Thursday.
1306.4195
The star formation history of the solar neighbourhood from the white dwarf luminosity function
Rowell
The termination in the WD LF is a standard diagnostic tool for measuring the total age of nearby stellar populations. In this paper, an algorithm is presented for inverting the full WD LF to obtain a maximum likelihood estimate of the time varying SFR of the host stellar population. Tests with synthetic data demonstrate that the algorithm converges over a wide class of underlying SFR forms. The algorithm successfully estimates the moving average SFR as a function of lookback time in the presence of realistic measurement noise, though suffers from degeneracies around discontinuities in the underlying SFR. The inversion results are most sensitive to the choice of WD cooling models, with the models produced by different groups giving quite different results. The results are relatively insensitive to the progenitor metallicity, IMF, initial-final mass relation and ratio of H/He atmosphere WDs. Application to two independent determinations of the Solar neighborhood WD LF give similar results. The SFR has a bimodal form, with broad peaks at 2-3 Gyr and 7-9 Gyr in the past, separated by a significant lull of magnitude 30-90% depending on choice of cooling models. The onset of SF occurs around 8-10 Gyr ago. The total integrated SFR is ~0.014 stars/pc3 in the Solar neighbourbood, for stars more massive than 0.6 M_sun.
1306.4157
Galaxy redshift surveys with sparse sampling
Chiang et al
A competitive study of the 3d-survey of galaxies require a large volume (V_survey ~ 10 Gpc^3), and thus expensive. A "sparse sampling" method offers a more affordable solution to this problem: within a survey footprint covering a given survey volume, observed only a fraction of the volume. The distribution of observed regions should be chosen such that their separation is smaller than the length scale corresponding to the wavenumber of interest. Then one can recover the PS of galaxies with precision expected for a survey covering a volume of V_survey (rather than the volume of the sum of observed regions) with the number density of galaxies given by the total number of observed galaxies divided by V_survey (rather than the number density of galaxies within an observed region). Find that regularly-spaced sampling yields an unbiased PS with no window function effect, and deviations from regularly-spaced sampling, which are unavoidable in realistic surveys, introduce calculable window function effects and increase the uncertainties of the recovered PS. Method is general, but discussed in terms of Hobby-Eberly telescope DE experiment.
1306.4415
The GRB redshift distribution: implications for abundance evolution, star formation, and cosmology
Wei et al
LGRBs from Swift do not trace the SFH in LCDM; confirm that the latest example of GRBs reveals an increasing evolution in the GRB rate relative to the SFR at high redshifts. [...Metallicity evolution may explain this, but doesn't quite work. Assume a different cosmology that makes it work....] Assuming that the GRB rate is related to the SFR and an evolving metallicity, find that the GRB data constrain the slope of the high-z SFR to be -4.6. With this updated SFH, find that in the R_h=ct universe, the observed redshift distribution can also be fitted very well.
1306.4312
Dust in the polar region as a major contributor to the IR emission of AGN
Hoenig, Kishimoto, et al
As the title says.
1306.4319
Baryons do trace dark matter 380,000 years after the big bang: search for compensated isocurvature perturbations with WMAP 9-year data
Grin, Hanson, Holder, Dore, Kamionkowski
Primordial isocurvature fluctuations between photons and either neutrinos or non-relativistic species such as baryons or DM are known to be sub-dominant to adiabatic fluctuations. However, perturbations in the relative densities of baryons and DM (known as compensated isocurvature perturbations, or CIPs) are poorly constrained. CIPs leave no imprint in the CMB on observable scales, at least at linear order in their amplitude and zeroth order in the amplitude of adiabatic perturbations. It is thus not yet empirically known if baryons trace dark matter at the surface of last scattering. If CIPs exist, they would spatially modulate the Silk damping scale and acoustic horizon, causing distinct fluctuations in the CMB temperature/polarization PS across the sky: this effect is first order in both the CIP and adiabatic mode amplitudes. Here, temperature data from the WMAP are used to conduct the first CMB-based observational search for CIPs, using off-diagonal correlations and the CMB trispectrum. Reconstruction noise from WL and point sources is shown to be negligible for this data set. No evidence for CIPs is observed, and a 95%-confidence upper limit of 1.1e-2 is imposed to the amplitude of a scale-invariant CIP PS. This limit agrees with CIP sensitivity forecasts for WMAP, and is competitive with smaller scale constraints from measurements of the baryon fraction in galaxy clusters. It is shown that the root-mean squared CIP amplitude on 5-100 deg scales is smaller than 0.07-0.17 (depending on the scale) at the 95% confidence level. Temperature data from the Planck satellite will provide an even more sensitive probe for the existence of CIPs, as will the upcoming ACTPol and SPTPol experiments on smaller angular scales.
1306.4328
The massive satellite population of Milky-Way sized galaxies
Rodriguez-Puebla, Avila-Reese, Drory
Occupational distributions for satellite galaxies m_s>4e7 Msun around MW-sized hosts are presented and used to predict the internal dynamics of these satellites. Create galaxy group mock catalog base on (sub)halo-to-stellar mass relations constrained with observations; the stellar MF of centrals and satellites, and the 2-t correlation function. 6.6% of MW-s galaxies host 2 sats in the mass range of the SMC and LMC. THe probabilities of the MW-s galaixes to have 1 sat>= the LMC or 2 sats >= te SMC or 3 sats >= Sgr are ~0.26, 0.14, and 0.14, respectively. MW-s hosting 3 sats >= Sgr (as the MW) are among the most common cases. However, the most and 2nd most massive sats in these systems are <LMC and SMC by ~0.7 and 0.8 dex. The N(>m_s) for MW-s galaxies is broad, the case of the MW being of low frequency but not an outlier. The Mh of MW-s galaxies correlates only weakly with N(>ms). THen, it is not possible to accurately determine the MW halo mass by mans of N(>ms); constrain a lower limit 1e12 Msun at 1sig level. Analysis strongly suggests that the abundance of massive subhalos agree with the abundance of massive sats in al MW-s hosts, i.e., there is not a (massive) sat missing problem for the LCDM. However, confirm that the max circular vel, vmax, of the subhalos of sats ms<1e8 Msun is systematically larger than the vmax inferred from current observational studies of the MW bright dwarf sats; at difference of previous works, this conclusion is based on an analysis of the overall population of MW-s galaxies. Some pieces of evidence suggest that the issue could refer only to sat dwarfs but not to central dwarfs; then, environmental processes associated to dwarfs inside host halos combined with SN-driven core expansion should be at the basis of the lowering of vmax.
1306.4337
The build-up of nuclear stellar cusps in extreme starburst galaxies and major mergers
Haan et al
Nuclear stellar cusps are defined as central excess light component in the stellar light profiles of galaxies and are suggested to be stellar relics of intense compact starbursts in the central ~100-500pc region of gas-rich major mergers. Probe the build-up of nuclear cusps during the actual starburst phase for a complete sample of LIRG systems (85 LIRGs with L_IR=1e11.4-12.5 L_sun) in the GOALS sample. Cusp properties are derived via 2-d fitting of the nuclear stellar light imaged in the NIR by HST and have been combined with MIR diagnostics for AGN/SB characterization. Find that nuclear stellar cusps are resolved in 76% of LIRGs (merger and non-interacting galaxies). The cusp strength and luminosity increases with FIR luminosity (excluding AGN) and merger state, confirming theoretical models that starburst activity is associated with the build-up of nuclear stellar cusps. Evidence for ultra compact nuclear starbursts is found in ~13% of LIRGs, which have a strong unresolved central NIR light component but no significant contribution of an AGN. The nuclear NIR surface density (measured within 1 kpc radius) increases by a factor of ~5 towards late merger stages. A careful comparison to local early type galaxies with comparable masses reveals (a) that local (U)LIRGs have a significantly larger cusp fraction and (b) that the majority of the cusp LIRGs have host galaxy luminosities (H-band) similar to core ellitpicals which is roughly one order in magnitude larger than for cusp ellipticals.
1306.4663
Modeling the pollution of pristine gas in the early universe
Pan et al
Theoretical and numerical investigation of the pollution of pristine gas in turbulent flows, designed to provide new tools for modeling the evolution of the 1st generation of stars. Cooling is different ing as with a metallicity below a critical value Z_c (1e-6~1e-3 Z_sun). Z_c is much smaller than the typical average metallicity <Z>; thus the mixing efficiency of the pristine gas in the interstellar medium plays a crucial role in the transition from Pop III to normal star formation. The small critical value Z_c corresponds to the far left tail of the probability distribution function of the metallicity. Based on closure models for the PDF formation of turbulent mixing, derive equations for the fraction of gas, P, lying below Z_c, in compressible turbulence. Simulation show that the evolution of the fraction P can be well approximated by a generalized self-convolution model, which predicts dP/dt = -n/tau_con P(1-P^(1/n)), where n is a measure of the locality of the PDF convolution and the timescale tau-con is determined by the rate at which turbulence stretches the pollutants. Using a suite of simulations with Mach numbers ranging from M=0.9 to 6.2, provide accurate fits to n and tau_con as a function of M, Z_c /<Z>, and the scale L_p at which pollutants are added to the flow. For P>0.9, mixing occurs only in the regions surrounding the pollutants, such that n=1. For smaller P, n is larger as mixing becomes more global. Show how the results can be used to construct one-zone models for the evolution of Pop III stars in a single high-redshift galaxy, as well as subgrid models for tracking the evolution of the first stars in large cosmological simulations.
1306.4195
The star formation history of the solar neighbourhood from the white dwarf luminosity function
Rowell
The termination in the WD LF is a standard diagnostic tool for measuring the total age of nearby stellar populations. In this paper, an algorithm is presented for inverting the full WD LF to obtain a maximum likelihood estimate of the time varying SFR of the host stellar population. Tests with synthetic data demonstrate that the algorithm converges over a wide class of underlying SFR forms. The algorithm successfully estimates the moving average SFR as a function of lookback time in the presence of realistic measurement noise, though suffers from degeneracies around discontinuities in the underlying SFR. The inversion results are most sensitive to the choice of WD cooling models, with the models produced by different groups giving quite different results. The results are relatively insensitive to the progenitor metallicity, IMF, initial-final mass relation and ratio of H/He atmosphere WDs. Application to two independent determinations of the Solar neighborhood WD LF give similar results. The SFR has a bimodal form, with broad peaks at 2-3 Gyr and 7-9 Gyr in the past, separated by a significant lull of magnitude 30-90% depending on choice of cooling models. The onset of SF occurs around 8-10 Gyr ago. The total integrated SFR is ~0.014 stars/pc3 in the Solar neighbourbood, for stars more massive than 0.6 M_sun.
1306.4157
Galaxy redshift surveys with sparse sampling
Chiang et al
A competitive study of the 3d-survey of galaxies require a large volume (V_survey ~ 10 Gpc^3), and thus expensive. A "sparse sampling" method offers a more affordable solution to this problem: within a survey footprint covering a given survey volume, observed only a fraction of the volume. The distribution of observed regions should be chosen such that their separation is smaller than the length scale corresponding to the wavenumber of interest. Then one can recover the PS of galaxies with precision expected for a survey covering a volume of V_survey (rather than the volume of the sum of observed regions) with the number density of galaxies given by the total number of observed galaxies divided by V_survey (rather than the number density of galaxies within an observed region). Find that regularly-spaced sampling yields an unbiased PS with no window function effect, and deviations from regularly-spaced sampling, which are unavoidable in realistic surveys, introduce calculable window function effects and increase the uncertainties of the recovered PS. Method is general, but discussed in terms of Hobby-Eberly telescope DE experiment.
1306.4415
The GRB redshift distribution: implications for abundance evolution, star formation, and cosmology
Wei et al
LGRBs from Swift do not trace the SFH in LCDM; confirm that the latest example of GRBs reveals an increasing evolution in the GRB rate relative to the SFR at high redshifts. [...Metallicity evolution may explain this, but doesn't quite work. Assume a different cosmology that makes it work....] Assuming that the GRB rate is related to the SFR and an evolving metallicity, find that the GRB data constrain the slope of the high-z SFR to be -4.6. With this updated SFH, find that in the R_h=ct universe, the observed redshift distribution can also be fitted very well.
1306.4312
Dust in the polar region as a major contributor to the IR emission of AGN
Hoenig, Kishimoto, et al
As the title says.
1306.4319
Baryons do trace dark matter 380,000 years after the big bang: search for compensated isocurvature perturbations with WMAP 9-year data
Grin, Hanson, Holder, Dore, Kamionkowski
Primordial isocurvature fluctuations between photons and either neutrinos or non-relativistic species such as baryons or DM are known to be sub-dominant to adiabatic fluctuations. However, perturbations in the relative densities of baryons and DM (known as compensated isocurvature perturbations, or CIPs) are poorly constrained. CIPs leave no imprint in the CMB on observable scales, at least at linear order in their amplitude and zeroth order in the amplitude of adiabatic perturbations. It is thus not yet empirically known if baryons trace dark matter at the surface of last scattering. If CIPs exist, they would spatially modulate the Silk damping scale and acoustic horizon, causing distinct fluctuations in the CMB temperature/polarization PS across the sky: this effect is first order in both the CIP and adiabatic mode amplitudes. Here, temperature data from the WMAP are used to conduct the first CMB-based observational search for CIPs, using off-diagonal correlations and the CMB trispectrum. Reconstruction noise from WL and point sources is shown to be negligible for this data set. No evidence for CIPs is observed, and a 95%-confidence upper limit of 1.1e-2 is imposed to the amplitude of a scale-invariant CIP PS. This limit agrees with CIP sensitivity forecasts for WMAP, and is competitive with smaller scale constraints from measurements of the baryon fraction in galaxy clusters. It is shown that the root-mean squared CIP amplitude on 5-100 deg scales is smaller than 0.07-0.17 (depending on the scale) at the 95% confidence level. Temperature data from the Planck satellite will provide an even more sensitive probe for the existence of CIPs, as will the upcoming ACTPol and SPTPol experiments on smaller angular scales.
1306.4328
The massive satellite population of Milky-Way sized galaxies
Rodriguez-Puebla, Avila-Reese, Drory
Occupational distributions for satellite galaxies m_s>4e7 Msun around MW-sized hosts are presented and used to predict the internal dynamics of these satellites. Create galaxy group mock catalog base on (sub)halo-to-stellar mass relations constrained with observations; the stellar MF of centrals and satellites, and the 2-t correlation function. 6.6% of MW-s galaxies host 2 sats in the mass range of the SMC and LMC. THe probabilities of the MW-s galaixes to have 1 sat>= the LMC or 2 sats >= te SMC or 3 sats >= Sgr are ~0.26, 0.14, and 0.14, respectively. MW-s hosting 3 sats >= Sgr (as the MW) are among the most common cases. However, the most and 2nd most massive sats in these systems are <LMC and SMC by ~0.7 and 0.8 dex. The N(>m_s) for MW-s galaxies is broad, the case of the MW being of low frequency but not an outlier. The Mh of MW-s galaxies correlates only weakly with N(>ms). THen, it is not possible to accurately determine the MW halo mass by mans of N(>ms); constrain a lower limit 1e12 Msun at 1sig level. Analysis strongly suggests that the abundance of massive subhalos agree with the abundance of massive sats in al MW-s hosts, i.e., there is not a (massive) sat missing problem for the LCDM. However, confirm that the max circular vel, vmax, of the subhalos of sats ms<1e8 Msun is systematically larger than the vmax inferred from current observational studies of the MW bright dwarf sats; at difference of previous works, this conclusion is based on an analysis of the overall population of MW-s galaxies. Some pieces of evidence suggest that the issue could refer only to sat dwarfs but not to central dwarfs; then, environmental processes associated to dwarfs inside host halos combined with SN-driven core expansion should be at the basis of the lowering of vmax.
1306.4337
The build-up of nuclear stellar cusps in extreme starburst galaxies and major mergers
Haan et al
Nuclear stellar cusps are defined as central excess light component in the stellar light profiles of galaxies and are suggested to be stellar relics of intense compact starbursts in the central ~100-500pc region of gas-rich major mergers. Probe the build-up of nuclear cusps during the actual starburst phase for a complete sample of LIRG systems (85 LIRGs with L_IR=1e11.4-12.5 L_sun) in the GOALS sample. Cusp properties are derived via 2-d fitting of the nuclear stellar light imaged in the NIR by HST and have been combined with MIR diagnostics for AGN/SB characterization. Find that nuclear stellar cusps are resolved in 76% of LIRGs (merger and non-interacting galaxies). The cusp strength and luminosity increases with FIR luminosity (excluding AGN) and merger state, confirming theoretical models that starburst activity is associated with the build-up of nuclear stellar cusps. Evidence for ultra compact nuclear starbursts is found in ~13% of LIRGs, which have a strong unresolved central NIR light component but no significant contribution of an AGN. The nuclear NIR surface density (measured within 1 kpc radius) increases by a factor of ~5 towards late merger stages. A careful comparison to local early type galaxies with comparable masses reveals (a) that local (U)LIRGs have a significantly larger cusp fraction and (b) that the majority of the cusp LIRGs have host galaxy luminosities (H-band) similar to core ellitpicals which is roughly one order in magnitude larger than for cusp ellipticals.
1306.4663
Modeling the pollution of pristine gas in the early universe
Pan et al
Theoretical and numerical investigation of the pollution of pristine gas in turbulent flows, designed to provide new tools for modeling the evolution of the 1st generation of stars. Cooling is different ing as with a metallicity below a critical value Z_c (1e-6~1e-3 Z_sun). Z_c is much smaller than the typical average metallicity <Z>; thus the mixing efficiency of the pristine gas in the interstellar medium plays a crucial role in the transition from Pop III to normal star formation. The small critical value Z_c corresponds to the far left tail of the probability distribution function of the metallicity. Based on closure models for the PDF formation of turbulent mixing, derive equations for the fraction of gas, P, lying below Z_c, in compressible turbulence. Simulation show that the evolution of the fraction P can be well approximated by a generalized self-convolution model, which predicts dP/dt = -n/tau_con P(1-P^(1/n)), where n is a measure of the locality of the PDF convolution and the timescale tau-con is determined by the rate at which turbulence stretches the pollutants. Using a suite of simulations with Mach numbers ranging from M=0.9 to 6.2, provide accurate fits to n and tau_con as a function of M, Z_c /<Z>, and the scale L_p at which pollutants are added to the flow. For P>0.9, mixing occurs only in the regions surrounding the pollutants, such that n=1. For smaller P, n is larger as mixing becomes more global. Show how the results can be used to construct one-zone models for the evolution of Pop III stars in a single high-redshift galaxy, as well as subgrid models for tracking the evolution of the first stars in large cosmological simulations.
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