Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userComparing IMF-sensitive indices of intermediate-mass quiescent galaxies in various environments
50
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Using samples drawn from the Sloan Digital Sky Survey, we study for the first time the relation between large-scale environments (Clusters, Groups and Voids) and the stellar Initial Mass Function (IMF). We perform an observational approach based on the comparison of IMF-sensitive indices of quiescent galaxies with similar mass in varying environments. These galaxies are selected within a narrow redshift interval ($ 0.020 < z < 0.055 $) and spanning a range in velocity dispersion from 100 to 200 kms$^{-1}$. The results of this paper are based upon analysis of composite spectra created by stacking the spectra of galaxies, binned by their velocity dispersion and redshift. The trends of spectral indices as measured from the stacked spectra, with respect to velocity dispersion, are compared in different environments. We find a lack of dependence of the IMF on the environment for intermediate-mass galaxy regime. We verify this finding by providing a more quantitative measurement of the IMF variations among galactic environments using MILES stellar population models with a precision of $DeltaGamma_{b}sim0.2$.
rate research
Read More
We present the stellar mass profiles of 147 isolated quiescent galaxies in very low-density environments (i.e., void regions) in the local Universe ($0.01<z<0.06$) from the Sloan Digital Sky Survey. These galaxies have stellar masses between $ 9.8lesssim log(M_{ast}/M_{odot})lesssim11.2$ and they represent $sim15%$ of the whole galaxy population in the void regions down to $M_{r} = -19$. We do not find any isolated quiescent galaxies with $log(M_{ast}/M_{odot})gtrsim11.2$. We compare the stellar mass profiles of these isolated quiescent galaxies with the profiles of stellar mass-matched samples of the quiescent galaxies in group and cluster environments. We find that, at fixed mass, quiescent galaxies in voids have similar central ($1$ kpc) mass densities ($Sigma_1$) and central velocity dispersions ($sigma_1$) compared to their counterparts in groups and clusters. We show that quiescent galaxies in voids have at most $10-25%$ smaller half-mass (and half-light) sizes compared to quiescent galaxies in groups and clusters. We conclude that for the intermediate stellar mass range of $10^{10}-10^{11}M_{odot}$ in the local Universe, environmental mechanisms have no significant additional effect on the mass profiles of the quiescent galaxies.
The model of a radial minor merger proposed by Quinn (1984), which successfully reproduces the observed regular shell systems in shell galaxies, is ideal for a test-particle simulation. We compare such a simulation with a self-consistent one. They agree very well in positions of the first generation of shells but potentially important effects -- dynamical friction and gradual decay of the dwarf galaxy -- are not present in the test-particle model, therefore we look for a proper way to include them.
We present J-band spectroscopy of passive galaxies focusing on the Na I doublet at 1.14 {mu}m. Like the Na I 0.82 {mu}m doublet, this feature is strong in low-mass stars and hence may provide a useful probe of the initial mass function (IMF). From high signal-to-noise composite spectra, we find that Na I 1.14 {mu}m increases steeply with increasing velocity dispersion, {sigma}, and for the most massive galaxies (sigma > 300 km/s) is much stronger than predicted from synthetic spectra with Milky-Way-like IMFs and solar abundances. Reproducing Na I 1.14 {mu}m at high {sigma} likely requires either a very high [Na/H], or a bottom-heavy IMF, or a combination of both. Using the Na D line to break the degeneracy between IMF and abundance, we infer [Na/H] $approx$ +0.5 and a steep IMF (single-slope-equivalent x $approx$ 3.2, where x = 2.35 for Salpeter), for the high-sigma galaxies. At lower mass ({sigma} = 50-100 km/s), the line strengths are compatible with MW-like IMFs and near-solar [Na/H]. We highlight two galaxies in our sample where strong gravitational lensing masses favour MW-like IMFs. Like the high-{sigma} sample on average, these galaxies have strong Na I 1.14 mu m; taken in isolation their sodium indices imply bottom-heavy IMFs which are hard to reconcile with the lensing masses. An alternative full-spectrum-fitting approach, applied to the high-sigma sample, recovers an IMF less heavy than Salpeter, but under-predicts the Na I 1.14 mu m line at the 5{sigma} level. We conclude that current models struggle to reproduce this feature in the most massive galaxies without breaking other constraints, and caution against over-reliance on the sodium lines in spectroscopic IMF studies.
Massive compact systems at 0.2<z<0.6 are the missing link between the predominantly compact population of massive quiescent galaxies at high redshift and their analogs and relics in the local volume. The evolution in number density of these extreme objects over cosmic time is the crucial constraining factor for the models of massive galaxy assembly. We select a large sample of ~200 intermediate-redshift massive compacts from the BOSS spectroscopic dataset by identifying point-like SDSS photometric sources with spectroscopic signatures of evolved redshifted galaxies. A subset of our targets have publicly available high-resolution ground-based images that we use to augment the dynamical and stellar population properties of these systems by their structural parameters. We confirm that all BOSS compact candidates are as compact as their high-redshift massive counterparts and less than half the size of similarly massive systems at z~0. We use the completeness-corrected numbers of BOSS compacts to compute lower limits on their number densities in narrow redshift bins spanning the range of our sample. The abundance of extremely dense quiescent galaxies at 0.2<z<0.6 is in excellent agreement with the number densities of these systems at high redshift. Our lower limits support the models of massive galaxy assembly through a series of minor mergers over the redshift range 0<z<2.
We analyze the relationships between atomic, neutral hydrogen (HI) and star formation (SF) in the 12 low-mass SHIELD galaxies. We compare high spectral (~0.82 km/s/channel) and spatial resolution (physical resolutions of 170 pc - 700 pc) HI imaging from the VLA with Halpha and far-ultraviolet imaging. We quantify the degree of co-spatiality between star forming regions and regions of high HI column densities. We calculate the global star formation efficiencies (SFE, $Sigma_{rm SFR}$ / $Sigma_{rm HI}$), and examine the relationships among the SFE and HI mass, HI column density, and star formation rate (SFR). The systems are consuming their cold neutral gas on timescales of order a few Gyr. While we derive an index for the Kennicutt-Schmidt relation of N ~ 0.68 $pm$ 0.04 for the SHIELD sample as a whole, the values of N vary considerably from system to system. By supplementing SHIELD results with those from other surveys, we find that HI mass and UV-based SFR are strongly correlated over five orders of magnitude. Identification of patterns within the SHIELD sample allows us to bin the galaxies into three general categories: 1) mainly co-spatial HI and SF regions, found in systems with highest peak HI column densities and highest total HI masses, 2) moderately correlated HI and SF regions, found in systems with moderate HI column densities, and 3) obvious offsets between HI and SF peaks, found in systems with the lowest total HI masses. SF in these galaxies is dominated by stochasticity and random fluctuations in their ISM.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
