Function at ~0.5<z<~0.9; (d) at M_1.6 > -25, the dust-to-total and PAH-to-total luminosity ratios increase with decreasing luminosity, but deeper data is required to confirm this result.
1308.4728
An observational correlation between stellar brightness variations and surface gravity
Bastien, Stassun, Basri, Pepper
Surface gravity is a basic stellar property, but typical uncertainty of 25-50 per cent if measured spectroscopically and 90-150% photometrically. Astroseismology measures gravity with an uncertainty of about 2%, but is restricted to relatively small samples of bright stars, most of which are giants. The availability of high-precision measurements of brightness variations for >150,000 stars provides an opportunity to investigate whether the variations can be used to determine surface gravities. The Fourier power of granulation on a star's surface correlates physically with surface gravity; if brightness variations on timescales of hours arise from granulation, then such variations should correlate with surface gravity. Report an analysis of archival data that reveals an observational correlation between surface gravity and the root-mean-square brightness variations on timescales of less than eight hours for stars with temperatures of 4500-6750K, log of surface gravities of 2.5-4.5 (cgs units), and having overall brightness variations <3 pp thousand. A straightforward observation of optical brightness variations therefore allows a determination of the surface gravity with a precision of <25% for inactive Sun-like stars at main-sequence to giant stages of evolution.
1308.4887
Evolution towards and beyond accretion-induced collapse of massive white dwarfs and formation of millisecond pulsars
Tauris, Sanyal, Yoon, Langer
Millisecond pulsars (MSPs) are generally believed to be old neutron stars (NSs), formed via type Ib/c core-collapse SNe, which have been spun up to high rotation rates via accretion from a companion star in a low-mass X-ray binary (LMXB). In an alternative formation channel, NSs are produced via the accretion-induced collapse (AIC) of massive WD in a close binary. Investigate binary evolution leading to AIC and examine if NSs formed in this way can subsequently be recycled to form MSPs and, if so, how they can observationally be distinguished from pulsars formed via the standard core-collapse SN channel in terms of their masses, spins, orbital periods and space velocities. Numerical calculations with a detailed stellar evolution code were used for the first time to study the combined pre- and post-AIC evolution of close binaries. Investigate the mass transfer onto a massive WD in 240 systems with 3 different types of non-degenerate donor stars: MS stars, red giants, and helium stars. When the WD is able to accrete sufficient mass (depending on the mass-transfer rate and the duration of the accretion phase) assumed it collapses to form a NS and study the dynamical effects of this implosion on the binary orbit. Subsequently, follow the mass-transfer epoch which resumes once the donor star refills its Roche lobe and calculate the continued LMXB evolution until the end. Demonstrate that the final properties of these MSPs are, in general, remarkably similar to those of MSPs formed via the standard core-collapse SN channel. However, the resultant MSPs created via the ACI channel preferentially form in certain orbital period intervals. Finally, discuss the link between AIC and young NSs in globular clusters. Calculations are applicable to progenitor binaries of SNe Ia under certain conditions.
Saturday, August 31, 2013
Friday, August 30, 2013
Day 495
Thursday. Still a week behind.
1308.3299
The Herschel Stripe 82 Survey (HerS): Maps and Early Catalog
Viero, ... Devlin, Dore, ... et al
Present the first set of maps and band-merged catalog from Herschel Stripe 82 survey; observations at 250, 350, and 500 um with SPIRE on Herschel. Covers 79 deg^2 along Stripe 82 to 13.0, 12.9, and 14.8 mJy beam-1 (including confusion), respectively. The band-merged catalog contains 2.7e4 sources detected at >5 sigma. HerS designed to measure correlations with external tracers of DM density field -- either point-like (i.e., galaxies selected from radio to X-ray) or extended (i.e., clusters and gravitational lensing) -- in order to measure the bias and redshift distribution of intensities of infrared-emitting dusty SF galaxies and AGN. By locating HeRS in Stripe 82, maximize the overlap with available and upcoming cosmological surveys. The maps and catalogs available online.
1308.4405
CANDELS multi-wavelength catalogs: source detection and photometry in the GOODS-South field
Guo, ... Koekemoer, Koo, ... et al
As the title says. HST/WFC3 F105W, F125W, F160W + existing public data. Catalog based on detection in F160W band. 34,930 sources; 50% completeness at 25.9, 26.6 and 28.1 AB in F160W band, for the CANDELS wide, deep, and HUDF regions, respectively.
1308.4612
Searching for millisecond pulsars: surveys, techniques and prospects
Stovall, Lorimer, Lynch
Searches for millisecond pulsars (periods < 20 ms) in the Galactic field have undergone a renaissance in the past five years. New or recently refurbished radio telescopes utilizing cooled receivers and state-of-the-art digital data acquisition systems are carrying out surveys of the entire sky at a variety of radio frequencies. Targeted searches for millisecond pulsars in point sources identified by the Fermi Gamma-ray space telescope have proved phenomenally successful, with over 50 discoveries in the past five years. The current sample of millisecond pulsars now numbers almost 200 and, for the first time in 25 years, now outnumbers their counterparts in Galactic globular clusters. While many of these searches are motivated to find pulsars which form part of pulsar timing arrays, a wide variety of interesting systems are now being found. Following a brief overview of the millisecond pulsar phenomenon, describe these searches and present some of the highlights of the new discoveries in the past decade. Conclude with predictions and prospects for ongoing and future surveys.
1308.4633
Optical proper motion measurements of the M87 jet: new results from the Hubble space telescope
Meyer, et al
Using over 13 yrs of archival imaging, reach accuracies below 0.1c in measuring the apparent velocities of individual knots in the jet. Confirm previous findings of speeds up to 4.5c in the inner 6" of the jet, and report new speeds for optical components in the outer part of the jet. Find evidence of significant motion transverse to the jet axis on the order of 0.6c in the inner jet features, and superluminal velocities parallel and transverse to the jet in the outer knot components, with an apparent ordering of velocity vectors possibly consistent with a helical jet pattern. Previous results suggested a global deceleration over the length of the jet in the form of decreasing maximum speeds of knot components from HST-1 outward, but results suggest that superluminal speeds persist out to knot C, with large differentials in very nearby features all along the jet. Find significant apparent accelerations in directions parallel and transverse to the jet axis, along with evidence for stationary features in knots D, E, and I. These results are expected to place important constraints on detailed models of kpc-scale relativistic jets.
1308.4646
Evolution in the H I gas content of galaxy groups: pre-processing and mass assembly in the current epoch
Hess, Wilcots
Assigned ALFALFA HI detections a group membership based on an existing magnitude/volume-limited SDSS DR7 group/cluster catalog. Additionally, assigned group "proximity" membership to HI detected objects whose optical counterpart falls below the limiting optical magnitude- thereby not contributing substantially to the estimate of the group stellar mass, but significantly to the total group HI mass. Find that only 25% of the HI detected galaxies reside in groups or clusters, in contrast to approximately half of all optically detected galaxies. Further, plot the relative positions of optical and HI detections in groups as a function of parent DM halo mass to reveal strong evidence that HI is being processed in galaxies as a result of the group environment: as optical membership increases, groups become increasingly deficient of HI rich galaxies at their center and the HI distribution of galaxies in the most massive groups starts to resemble the distribution observed in comparatively more extreme cluster environments. Find that the lowest HI mass objects lose their gas first as they are processed in the group environment, and it is evident that the infall of gas rich objects is important to the continuing growth of large scale structure at the present epoch, replenishing the neutral gas supply of groups. Finally, compare results to those of cosmological simulations and find that current models cannot simultaneously predict the HI selected halo occupation distribution for both low and high mass haloes.
1308.4663
S\'{e}rsic galaxy models in weak lensing shape measurement: model bias, noise bias and their interaction
Kacprzak, Bridle, Rowe, Voigt, Zuntz, Hirsch, MacCrann
In galaxy shape measurements: Model bias occurs when the true galaxy shape is not well represented by the fitted model. Noise bias occurs due to the non-linear relationship between image pixels and galaxy shape. In this paper, investigate the potential interplay between these two effects when an imperfect model is used in the presence of high noise. Present analytical expressions for this bias, which depends on the residual difference between the model and real data. They can lead to biases not accounted for in previous calibration schemes. By measuring the model bias, noise bias and their interaction, provide a complete statistical framework for measuring galaxy shapes with model fitting methods from GREAT like images. Demonstrate the noise and model interaction bias using a simple toy model, which indicates that this effect can potentially be significant Using real galaxy images from the COSMOS quantify the strength of the model bias, noise bias and their interaction. Find that the interaction term is often a similar size to the model bias term, and is smaller than the requirements of the current and shortly upcoming galaxy surveys.
1308.3299
The Herschel Stripe 82 Survey (HerS): Maps and Early Catalog
Viero, ... Devlin, Dore, ... et al
Present the first set of maps and band-merged catalog from Herschel Stripe 82 survey; observations at 250, 350, and 500 um with SPIRE on Herschel. Covers 79 deg^2 along Stripe 82 to 13.0, 12.9, and 14.8 mJy beam-1 (including confusion), respectively. The band-merged catalog contains 2.7e4 sources detected at >5 sigma. HerS designed to measure correlations with external tracers of DM density field -- either point-like (i.e., galaxies selected from radio to X-ray) or extended (i.e., clusters and gravitational lensing) -- in order to measure the bias and redshift distribution of intensities of infrared-emitting dusty SF galaxies and AGN. By locating HeRS in Stripe 82, maximize the overlap with available and upcoming cosmological surveys. The maps and catalogs available online.
1308.4405
CANDELS multi-wavelength catalogs: source detection and photometry in the GOODS-South field
Guo, ... Koekemoer, Koo, ... et al
As the title says. HST/WFC3 F105W, F125W, F160W + existing public data. Catalog based on detection in F160W band. 34,930 sources; 50% completeness at 25.9, 26.6 and 28.1 AB in F160W band, for the CANDELS wide, deep, and HUDF regions, respectively.
1308.4612
Searching for millisecond pulsars: surveys, techniques and prospects
Stovall, Lorimer, Lynch
Searches for millisecond pulsars (periods < 20 ms) in the Galactic field have undergone a renaissance in the past five years. New or recently refurbished radio telescopes utilizing cooled receivers and state-of-the-art digital data acquisition systems are carrying out surveys of the entire sky at a variety of radio frequencies. Targeted searches for millisecond pulsars in point sources identified by the Fermi Gamma-ray space telescope have proved phenomenally successful, with over 50 discoveries in the past five years. The current sample of millisecond pulsars now numbers almost 200 and, for the first time in 25 years, now outnumbers their counterparts in Galactic globular clusters. While many of these searches are motivated to find pulsars which form part of pulsar timing arrays, a wide variety of interesting systems are now being found. Following a brief overview of the millisecond pulsar phenomenon, describe these searches and present some of the highlights of the new discoveries in the past decade. Conclude with predictions and prospects for ongoing and future surveys.
1308.4633
Optical proper motion measurements of the M87 jet: new results from the Hubble space telescope
Meyer, et al
Using over 13 yrs of archival imaging, reach accuracies below 0.1c in measuring the apparent velocities of individual knots in the jet. Confirm previous findings of speeds up to 4.5c in the inner 6" of the jet, and report new speeds for optical components in the outer part of the jet. Find evidence of significant motion transverse to the jet axis on the order of 0.6c in the inner jet features, and superluminal velocities parallel and transverse to the jet in the outer knot components, with an apparent ordering of velocity vectors possibly consistent with a helical jet pattern. Previous results suggested a global deceleration over the length of the jet in the form of decreasing maximum speeds of knot components from HST-1 outward, but results suggest that superluminal speeds persist out to knot C, with large differentials in very nearby features all along the jet. Find significant apparent accelerations in directions parallel and transverse to the jet axis, along with evidence for stationary features in knots D, E, and I. These results are expected to place important constraints on detailed models of kpc-scale relativistic jets.
1308.4646
Evolution in the H I gas content of galaxy groups: pre-processing and mass assembly in the current epoch
Hess, Wilcots
Assigned ALFALFA HI detections a group membership based on an existing magnitude/volume-limited SDSS DR7 group/cluster catalog. Additionally, assigned group "proximity" membership to HI detected objects whose optical counterpart falls below the limiting optical magnitude- thereby not contributing substantially to the estimate of the group stellar mass, but significantly to the total group HI mass. Find that only 25% of the HI detected galaxies reside in groups or clusters, in contrast to approximately half of all optically detected galaxies. Further, plot the relative positions of optical and HI detections in groups as a function of parent DM halo mass to reveal strong evidence that HI is being processed in galaxies as a result of the group environment: as optical membership increases, groups become increasingly deficient of HI rich galaxies at their center and the HI distribution of galaxies in the most massive groups starts to resemble the distribution observed in comparatively more extreme cluster environments. Find that the lowest HI mass objects lose their gas first as they are processed in the group environment, and it is evident that the infall of gas rich objects is important to the continuing growth of large scale structure at the present epoch, replenishing the neutral gas supply of groups. Finally, compare results to those of cosmological simulations and find that current models cannot simultaneously predict the HI selected halo occupation distribution for both low and high mass haloes.
1308.4663
S\'{e}rsic galaxy models in weak lensing shape measurement: model bias, noise bias and their interaction
Kacprzak, Bridle, Rowe, Voigt, Zuntz, Hirsch, MacCrann
In galaxy shape measurements: Model bias occurs when the true galaxy shape is not well represented by the fitted model. Noise bias occurs due to the non-linear relationship between image pixels and galaxy shape. In this paper, investigate the potential interplay between these two effects when an imperfect model is used in the presence of high noise. Present analytical expressions for this bias, which depends on the residual difference between the model and real data. They can lead to biases not accounted for in previous calibration schemes. By measuring the model bias, noise bias and their interaction, provide a complete statistical framework for measuring galaxy shapes with model fitting methods from GREAT like images. Demonstrate the noise and model interaction bias using a simple toy model, which indicates that this effect can potentially be significant Using real galaxy images from the COSMOS quantify the strength of the model bias, noise bias and their interaction. Find that the interaction term is often a similar size to the model bias term, and is smaller than the requirements of the current and shortly upcoming galaxy surveys.
Thursday, August 29, 2013
Day 494
Wednesday.
1308.4132
How dead are dead galaxies? Mid-infrared fluxes of quiescent galaxies at redshift 0.3 < z < 2.5: implications for star formation rates and dust heating
Fumagalli, ... van Dokkum, ... Kriek, ... Rix, ... et al
Investigate SFRs of quiescent galaxies at 0.3<z<2.5 using 3d-HST WFC3 grism spectroscopy and Spitzer MIR data. Select quiescent galaxies on the basis of the widely used UVJ color-color criteria. SED fitting (rest frame optical and NIR) indicates very low SFRs for quiescent galaxies (sSFR~1e-12/yr). However, SED fitting can miss SF if it is hidden behind high dust obscuration and ionizing radiation is re-emitted in the MIR. It is therefore fundamental to measure the dust-obscured SFRs with a MIR indicator. Stack the MIPS-24um images of quiescent objects in 5 redshift bins centered on z=0.5, 0.9, 1.2, 1.7, 2.2 and perform aperture photometry. Including direct 24um detections, find sSFR~1e-11.9 * (1+z)^4 /yr. These values are higher than those indicated by SED fitting, but at each redshift they are 20-40 times lower than those of typical SF galaxies. The true SFRs of quiescent galaxies might be even lower, as it is shown that the MIR fluxes can be due to processes unrelated to ongoing SF, such as cirrus dust heated by old stellar populations and circumstellar dust. Measurements show that SF quenching is very efficient at every redshift. The measured SFR values are at z>1.5 marginally consistent with the ones expected from gas recycling (assuming that mass loss from evolved stars refuels SF) and well above that at lower redshifts.
1308.4141
21-cm absorption from galaxies at $z\sim0.3$
Gupta et al
As the title says. Two intervening systems towards quasars detected.
1308.4142
The locations of halo formation and the peaks formalism
Hahn, Paranjape
Investigate a fundamental problem of structure formation: predicting the mass function of collapsed, virialized structures from the properties of the Lagrangian density field. In this paper, focus on structure formation from a perturbation spectrum with a small-scale cut-off (as in warm dark matter cosmologies) in which the number of density peaks - and the resulting number of virialized objects - is finite. The PS cut-off results in a strong suppression of low mass objects, providing additional leverage to rigorously test which perturbations collapse and to what mass. Find that all haloes are consistent with forming near peaks of the initial density field. The density of a proto-halo depends strongly on the ellipticity of the Lagrangian velocity shear field, but not on its prolateness. Demonstrate that, while standard excursion set theory with correlated steps completely fails to reproduce the mass function, the inclusion of the peaks constraint leads to the correct number of haloes but significantly underpredicts the masses of low-mass objects (with the halo mass function at low masses behaving like dn/dln m ~ m^2/3). This prediction is very robust and cannot be easily altered within the framework of a single collapse barrier. The nature of collapse in the presence of a small-scale cut-off thus reveals that excursion set calculations require a more detailed understanding of the collapse-time of a general ellipsoidal perturbation in order to predict the ultimate collapsed mass of a peak - a problem that has been hidden in the large abundance of small-scale structure in CDM. Demonstrate how this problem can be resolved within the excursion set framework.
1308.4145
The first analytical expression to estimate photometric redshifts suggested by a machine
Krone-Martins, Ishida, de Souza
A simple and reliable analytic, functional form to determine photo-z of galaxies; derived from 41k galaxies from SDSS DR10 spectroscopic sample. The method automatically dropped the u and z bands, relying only on g,r, and i for the final solution. Apply this expression to the other 1.4M galaxies with z_spec, achieve a mean dz/(1+z_s)<0.0086 and scatter 0.045 wen averaged up to z<1.0. This work is the first use of symbolic regression in cosmology, representing a leap forward in astronomy-data-mining connection.
1308.4150
Damn you, little h! (or, real-world applications of the Hubble constant using observed and simulated data)
Croton
He Hubble constant H0, or its dimensionless equivalent, "littel h", is a fundamental cosmological property that is now known to an accuracy better than a few percent. Despite its osmological nature, little h commonly appears in the measured properties of individual galaxies. This can pose unique challenges for users of such data, particularly with survey data. In this paper, show how little h arises in the measurement of galaxies, how to compare like-properties from different datasets that have assumed different little h cosmologies, and how to fairly compare theoretical data with observed data, where little h can manifest in vastly different ways. This last point is particularly important when observations are used to calibrate galaxy formation models, as calibrating the wrong (or no) little h can lead to disastrous results when the model is later converted to the correct h cosmology. Argue that in this modern age, little h is an anachronism, being one of the least uncertain parameters in astrophysics, and propose that observers and theorists instead treat this uncertainty like any other. Conclude with a "cheat sheet" of nine points that should be followed when dealing with little h in data analysis.
1308.4164
DESI and other dark energy experiments in the era of neutrino mass measurements
Font-Ribera, McDonald, Mostek, Reid, Seo, Slosar
Fisher matrix projections for future cosmological parameter measurements, including neutrino masses, DE, curvature, modified gravity, the inflationary perturbation spectrum, non-Gaussianity, and dark radiation. Focus on DESI and generally redshift surveys (BOSS, HETDEX, eBOSS, Euclid, and WFIRST), but also include CMB (Planck) and WL (DES and LSST) constraints. The goal is to present a consistent set of projections, for concrete experiments, which are otherwise scattered throughout many papers and proposals. Include neutrino mass as a free parameter in most projections, as it will inevitably be relevant -- DESI and other experiments can measure the sum of neutrino masses to ~0.02 eV or better, where the minimum possible sum is ~0.06 eV. Note that the BAO-only use of galaxy clustering is substantially degraded as a DE probe in the presence of neutrino mass uncertainty -- using broadband galaxy power is critical, especially pushing it to as small a scale as possible, and big gains are achieved by combining lensing survey constraints with redshift survey constraints. Do not try to be especially innovative, e.g., in careful treatments of potential systematic errors -- these projections are intended as a straightforward baseline for comparison to more detailed analyses.
1308.4299
Dust properties of clumpy disc galaxies at z~1.3 with Herschel-SPIRE
Wisnioski, Glazebrook, Blake, Swinbank
Present FIR derived dust properties from Herschel SPIRE of the WiggleZ kinematic sample of13 SF galaxies at z~1.3, with existing ancillary ~kpc resolution integral field spectroscopy. Detect 3 galaxies individually and place limits on the remainder by stacking. The detected galaxies, two clumpy disks and one merger, have cold dust temperatures of ~26 K and have IR luminosities of ~1.2e12 Lsun, determined by modified BB fitting. The 2 detected disc galaxies have the largest Ha surface areas of the sample and have the reddest UV to NIR SED. The likely source of the IR luminosity in these objects is dust heated by the interstellar radiation field and young stellar emission from the clumps within the discs. The source of IR luminosity for the merger is likely a dust heated by a starburst resulting from the merger. The WiggleZ detections are among the coldest and lowest luminosity individual objects detected in the FIR at z>1. When combining the kinematic data, find that none of the compact galaxies nor the 'dispersion dominated' galaxies of the WiggleZ kinematic sample are detected, implying that they have warmer dust temperatures. The compact objects show the highest Ha velocity dispersions in the sample, in qualitative agreement with bulge formation models. These FR results strengthen the interpretation that the majority of galaxies in this sample constitute different stages in clumpy disc formation as presented from ancillary kinematic analysis.
1308.4132
How dead are dead galaxies? Mid-infrared fluxes of quiescent galaxies at redshift 0.3 < z < 2.5: implications for star formation rates and dust heating
Fumagalli, ... van Dokkum, ... Kriek, ... Rix, ... et al
Investigate SFRs of quiescent galaxies at 0.3<z<2.5 using 3d-HST WFC3 grism spectroscopy and Spitzer MIR data. Select quiescent galaxies on the basis of the widely used UVJ color-color criteria. SED fitting (rest frame optical and NIR) indicates very low SFRs for quiescent galaxies (sSFR~1e-12/yr). However, SED fitting can miss SF if it is hidden behind high dust obscuration and ionizing radiation is re-emitted in the MIR. It is therefore fundamental to measure the dust-obscured SFRs with a MIR indicator. Stack the MIPS-24um images of quiescent objects in 5 redshift bins centered on z=0.5, 0.9, 1.2, 1.7, 2.2 and perform aperture photometry. Including direct 24um detections, find sSFR~1e-11.9 * (1+z)^4 /yr. These values are higher than those indicated by SED fitting, but at each redshift they are 20-40 times lower than those of typical SF galaxies. The true SFRs of quiescent galaxies might be even lower, as it is shown that the MIR fluxes can be due to processes unrelated to ongoing SF, such as cirrus dust heated by old stellar populations and circumstellar dust. Measurements show that SF quenching is very efficient at every redshift. The measured SFR values are at z>1.5 marginally consistent with the ones expected from gas recycling (assuming that mass loss from evolved stars refuels SF) and well above that at lower redshifts.
1308.4141
21-cm absorption from galaxies at $z\sim0.3$
Gupta et al
As the title says. Two intervening systems towards quasars detected.
1308.4142
The locations of halo formation and the peaks formalism
Hahn, Paranjape
Investigate a fundamental problem of structure formation: predicting the mass function of collapsed, virialized structures from the properties of the Lagrangian density field. In this paper, focus on structure formation from a perturbation spectrum with a small-scale cut-off (as in warm dark matter cosmologies) in which the number of density peaks - and the resulting number of virialized objects - is finite. The PS cut-off results in a strong suppression of low mass objects, providing additional leverage to rigorously test which perturbations collapse and to what mass. Find that all haloes are consistent with forming near peaks of the initial density field. The density of a proto-halo depends strongly on the ellipticity of the Lagrangian velocity shear field, but not on its prolateness. Demonstrate that, while standard excursion set theory with correlated steps completely fails to reproduce the mass function, the inclusion of the peaks constraint leads to the correct number of haloes but significantly underpredicts the masses of low-mass objects (with the halo mass function at low masses behaving like dn/dln m ~ m^2/3). This prediction is very robust and cannot be easily altered within the framework of a single collapse barrier. The nature of collapse in the presence of a small-scale cut-off thus reveals that excursion set calculations require a more detailed understanding of the collapse-time of a general ellipsoidal perturbation in order to predict the ultimate collapsed mass of a peak - a problem that has been hidden in the large abundance of small-scale structure in CDM. Demonstrate how this problem can be resolved within the excursion set framework.
1308.4145
The first analytical expression to estimate photometric redshifts suggested by a machine
Krone-Martins, Ishida, de Souza
A simple and reliable analytic, functional form to determine photo-z of galaxies; derived from 41k galaxies from SDSS DR10 spectroscopic sample. The method automatically dropped the u and z bands, relying only on g,r, and i for the final solution. Apply this expression to the other 1.4M galaxies with z_spec, achieve a mean dz/(1+z_s)<0.0086 and scatter 0.045 wen averaged up to z<1.0. This work is the first use of symbolic regression in cosmology, representing a leap forward in astronomy-data-mining connection.
1308.4150
Damn you, little h! (or, real-world applications of the Hubble constant using observed and simulated data)
Croton
He Hubble constant H0, or its dimensionless equivalent, "littel h", is a fundamental cosmological property that is now known to an accuracy better than a few percent. Despite its osmological nature, little h commonly appears in the measured properties of individual galaxies. This can pose unique challenges for users of such data, particularly with survey data. In this paper, show how little h arises in the measurement of galaxies, how to compare like-properties from different datasets that have assumed different little h cosmologies, and how to fairly compare theoretical data with observed data, where little h can manifest in vastly different ways. This last point is particularly important when observations are used to calibrate galaxy formation models, as calibrating the wrong (or no) little h can lead to disastrous results when the model is later converted to the correct h cosmology. Argue that in this modern age, little h is an anachronism, being one of the least uncertain parameters in astrophysics, and propose that observers and theorists instead treat this uncertainty like any other. Conclude with a "cheat sheet" of nine points that should be followed when dealing with little h in data analysis.
1308.4164
DESI and other dark energy experiments in the era of neutrino mass measurements
Font-Ribera, McDonald, Mostek, Reid, Seo, Slosar
Fisher matrix projections for future cosmological parameter measurements, including neutrino masses, DE, curvature, modified gravity, the inflationary perturbation spectrum, non-Gaussianity, and dark radiation. Focus on DESI and generally redshift surveys (BOSS, HETDEX, eBOSS, Euclid, and WFIRST), but also include CMB (Planck) and WL (DES and LSST) constraints. The goal is to present a consistent set of projections, for concrete experiments, which are otherwise scattered throughout many papers and proposals. Include neutrino mass as a free parameter in most projections, as it will inevitably be relevant -- DESI and other experiments can measure the sum of neutrino masses to ~0.02 eV or better, where the minimum possible sum is ~0.06 eV. Note that the BAO-only use of galaxy clustering is substantially degraded as a DE probe in the presence of neutrino mass uncertainty -- using broadband galaxy power is critical, especially pushing it to as small a scale as possible, and big gains are achieved by combining lensing survey constraints with redshift survey constraints. Do not try to be especially innovative, e.g., in careful treatments of potential systematic errors -- these projections are intended as a straightforward baseline for comparison to more detailed analyses.
1308.4299
Dust properties of clumpy disc galaxies at z~1.3 with Herschel-SPIRE
Wisnioski, Glazebrook, Blake, Swinbank
Present FIR derived dust properties from Herschel SPIRE of the WiggleZ kinematic sample of13 SF galaxies at z~1.3, with existing ancillary ~kpc resolution integral field spectroscopy. Detect 3 galaxies individually and place limits on the remainder by stacking. The detected galaxies, two clumpy disks and one merger, have cold dust temperatures of ~26 K and have IR luminosities of ~1.2e12 Lsun, determined by modified BB fitting. The 2 detected disc galaxies have the largest Ha surface areas of the sample and have the reddest UV to NIR SED. The likely source of the IR luminosity in these objects is dust heated by the interstellar radiation field and young stellar emission from the clumps within the discs. The source of IR luminosity for the merger is likely a dust heated by a starburst resulting from the merger. The WiggleZ detections are among the coldest and lowest luminosity individual objects detected in the FIR at z>1. When combining the kinematic data, find that none of the compact galaxies nor the 'dispersion dominated' galaxies of the WiggleZ kinematic sample are detected, implying that they have warmer dust temperatures. The compact objects show the highest Ha velocity dispersions in the sample, in qualitative agreement with bulge formation models. These FR results strengthen the interpretation that the majority of galaxies in this sample constitute different stages in clumpy disc formation as presented from ancillary kinematic analysis.
Wednesday, August 28, 2013
Day 493
Tuesday. Catching up from last week.
1308.4131
The baryon cycle of dwarf galaxies: dark, bursty, gas-rich polluters
Shen, Madau, Conroy, Governato, Mayer
Results from a cosmo hi-res LCDM "zoom-in" simulation of a group of 7 field dwarf galaxies with present-day virial masses in the range M_vir = 4.4e8-3.6e10 Msun. The simulation includes a blastwave scheme for SN feedback, a SF recipe based on a high gas density threshold, metal-dependent radiative cooling a scheme for the turbulent diffusion of metals and thermal energy, and a uniform UV background that modifies the ionization and excitation state of the gas. The properties of the simulated dwarfs are strongly modulated by the depth of the gravitational potential well. All 3 haloes with M_vir < 1e9 Msun are devoid of stars, as they never reach the density threshold for SF of 100 atoms/cc. The other 4, M_vir > 1e9 Msun dwarfs have blue colors, low SF efficiencies, high cold gas to stellar mass ratios, and low stellar metallicities. Their bursty SFHs are characterized by peak sSFRs in excess of 40-100 1/Gyr [units?], far outside the realm of normal, more massive galaxies, and in agreement with observations of extreme emission-line star bursting dwarfs by the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS). Metal-enriched galactic outflows produce sub-solar effective yields and pollute with heavy elements a Mpc-size region of the intergalactic medium, but are not sufficient to completely quench SF activity and are not ubiquitous in the dwarfs. Within the limited size of the sample, simulations appear to simultaneously reproduce the observed stellar mass and cold gas content, resolved SFHs, stellar kinematics, and metallicities of field dwarfs in the Local Volume.
The baryon cycle of dwarf galaxies: dark, bursty, gas-rich polluters
Shen, Madau, Conroy, Governato, Mayer
Results from a cosmo hi-res LCDM "zoom-in" simulation of a group of 7 field dwarf galaxies with present-day virial masses in the range M_vir = 4.4e8-3.6e10 Msun. The simulation includes a blastwave scheme for SN feedback, a SF recipe based on a high gas density threshold, metal-dependent radiative cooling a scheme for the turbulent diffusion of metals and thermal energy, and a uniform UV background that modifies the ionization and excitation state of the gas. The properties of the simulated dwarfs are strongly modulated by the depth of the gravitational potential well. All 3 haloes with M_vir < 1e9 Msun are devoid of stars, as they never reach the density threshold for SF of 100 atoms/cc. The other 4, M_vir > 1e9 Msun dwarfs have blue colors, low SF efficiencies, high cold gas to stellar mass ratios, and low stellar metallicities. Their bursty SFHs are characterized by peak sSFRs in excess of 40-100 1/Gyr [units?], far outside the realm of normal, more massive galaxies, and in agreement with observations of extreme emission-line star bursting dwarfs by the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS). Metal-enriched galactic outflows produce sub-solar effective yields and pollute with heavy elements a Mpc-size region of the intergalactic medium, but are not sufficient to completely quench SF activity and are not ubiquitous in the dwarfs. Within the limited size of the sample, simulations appear to simultaneously reproduce the observed stellar mass and cold gas content, resolved SFHs, stellar kinematics, and metallicities of field dwarfs in the Local Volume.
Tuesday, August 27, 2013
Day 492
Monday, at Penn.
1308.3713
Heavy dust obscuration of z=7 galaxies in a cosmological hydrodynamic simulation
Kimm, Cen
HST observations show that galaxies at z~7 have very blue UV colors, consistent with these systems being dominated by young stellar populations with moderate or little attenuation by dust. Investigate UV and optical properties of the high-z galaxies in the standard CDM model using a high-resolution AMR cosmological hydro sims. For this purpose, perform panchromatic 3-dimensional dust radiative transfer calculations on 198 galaxies of stellar mass 5e8-3e10 Msun with 3 parameters, the dust-to-metal ratio, the extinction curve, and the fraction of directly escaped light from stars (\fesc). The stellar mass function is found to be in broad agreement with Gonzalez et al., independent of these parameters. Find that the heavily dust-attenuated galaxies (A_V~1.8) can also reasonably match modest UV-optical [rest-frame?] colors, blue UV slopes, as well as UV luminosity functions, provided that a significant fraction (~10%) of light directly escapes from them. The observed UV slope and scatter are better explained with a SMC-type extinction curve, whereas MW-type dust predicts too blue UV colors due to the 2175A bump. Expect that upcoming observations by ALMA will be able to test this heavily obscured model. [cf. paper by Mariska+Conroy]
1308.3719
Consequences of radiative and mechanical feedback from black holes in galaxy mergers
Choi, Naab, Ostriker, Johansson, Moster
Use hydro sims to study the effect of AGN mechanical and radiation feedback on the formation of bulge dominated galaxies via mergers of disk galaxies. The merging galaxies have mass-ratios of 1:1 to 6:1 and include pre-existing hot gaseous halos to account for the global impact of AGN feedback. Compare 3 models: (1) no BH and no AGN feedback; (2) thermal AGN feedback; and (3) mechanical and radiative AGN feedback. The last model is motivated by observations of broad absorption line quasars which show winds with initial velocities of v_w ~ 10,000 km/s and also heating associated with the central AGN X-ray radiation. The primary changes in gas properties due to mechanical AGN feedback are lower thermal X-ray luminosity from the final galaxy - in better agreement with observations - and galactic outflows with higher velocity ~1000 km/s, similar to recent direct observations of nearby merger remnants. The kinetic energy of the outflowing gas is a factor of ~20 higher than in the thermal feedback case. All merger remnants with momentum-based AGN feedback, independent of their progenitor mass-ratios, follow the observed relations between stellar velocity dispersion and BH mass (M_BH-sigma) as well as X-ray luminosity (L_X-sigma) with 1e37.5 < L_X (0.3-8 keV) < 1e39.2 for velocity dispersions in the range of 120 km/s < sigma < 190 km/s. In addition, the mechanical feedback produces a much greater AGN variability. Also show that gas is more rapidly and impulsively stripped from the galactic centers driving a moderate increase in galaxy size and decrease in central density with the mechanical AGN feedback model. However, the BH mass growth required to produce the observed galaxy size and central density evolution is inconsistent with the observed M_BH-sigma relation.
1308.3875
Initial results from a laboratory emulation of weak gravitational lensing measurements
Seshadri, Shapiro, Goodsall, Fucik, Hirata, Rhodes, Rowe, Smith
To validate the performance of the WFIRST IR detectors, performed a lab emulation of WL measurements: experiments used a custom precision projector system to image a target mask composed of a grid of pinholes, emulating stellar point sources, onto a 1.7 micron cut-off Teledyne HdCdTe/H2RG detector. Use a 880 nm LED illumination source and f/22 pupil stop to produce undersampled PSF similar to those expected from WFIRST. Also emulated the WFIRST image reconstruction strategy, using the IMage COMbination (IMCOM) algorithm to derive oversampled imaged from dithered, undersampled input images. Created shear maps for this data and computed shear correlation functions to mimic a real WL analysis. After removing only 2nd order polynomial fits to the shear maps, found that the correlation functions could be reduced to O(1e-6). This places a conservative upper limit on the detector-induced bias to the correlation function (under the given test conditions). This bias is two orders of magnitude lower than the expected WL signal. Restricted to scales relevant to DE analyses (sky separations > 0.5 arcmin), the bias is O(1e-7): comparable to the requirement for future weak lensing missions to avoid biasing cosmological parameter estimates. Experiment will need to be upgraded and repeated under different configurations to fully characterize the shape measurement performance of WFIRST IR detectors.
1308.3976
Pulsar scattering in space and time
Wucknitz
Report on a recent global VLBI experiment in which the simultaneous scatter broadening in the spatial and time domain is studied. Depending on the distribution of scattering screen(s), geometry predicts that the less spatially broadened parts of the signal arrive earlier than the more broadened parts. This means that over one pulse period, the size of the scattering disk should grow from pointlike to the maximum size. An equivalent description is that the pulse profile shows less temporal broadening on the longer baselines. Present first results that are consistent with the expected expanding rings. Also briefly discuss how the autocorrelations can be used for amplitude calibration. This requires a thorough investigation of the digitization and the sampler statistics and is not fully solved yet.
1308.4099
Null tests of the cosmological constant using supernovae
Yahya, Seikel, Clarkson, Maartens, Smith
In addition to using generic observational tests, one can also design tests that target the specific properties of the cosmological constant. These null tests do not rely on parameterizations of observables, but focus on quantities that are constant only if DE is a cosmological constant. Use SN data in null tests that are based on luminosity distance. In order to extract derivatives of the distance in a model-independent way, use Gaussian Processes [?]. Find that the concordance model is compatible with the Union 2.1 data, but the error bars are fairly large. Simulated datasets are generated for the DES SN survey and show that this survey will allow for a sharper null test of the cosmological constant if flat Universe is assumed. Allowing for spatial curvature degrades the power of the null test. [how exactly is the null test conducted?]
1308.3713
Heavy dust obscuration of z=7 galaxies in a cosmological hydrodynamic simulation
Kimm, Cen
HST observations show that galaxies at z~7 have very blue UV colors, consistent with these systems being dominated by young stellar populations with moderate or little attenuation by dust. Investigate UV and optical properties of the high-z galaxies in the standard CDM model using a high-resolution AMR cosmological hydro sims. For this purpose, perform panchromatic 3-dimensional dust radiative transfer calculations on 198 galaxies of stellar mass 5e8-3e10 Msun with 3 parameters, the dust-to-metal ratio, the extinction curve, and the fraction of directly escaped light from stars (\fesc). The stellar mass function is found to be in broad agreement with Gonzalez et al., independent of these parameters. Find that the heavily dust-attenuated galaxies (A_V~1.8) can also reasonably match modest UV-optical [rest-frame?] colors, blue UV slopes, as well as UV luminosity functions, provided that a significant fraction (~10%) of light directly escapes from them. The observed UV slope and scatter are better explained with a SMC-type extinction curve, whereas MW-type dust predicts too blue UV colors due to the 2175A bump. Expect that upcoming observations by ALMA will be able to test this heavily obscured model. [cf. paper by Mariska+Conroy]
1308.3719
Consequences of radiative and mechanical feedback from black holes in galaxy mergers
Choi, Naab, Ostriker, Johansson, Moster
Use hydro sims to study the effect of AGN mechanical and radiation feedback on the formation of bulge dominated galaxies via mergers of disk galaxies. The merging galaxies have mass-ratios of 1:1 to 6:1 and include pre-existing hot gaseous halos to account for the global impact of AGN feedback. Compare 3 models: (1) no BH and no AGN feedback; (2) thermal AGN feedback; and (3) mechanical and radiative AGN feedback. The last model is motivated by observations of broad absorption line quasars which show winds with initial velocities of v_w ~ 10,000 km/s and also heating associated with the central AGN X-ray radiation. The primary changes in gas properties due to mechanical AGN feedback are lower thermal X-ray luminosity from the final galaxy - in better agreement with observations - and galactic outflows with higher velocity ~1000 km/s, similar to recent direct observations of nearby merger remnants. The kinetic energy of the outflowing gas is a factor of ~20 higher than in the thermal feedback case. All merger remnants with momentum-based AGN feedback, independent of their progenitor mass-ratios, follow the observed relations between stellar velocity dispersion and BH mass (M_BH-sigma) as well as X-ray luminosity (L_X-sigma) with 1e37.5 < L_X (0.3-8 keV) < 1e39.2 for velocity dispersions in the range of 120 km/s < sigma < 190 km/s. In addition, the mechanical feedback produces a much greater AGN variability. Also show that gas is more rapidly and impulsively stripped from the galactic centers driving a moderate increase in galaxy size and decrease in central density with the mechanical AGN feedback model. However, the BH mass growth required to produce the observed galaxy size and central density evolution is inconsistent with the observed M_BH-sigma relation.
1308.3875
Initial results from a laboratory emulation of weak gravitational lensing measurements
Seshadri, Shapiro, Goodsall, Fucik, Hirata, Rhodes, Rowe, Smith
To validate the performance of the WFIRST IR detectors, performed a lab emulation of WL measurements: experiments used a custom precision projector system to image a target mask composed of a grid of pinholes, emulating stellar point sources, onto a 1.7 micron cut-off Teledyne HdCdTe/H2RG detector. Use a 880 nm LED illumination source and f/22 pupil stop to produce undersampled PSF similar to those expected from WFIRST. Also emulated the WFIRST image reconstruction strategy, using the IMage COMbination (IMCOM) algorithm to derive oversampled imaged from dithered, undersampled input images. Created shear maps for this data and computed shear correlation functions to mimic a real WL analysis. After removing only 2nd order polynomial fits to the shear maps, found that the correlation functions could be reduced to O(1e-6). This places a conservative upper limit on the detector-induced bias to the correlation function (under the given test conditions). This bias is two orders of magnitude lower than the expected WL signal. Restricted to scales relevant to DE analyses (sky separations > 0.5 arcmin), the bias is O(1e-7): comparable to the requirement for future weak lensing missions to avoid biasing cosmological parameter estimates. Experiment will need to be upgraded and repeated under different configurations to fully characterize the shape measurement performance of WFIRST IR detectors.
1308.3976
Pulsar scattering in space and time
Wucknitz
Report on a recent global VLBI experiment in which the simultaneous scatter broadening in the spatial and time domain is studied. Depending on the distribution of scattering screen(s), geometry predicts that the less spatially broadened parts of the signal arrive earlier than the more broadened parts. This means that over one pulse period, the size of the scattering disk should grow from pointlike to the maximum size. An equivalent description is that the pulse profile shows less temporal broadening on the longer baselines. Present first results that are consistent with the expected expanding rings. Also briefly discuss how the autocorrelations can be used for amplitude calibration. This requires a thorough investigation of the digitization and the sampler statistics and is not fully solved yet.
1308.4099
Null tests of the cosmological constant using supernovae
Yahya, Seikel, Clarkson, Maartens, Smith
In addition to using generic observational tests, one can also design tests that target the specific properties of the cosmological constant. These null tests do not rely on parameterizations of observables, but focus on quantities that are constant only if DE is a cosmological constant. Use SN data in null tests that are based on luminosity distance. In order to extract derivatives of the distance in a model-independent way, use Gaussian Processes [?]. Find that the concordance model is compatible with the Union 2.1 data, but the error bars are fairly large. Simulated datasets are generated for the DES SN survey and show that this survey will allow for a sharper null test of the cosmological constant if flat Universe is assumed. Allowing for spatial curvature degrades the power of the null test. [how exactly is the null test conducted?]
Monday, August 26, 2013
Day 491
Monday, on the road. Tuesday, Wednesday, Thursday. When am I going to read all these abstracts? Friday, on the train to NYC.
1308.3496
Galaxy Zoo 2: detailed morphological classifications for 304,122 galaxies from the Sloan Digital Sky Survey
Willett et al
Present data release for Galaxy Zoo 2 (GZ2), a citizen science project with more than 16 million morphological classifications of 304,122 galaxies drawn from SDSS [where does the 16M come from?]. Morphology is a powerful probe for quantifying a galaxy's dynamical history; however, automatic classifications of morphology (either by computer analysis of images or by using other physical parameters as proxies) still have drawbacks when compared to visual inspection. The large number of images available in current surveys makes visual inspection of each galaxy impractical for individual astronomers. GZ2 uses classifications from volunteer citizen scientists to measure morphologies for all galaxies in the DR7 Legacy survey with m_r>17, in addition to deeper images from SDSS Stripe 82. While the original Galaxy Zoo project identified galaxies as early-typs, late-types, or mergers, GZ2 measures finer morphological features. THese include bars, bulges, and the shapes of edge-on disks, as well as quantifying the relative strengths of galactic bulges and spiral arms. This paper presents the ful public data release for the project, including measures of accuracy and bias. The majority (>90%) of GZ2 classifications agree with those made by professional astronomers, especially for morphological T-types, strong bars, and arm curvature. Both the raw and reduced data products can be obtained in electronic format at http://data.galaxyzoo.org.
1308.3551
Window effect in the power spectrum analysis of a galaxy redshift survey
Sato, et al
Investigate the effect of the window function on the multipole power spectrum in two different ways. Consider the convolved PS including the window effect, which is obtained by following the familiar (FKP) method developed by Feldman, Kaiser and Peacock. Show how the convolved multipole PS is related to the original PS, using the multipole moments of the window function. Second, investigate the deconvolved PS, which is obtained by using the Fourier deconvolution theorem. In the second approach, measure the multipole PS deconvolved from the window effect. Demonstrate how to deal with the window effect in these two approaches, applying them to the SDSS LRG sample.
1308.3617
The peculiar light curve of the Symbiotic Star AX Per of the last 125 years
Leibowitz, Formiggini
Analyze the last 125 years optical light curve of the symbiotic star AX Per through correlations discovered in its PS. The data were assembled from the literature and from the AAVSO database. A series of 6 major outbursts dominate the light curve. They are presented in the PS as 13 harmonics of the fundamental frequency fa=1/Pa=1/23172 day^-1. Refer to them as the "red" frequencies. Oscillations with the binary periodicity of the system Pb=1/fb=381.48d are also seen in the light curve, with particularly large amplitudes during outbursts. The fb peak in the PS is accompanied by 13 other peaks on each side, which is referred as the "blue" frequencies. A distinct structure in the frequency distribution of the blue peaks, as well as in their peak power are best interpreted as reflecting beating of the 13 "red" frequencies with the binary one. Suggest that the major outbursts of the system result from events of intense mass loss from the giant star. Mass accretion onto the hot component, partially through the L1 point of the system, took place in the last 125 years at a rate that oscillated with the 13 first harmonics of the fa frequency. The binary orbit is slightly eccentric and periastron passages induced modulation of the L1 accretion at the binary frequency. Hence the fb oscillations in the brightness of the star of amplitude that is modulated by the "red" frequencies of the system.
1308.3704
Searching for Oscillations in the primordial power spectrum: perturbative approach (Paper I)
Meerburg, Spergel, Wandelt
Present a new method for searching for oscillatory features in the primordial PS. A wide variety of models predict these features in one of two different flavors: logarithmically spaced oscillations and linearly spaced oscillations. The proposed method treats the oscillations as perturbations on top of the scale-invariant PS, allowing variation of all cosmological parameters. This perturbative approach reduces the computational requirements for the search as the transfer functions and their derivatives can be precomputed. Show that the most significant degeneracy in the analysis is between the distance to last scattering and the overall amplitude at low frequencies. For models with logarithmic oscillations, this degeneracy leads to an uncertainty in the phase. For linear spaced oscillations, it affects the frequency of the oscillations. In this paper (one out of two), test code on simulated Planck-like data, and show ability to recover fiducial input oscillations with an amplitude of a few times order 1e-2. Apply the code to WMAP9 data and confirm the existence of two intriguing resonant frequencies for log spaced oscillations. For linear spaced oscillations, find a single resonance peak. Use numerical simulations to assess the significance of these features and conclude that the data do not provide compelling evidence for the existence of oscillatory features in the primordial spectrum.
1308.3705
Searching for oscillations in the primordial power spectrum: constraints from Planck (Paper II)
Meerburg, Spergel
Continuation of the above. Log-spaced resonant features in WMAP9 has little to no significance. Confirm the presence of a several low frequency peaks earlier identified by the Planck team, but with a better improvement of fit (delta chi^2~12). Further investigate this improvement by allowing the lensing potential to vary as well, showing mild correlation between the amplitude of the oscillations and the lensing amplitude. Find that the improvement of the fit increases even more (~14) for the low frequencies that modify the spectrum in a way that mimics the lensing effect. Since these features were not present in the WMAP data, they are primarily due to better measurements of Planck at small angular scales. For linear spaced oscillations, find a maximum delta chi^2~13 scanning two orders of magnitude in frequency space, and the biggest improvements are at extremely high frequencies. Recover a best fit frequency very close to the one found in WMAP9, which confirms that the fit improvement is driven by low l. Further comparisons with WMAP9 show Planck contains many more features, both for linear and log space oscillations, but with a smaller improvement of fit. Discuss the improvement as a function of the number of modes and study the effect of the 217 GHz map, which appears to drive most of the improvement for log spaced oscillations. Conclude that none of the detected features are statistically significant.
1308.3707
Galaxy pairs in the Sloan digital sky survey - VIII: the observational properties of post-merger galaxies
Ellison, Mendel, Patton, Scudder
Present a study of 10,800 galaxies in close pairs and a sample of 97 post-mergers identified in SDSS. Find that the average central SFR enhancement (x3.5) and the fraction of starbursts (20%) peak in the post merger sample. The post-mergers also show a stronger deficit in gas phase metallicity that the closest pairs, being more metal-poor than their control by -0.09 dex. Combined with the observed trends in SFR and the timescales predicted in merger simulations, estimate that the post-mergers in sample have undergone coalescence iwthin the last few hundred Myr. In contrast with the incidence of SF galaxies, the frequency of AGN peaks in the post-mergers, outnumbering AGN in the control sample by a factor of 3.75. Moreover, amongst the galaxies that host an AGN, the black hole accretion rates in the closest pairs and post-mergers are higher by a factor of ~3 than AGN in the control sample. These results are consistent with a picture in the which star formation is initiated early on in the encounter, with AGN activity peaking post-coalescence.
Galaxy Zoo 2: detailed morphological classifications for 304,122 galaxies from the Sloan Digital Sky Survey
Willett et al
Present data release for Galaxy Zoo 2 (GZ2), a citizen science project with more than 16 million morphological classifications of 304,122 galaxies drawn from SDSS [where does the 16M come from?]. Morphology is a powerful probe for quantifying a galaxy's dynamical history; however, automatic classifications of morphology (either by computer analysis of images or by using other physical parameters as proxies) still have drawbacks when compared to visual inspection. The large number of images available in current surveys makes visual inspection of each galaxy impractical for individual astronomers. GZ2 uses classifications from volunteer citizen scientists to measure morphologies for all galaxies in the DR7 Legacy survey with m_r>17, in addition to deeper images from SDSS Stripe 82. While the original Galaxy Zoo project identified galaxies as early-typs, late-types, or mergers, GZ2 measures finer morphological features. THese include bars, bulges, and the shapes of edge-on disks, as well as quantifying the relative strengths of galactic bulges and spiral arms. This paper presents the ful public data release for the project, including measures of accuracy and bias. The majority (>90%) of GZ2 classifications agree with those made by professional astronomers, especially for morphological T-types, strong bars, and arm curvature. Both the raw and reduced data products can be obtained in electronic format at http://data.galaxyzoo.org.
1308.3551
Window effect in the power spectrum analysis of a galaxy redshift survey
Sato, et al
Investigate the effect of the window function on the multipole power spectrum in two different ways. Consider the convolved PS including the window effect, which is obtained by following the familiar (FKP) method developed by Feldman, Kaiser and Peacock. Show how the convolved multipole PS is related to the original PS, using the multipole moments of the window function. Second, investigate the deconvolved PS, which is obtained by using the Fourier deconvolution theorem. In the second approach, measure the multipole PS deconvolved from the window effect. Demonstrate how to deal with the window effect in these two approaches, applying them to the SDSS LRG sample.
1308.3617
The peculiar light curve of the Symbiotic Star AX Per of the last 125 years
Leibowitz, Formiggini
Analyze the last 125 years optical light curve of the symbiotic star AX Per through correlations discovered in its PS. The data were assembled from the literature and from the AAVSO database. A series of 6 major outbursts dominate the light curve. They are presented in the PS as 13 harmonics of the fundamental frequency fa=1/Pa=1/23172 day^-1. Refer to them as the "red" frequencies. Oscillations with the binary periodicity of the system Pb=1/fb=381.48d are also seen in the light curve, with particularly large amplitudes during outbursts. The fb peak in the PS is accompanied by 13 other peaks on each side, which is referred as the "blue" frequencies. A distinct structure in the frequency distribution of the blue peaks, as well as in their peak power are best interpreted as reflecting beating of the 13 "red" frequencies with the binary one. Suggest that the major outbursts of the system result from events of intense mass loss from the giant star. Mass accretion onto the hot component, partially through the L1 point of the system, took place in the last 125 years at a rate that oscillated with the 13 first harmonics of the fa frequency. The binary orbit is slightly eccentric and periastron passages induced modulation of the L1 accretion at the binary frequency. Hence the fb oscillations in the brightness of the star of amplitude that is modulated by the "red" frequencies of the system.
1308.3704
Searching for Oscillations in the primordial power spectrum: perturbative approach (Paper I)
Meerburg, Spergel, Wandelt
Present a new method for searching for oscillatory features in the primordial PS. A wide variety of models predict these features in one of two different flavors: logarithmically spaced oscillations and linearly spaced oscillations. The proposed method treats the oscillations as perturbations on top of the scale-invariant PS, allowing variation of all cosmological parameters. This perturbative approach reduces the computational requirements for the search as the transfer functions and their derivatives can be precomputed. Show that the most significant degeneracy in the analysis is between the distance to last scattering and the overall amplitude at low frequencies. For models with logarithmic oscillations, this degeneracy leads to an uncertainty in the phase. For linear spaced oscillations, it affects the frequency of the oscillations. In this paper (one out of two), test code on simulated Planck-like data, and show ability to recover fiducial input oscillations with an amplitude of a few times order 1e-2. Apply the code to WMAP9 data and confirm the existence of two intriguing resonant frequencies for log spaced oscillations. For linear spaced oscillations, find a single resonance peak. Use numerical simulations to assess the significance of these features and conclude that the data do not provide compelling evidence for the existence of oscillatory features in the primordial spectrum.
1308.3705
Searching for oscillations in the primordial power spectrum: constraints from Planck (Paper II)
Meerburg, Spergel
Continuation of the above. Log-spaced resonant features in WMAP9 has little to no significance. Confirm the presence of a several low frequency peaks earlier identified by the Planck team, but with a better improvement of fit (delta chi^2~12). Further investigate this improvement by allowing the lensing potential to vary as well, showing mild correlation between the amplitude of the oscillations and the lensing amplitude. Find that the improvement of the fit increases even more (~14) for the low frequencies that modify the spectrum in a way that mimics the lensing effect. Since these features were not present in the WMAP data, they are primarily due to better measurements of Planck at small angular scales. For linear spaced oscillations, find a maximum delta chi^2~13 scanning two orders of magnitude in frequency space, and the biggest improvements are at extremely high frequencies. Recover a best fit frequency very close to the one found in WMAP9, which confirms that the fit improvement is driven by low l. Further comparisons with WMAP9 show Planck contains many more features, both for linear and log space oscillations, but with a smaller improvement of fit. Discuss the improvement as a function of the number of modes and study the effect of the 217 GHz map, which appears to drive most of the improvement for log spaced oscillations. Conclude that none of the detected features are statistically significant.
1308.3707
Galaxy pairs in the Sloan digital sky survey - VIII: the observational properties of post-merger galaxies
Ellison, Mendel, Patton, Scudder
Present a study of 10,800 galaxies in close pairs and a sample of 97 post-mergers identified in SDSS. Find that the average central SFR enhancement (x3.5) and the fraction of starbursts (20%) peak in the post merger sample. The post-mergers also show a stronger deficit in gas phase metallicity that the closest pairs, being more metal-poor than their control by -0.09 dex. Combined with the observed trends in SFR and the timescales predicted in merger simulations, estimate that the post-mergers in sample have undergone coalescence iwthin the last few hundred Myr. In contrast with the incidence of SF galaxies, the frequency of AGN peaks in the post-mergers, outnumbering AGN in the control sample by a factor of 3.75. Moreover, amongst the galaxies that host an AGN, the black hole accretion rates in the closest pairs and post-mergers are higher by a factor of ~3 than AGN in the control sample. These results are consistent with a picture in the which star formation is initiated early on in the encounter, with AGN activity peaking post-coalescence.
Monday, August 19, 2013
Day 490
Saturday.
1308.3249
Galactic abundance gradients from Cepheids: alpha and heavy elements in the outer disk
Lemasle, et al
Galactic abundance gradients set strong constraints to chemo-dynamical evolutionary models of the MW. Given the PL relations that provide accurate distances and the large number of spectral lines, Cepheids are excellent tracers of the present-day abundance gradients. Want to measure the Galactic abundance gradient of several chemical elements. While the slope of the Cepheid Fe gradient did not vary much from the very first studies, the gradients of the other elements are not that well constrained. In this paper, focus on the inner and outer regions of the Galactic thin disk. Use HR spectra to measure abundances of several light (Na, Al), alpha (Mg, Si, S, Ca) and heavy (Y, Zr, La, Ce, Nd, Eu) in a sample of 65 MW Cepheids. Combining these results with accurate distances from period-Wesenheit relations in the NIR enables us to determine the abundance gradients in the MW. Results are in good agreement with previous studies on either Cepheids or other tracers. In particular, confirm an upward shift of approximately 0.2 dex for the Mg abundances, as has recently been reported. Also confirm the existence of a gradient for all the heavy elements studied in the context of a LTE analysis. However, for Y, Nd, and especially La, find lower abundances for Cepheids in the outer disk than reported in previous studies, leading to steeper gradients. This effect can be explained by the differences in the line lists used by different groups. Data do not support a flattening of the gradients in the outer disk, in agreement with recent Cepheid studies and chemo-dynamical simulations. This is in contrast to the open cluster observations but remains compatible with a picture where the transition zone between the inner disk and the outer disk would move outward with time.
1308.3255
A new life for sterile neutrinos: resolving inconsistencies using hot dark matter
Hamann, Hasenkamp
If LCDM is extended by a hot dark matter component, which could be interpreted as a sterile neutrino, the data sets can be combined consistently. A combination of Planck data, WMAP-9 polarization data, measurements of the BAO scale, the HST measurement of H_0, Planck galaxy cluster counts and galaxy shear data from the CFHTLens survey yields Delta N_eff=0.61pm0.30 and m_s^eff=0.41 pm 0.13 eV at 1 sigma. The former is driven mainly by the large H_0 of the HST measurement, while the latter is driven by cluster data. CFHTLens galaxy shear data prefer Delta N_eff>0 and a non-zero mass. Taken together, find hints for the presence of a hot DM component at 3 sigma. A sterile neutrino motivated by the reactor and gallium anomalies appears rejected at even higher significance and an accelerator anomaly sterile neutrino is found in tension at 2 sigma.
1308.3346
Probing the Sun's inner core using solar neutrinos: a new diagnostic method
Lopes
The electronic density in the Sun's inner core is inferred from the 8B, 7Be and pep neutrino flux measurements of the Super-Kamiokande, SNO and Borexino experiments. Developed a new method in which the KamLAND detector determinations of the neutrino fundamental oscillation parameters [?]: the mass difference and the vacuum oscillation angle. Results suggest that the solar electronic density in the Sun's inner core (for a radius smaller than 10% of the solar radius) is well above the current prediction of the standard solar model, and by as much as 25%. A potential confirmation of these preliminary findings can be achieved when neutrino detectors are able to reduce the error of the electron-neutrino survival probability by a factor of 15.
Saturday, August 17, 2013
Day 489
Friday, on the plane.
1308.3232
Using cumulative number densities to compare galaxies across cosmic time
Behroozi, Marchesini, Wechsler, Muzzin, Papovich, Stefanon
To estimate the evolution of specific galaxy populations, compare galaxies across redshifts at fixed cumulative number density [I guess the brightest remain the brightest, so they must be the same population? Can only track the brightest galaxy evolution this way?]. This method ignores scatter in mass accretion histories and galaxy-galaxy mergers, which can lead to errors when comparing galaxies over large redshift ranges (Delta z>1). Use abundance matching in the LCDM paradigm to estimate the median change in number density with redshift and provide a simple fit (0.16 dex per unit Delta z) for progenitors of z=0 galaxies. Find that galaxy descendants do not evolve in the same way as galaxy progenitors, largely due to scatter in mass accretion histories. Also provide estimates for the 1-sigma range of number densities corresponding to galaxy progenitors and descendants. Finally, discuss some limits on number density comparisons, which arise due to difficulties measuring physical quantities (e.g., stellar mass) consistently across redshifts. A public tool to calculate number density evolution for galaxies, as well as approximate halo masses, is available online.
1308.3236
Jet luminosity from neutrino-dominated accretion flows in GRBs
Kawanaka
A hyperaccretion disk around a stellar-mass BH is a plausible model for the central engine that powers GRBs. Estimate the luminosity of a jet driven by magnetohydrodynamic processes such as the Blandford-Znajek (BZ) mechanism as a function of mass accretion rate, the BH mass, and the other accretion parameters. Show that the jet is most efficient when the accretion flow is cooled via optically-thin neutrino emission, and that its luminosity is much larger than the energy deposition rate through neutrino annihilation provided that the BH is spinning rapidly enough. Find a significant jump in the jet luminosity at the transition mass accretion rate between the advection dominated accretion flow (ADAF) regime and the neutrino-dominated accretion flow (NDAF) regime. This may cause the large variability observed in the prompt emission of GRBs.
1308.3240
Precision measures of the primordial abundance of deuterium
Cooke, Pettini, Jorgenson, Murphy, Steidel
D absorption found in the very metal-poor ([Fe/H]=-2.87) damped Ly-a system at z_abs=3.067 towards QSO SDSS J1358+6522. On the basis of 13 resolved D I absorption lines and the damping wings of the H I Ly-a transition, obtain a new, precise measure of the primordial abundance of D. Reanalyze all of the known D absorption-ine systems that satisfy a set of strict criteria, to bolster the present statistics of Precision D/H measures. Adopted a blind analysis strategy, and developed a SW package that is specifically designed for precision D/H abundance measurements. For this reanalyzed sample of systems, obtain a weighted mean of (D/H)_p = 2.53e-5, corresponding to a Universal baryon density 100 Omega_b h^2=2.2 for the standard model of BBN [about right, I guess]. By combining measure of (D/H)_p with observations of the CMB, derive the effective number of light fermion species, N_eff=3.28. Rule out the existence of an additional (sterile) neutrino (i.e., N_eff=4.046) at 99.3 confidence (2.7 sigma), provided that N_eff and the baryon-to-photon ratio (eta_10) did not change between BBN and recombination. Also place a strong bound on the lepton asymmetry, xi_D=0.05pm0.13 based only on the CMB+(D/H)_p observations. Combining xi_D with the current best literature measure of Y_p, find |xi|<=0.066. In future, improved measurements of several key reaction rates, in particular d(p,gamma)3He, and further measures of (D/H)_p with a precision comparable to those considered here, should allow even more stringent limits to be placed on new physics beyond the standard model.
1308.3232
Using cumulative number densities to compare galaxies across cosmic time
Behroozi, Marchesini, Wechsler, Muzzin, Papovich, Stefanon
To estimate the evolution of specific galaxy populations, compare galaxies across redshifts at fixed cumulative number density [I guess the brightest remain the brightest, so they must be the same population? Can only track the brightest galaxy evolution this way?]. This method ignores scatter in mass accretion histories and galaxy-galaxy mergers, which can lead to errors when comparing galaxies over large redshift ranges (Delta z>1). Use abundance matching in the LCDM paradigm to estimate the median change in number density with redshift and provide a simple fit (0.16 dex per unit Delta z) for progenitors of z=0 galaxies. Find that galaxy descendants do not evolve in the same way as galaxy progenitors, largely due to scatter in mass accretion histories. Also provide estimates for the 1-sigma range of number densities corresponding to galaxy progenitors and descendants. Finally, discuss some limits on number density comparisons, which arise due to difficulties measuring physical quantities (e.g., stellar mass) consistently across redshifts. A public tool to calculate number density evolution for galaxies, as well as approximate halo masses, is available online.
1308.3236
Jet luminosity from neutrino-dominated accretion flows in GRBs
Kawanaka
A hyperaccretion disk around a stellar-mass BH is a plausible model for the central engine that powers GRBs. Estimate the luminosity of a jet driven by magnetohydrodynamic processes such as the Blandford-Znajek (BZ) mechanism as a function of mass accretion rate, the BH mass, and the other accretion parameters. Show that the jet is most efficient when the accretion flow is cooled via optically-thin neutrino emission, and that its luminosity is much larger than the energy deposition rate through neutrino annihilation provided that the BH is spinning rapidly enough. Find a significant jump in the jet luminosity at the transition mass accretion rate between the advection dominated accretion flow (ADAF) regime and the neutrino-dominated accretion flow (NDAF) regime. This may cause the large variability observed in the prompt emission of GRBs.
1308.3240
Precision measures of the primordial abundance of deuterium
Cooke, Pettini, Jorgenson, Murphy, Steidel
D absorption found in the very metal-poor ([Fe/H]=-2.87) damped Ly-a system at z_abs=3.067 towards QSO SDSS J1358+6522. On the basis of 13 resolved D I absorption lines and the damping wings of the H I Ly-a transition, obtain a new, precise measure of the primordial abundance of D. Reanalyze all of the known D absorption-ine systems that satisfy a set of strict criteria, to bolster the present statistics of Precision D/H measures. Adopted a blind analysis strategy, and developed a SW package that is specifically designed for precision D/H abundance measurements. For this reanalyzed sample of systems, obtain a weighted mean of (D/H)_p = 2.53e-5, corresponding to a Universal baryon density 100 Omega_b h^2=2.2 for the standard model of BBN [about right, I guess]. By combining measure of (D/H)_p with observations of the CMB, derive the effective number of light fermion species, N_eff=3.28. Rule out the existence of an additional (sterile) neutrino (i.e., N_eff=4.046) at 99.3 confidence (2.7 sigma), provided that N_eff and the baryon-to-photon ratio (eta_10) did not change between BBN and recombination. Also place a strong bound on the lepton asymmetry, xi_D=0.05pm0.13 based only on the CMB+(D/H)_p observations. Combining xi_D with the current best literature measure of Y_p, find |xi|<=0.066. In future, improved measurements of several key reaction rates, in particular d(p,gamma)3He, and further measures of (D/H)_p with a precision comparable to those considered here, should allow even more stringent limits to be placed on new physics beyond the standard model.
Friday, August 16, 2013
Day 488
Thursday.
1308.2670
Spitzer, Gaia, and the Potential of the Milky Way
Price-Whelan, Johnston
Near-future data from ESA's Gaia mission will provide precise, full phase-space information for hundreds of millions of stars out to heliocentric distances of ~10 kpc [a good chunk of the MW]. This "horizon" for full phase-space measurements is imposed by the Gaia parallax errors degrading to worse than 10%, and could be significantly extended by an accurate distance indicator. Recent work has demonstrated how Spitzer observations of RR Lyrae stars can be used to make distance estimates accurate to 2%, effectively extending the Gaia, precise-data horizon by a factor of ten in distance and a factor of 1000 in volume. This Letter presents one approach to exploit data of such accuracy to measure the Galactic potential using small samples of stars associated with debris from satellite [satellite galaxies] destruction. The method is tested with synthetic observations of 100 stars from the end point of a simulation of satellite destruction: the shape, orientation, and depth of the potential used in the simulation are recovered to within a few percent. The success of this simple test with such a small sample in a single debris stream [I guess this stream probes the MW gravitational potential?] suggests that constraints from multiple streams could be combined to examine the Galaxy's DM halo in even more detail -- a truly unique opportunity that is enabled by the combination of Spitzer and Gaia with an intimate perspective on the Galaxy.
1308.2682
The stellar halos of massive elliptical galaxies II: detailed abundance ratios at large radius
Greene, Murphy, Graves, Gunn, Raskutti, Comerford, Gebhardt
Observations consistent with a picture in which the stellar outskirts are built up through minor mergers with disky galaxies whose SF is truncated early (z~1.5-2). Study the radial dependence in stellar populations of 33 nearby early-type galaxies with central stellar velocity dispersions sigma*>150 km/s. Measure stellar population properties in composite spectra, and use ratios of these composites to highlight the largest spectral changes as a function of radius. Based on stellar population modeling, The typical star at 2 R_e is old (~10 Gyr), relatively metal poor ([Fe/H]-0.5), and alpha-enhanced ([Mg/Fe]~0.3). The stars were made rapidly at z~1.5-2 in shallow potential wells. Declining radial gradients in [C/Fe], which follow [Fe/H], also arise from rapid SF timescales due to declining carbon yields from low-metallicity massive stars. In contrast, [N/Fe] remains high at large radius. Stars at large radius have different abundance ratio patterns from stars in the center of any present-day galaxy, but are similar to MW thick disk stars.
1308.2869
Do intermediate-mass black holes exist in globular clusters?
Sun, et al
Current radio observations (discrepancy between radio observation and dynamical modeling) cannot rule out the possibility that IMBHs may exist in GCs.
1308.2964
The formation of eccentric compact binary inspirals and the role of gravitational wave emission in binary-single stellar encounters
Samsing, MacLeod, Ramirez-Ruiz
The insprial and merger of eccentric binaries leads to gravitational waveforms distinct from those generated by circularly merging binaries. Study binary-single stellar scatterings occurring in dense stellar systems as a source of eccentrically-inspiraling binaries. Many interactions between compact binaries and single objects are characterized by chaotic resonances in which the binary-single system undergoes many exchanges before reaching a final state. During these chaotic resonances, a pair of objects has a non-negligible probability of experiencing a very close passage. Significant orbital energy and angular momentum are carried away from the system by GW radiation in these close passages and in some cases this implies an inspiral time shorter than the orbital period of the bound third body. Derive the cross section for such dynamical inspiral outcomes through analytical arguments and through numerical scattering experiments including GW losses. Show that the cross section for dynamical inspirals grows with increasing target binary semi-major axis, a, and that for equal-mass binaries it scales as a^2/7. Thus, expect wide target binaries to predominantly contribute to the production of these relativistic outcomes. Estimate that eccentric inspirals account for approximately one percent of dynamically assembled non-eccentric merging binaries. While these events are rare, show that binary-single scatterings are a more effective formation channel than single-single captures for the production of eccentrically-inspiraling binaries, even given modest binary fractions.
1308.2974
Evolution of the stellar-to-dark matter relation: separating star-forming and passive galaxies from z=1 to 0
Tinker, Leauthaud, Bundy, George, Behroozi, Massey, Rhodes, Wechsler
Use measurements of stellar MF, galaxy clustering, and gg lensing within COSMOS to constrain the stellar-to-halo mass relation (SHMR) of SF and quiescent galaxies over the redshift range z=0.2-1.0. For massive galaxies, M*>1e10.6 Msun, results indicate that SF galaxies grow proportionately as fast as their DM haloes while quiescent galaxies are outpaced by DM growth. At lower masses, there is minimal difference in the SHMRs, implying that the majority low-mass quiescent galaxies have only recently been quenched of their SF. Analysis also affords a breakdown of all COSMOS galaxies into the relative numbers of central and satellite galaxies for both populations. At z=1, satellite galaxies dominate the red sequence below the knee in the stellar mass function. But the number of quiescent satellites exhibits minimal redshift evolution; all evolution in the red sequence is due to low-mass central galaxies being quenched of their star formation. At M*~1e10 Msun, the fraction of central galaxies on the red sequence increases by a factor of ten over redshift baseline, while the fraction of quenched satellite galaxies at that mass is constant with redshift. Define a "migration rate" to the red sequence as the time derivative of the passive galaxy abundances. Find that the migration rate of central galaxies to the red sequence increases by nearly an order of magnitude from z=1 to 0. These results imply that the efficiency of quenching SF for centrals is increasing with cosmic time, while the mechanisms that quench the SF of satellite galaxies in groups and clusters is losing efficiency.
1308.2670
Spitzer, Gaia, and the Potential of the Milky Way
Price-Whelan, Johnston
Near-future data from ESA's Gaia mission will provide precise, full phase-space information for hundreds of millions of stars out to heliocentric distances of ~10 kpc [a good chunk of the MW]. This "horizon" for full phase-space measurements is imposed by the Gaia parallax errors degrading to worse than 10%, and could be significantly extended by an accurate distance indicator. Recent work has demonstrated how Spitzer observations of RR Lyrae stars can be used to make distance estimates accurate to 2%, effectively extending the Gaia, precise-data horizon by a factor of ten in distance and a factor of 1000 in volume. This Letter presents one approach to exploit data of such accuracy to measure the Galactic potential using small samples of stars associated with debris from satellite [satellite galaxies] destruction. The method is tested with synthetic observations of 100 stars from the end point of a simulation of satellite destruction: the shape, orientation, and depth of the potential used in the simulation are recovered to within a few percent. The success of this simple test with such a small sample in a single debris stream [I guess this stream probes the MW gravitational potential?] suggests that constraints from multiple streams could be combined to examine the Galaxy's DM halo in even more detail -- a truly unique opportunity that is enabled by the combination of Spitzer and Gaia with an intimate perspective on the Galaxy.
1308.2682
The stellar halos of massive elliptical galaxies II: detailed abundance ratios at large radius
Greene, Murphy, Graves, Gunn, Raskutti, Comerford, Gebhardt
Observations consistent with a picture in which the stellar outskirts are built up through minor mergers with disky galaxies whose SF is truncated early (z~1.5-2). Study the radial dependence in stellar populations of 33 nearby early-type galaxies with central stellar velocity dispersions sigma*>150 km/s. Measure stellar population properties in composite spectra, and use ratios of these composites to highlight the largest spectral changes as a function of radius. Based on stellar population modeling, The typical star at 2 R_e is old (~10 Gyr), relatively metal poor ([Fe/H]-0.5), and alpha-enhanced ([Mg/Fe]~0.3). The stars were made rapidly at z~1.5-2 in shallow potential wells. Declining radial gradients in [C/Fe], which follow [Fe/H], also arise from rapid SF timescales due to declining carbon yields from low-metallicity massive stars. In contrast, [N/Fe] remains high at large radius. Stars at large radius have different abundance ratio patterns from stars in the center of any present-day galaxy, but are similar to MW thick disk stars.
1308.2869
Do intermediate-mass black holes exist in globular clusters?
Sun, et al
Current radio observations (discrepancy between radio observation and dynamical modeling) cannot rule out the possibility that IMBHs may exist in GCs.
1308.2964
The formation of eccentric compact binary inspirals and the role of gravitational wave emission in binary-single stellar encounters
Samsing, MacLeod, Ramirez-Ruiz
The insprial and merger of eccentric binaries leads to gravitational waveforms distinct from those generated by circularly merging binaries. Study binary-single stellar scatterings occurring in dense stellar systems as a source of eccentrically-inspiraling binaries. Many interactions between compact binaries and single objects are characterized by chaotic resonances in which the binary-single system undergoes many exchanges before reaching a final state. During these chaotic resonances, a pair of objects has a non-negligible probability of experiencing a very close passage. Significant orbital energy and angular momentum are carried away from the system by GW radiation in these close passages and in some cases this implies an inspiral time shorter than the orbital period of the bound third body. Derive the cross section for such dynamical inspiral outcomes through analytical arguments and through numerical scattering experiments including GW losses. Show that the cross section for dynamical inspirals grows with increasing target binary semi-major axis, a, and that for equal-mass binaries it scales as a^2/7. Thus, expect wide target binaries to predominantly contribute to the production of these relativistic outcomes. Estimate that eccentric inspirals account for approximately one percent of dynamically assembled non-eccentric merging binaries. While these events are rare, show that binary-single scatterings are a more effective formation channel than single-single captures for the production of eccentrically-inspiraling binaries, even given modest binary fractions.
1308.2974
Evolution of the stellar-to-dark matter relation: separating star-forming and passive galaxies from z=1 to 0
Tinker, Leauthaud, Bundy, George, Behroozi, Massey, Rhodes, Wechsler
Use measurements of stellar MF, galaxy clustering, and gg lensing within COSMOS to constrain the stellar-to-halo mass relation (SHMR) of SF and quiescent galaxies over the redshift range z=0.2-1.0. For massive galaxies, M*>1e10.6 Msun, results indicate that SF galaxies grow proportionately as fast as their DM haloes while quiescent galaxies are outpaced by DM growth. At lower masses, there is minimal difference in the SHMRs, implying that the majority low-mass quiescent galaxies have only recently been quenched of their SF. Analysis also affords a breakdown of all COSMOS galaxies into the relative numbers of central and satellite galaxies for both populations. At z=1, satellite galaxies dominate the red sequence below the knee in the stellar mass function. But the number of quiescent satellites exhibits minimal redshift evolution; all evolution in the red sequence is due to low-mass central galaxies being quenched of their star formation. At M*~1e10 Msun, the fraction of central galaxies on the red sequence increases by a factor of ten over redshift baseline, while the fraction of quenched satellite galaxies at that mass is constant with redshift. Define a "migration rate" to the red sequence as the time derivative of the passive galaxy abundances. Find that the migration rate of central galaxies to the red sequence increases by nearly an order of magnitude from z=1 to 0. These results imply that the efficiency of quenching SF for centrals is increasing with cosmic time, while the mechanisms that quench the SF of satellite galaxies in groups and clusters is losing efficiency.
Wednesday, August 14, 2013
Day 487
Wednesday.
NYT article: http://www.nytimes.com/2013/08/13/science/how-to-share-scientific-data.html
Who will pay for public access to research data?Berman
The US office of science and technology policy (OSTP) released a memo calling for public access for publications and data resulting from federally sponsored research grants. The memo directed federal agencies with more than $100 M R&D expenditures to "develop a plan to support increased public access to the results of research funded by the Federal Government." A subsequent NYT page sported the headline "We paid for the research, so let's see it." So who pays for data infrastructure?
1308.2227
A search for RR Lyrae stars in Segue 2 and Segue 3
Boettcher, Willman, Fadely, ... et al
Search for RR Lyrae stars in ultra-faint MW companions Segue 2 and 3. In Segue 2, Find a RRab star ["fundamental mode" RR Lyrae] with period P_ab=0.748 days. Revisit inverse correlation between <P_ab> and <[Fe/H]> established in the literature for MW dwarf galaxies and their RR Lyrae. The long period of Segue 2's RRab star, as well as the known significant spread in metallicity in this dwarf galaxy are consistent with the observed trend in <P_ab> and <[Fe/H]>. Derive the first robust distance to Segue 2, using both its RRab star and spectroscopically confirmed blue horizontal branch stars. Using [Fe/H]=-2.16 and -2.44 dex, find d_RRL=36.6 and 37.7 (pm 2.5-ish) kpc; assuming [Fe/H]=-2.257 dex, find d_BHB=34.4pm2.6kpc. Although no RRLyrae were present in the Segue 3 field, find a candidate eclipsing binary star system.
1308.2252
KeSeF - Kepler Self Follow-up Mission
Ofir
The Kepler spacecraft is currently unable to hold steady pointing and it is slowly drifting during observations. If one has to deal with targets that drift across the CCDs, one should at least be able to track to targets well enough to correct for some -- if not most -- of the problems caused by this drift. Propose to observe as many stars as possible in short cadence. Propose that at least all currently known planetary candidate host stars will be so observed, with possibly known Kepler eclipsing binaries, astroseismology targets, guest observer targets and new targets in increasingly lower priority. Also outline the modifications needed to flight SW in order to allow for such observations to take place, aiming to provide ample non-photometric data that should allow post-processing to recover most of the pre-failure photometric performance. In total, the KeSeF Mission will allow Kepler to follow up it's own previous discoveries in a way that is not otherwise possible. By doing so it will enable to continue persuing nearly all the science goals that made the original mission choose staring at a single field of view in the first place. [confusing last sentence. I guess the drift doesn't allow Kepler to stare at one point anymore.]
1308.2367
The 9 and 18 micron luminosity function of various types of galaxies with AKARI: implication for the dust torus structure of AGN
Toba et al
Present the 9 and 18 micron LFs of galaxies at 0.006<z<0.8 (avg z ~0.04) using AKARI MIR all-sky survey catalog. 243 galaxies at 9 um and 255 galaxies at 18 um from SDSS spectroscopy region; classified by their optical emission lines, such as Ha or [OIII]/Hbeta and [NII]/H_alpha into 5 types: Type 1 AGN, Type 2, low-ionization narrow emission lines (LINER); galaxies with both SF and narrow-line AGN activity (composite galaxies); and star forming galaxies (SF). Find that (i) the number density ratio of Type 2 to Type 1 AGNs is 1.73, which is larger than a result obtained from the optical LF and (ii) this ratio decreases with increasing 18 um luminosity.
1308.2398
Photometric identification of objects from Galaxy Evolution Explorer survey and Sloan digital sky survey
Preethi, et al
Used GALEX and SESS to get 7-band photometric mag of 80k objects near the North Galactic Pole. Although these have been identified as stars by the SDSS pipeline, found through fitting with model SEDs that most were in fact of extragalactic origin. [really? how was the original 80k "stellar" object chosen?] Only about 9% of these objects turned out to be MS stars, and about 11% were WDs and RGs collectively, while galaxies and quasars contributed to the remaining 80% of the data. Classified these objects into different spectral types (for the stars) and into different galactic types (for the galaxies). As part of the fitting procedure, derive the distance and extinction to each object and the photometric redshift towards galaxies and quasars. This method easily allows for the addition of any number of observations to cover a more diverse range of wavelengths, as well as the addition of any number of model templates. The primary objective of this work is to eventually derive a 3d extinction map of the MW galaxy [cool!].
1308.2533
Detecting filamentary pattern in the cosmic web: a catalogue of filaments for the SDSS
Tempel et al
The main feature of the spatial large-scale galaxy distribution is its intricate network of galaxy filaments. This network is spanned by the galaxy locations that can be interpreted as 3d point distribution. The global properties of the point process can be measured by different statistical methods, which, however, do not describe directly the structure elements. The morphology of the large scale structure is an important property of galaxy distribution. Apply an object point process with interactions (the Bisous model) to trace and extract the filamentary network in the presently largest galaxy redshift survey, SDSS. Search for filaments in the galaxy dsitribution having a radius of about 0.5 Mpc/h. Divide the detected network into single filaments and present a public catalogue of filaments. Study the filament length distribution and show that the longest filaments reach the length of 60 Mpc/h. The filaments contain 35-40% of the total galaxy luminosity and they cover roughly 5-8% of the total volume, in good agreement with N-body simulations and previous observational results.
1308.2534
Dark Matter
Einasto
Review of the development of the concept of DM. The DM story passed through several stages from a minor observational puzzle to a major challenge for theory of elementary particles. Modern data suggest that DM is the dominant matter component in the Universe, and that it consists of some unknown non-baryonic particles. DM is the dominant matter component in the Universe, thus properties of Dm particles determine the structure of the cosmic web.
1308.2551
Predictions for BAO distance estimates from the cross-correlaton of the Lyman-alpha forest and redshifted 21-cm emission
Sarkar, Bharadwaj
Investigate the possibility of using cross-correlation of Ly-a forest and redshifted 21-cm emission to detect the BAO. The standard Fisher matrix formalism used to determine the accuracy with which it will be possible to measure cosmological distances using this signal. Earlier predictions indicate that it will be possible to measure the dilation factor D_V with 1.9% accuracy at z=2.5 from the BOSS Ly-a forest auto-correlation. Investigate if it is possible to improve the accuracy using the cross-correlation. Use a simple parameterization of the Ly-a forest survey which very loosely matches some properties of BOSS and predicts delta D_V/D_V=2.0% for the auto-correlation at z=2.5. For the redshifted 21-cm observations, consider individual antennas of 2m*2m distributed such that the baselines within 250m are uniformly sampled. Assumed that the observations span z=2 to 3 and coveres the 10k deg^2 sky coverage of BOSS. Find that for 2 years of observation with an array of 2k antennas, the cross-corelation is 1.7 times more sensitive that the Ly-a forest auto-correlation. The cross-correlation is 2.7 times more sensitive than the auto-correlation if we have 4k antennas and 4 years of observation. In conclusion, find that it is possible to significantly increase the accuracy of the distance estimates by considering the cross-correlation signal. [question: how significant is the 21cm signal from z=2-3?]
1308.2816
Galaxy spin alignment in filaments and sheets: observational evidence
Tempel, Libeskind
Galaxy properties are known to be affected by their environment. One important question is how their angular momentum reflects the surrounding cosmic web. Use the SDS to investigate the spin axes of spiral and elliptical galaxies relative to their surrounding filament/sheet orientations. To detect filaments a marked point process with interactions (the "Bisous model") is used. Sheets are found by detecting "flattened" filaments. The minor axis of ellipticals are found to be preferential perpendicular to hosting filaments. A weak correlation is found with sheets [what do you mean? correlation of sheets and what?]. These findings are consistent with the notion that elliptical galaxies formed via mergers which predominantly occurred along the filaments. The spin axis of spiral galaxies is found to align with the host filament [really?? that would be cool, but I thought previous studies didn't find any correlation. Does this result contradict them?], with no correlation between spiral spin and sheet normal. When examined as a function of distance from the filament axis, a much stronger correlation is found in outer parts, suggesting that the alignment is driven by the laminar infall of gas from sheets to filaments [that would be so cool]. When compared with numerical simulations, results suggest that the connection between DM halo and galaxy spin is not straightforward. Results provide an important input to the understanding of how galaxies acquire their angular momentum.
1308.2669
The AGORA high-resolution galaxy simulations comparison project
Kim, Abel, ... Conroy, Dekel, Gnedin, Hahn, Hopkins, Klypin, Kravtsov, Krumholz, et al
AGORA project: a comprehensive numerical study of well-resolved galaxies within the LCDM cosmology. Cosmological hydrodynamic sims with force resolutions of ~100 proper pc or better will be run with a variety of code platforms to follow the hierarchical growth, SFH, morphological transformation, and the cycle of baryons in and out of 8 galaxies with halo masses M_vir ~ 1e10, 11, 12, and 13 Msun at z=0 and two different ("violent" and "quiescent") assembly histories. The numerical techniques and implementations used in this project include the smoothed particle hydrodynamics codes GADGET and GASOLINE, and the adaptive mesh refinement codes ART, ENZO, and RAMSES. The codes will share common initial conditions and common astrophysics packages including UV background, metal-dependent radiative cooling, metal and energy yields of supernovae, and stellar IMF. These are described in detail in the paper. Subgrid SF and feedback prescriptions will be tuned to provide a realistic interstellar and circumgalactic medium using a non-cosmological disk galaxy simulation. Cosmological runs will be systematically compared with each other using a common analysis toolkit [like what? PS?], and validated against observations to verify that the solutions are robust -- i.e., that the astrophysical assumptions are responsible for any success, rather than artifacts of particular implementations. The goals of the AGORA project are, broadly speaking, to raise the realism and the predictive power of galaxy simulations and the understanding of the feedback processes that regulate galaxy "metabolism." The proof-of-concept DM-only test of the formation of a galactic halo with a z=0 mass of M_vir ~ 1.7e11 Msun by 9 different versions of the participating codes is also presented to validate the infrastructure of the project.
NYT article: http://www.nytimes.com/2013/08/13/science/how-to-share-scientific-data.html
Who will pay for public access to research data?Berman
The US office of science and technology policy (OSTP) released a memo calling for public access for publications and data resulting from federally sponsored research grants. The memo directed federal agencies with more than $100 M R&D expenditures to "develop a plan to support increased public access to the results of research funded by the Federal Government." A subsequent NYT page sported the headline "We paid for the research, so let's see it." So who pays for data infrastructure?
1308.2227
A search for RR Lyrae stars in Segue 2 and Segue 3
Boettcher, Willman, Fadely, ... et al
Search for RR Lyrae stars in ultra-faint MW companions Segue 2 and 3. In Segue 2, Find a RRab star ["fundamental mode" RR Lyrae] with period P_ab=0.748 days. Revisit inverse correlation between <P_ab> and <[Fe/H]> established in the literature for MW dwarf galaxies and their RR Lyrae. The long period of Segue 2's RRab star, as well as the known significant spread in metallicity in this dwarf galaxy are consistent with the observed trend in <P_ab> and <[Fe/H]>. Derive the first robust distance to Segue 2, using both its RRab star and spectroscopically confirmed blue horizontal branch stars. Using [Fe/H]=-2.16 and -2.44 dex, find d_RRL=36.6 and 37.7 (pm 2.5-ish) kpc; assuming [Fe/H]=-2.257 dex, find d_BHB=34.4pm2.6kpc. Although no RRLyrae were present in the Segue 3 field, find a candidate eclipsing binary star system.
1308.2252
KeSeF - Kepler Self Follow-up Mission
Ofir
The Kepler spacecraft is currently unable to hold steady pointing and it is slowly drifting during observations. If one has to deal with targets that drift across the CCDs, one should at least be able to track to targets well enough to correct for some -- if not most -- of the problems caused by this drift. Propose to observe as many stars as possible in short cadence. Propose that at least all currently known planetary candidate host stars will be so observed, with possibly known Kepler eclipsing binaries, astroseismology targets, guest observer targets and new targets in increasingly lower priority. Also outline the modifications needed to flight SW in order to allow for such observations to take place, aiming to provide ample non-photometric data that should allow post-processing to recover most of the pre-failure photometric performance. In total, the KeSeF Mission will allow Kepler to follow up it's own previous discoveries in a way that is not otherwise possible. By doing so it will enable to continue persuing nearly all the science goals that made the original mission choose staring at a single field of view in the first place. [confusing last sentence. I guess the drift doesn't allow Kepler to stare at one point anymore.]
1308.2367
The 9 and 18 micron luminosity function of various types of galaxies with AKARI: implication for the dust torus structure of AGN
Toba et al
Present the 9 and 18 micron LFs of galaxies at 0.006<z<0.8 (avg z ~0.04) using AKARI MIR all-sky survey catalog. 243 galaxies at 9 um and 255 galaxies at 18 um from SDSS spectroscopy region; classified by their optical emission lines, such as Ha or [OIII]/Hbeta and [NII]/H_alpha into 5 types: Type 1 AGN, Type 2, low-ionization narrow emission lines (LINER); galaxies with both SF and narrow-line AGN activity (composite galaxies); and star forming galaxies (SF). Find that (i) the number density ratio of Type 2 to Type 1 AGNs is 1.73, which is larger than a result obtained from the optical LF and (ii) this ratio decreases with increasing 18 um luminosity.
1308.2398
Photometric identification of objects from Galaxy Evolution Explorer survey and Sloan digital sky survey
Preethi, et al
Used GALEX and SESS to get 7-band photometric mag of 80k objects near the North Galactic Pole. Although these have been identified as stars by the SDSS pipeline, found through fitting with model SEDs that most were in fact of extragalactic origin. [really? how was the original 80k "stellar" object chosen?] Only about 9% of these objects turned out to be MS stars, and about 11% were WDs and RGs collectively, while galaxies and quasars contributed to the remaining 80% of the data. Classified these objects into different spectral types (for the stars) and into different galactic types (for the galaxies). As part of the fitting procedure, derive the distance and extinction to each object and the photometric redshift towards galaxies and quasars. This method easily allows for the addition of any number of observations to cover a more diverse range of wavelengths, as well as the addition of any number of model templates. The primary objective of this work is to eventually derive a 3d extinction map of the MW galaxy [cool!].
1308.2533
Detecting filamentary pattern in the cosmic web: a catalogue of filaments for the SDSS
Tempel et al
The main feature of the spatial large-scale galaxy distribution is its intricate network of galaxy filaments. This network is spanned by the galaxy locations that can be interpreted as 3d point distribution. The global properties of the point process can be measured by different statistical methods, which, however, do not describe directly the structure elements. The morphology of the large scale structure is an important property of galaxy distribution. Apply an object point process with interactions (the Bisous model) to trace and extract the filamentary network in the presently largest galaxy redshift survey, SDSS. Search for filaments in the galaxy dsitribution having a radius of about 0.5 Mpc/h. Divide the detected network into single filaments and present a public catalogue of filaments. Study the filament length distribution and show that the longest filaments reach the length of 60 Mpc/h. The filaments contain 35-40% of the total galaxy luminosity and they cover roughly 5-8% of the total volume, in good agreement with N-body simulations and previous observational results.
1308.2534
Dark Matter
Einasto
Review of the development of the concept of DM. The DM story passed through several stages from a minor observational puzzle to a major challenge for theory of elementary particles. Modern data suggest that DM is the dominant matter component in the Universe, and that it consists of some unknown non-baryonic particles. DM is the dominant matter component in the Universe, thus properties of Dm particles determine the structure of the cosmic web.
1308.2551
Predictions for BAO distance estimates from the cross-correlaton of the Lyman-alpha forest and redshifted 21-cm emission
Sarkar, Bharadwaj
Investigate the possibility of using cross-correlation of Ly-a forest and redshifted 21-cm emission to detect the BAO. The standard Fisher matrix formalism used to determine the accuracy with which it will be possible to measure cosmological distances using this signal. Earlier predictions indicate that it will be possible to measure the dilation factor D_V with 1.9% accuracy at z=2.5 from the BOSS Ly-a forest auto-correlation. Investigate if it is possible to improve the accuracy using the cross-correlation. Use a simple parameterization of the Ly-a forest survey which very loosely matches some properties of BOSS and predicts delta D_V/D_V=2.0% for the auto-correlation at z=2.5. For the redshifted 21-cm observations, consider individual antennas of 2m*2m distributed such that the baselines within 250m are uniformly sampled. Assumed that the observations span z=2 to 3 and coveres the 10k deg^2 sky coverage of BOSS. Find that for 2 years of observation with an array of 2k antennas, the cross-corelation is 1.7 times more sensitive that the Ly-a forest auto-correlation. The cross-correlation is 2.7 times more sensitive than the auto-correlation if we have 4k antennas and 4 years of observation. In conclusion, find that it is possible to significantly increase the accuracy of the distance estimates by considering the cross-correlation signal. [question: how significant is the 21cm signal from z=2-3?]
1308.2816
Galaxy spin alignment in filaments and sheets: observational evidence
Tempel, Libeskind
Galaxy properties are known to be affected by their environment. One important question is how their angular momentum reflects the surrounding cosmic web. Use the SDS to investigate the spin axes of spiral and elliptical galaxies relative to their surrounding filament/sheet orientations. To detect filaments a marked point process with interactions (the "Bisous model") is used. Sheets are found by detecting "flattened" filaments. The minor axis of ellipticals are found to be preferential perpendicular to hosting filaments. A weak correlation is found with sheets [what do you mean? correlation of sheets and what?]. These findings are consistent with the notion that elliptical galaxies formed via mergers which predominantly occurred along the filaments. The spin axis of spiral galaxies is found to align with the host filament [really?? that would be cool, but I thought previous studies didn't find any correlation. Does this result contradict them?], with no correlation between spiral spin and sheet normal. When examined as a function of distance from the filament axis, a much stronger correlation is found in outer parts, suggesting that the alignment is driven by the laminar infall of gas from sheets to filaments [that would be so cool]. When compared with numerical simulations, results suggest that the connection between DM halo and galaxy spin is not straightforward. Results provide an important input to the understanding of how galaxies acquire their angular momentum.
1308.2669
The AGORA high-resolution galaxy simulations comparison project
Kim, Abel, ... Conroy, Dekel, Gnedin, Hahn, Hopkins, Klypin, Kravtsov, Krumholz, et al
AGORA project: a comprehensive numerical study of well-resolved galaxies within the LCDM cosmology. Cosmological hydrodynamic sims with force resolutions of ~100 proper pc or better will be run with a variety of code platforms to follow the hierarchical growth, SFH, morphological transformation, and the cycle of baryons in and out of 8 galaxies with halo masses M_vir ~ 1e10, 11, 12, and 13 Msun at z=0 and two different ("violent" and "quiescent") assembly histories. The numerical techniques and implementations used in this project include the smoothed particle hydrodynamics codes GADGET and GASOLINE, and the adaptive mesh refinement codes ART, ENZO, and RAMSES. The codes will share common initial conditions and common astrophysics packages including UV background, metal-dependent radiative cooling, metal and energy yields of supernovae, and stellar IMF. These are described in detail in the paper. Subgrid SF and feedback prescriptions will be tuned to provide a realistic interstellar and circumgalactic medium using a non-cosmological disk galaxy simulation. Cosmological runs will be systematically compared with each other using a common analysis toolkit [like what? PS?], and validated against observations to verify that the solutions are robust -- i.e., that the astrophysical assumptions are responsible for any success, rather than artifacts of particular implementations. The goals of the AGORA project are, broadly speaking, to raise the realism and the predictive power of galaxy simulations and the understanding of the feedback processes that regulate galaxy "metabolism." The proof-of-concept DM-only test of the formation of a galactic halo with a z=0 mass of M_vir ~ 1.7e11 Msun by 9 different versions of the participating codes is also presented to validate the infrastructure of the project.
Day 486
Tuesday.
1308.1669
Confronting simulations of optically thick gas in massive haloes with observations at z=2-3
Fumagalli, Hennawi, Prochaska, Kasen, Dekel, Cervino, Primack
Predict distribution of neutral hydrogen around 21 galaxies in the halo mass range M_vir~3e11-4e12 Msun at z~2, with high-res hydro sims. Covering fraction of optically-thick gas interior to the virial radius varies between f_c~0.5-0.2, with significant scatter among haloes. Contrary to recent claims, both the mass fraction of cold (T<=3e4 K) gas within the virial radius and the covering fraction of optically-thick absorbers are found to be only weakly dependent on halo mass, even above the critical values for the formation of stable virial shocks. Massive simulated haloes with M_vir >= 1e12 Msun underpredict the covering fraction of optically-thick gas observed in the environs of quasar host galaxies by a large factor. The reasons for this discrepancy, possibly related to the treatment of feedback and hydrodynamic instability in simulations or to the fact that quasars may represent a special phase in the life of a galaxy, remain unclear. Conversely, do not find statistically significant difference between the predicted covering fraction and observations in the lower mass haloes M_vir >= 5e11 Msun hosting Lyman break galaxies. However, current samples of quasar-galaxy pairs are too small for conclusive comparisons, limiting the ability to test current theories for cold-gas accretion. To overcome this limitation, propose an alternative method for mapping the distribution of optically-thick gas around distant galaxies based on the small-scale auto-correlation function of optically-thick gas clouds measured in the foreground of close quasar paris. With numerical models, show that this new observable provides statistical information on the size of the CGM, its covering factor, and the underlying dark haloes hosting Lyman Limit systems at z~2-3, without the need to compile large samples of galaxy-quasar pairs.
1308.1675
The contribution of haloes with different mass ratios to the overall growth of cluster-sized haloes
Lemze, et al
New observational test for a key prediction of the LCDM: the contributions of mergers with different halo-to-main-cluster mass ratios to cluster-sized halo growth [?]. Perform test by dynamically analyzing seven galaxy clusters, spanning the redshift range 0.13<z_c<0.45 and caustic mass range 0.4-1.5e15 Msun/h_0.73, with an average of 293 spectroscopically-confirmed bound galaxies to each cluster. The large radial coverage (a few virial radii), which covers the whole infall regions, with a high number of spectroscopically identified galaxies enables this new study. For each cluster, identify bound galaxies. Out of these galaxies, identify infalling [how?] and accreted haloes [a sub-halo within a cluster? ...or a neighboring halo?] and estimate their masses and their dynamical states. Using the estimated masses, derive the contribution of different mass ratios to cluster-sized halo growth. For mass ratios between ~0.2 and ~0.7, find a ~1 sigma agreement with LCDM expectations based on the Millennium simulations I and II [statistics on 7 clusters??]. At low mass ratios <0.2, derived contribution is underestimated since the detection efficiency decreases at low masses, ~2e14 Msun/h_73. At large mass ratios, >~0.7, do not detect haloes probably because the sample (chosen to be quite X-ray related) is biased against large mass ratios. Therefore, at large mass ratios, the derived contribution is also underestimated.
1308.1692
CLASH: a census of magnified star-forming galaxies at z~6-8
Bradley, Zitrin, Coe, ... Broadhurst, et al
18 lensing clusters, HST 16-band observations of CLASH for z~6-8 galaxies. Discovery of 206, 45, 13 LBG candidates at z~6, 7, and 8 respectively, identified from purely photometric redshift selections. This large sample, representing nearly an order of magnitude increasei n the number of magnified SF galaxies at z~6-8 presented to date, is unique in that there are observations in 4 WVC3/UVIS UV, 7 ACS/WFC optical and all 5 WFC3/IR broad-band filters, which enable very accurate photometric redshift selections. Construct detailed lensing models for all 18 clusters (although some are preliminary) to estimate object magnifications and to identify 2 new multiply-lenzed z>~6 candidates. The median magnifications for these 18 clusters are 4, 4, and 5 for the z~6,7, and 8 samples, respectively, over an average area of 4.5 arcmin^2 per cluster. Compare observed number counts with expectations based on convolving "blank" field UV luminosity functions through cluster lens models, and find agreement down to ~27 mag, where it begins to suffer fro significant incompleteness. In all 3 redshift bins, find a higher number density at brighter observed magnitudes than the field predictions, in excellent agreement with the lensed expectations and clearly demonstrating the enhanced efficiency of lensing clusters over field surveys. Lensing clusters appear to be a powerful tool in the discovery and study of high-z galaxies and allow for the first glimpse of faint galaxies beyond the reach of the deepest HST legacy field surveys, a technique that will continue to be exploited with the upcoming ultradeep Hubble Frontier Fields campaign.
1308.1703
The distribution of dark matter in the milky way's disk
Kuhlen, Pillepich, Guedes, Madau
Analysis of the effects of dissipational baryonic physics on the local DM distribution at the location of the Sun, with an emphasis on the consequences for direct detection experiments. Find that 2 distinct processes lead to a 30% enhancement of DM in the disk plane: the accretion and disruption of satellites resulting in a DM component with net angular momentum and the contraction of baryons pulling DM into the disk plane without forcing it to co-rotate [interesting]. The co-rotating dark disk in Eris [what is Eris? the sim?] is less massive than what has been suggested by previous work, contributing only 9% of the local DM density. The speed distribution in Eris is broadened and shifted to higher speed compared to its DM-only twin simulation ErisDark. At high speed f(v) falls more steeply in Eris than in ErisDark or the Standard Halo Model (SHM), easing the tension between recent results from the CDMS-II and XENON100 experiments. The non-Maxwellian aspects of f(v) are still present, but much less pronounced in Eris than in DM-only runs. The weak dark disk increases the time-averaged scattering rate by only a few percent a low recoil energies. On the high velocity tail, however, the increase in typical speeds due to baryonic contraction results in strongly enhanced mean scattering rates compared to ErisDark, although still suppressed compared to the SHM. Similar trends are seen regarding the amplitude of the annual modulations, while the modulated fraction in increased compared to the SHM and decreased compared to ErisDark.
1308.1873
Formulation of non-steady-state dust formation process in astrophysical environments
Nozawa, Kozasa
The non-steady-state formation of small clusters and the growth of grains accompanied by chemical reactions are formulated under the consideration that the collision of key gas species (key molecule) controls the kinetics of dust formation process. The formula allows evaluation of the size distribution and condensation efficiency of dust formed in astrophysical environments. Apply the formulation to the formation of C and NgSiO3 grains in the ejecta of supernovae, as an example, to investigate how the non-steady effect influences the formation process, condensation efficiency f_con, and average radius a_ave of newly formed grains in comparison with the results calculated with the steady-state nucleation rate. Show that the steady-state nucleation rate is a good approximation if the collision timescale of key molecule tau_coll is much smaller than the timescale tau_sat with which the supersaturation ratio increases; otherwise the effect of the non-steady state becomes remarkable, leading to a lower f_con and a larger a_ave. Examining the results of calculations, reveals that the steady-state nucleation rate is applicable if the cooling gas satisfies Lambda = tau_sat/tau_coll > 30 during the formation of dust, and find that f_con and a_ave are uniquely determined by Lambda_on at the onset time t_on of dust formation The approximation formulae for f_con and a_ave as a function of Lambda_on could be useful in estimating the mass and typical size of newly formed grains from observed or model-predicted physical properties not only in SNe ejecta but also in mass-loss winds from evolved stars.
1308.1908
A new approach to developing interactive software modules through graduate education
Sanders, Faesi, Goodman
Discuss a set of 15 new interactive, educational, online software modules developed by Harvard University graduate students to demonstrate various concepts related to astronomy and physics. Their achievement demonstrates that only SW tools for education and outreach on specialized topics can be produced while simultaneously fulfilling project-based learning objectives. Describe a set of technologies suitable for module development and present in detail 4 examples of modules developed by the students. Offer recommendations for incorporating educational SW development within a graduate curriculum and conclude by discussing the relevance of this novel approach to new online learning environments like edX.
1308.1953
THe effect of gravitational focusing on annual modulation
Lee, Lisanti, Peter, Safdi
The scattering rate at DM direct-detection experiments should modulate annually due to the Earth's orbit around the Sun. The rate is typically thought to be extremized around June 1, when the relative velocity of the Earth with respect to the DM wind is maximal. Point out that gravitational focusing can alter this modulation phase. Unbound DM particles are focused by the Sun's gravitational potential, affecting their phase-space density in the lab frame. Gravitational focusing can result in a significant overall shift in the annual-modulation phase, which is most relevant for DM with low scattering speeds. The induced phase shift for light O(10) GeV DM may also be significant, depending on the threshold energy of the experiment.
1308.1958
The rich globular cluster system of Abell 1689 and the radial dependence of the globular cluster formation efficiency
Alamo-Martinez et al
Study the rich GC system in the center of the massive cluster of galaxies Abell 1789 (z=0.18), one of the most powerful gravitational lenses known. HST magnitude I_814=29 mag reached, in 28 orbits, with >90% completeness and sample the brightest ~5% of the GC system. Assuming the well-known Gaussian form of the GCLF, estimate a total population of N(GC_total) = 162,850 GCs within a projected radius of 400 kpc. As many as half may comprise as intracluster component. Even with the sizable uncertainties, which mainly result from the uncertain GCLF parameters, this is by far the largest GC system studied to date. The specific frequency S_N [number of GC's per unit galaxy luminosity] is high, but not uncommon for central galaxies in massive clusters, rising from S_N~5 near the center to ~12 at large radii. Passive galaxy fading would increase S_N by ~20% at z=0. Construct the radial mass profiles of the GCs, stars, intracluster gas, and lensing-derived total mass, and compare the mass fractions as a function of radius. The estimated mass in GCs, M(GC_total)=3.9e10 Msun, is comparable to ~80% of the total stellar mass of the MW. The shape of the GC mass profile appears intermediate between those of the stellar mass and total cluster mass. Despite the extreme nature of this system, the ratios of the GC mass to the baryonic and total masses, and thus the GC formation efficiency, are typical of those in other rich clusters when comparing at the same physical radii. The GC formation efficiency is not constant, but varies with radius, in a matter that appears similar for different clusters; speculate on the reasons for this similarity in profile.
1308.2030
A predicted new population of UV-faint galaxies at z>4
Wyithe, Loeb, Oesch
Show: a bursty model of high redshift SF explains several puzzling observations of the high-z galaxy population. Begin by pointing out that the observed sSFR requires a duty-cycle of ~10%, which is much lower than found in many hydro-dynamical simulations. This value follows directly from the fact that the observed SFR in galaxies integrated over a Hubble time exceeds the observed stellar mass by an order of magnitude. Use the large observed sSFR which includes merger driven SF regulated by SNe feedback. This model reproduces the SFR density function and the stellar mass function of galaxies at 4<z<7. A prediction of the model is that the sSFR does not evolve very rapidly with either mass or redshift, in agreement with observation. This is in contrast to results from hydrodynamical sims where the SF closely follows the accretion rate, and so increases strongly towards high z. The bursty SF model naturally explains the observation that there is not enough stellar mass at z~2-4 to account for all of the SF observed, without invoking properties like an evolving IMF of stars. The finding of a duty cycle that is ~10% implies that there should be ten times the number of known galaxies at fixed stellar mass that have not yet been detected through standard UV selection at high z. Therefore predict the existence of a large undetected population of UV-faint galaxies that accounts for most of the stellar mass density at z~4-8.
1308.1669
Confronting simulations of optically thick gas in massive haloes with observations at z=2-3
Fumagalli, Hennawi, Prochaska, Kasen, Dekel, Cervino, Primack
Predict distribution of neutral hydrogen around 21 galaxies in the halo mass range M_vir~3e11-4e12 Msun at z~2, with high-res hydro sims. Covering fraction of optically-thick gas interior to the virial radius varies between f_c~0.5-0.2, with significant scatter among haloes. Contrary to recent claims, both the mass fraction of cold (T<=3e4 K) gas within the virial radius and the covering fraction of optically-thick absorbers are found to be only weakly dependent on halo mass, even above the critical values for the formation of stable virial shocks. Massive simulated haloes with M_vir >= 1e12 Msun underpredict the covering fraction of optically-thick gas observed in the environs of quasar host galaxies by a large factor. The reasons for this discrepancy, possibly related to the treatment of feedback and hydrodynamic instability in simulations or to the fact that quasars may represent a special phase in the life of a galaxy, remain unclear. Conversely, do not find statistically significant difference between the predicted covering fraction and observations in the lower mass haloes M_vir >= 5e11 Msun hosting Lyman break galaxies. However, current samples of quasar-galaxy pairs are too small for conclusive comparisons, limiting the ability to test current theories for cold-gas accretion. To overcome this limitation, propose an alternative method for mapping the distribution of optically-thick gas around distant galaxies based on the small-scale auto-correlation function of optically-thick gas clouds measured in the foreground of close quasar paris. With numerical models, show that this new observable provides statistical information on the size of the CGM, its covering factor, and the underlying dark haloes hosting Lyman Limit systems at z~2-3, without the need to compile large samples of galaxy-quasar pairs.
1308.1675
The contribution of haloes with different mass ratios to the overall growth of cluster-sized haloes
Lemze, et al
New observational test for a key prediction of the LCDM: the contributions of mergers with different halo-to-main-cluster mass ratios to cluster-sized halo growth [?]. Perform test by dynamically analyzing seven galaxy clusters, spanning the redshift range 0.13<z_c<0.45 and caustic mass range 0.4-1.5e15 Msun/h_0.73, with an average of 293 spectroscopically-confirmed bound galaxies to each cluster. The large radial coverage (a few virial radii), which covers the whole infall regions, with a high number of spectroscopically identified galaxies enables this new study. For each cluster, identify bound galaxies. Out of these galaxies, identify infalling [how?] and accreted haloes [a sub-halo within a cluster? ...or a neighboring halo?] and estimate their masses and their dynamical states. Using the estimated masses, derive the contribution of different mass ratios to cluster-sized halo growth. For mass ratios between ~0.2 and ~0.7, find a ~1 sigma agreement with LCDM expectations based on the Millennium simulations I and II [statistics on 7 clusters??]. At low mass ratios <0.2, derived contribution is underestimated since the detection efficiency decreases at low masses, ~2e14 Msun/h_73. At large mass ratios, >~0.7, do not detect haloes probably because the sample (chosen to be quite X-ray related) is biased against large mass ratios. Therefore, at large mass ratios, the derived contribution is also underestimated.
1308.1692
CLASH: a census of magnified star-forming galaxies at z~6-8
Bradley, Zitrin, Coe, ... Broadhurst, et al
18 lensing clusters, HST 16-band observations of CLASH for z~6-8 galaxies. Discovery of 206, 45, 13 LBG candidates at z~6, 7, and 8 respectively, identified from purely photometric redshift selections. This large sample, representing nearly an order of magnitude increasei n the number of magnified SF galaxies at z~6-8 presented to date, is unique in that there are observations in 4 WVC3/UVIS UV, 7 ACS/WFC optical and all 5 WFC3/IR broad-band filters, which enable very accurate photometric redshift selections. Construct detailed lensing models for all 18 clusters (although some are preliminary) to estimate object magnifications and to identify 2 new multiply-lenzed z>~6 candidates. The median magnifications for these 18 clusters are 4, 4, and 5 for the z~6,7, and 8 samples, respectively, over an average area of 4.5 arcmin^2 per cluster. Compare observed number counts with expectations based on convolving "blank" field UV luminosity functions through cluster lens models, and find agreement down to ~27 mag, where it begins to suffer fro significant incompleteness. In all 3 redshift bins, find a higher number density at brighter observed magnitudes than the field predictions, in excellent agreement with the lensed expectations and clearly demonstrating the enhanced efficiency of lensing clusters over field surveys. Lensing clusters appear to be a powerful tool in the discovery and study of high-z galaxies and allow for the first glimpse of faint galaxies beyond the reach of the deepest HST legacy field surveys, a technique that will continue to be exploited with the upcoming ultradeep Hubble Frontier Fields campaign.
1308.1703
The distribution of dark matter in the milky way's disk
Kuhlen, Pillepich, Guedes, Madau
Analysis of the effects of dissipational baryonic physics on the local DM distribution at the location of the Sun, with an emphasis on the consequences for direct detection experiments. Find that 2 distinct processes lead to a 30% enhancement of DM in the disk plane: the accretion and disruption of satellites resulting in a DM component with net angular momentum and the contraction of baryons pulling DM into the disk plane without forcing it to co-rotate [interesting]. The co-rotating dark disk in Eris [what is Eris? the sim?] is less massive than what has been suggested by previous work, contributing only 9% of the local DM density. The speed distribution in Eris is broadened and shifted to higher speed compared to its DM-only twin simulation ErisDark. At high speed f(v) falls more steeply in Eris than in ErisDark or the Standard Halo Model (SHM), easing the tension between recent results from the CDMS-II and XENON100 experiments. The non-Maxwellian aspects of f(v) are still present, but much less pronounced in Eris than in DM-only runs. The weak dark disk increases the time-averaged scattering rate by only a few percent a low recoil energies. On the high velocity tail, however, the increase in typical speeds due to baryonic contraction results in strongly enhanced mean scattering rates compared to ErisDark, although still suppressed compared to the SHM. Similar trends are seen regarding the amplitude of the annual modulations, while the modulated fraction in increased compared to the SHM and decreased compared to ErisDark.
1308.1873
Formulation of non-steady-state dust formation process in astrophysical environments
Nozawa, Kozasa
The non-steady-state formation of small clusters and the growth of grains accompanied by chemical reactions are formulated under the consideration that the collision of key gas species (key molecule) controls the kinetics of dust formation process. The formula allows evaluation of the size distribution and condensation efficiency of dust formed in astrophysical environments. Apply the formulation to the formation of C and NgSiO3 grains in the ejecta of supernovae, as an example, to investigate how the non-steady effect influences the formation process, condensation efficiency f_con, and average radius a_ave of newly formed grains in comparison with the results calculated with the steady-state nucleation rate. Show that the steady-state nucleation rate is a good approximation if the collision timescale of key molecule tau_coll is much smaller than the timescale tau_sat with which the supersaturation ratio increases; otherwise the effect of the non-steady state becomes remarkable, leading to a lower f_con and a larger a_ave. Examining the results of calculations, reveals that the steady-state nucleation rate is applicable if the cooling gas satisfies Lambda = tau_sat/tau_coll > 30 during the formation of dust, and find that f_con and a_ave are uniquely determined by Lambda_on at the onset time t_on of dust formation The approximation formulae for f_con and a_ave as a function of Lambda_on could be useful in estimating the mass and typical size of newly formed grains from observed or model-predicted physical properties not only in SNe ejecta but also in mass-loss winds from evolved stars.
1308.1908
A new approach to developing interactive software modules through graduate education
Sanders, Faesi, Goodman
Discuss a set of 15 new interactive, educational, online software modules developed by Harvard University graduate students to demonstrate various concepts related to astronomy and physics. Their achievement demonstrates that only SW tools for education and outreach on specialized topics can be produced while simultaneously fulfilling project-based learning objectives. Describe a set of technologies suitable for module development and present in detail 4 examples of modules developed by the students. Offer recommendations for incorporating educational SW development within a graduate curriculum and conclude by discussing the relevance of this novel approach to new online learning environments like edX.
1308.1953
THe effect of gravitational focusing on annual modulation
Lee, Lisanti, Peter, Safdi
The scattering rate at DM direct-detection experiments should modulate annually due to the Earth's orbit around the Sun. The rate is typically thought to be extremized around June 1, when the relative velocity of the Earth with respect to the DM wind is maximal. Point out that gravitational focusing can alter this modulation phase. Unbound DM particles are focused by the Sun's gravitational potential, affecting their phase-space density in the lab frame. Gravitational focusing can result in a significant overall shift in the annual-modulation phase, which is most relevant for DM with low scattering speeds. The induced phase shift for light O(10) GeV DM may also be significant, depending on the threshold energy of the experiment.
1308.1958
The rich globular cluster system of Abell 1689 and the radial dependence of the globular cluster formation efficiency
Alamo-Martinez et al
Study the rich GC system in the center of the massive cluster of galaxies Abell 1789 (z=0.18), one of the most powerful gravitational lenses known. HST magnitude I_814=29 mag reached, in 28 orbits, with >90% completeness and sample the brightest ~5% of the GC system. Assuming the well-known Gaussian form of the GCLF, estimate a total population of N(GC_total) = 162,850 GCs within a projected radius of 400 kpc. As many as half may comprise as intracluster component. Even with the sizable uncertainties, which mainly result from the uncertain GCLF parameters, this is by far the largest GC system studied to date. The specific frequency S_N [number of GC's per unit galaxy luminosity] is high, but not uncommon for central galaxies in massive clusters, rising from S_N~5 near the center to ~12 at large radii. Passive galaxy fading would increase S_N by ~20% at z=0. Construct the radial mass profiles of the GCs, stars, intracluster gas, and lensing-derived total mass, and compare the mass fractions as a function of radius. The estimated mass in GCs, M(GC_total)=3.9e10 Msun, is comparable to ~80% of the total stellar mass of the MW. The shape of the GC mass profile appears intermediate between those of the stellar mass and total cluster mass. Despite the extreme nature of this system, the ratios of the GC mass to the baryonic and total masses, and thus the GC formation efficiency, are typical of those in other rich clusters when comparing at the same physical radii. The GC formation efficiency is not constant, but varies with radius, in a matter that appears similar for different clusters; speculate on the reasons for this similarity in profile.
1308.2030
A predicted new population of UV-faint galaxies at z>4
Wyithe, Loeb, Oesch
Show: a bursty model of high redshift SF explains several puzzling observations of the high-z galaxy population. Begin by pointing out that the observed sSFR requires a duty-cycle of ~10%, which is much lower than found in many hydro-dynamical simulations. This value follows directly from the fact that the observed SFR in galaxies integrated over a Hubble time exceeds the observed stellar mass by an order of magnitude. Use the large observed sSFR which includes merger driven SF regulated by SNe feedback. This model reproduces the SFR density function and the stellar mass function of galaxies at 4<z<7. A prediction of the model is that the sSFR does not evolve very rapidly with either mass or redshift, in agreement with observation. This is in contrast to results from hydrodynamical sims where the SF closely follows the accretion rate, and so increases strongly towards high z. The bursty SF model naturally explains the observation that there is not enough stellar mass at z~2-4 to account for all of the SF observed, without invoking properties like an evolving IMF of stars. The finding of a duty cycle that is ~10% implies that there should be ten times the number of known galaxies at fixed stellar mass that have not yet been detected through standard UV selection at high z. Therefore predict the existence of a large undetected population of UV-faint galaxies that accounts for most of the stellar mass density at z~4-8.
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