1,640 research outputs found
The Mass Function of the Stellar Component of Galaxies in the Sloan Digital Sky Survey
Using the MOPED algorithm we determine non-parametrically the Stellar Mass
Function of 96,545 galaxies from the Sloan Digital Sky Survey data release one.
By using the reconstructed spectrum due to starlight we can eliminate
contamination from either emission lines or AGN components. Our results give
excellent agreement with previous works, but extend their range by more than
two decades in mass to 10^{7.5} < M_s/h^{-2}M_\odot < 10^{12}. We present both
a standard Schechter fit and a fit modified to include an extra, high-mass
contribution, possibly from cluster cD galaxies. The Schechter fit parameters
are , and . Our sample also
yields an estimate for the contribution from baryons in stars to the critical
density of , in good agreement
with other indicators. Error bars are statistical and a Salpeter IMF is assumed
throughout. We find no evolution of the mass function in the redshift range
indicating that almost all present day stars were already
formed at with little or no star formation activity since then
and that the evolution seen in the luminosity function must be largely due to
stellar fading.Comment: submitted to MNRA
Does stellar mass assembly history vary with environment?
Using the publicly available VESPA database of SDSS Data Release 7 spectra,
we calculate the stellar Mass Weighted Age (hereafter MWA) as a function of
local galaxy density and dark matter halo mass. We compare our results with
semi-analytic models from the public Millennium Simulation. We find that the
stellar MWA has a large scatter which is inherent in the data and consistent
with that seen in semi-analytic models. The stellar MWA is consistent with
being independent (to first order) with local galaxy density, which is also
seen in semi-analytic models.
As a function of increasing dark matter halo mass (using the SDSS New York
Value Added Group catalogues), we find that the average stellar MWA for member
galaxies increases, which is again found in semi-analytic models. Furthermore
we use public dark matter Mass Accretion History (MAH) code calibrated on
simulations, to calculate the dark matter Mass Weighted Age as a function of
dark matter halo mass. In agreement with earlier analyses, we find that the
stellar MWA and the dark matter MWA are anti correlated for large mass halos,
i.e, dark matter accretion does not seem to be the primary factor in
determining when stellar mass was compiled. This effect can be described by
down-sizing.Comment: 11 pages, 3 figures, submitted to MNRA
Recovering galaxy star formation and metallicity histories from spectra using VESPA
We introduce VErsatile SPectral Analysis (VESPA): a new method which aims to
recover robust star formation and metallicity histories from galactic spectra.
VESPA uses the full spectral range to construct a galaxy history from synthetic
models. We investigate the use of an adaptative parametrization grid to recover
reliable star formation histories on a galaxy-by-galaxy basis. Our goal is
robustness as opposed to high resolution histories, and the method is designed
to return high time resolution only where the data demand it. In this paper we
detail the method and we present our findings when we apply VESPA to synthetic
and real Sloan Digital Sky Survey (SDSS) spectroscopic data. We show that the
number of parameters that can be recovered from a spectrum depends strongly on
the signal-to-noise, wavelength coverage and presence or absence of a young
population. For a typical SDSS sample of galaxies, we can normally recover
between 2 to 5 stellar populations. We find very good agreement between VESPA
and our previous analysis of the SDSS sample with MOPED.Comment: In press MNRAS, minor revisions to match accepted version by the
journa
Implications of multiple high-redshift galaxy clusters
To date, 14 high-redshift (z>1.0) galaxy clusters with mass measurements have
been observed, spectroscopically confirmed and are reported in the literature.
These objects should be exceedingly rare in the standard LCDM model. We
conservatively approximate the selection functions of these clusters' parent
surveys, and quantify the tension between the abundances of massive clusters as
predicted by the standard LCDM model and the observed ones. We alleviate the
tension considering non-Gaussian primordial perturbations of the local type,
characterized by the parameter fnl and derive constraints on fnl arising from
the mere existence of these clusters. At the 95% confidence level, fnl>467 with
cosmological parameters fixed to their most likely WMAP5 values, or fnl > 123
(at 95% confidence) if we marginalize over WMAP5 parameters priors. In
combination with fnl constraints from Cosmic Microwave Background and halo
bias, this determination implies a scale-dependence of fnl at approx. 3 sigma.
Given the assumptions made in the analysis, we expect any future improvements
to the modeling of the non-Gaussian mass function, survey volumes, or selection
functions to increase the significance of fnl>0 found here. In order to
reconcile these massive, high-z clusters with an fnl=0, their masses would need
to be systematically lowered by 1.5 sigma or the sigma8 parameter should be
approx. 3 sigma higher than CMB (and large-scale structure) constraints. The
existence of these objects is a puzzle: it either represents a challenge to the
LCDM paradigme or it is an indication that the mass estimates of clusters is
dramatically more uncertain than we think.Comment: 11 pages, 7 figures, modified to match published versio
The ages, metallicities and star formation histories of early-type galaxies in SDSS
We use the spectra of ~ 22,000 early-type galaxies, selected from the Sloan
Digital Sky Survey, to infer the ages, metallicities and star formation
histories of these galaxies. We find clear evidence of "downsizing", i.e.
galaxies with larger velocity dispersion have older stellar populations. In
particular, most early-type galaxies with velocity dispersion exceeding 200 km
s-1 formed more than 90% of their current stellar mass at redshift z > 2.5.
Therefore, star formation was suppressed around this redshift. We also show
that chemical enrichment was rapid, lasting 1-2 Gyr and find evidence that
[Fe/H] is sub-solar. We study the robustness of these results by comparing
three different approaches: using (i) Lick absorption line indices; (ii)
fitting a single-burst stellar population model to the whole spectrum
(lines+continuum); and (iii) reconstructing the star formation and metallicity
histories in multiple age-bins, providing a method to measure mass-weighted
ages and metallicities. We find good agreement between the luminosity-weighted
ages and metallicities computed with these three methods.Comment: Submitted to Ap
Environment and the cosmic evolution of star formation
We present a mark correlation analysis of the galaxies in the Sloan Digital
Sky Survey using weights provided by MOPED. The large size of the sample
permits statistically significant statements about how galaxies with different
metallicities and star formation histories are spatially correlated. Massive
objects formed a larger fraction of their stars at higher redshifts and over
shorter timescales than did less massive objects (sometimes called
down-sizing). We find that those galaxies which dominated the cosmic star
formation at z~3 are predominantly in clusters today, whereas galaxies which
dominate the star formation at z~0 inhabit substantially lower mass objects in
less dense regions today. Hence, our results indicate that star formation and
chemical enrichment occured first in the denser regions of the Universe, and
moved to less dense regions at later times.Comment: 4 pages, 4 figures, submitted to ApJ
Mechanism of NSF: New evidence challenging the prevailing theory
Nephrogenic systemic fibrosis (NSF) has been associated with the administration of gadolinium-based contrast agents in patients with severely impaired renal function (SIRF), endstage renal disease (ESRD), or acute renal failure (ARF). Since the vast majority of these patients do not get NSF, it is highly likely that patient factors play a role in its development. Although free or dechelated gadolinium is thought by some to be the only trigger of NSF, recent evidence suggests that chelated gadolinium may be important. Chelated gadolinium such as Omniscan (gadodiamide) and Magnevist (gadopentetate) can directly stimulate macrophages and monocytes in vitro to release profibrotic cytokines and growth factors capable of initiating and supporting the tissue fibrosis that is characteristic of NSF. In addition, an effect of chelated gadolinium on fibroblasts has also been demonstrated. Chelated gadolinium in the form of Omniscan, Magnevist, MultiHance, and ProHance increased proliferation of human dermal fibroblasts. Indeed, increased numbers of macrophages, together with activated fibroblasts and fibrocytes, are essential cells in the fibrotic process and are present in NSF skin. Accordingly, it is important that chelated gadolinium, in combination with patient cofactors, is considered in the etiology of NSF associated with enhanced scans
Mule Deer Research and Management in the Bitterroot Valley, Western Montana
Mule deer in the Sapphire Mountains on the east side of the Bitterroot Valley exist across a variety of habitats, densities, and management strategies, including the most popular trophy buck management area in the state of Montana (Hunting District 270 in the south end of the Sapphires). As in many other western states, mule deer populations have declined over recent decades, despite relatively good fawn recruitment. Beginning in winter 2015-2016, we used ground-based darting to deploy GPS collars on 30 adult female deer in HD270 and HD204 (north end of the Sapphires) to evaluate seasonal movements and causes of mortality. These areas were chosen not only because they represent a spectrum of environmental and management conditions, but because extensive data on habitat and forage quality in this area was collected as part of preceding elk habitat research. To date, we have observed a wide variety of movement strategies, from resident deer maintaining a small home range year-round in areas of high private land ownership to migratory deer moving from summer to winter range. Causes of mortality consisted of coyote predation (n=2), human hunting (n=1), and unknown mortality (n=1) in HD204, and natural mortality (n=1) and mountain lion predation (n=2) in HD270. This is an ongoing study by which we hope to evaluate factors limiting deer populations to help inform future management
Evaluating Bottom-Up and Top-Down Effects on Elk Survival and Recruitment: Year Two Update of a Case Study in the Bitterroot Valley
Understanding the contribution of recruitment to population growth rate in ungulates is a fundamental challenge to wildlife managers attempting to integrate carnivore and ungulate management. Like much of western Montana, in the Bitterroot Valley, the decline of elk (Cervus elaphus) populations and calf recruitment occurred concurrently with wolf (Canis lupus) recovery. However, a multitude of abiotic, bottom-up and top-down factors likely affect recruitment rates. We studied cause-specific mortality of elk calves to understand the role of competing mortality risk on calf recruitment in the East Fork and West Fork of the Bitterroot Valley, Montana. A total of 66 and 76 neonatal elk calves were captured in spring 2011 and 2012, respectively, and an additional 31 and 29 6-month-olds in late November 2011 and 2012. We analyzed calf survival using a Weibull parametric survival model, and cause-specific mortality using cumulative incidence functions. Preliminary analyses for the first 20 months of the research indicate mountain lions as the leading cause of mortality for elk calves during both summer and winter. We are also evaluating the role of summer forage resources on maternal condition, calf birth weights and survival. Preliminary results from nutritional work suggest potential bottom-up differences influencing resilience of elk populations to top-down predation. Our study fills a critical knowledge gap regarding the role of summer vs winter mortality in elk and the role of nutrition. The study will complement previous studies and help wildlife managers integrate carnivore and ungulate management across western Montana following carnivore recovery
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