arXiv subjects

Louis E. Abramson

Publications and source records attributed to Louis E. Abramson.

25 records · Page 2Linked to original sources

arXiv2016

On the Origin and Evolution of the Galaxy Stellar Mass Function

Here we explore the evolution of galaxy ensembles at early times by writing the in situ stellar mass growth of galaxies purely as a stationary stochastic (e.g., quasi-steady state) process. By combining the mathematics of such processes with Newtonian gravity and a mean local star formation efficiency, we show that the stellar mass evolution of galaxy ensembles is directly related to the average acceleration of baryons onto dark matter halos at the onset of star formation, with explicit dependencies on initial local matter densities and halo mass. The density term specifically implies more rapid average rates of growth in higher density regions of the universe compared to low density regions, i.e., assembly bias. With this framework, using standard cosmological parameters, a mean star formation efficiency derived by other authors, and knowledge of the shape of the cosmological matter power spectrum at small scales, we analytically derive (1) the characteristic stellar masses of galaxies (M*), (2) the power-law low-mass slope (alpha) and normalization (phi*) of the stellar mass function, and (3) the evolution of the stellar mass function in time over 12.5 > z > 2. Correspondingly, the rise in the cosmic star formation rate density over these epochs, while the universe can sustain unabated fueling of star formation, also emerges naturally. All of our findings are consistent with the deepest available data, including the expectation of alpha~-7/5; i.e., a stellar mass function low-mass slope that is notably shallower than that of the halo mass function, and with no systematic deviations from a mean star formation efficiency with density or mass, nor any explicit, additional feedback mechanisms. These derivations yield a compelling richness and complexity but also show that very few astrophysical details are required to understand the evolution of cosmic ensemble of galaxies at early times.

astro-ph.GA↗

arXiv2016

On the Progenitor of the Type IIb Supernova 2016gkg

We present a detection in pre-explosion Hubble Space Telescope (HST) imaging of a point source consistent with being the progenitor star of the Type IIb supernova (SN IIb) 2016gkg. Post-explosion imaging from the Keck Adaptive Optics system was used to perform relative astrometry between the Keck and HST imaging. We identify a single point source in the HST images coincident with the SN position to 0.89-sigma. The HST photometry is consistent with the progenitor star being an A0Ia star with T=9500 K and log (L/Lsun)=5.15. We find that the SN 2016gkg progenitor star appears more consistent with binary than single-star evolutionary models. In addition, early-time light curve data from SN 2016gkg revealed a rapid rise in luminosity within ~0.4 days of non-detection limits, consistent with models of the cooling phase after shock break-out. We use these data to determine an explosion date of 20.15 September 2016 and progenitor star radius of log (R/Rsun)=2.41, which agrees with photometry from the progenitor star. Our findings are also consistent with detections of other SNe IIb progenitor stars, although more luminous and bluer than most other examples.

astro-ph.SR↗

arXiv2014

Matching the Evolution of the Stellar Mass Function Using Log-normal Star Formation Histories

We show that a model consisting of individual, log-normal star formation histories for a volume-limited sample of $z\approx0$ galaxies reproduces the evolution of the total and quiescent stellar mass functions at $z\lesssim2.5$ and stellar masses $M_*\geq10^{10}\,{\rm M_\odot}$. This model has previously been shown to reproduce the star formation rate/stellar mass relation (${\rm SFR}$--$M_*$) over the same interval, is fully consistent with the observed evolution of the cosmic ${\rm SFR}$ density at $z\leq8$, and entails no explicit "quenching" prescription. We interpret these results/features in the context of other models demonstrating a similar ability to reproduce the evolution of (1) the cosmic ${\rm SFR}$ density, (2) the total/quiescent stellar mass functions, and (3) the ${\rm SFR}$--$M_*$ relation, proposing that the key difference between modeling approaches is the extent to which they stress/address diversity in the (starforming) galaxy population. Finally, we suggest that observations revealing the timescale associated with dispersion in ${\rm SFR}(M_*)$ will help establish which models are the most relevant to galaxy evolution.

astro-ph.GA↗

arXiv2014

The IMACS Cluster Building Survey: V. Further Evidence for Starburst Recycling from Quantitative Galaxy Morphologies

Using $J$ and $K_s$ band imaging obtained as part of the IMACS Cluster Building Survey (ICBS) we measure Sérsic indices for 2160 field and cluster galaxies at $0.31 < z < 0.54$. Using both mass- and magnitude-limited samples, we compare the distributions for spectroscopically determined passive, continuously starforming, starburst, and poststarburst systems and show that previously established spatial and statistical connections between these types extend to their gross morphologies. Outside of cluster cores, we find close structural ties between starburst and continuously starforming, as well as poststarburst and passive types, but not between starbursts and poststarbursts. These results independently support two conclusions presented in Paper II of this ICBS series (Dressler et al.): 1) most starbursts are the product of a non-disruptive triggering mechanism that is insensitive to global environment, such as minor-mergers; 2) starbursts and poststarbursts generally represent transient phases in the lives of "normal" starforming and quiescent galaxies, respectively, originating from and returning to these systems in closed "recycling" loops. In this picture, spectroscopically identified poststarbursts constitute a minority of all recently terminated starbursts, largely ruling-out the typical starburst as a quenching event in all but the densest environments.

astro-ph.CO↗

arXiv2014

The Circular Velocity Function of Group Galaxies

A robust prediction of $Λ{\rm CDM}$ cosmology is the halo circular velocity function (CVF), a dynamical cousin of the halo mass function. The correspondence between theoretical and observed CVFs is uncertain, however: cluster galaxies are reported to exhibit a power-law CVF consistent with $N$-body simulations, but that of the field is distinctly Schechter-like, flattened relative to $Λ{\rm CDM}$ expectations at circular velocities $v_c \lesssim 200\, {\rm km\, s^{-1}}$. Groups offer a powerful probe of the role environment plays in this discrepancy as they bridge the field and clusters. Here, we construct the CVF for a large, mass- and multiplicity-complete sample of group galaxies from the Sloan Digital Sky Survey. Using independent photometric $v_c$ estimators, we find no transition from a field- to $Λ{\rm CDM}$-shaped CVF above $v_c = 50\, {\rm km\, s^{-1}}$ as a function of group halo mass. All groups with $12.4 \lesssim \log M_{\rm halo} / M_{\odot} \lesssim 15.1$ (Local Group analogs to rich clusters) display similar Schechter-like CVFs marginally suppressed at low-$v_c$ compared to that of the field. Conversely, some agreement with $N$-body results emerges for samples saturated with late-type galaxies, with isolated late-types displaying a CVF similar in shape to $Λ{\rm CDM}$ predictions. We conclude that the flattening of the low-$v_c$ slope in groups is due to their depressed late-type fractions -- environment affecting the CVF only to the extent that it correlates with this quantity -- and that previous cluster analyses may suffer from interloper contamination. These results serve as useful benchmarks for cosmological simulations of galaxy formation.

astro-ph.CO↗

arXiv2014

The Mass-Independence of Specific Star Formation Rates in Galactic Disks

The slope of the star formation rate/stellar mass relation (the SFR "Main Sequence"; ${\rm SFR}-M_*$) is not quite unity: specific star formation rates $({\rm SFR}/M_*)$ are weakly-but-significantly anti-correlated with $M_*$. Here we demonstrate that this trend may simply reflect the well-known increase in bulge mass-fractions -- portions of a galaxy not forming stars -- with $M_*$. Using a large set of bulge/disk decompositions and SFR estimates derived from the Sloan Digital Sky Survey, we show that re-normalizing SFR by disk stellar mass $({\rm sSFR_{\rm disk}\equiv SFR}/M_{*,{\rm disk}})$ reduces the $M_*$-dependence of SF efficiency by $\sim0.25$ dex per dex, erasing it entirely in some subsamples. Quantitatively, we find $\log {\rm sSFR_{disk}}-\log M_*$ to have a slope $β_{\rm disk}\in[-0.20,0.00]\pm0.02$ (depending on SFR estimator and Main Sequence definition) for star-forming galaxies with $M_*\geq10^{10}M_{\odot}$ and bulge mass-fractions $B/T\lesssim0.6$, generally consistent with a pure-disk control sample ($β_{\rm control}=-0.05\pm0.04$). That $\langle{\rm SFR}/M_{*,{\rm disk}}\rangle$ is (largely) independent of host mass for star-forming disks has strong implications for aspects of galaxy evolution inferred from any ${\rm SFR}-M_*$ relation, including: manifestations of "mass quenching" (bulge growth), factors shaping the star-forming stellar mass function (uniform $d\log M_*/dt$ for low-mass, disk-dominated galaxies), and diversity in star formation histories (dispersion in ${\rm SFR}(M_*,t)$). Our results emphasize the need to treat galaxies as composite systems -- not integrated masses -- in observational and theoretical work.

astro-ph.GA↗

arXiv2012

SGAS 143845.1+145407: A Big, Cool Starburst at Redshift 0.816

We present the discovery and a detailed multi-wavelength study of a strongly-lensed luminous infrared galaxy at z=0.816. Unlike most known lensed galaxies discovered at optical or near-infrared wavelengths this lensed source is red, r-Ks = 3.9 [AB], which the data presented here demonstrate is due to ongoing dusty star formation. The overall lensing magnification (a factor of 17) facilitates observations from the blue optical through to 500micron, fully capturing both the stellar photospheric emission as well as the re-processed thermal dust emission. We also present optical and near-IR spectroscopy. These extensive data show that this lensed galaxy is in many ways typical of IR-detected sources at z~1, with both a total luminosity and size in accordance with other (albeit much less detailed) measurements in samples of galaxies observed in deep fields with the Spitzer telescope. Its far-infrared spectral energy distribution is well-fit by local templates that are an order of magnitude less luminous than the lensed galaxy; local templates of comparable luminosity are too hot to fit. Its size (D~7kpc) is much larger than local luminous infrared galaxies, but in line with sizes observed for such galaxies at z~1. The star formation appears uniform across this spatial scale. In this source, the luminosity of which is typical of sources that dominate the cosmic infrared background, we find that star formation is spatially extended and well organised, quite unlike the compact merger-driven starbursts which are typical for sources of this luminosity at z~0.

astro-ph.CO↗