3,547 research outputs found
Ionized Gas in Damped Lyman Alpha Protogalaxies: II. Comparison Between Models and the Kinematic Data
We test semi-analytic models for galaxy formation with accurate kinematic
data of damped Lyman alpha protogalaxies (DLAs) presented in the companion
paper I. The models envisage centrifugally supported exponential disks at the
centers of dark matter halos which are filled with ionized gas undergoing
radial infall to the disks. The halo masses are drawn from cross-section
weighted mass distributions predicted by CDM cosmogonies, or by the null
hypothesis (TF model) that the dark matter mass distribution has not evolved
since z ~ 3. In our models, C IV absorption lines detected in DLAs arise in
infalling ionized clouds while the low-ion absorption lines arise from neutral
gas in the disks. Using Monte Carlo methods we find: (a) The CDM models are
incompatible with the low-ion statistics at more than 99% confidence whereas
some TF models cannot be excluded at more than 88% confidence. (b) Both CDM and
TF models agree with the observed distribution of C IV velocity widths. (c) The
CDM models generate differences between the mean velocities of C IV and low ion
profiles in agreement with the data, while the TF model produces differences in
the means that are too large. (d) Both CDM and TF models produce ratios of C IV
to low-ion velocity widths that are too large. (e) Both CDM and TF models
generate C IV versus low-ion cross-correlation functions incompatible with the
data.
While it is possible to select model parameters resulting in consistency with
the data, the disk-halo configuration assumed in both cosmogonies still does
not produce significant overlap in velocity space between C IV low-ion velocity
profiles. We conjecture that including angular momentum of the infalling clouds
will increase the overlap between C IV and low-ion profiles.Comment: 18 pages, 12 Figures, Accepted for publication in the Dec. 20 issue
of the Astrophysical Journa
Parametrizing the Stellar Haloes of Galaxies
We study the stellar haloes of galaxies out to 70-100 kpc as a function of
stellar mass and galaxy type by stacking aligned and band images from a
sample of 45508 galaxies from SDSS DR9 in the redshift range
and in the mass range r. We derive surface brightness profiles to a depth of
almost . We find that the
ellipticity of the stellar halo is a function of galaxy stellar mass and that
the haloes of high concentration () galaxies are more elliptical than
those of low concentration () galaxies. The - colour profile of
high concentration galaxies reveals that the - colour of the stellar
population in the stellar halo is bluer than in the main galaxy, and the colour
of the stellar halo is redder for higher mass galaxies. We further demonstrate
that the full two-dimensional surface intensity distribution of our galaxy
stacks can only be fit through multi-component S\'{e}rsic models. Using the
fraction of light in the outer component of the models as a proxy for the
fraction of accreted stellar light, we show that this fraction is a function of
stellar mass and galaxy type. For high concentration galaxies, the fraction of
accreted stellar light rises from to for galaxies in the stellar
mass range from to . The fraction of
accreted light is much smaller in low concentration systems, increasing from
to over the same mass range. This work provides important
constraints for the theoretical understanding of the formation of stellar
haloes of galaxies.Comment: Submitted to MNRAS, 18 pages, 19 figure
Production and Evolution of Perturbations of Sterile Neutrino Dark Matter
Sterile neutrinos, fermions with no standard model couplings [SU(2)
singlets], are predicted by most extensions of the standard model, and may be
the dark matter. I describe the nonthermal production and linear perturbation
evolution in the early universe of this dark matter candidate. I calculate
production of sterile neutrino dark matter including effects of Friedmann
dynamics dictated by the quark-hadron transition and particle population, the
alteration of finite temperature effective mass of active neutrinos due to the
presence of thermal leptons, and heating of the coupled species due to the
disappearance of degrees of freedom in the plasma. These effects leave the
sterile neutrinos with a non-trivial momentum distribution. I also calculate
the evolution of sterile neutrino density perturbations in the early universe
through the linear regime and provide a fitting function form for the transfer
function describing the suppression of small scale fluctuations for this warm
dark matter candidate. The results presented here differ quantitatively from
previous work due to the inclusion here of the relevant physical effects during
the production epoch.Comment: v4: matches version in Phys. Rev.
The Formation of Low-Mass Cluster Galaxies and the Universal Initial Galaxy Mass Function
Clusters of galaxies have an observed over-density of low-luminosity systems
in comparison to the field, although it is not yet agreed whether this effect
is the result of initial galaxy mass functions that vary with environment or
galaxy evolutionary effects. In this letter we argue that this over-density is
the result of low-mass systems with red colors that are over-populating the
faint-end of the observed luminosity function in the nearby rich cluster Abell
0426. We show that the luminosity function of Abell 0426 becomes steeper, from
the field value alpha = -1.25+/-0.05 to alpha=-1.44+/-0.04, due to a recently
identified population of red low-mass cluster galaxies that are possibly the
remnants of dynamical stripped high-mass systems. We further demonstrate,
through simple models of stripping effects, how cluster luminosity functions
can become artificially steep over time from the production of these low-mass
cluster galaxies.Comment: Accepted to ApJ letter
Linear Cosmological Structure Limits on Warm Dark Matter
I consider constraints from observations on a cutoff scale in clustering due
to free streaming of the dark matter in a warm dark matter cosmological model
with a cosmological constant. The limits are derived in the framework of a
sterile neutrino warm dark matter universe, but can be applied to gravitinos
and other models with small scale suppression in the linear matter power
spectrum. With freedom in all cosmological parameters including the free
streaming scale of the sterile neutrino dark matter, limits are derived using
observations of the fluctuations in the cosmic microwave background, the 3D
clustering of galaxies and 1D clustering of gas in the Lyman-alpha (Ly-alpha)
forest in the Sloan Digital Sky Survey (SDSS), as well as the Ly-alpha forest
in high-resolution spectroscopic observations. In the most conservative case,
using only the SDSS main-galaxy 3D power-spectrum shape, the limit is m_s >
0.11 keV; including the SDSS Ly-alpha forest, this limit improves to m_s > 1.7
keV. More stringent constraints may be placed from the inferred matter power
spectrum from high-resolution Ly-alpha forest observations, which has
significant systematic uncertainties; in this case, the limit improves to m_s >
3.0 keV (all at 95% CL).Comment: 6 pages, 4 figures; v2: matches PRD version, with note added
regarding astro-ph/060243
The triggering probability of radio-loud AGN: A comparison of high and low excitation radio galaxies in hosts of different colors
Low luminosity radio-loud active galactic nuclei (AGN) are generally found in
massive red elliptical galaxies, where they are thought to be powered through
gas accretion from their surrounding hot halos in a radiatively inefficient
manner. These AGN are often referred to as "low-excitation" radio galaxies
(LERGs). When radio-loud AGN are found in galaxies with a young stellar
population and active star formation, they are usually high-power
radiatively-efficient radio AGN ("high-excitation", HERG). Using a sample of
low-redshift radio galaxies identified within the Sloan Digital Sky Survey
(SDSS), we determine the fraction of galaxies that host a radio-loud AGN,
, as a function of host galaxy stellar mass, , star formation
rate, color (defined by the 4000 \angstrom break strength), radio luminosity
and excitation state (HERG/LERG).
We find the following: 1. LERGs are predominantly found in red galaxies. 2.
The radio-loud AGN fraction of LERGs hosted by galaxies of any color follows a
power law. 3. The fraction of red galaxies
hosting a LERG decreases strongly for increasing radio luminosity. For massive
blue galaxies this is not the case. 4. The fraction of green galaxies hosting a
LERG is lower than that of either red or blue galaxies, at all radio
luminosities. 5. The radio-loud AGN fraction of HERGs hosted by galaxies of any
color follows a power law. 6. HERGs have a
strong preference to be hosted by green or blue galaxies. 7. The fraction of
galaxies hosting a HERG shows only a weak dependence on radio luminosity cut.
8. For both HERGs and LERGs, the hosting probability of blue galaxies shows a
strong dependence on star formation rate. This is not observed in galaxies of a
different color.[abridged]Comment: 7 pages, 6 figure
Clustering of Galaxies in a Hierarchical Universe: I. Methods and Results at z=0
We introduce a new technique for following the formation and evolution of
galaxies in cosmological N-body simulations. Dissipationless simulations are
used to track the formation and merging of dark matter halos as a function of
redshift. Simple prescriptions, taken directly from semi-analytic models of
galaxy formation, are adopted for cooling, star formation, supernova feedback
and the merging of galaxies within the halos. This scheme enables us to study
the clustering properties of galaxies and to investigate how selection by type,
colour or luminosity influences the results. In this paper, we study properties
of the galaxy distribution at z=0. These include luminosity functions, colours,
correlation functions, pairwise peculiar velocities, cluster M/L ratios and
star formation rates. We focus on two variants of a CDM cosmology: a high-
density model with Gamma=0.21 (TCDM) and a low-density model with Omega=0.3 and
Lambda=0.7 (LCDM). Both are normalized to reproduce the I-band Tully-Fisher
relation near a circular velocity of 220 km/s. Our results depend strongly both
on this normalization and on the prescriptions for star formation and feedback.
Very different assumptions are required to obtain an acceptable model in the
two cases. For TCDM, efficient feedback is required to suppress the growth of
galaxies low-mass field halos. Without it, there are too many galaxies and the
correlation function turns over below 1 Mpc. For LCDM, feedback must be weak,
otherwise too few L* galaxies are produced and the correlation function is too
steep. Given the uncertainties in modelling some of the key physical processes,
we conclude that it is not yet possible to draw conclusions about the values of
cosmological parameters from studies of this kind. Further work on global star
formation and feedback effects is required to narrow the range of possibilitiesComment: 43 pages, Latex, 16 figures included, 2 additional GIF format
figures, submitted to MNRA
Morphological Evolution and the Ages of Early-Type Galaxies in Clusters
Morphological and spectroscopic studies of high redshift clusters indicate
that a significant fraction of present-day early-type galaxies was transformed
from star forming galaxies at z<1. On the other hand, the slow luminosity
evolution of early-type galaxies and the low scatter in their color-magnitude
relation indicate a high formation redshift of their stars. In this paper we
construct models which reconcile these apparently contradictory lines of
evidence, and we quantify the effects of morphological evolution on the
observed photometric properties of early-type galaxies in distant clusters. We
show that in the case of strong morphological evolution the apparent luminosity
and color evolution of early-type galaxies are similar to that of a single age
stellar population formed at z=infinity, irrespective of the true star
formation history of the galaxies. Furthermore, the scatter in age, and hence
the scatter in color and luminosity, is approximately constant with redshift.
These results are consequences of the ``progenitor bias'': the progenitors of
the youngest low redshift early-type galaxies drop out of the sample at high
redshift. We construct models which reproduce the observed evolution of the
number fraction of early-type galaxies in rich clusters and their color and
luminosity evolution simultaneously. Our modelling indicates that approx. 50%
of early-type galaxies were transformed from other galaxy types at z<1, and
their progenitor galaxies may have had roughly constant star formation rates
prior to morphological transformation. After correcting the observed evolution
of the mean M/L_B ratio for the maximum progenitor bias we find that the mean
luminosity weighted formation redshift of stars in early-type galaxies
z_*=2.0^{+0.3}_{-0.2} for Omega_m=0.3 and Omega_Lambda=0.7. [ABRIDGED]Comment: Accepted for publication in The Astrophysical Journal. 13 pages, 6
figure
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