545 research outputs found
The Connection between Galaxies and Dark Matter Structures in the Local Universe
We provide new constraints on the connection between galaxies in the local
universe, identified by the Sloan Digital Sky Survey (SDSS), and dark matter
halos and their constituent substructures in the CDM model using WMAP7
cosmological parameters. Predictions for the abundance and clustering
properties of dark matter halos, and the relationship between dark matter hosts
and substructures, are based on a high-resolution cosmological simulation, the
Bolshoi simulation. We associate galaxies with halos and subhalos using subhalo
abundance matching, performing a comprehensive analysis which investigates the
underlying assumptions of this technique including (a) which halo property is
most closely associated with galaxy stellar masses and luminosities, (b) how
much scatter is in this relationship, and (c) how much subhalos can be stripped
before their galaxies are destroyed. The models are jointly constrained by new
measurements of the projected two-point galaxy clustering and the observed
conditional stellar mass function of galaxies in groups. The data put tight
constraints on the satellite fraction of galaxies as a function of galaxy
stellar mass, on the scatter between halo and galaxy properties, and on the
underlying conditional stellar mass function. These data rule out several halo
properties commonly used in abundance matching, largely because the satellite
fractions in the models disagree with those data. We show that an abundance
matching model that associates galaxies with the peak circular velocity of
their halos is in good agreement with the data, when scatter of
dex in stellar mass at a given peak velocity is included. This will yield
important constraints for galaxy formation models, and also provides
encouraging indications that the galaxy--halo connection can be modeled with
sufficient fidelity for future precision studies of the dark Universe.Comment: 35 pages, 28 figures. Improvements to figures and tex
An Increasing Stellar Baryon Fraction in Bright Galaxies at High Redshift
Recent observations have shown that the characteristic luminosity of the
rest-frame ultraviolet (UV) luminosity function does not significantly evolve
at 4 < z < 7 and is approximately M*_UV ~ -21. We investigate this apparent
non-evolution by examining a sample of 178 bright, M_UV < -21 galaxies at z=4
to 7, analyzing their stellar populations and host halo masses. Including deep
Spitzer/IRAC imaging to constrain the rest-frame optical light, we find that
M*_UV galaxies at z=4-7 have similar stellar masses of log(M/Msol)=9.6-9.9 and
are thus relatively massive for these high redshifts. However, bright galaxies
at z=4-7 are less massive and have younger inferred ages than similarly bright
galaxies at z=2-3, even though the two populations have similar star formation
rates and levels of dust attenuation. We match the abundances of these bright
z=4-7 galaxies to halo mass functions from the Bolshoi Lambda-CDM simulation to
estimate the halo masses. We find that the typical halo masses in ~M*_UV
galaxies decrease from log(M_h/Msol)=11.9 at z=4 to log(M_h/Msol)=11.4 at z=7.
Thus, although we are studying galaxies at a similar mass across multiple
redshifts, these galaxies live in lower mass halos at higher redshift. The
stellar baryon fraction in units of the cosmic mean Omega_b/Omega_m rises from
5.1% at z=4 to 11.7% at z=7; this evolution is significant at the ~3-sigma
level. This rise does not agree with simple expectations of how galaxies grow,
and implies that some effect, perhaps a diminishing efficiency of feedback, is
allowing a higher fraction of available baryons to be converted into stars at
high redshifts.Comment: Accepted to ApJ. 15 pages, 5 figures, 6 table
The prefrontal cortex of the bottlenose dolphin (Tursiops truncatus Montagu, 1821): a tractography study and comparison with the human
Cetaceans are well known for their remarkable cognitive abilities including self-recognition, sound imitation and decision making. In other mammals, the prefrontal cortex (PFC) takes a key role in such cognitive feats. In cetaceans, however, a PFC could up to now not be discerned based on its usual topography. Classical in vivo methods like tract tracing are legally not possible to perform in Cetacea, leaving diffusion-weighted imaging (DWI) as the most viable alternative. This is the first investigation focussed on the identification of the cetacean PFC homologue. In our study, we applied the constrained spherical deconvolution (CSD) algorithm on 3Â T DWI scans of three formalin-fixed brains of bottlenose dolphins (Tursiops truncatus) and compared the obtained results to human brains, using the same methodology. We first identified fibres related to the medio-dorsal thalamic nuclei (MD) and then seeded the obtained putative PFC in the dolphin as well as the known PFC in humans. Our results outlined the dolphin PFC in areas not previously studied, in the cranio-lateral, ectolateral and opercular gyri, and furthermore demonstrated a similar connectivity pattern between the human and dolphin PFC. The antero-lateral rotation of the PFC, like in other areas, might be the result of the telescoping process which occurred in these animals during evolution
Semi-analytic forecasts for JWST -- IV. Implications for cosmic reionization and LyC escape fraction
Improved Mock Galaxy Catalogs for the DEEP2 Galaxy Redshift Survey from Subhalo Abundance and Environment Matching
We develop empirical methods for modeling the galaxy population and
populating cosmological N-body simulations with mock galaxies according to the
observed properties of galaxies in survey data. We use these techniques to
produce a new set of mock catalogs for the DEEP2 Galaxy Redshift Survey based
on the output of the high-resolution Bolshoi simulation, as well as two other
simulations with different cosmological parameters, all of which we release for
public use. The mock-catalog creation technique uses subhalo abundance matching
to assign galaxy luminosities to simulated dark-matter halos. It then adds
color information to the resulting mock galaxies in a manner that depends on
the local galaxy density, in order to reproduce the measured color-environment
relation in the data. In the course of constructing the catalogs, we test
various models for including scatter in the relation between halo mass and
galaxy luminosity, within the abundance-matching framework. We find that there
is no constant-scatter model that can simultaneously reproduce both the
luminosity function and the autocorrelation function of DEEP2. This result has
implications for galaxy-formation theory, and it restricts the range of
contexts in which the mocks can be usefully applied. Nevertheless, careful
comparisons show that our new mocks accurately reproduce a wide range of the
other properties of the DEEP2 catalog, suggesting that they can be used to gain
a detailed understanding of various selection effects in DEEP2.Comment: 24 pages, 13 figures, matches version accepted for publication in
ApJS. Catalogs are available for download from the URL referenced in the
Appendi
A Stellar Mass Threshold for Quenching of Field Galaxies
We demonstrate that dwarf galaxies (10^7 < M_stellar < 10^9 Msun) with no
active star formation are extremely rare (<0.06%) in the field. Our sample is
based on the NASA-Sloan Atlas which is a re-analysis of the Sloan Digital Sky
Survey Data Release 8. We examine the relative number of quenched versus star
forming dwarf galaxies, defining quenched galaxies as having no Halpha emission
(EW_Halpha < 2 AA) and a strong 4000AA-break. The fraction of quenched dwarf
galaxies decreases rapidly with increasing distance from a massive host,
leveling off for distances beyond 1.5 Mpc. We define galaxies beyond 1.5 Mpc of
a massive host galaxy to be in the field. We demonstrate that there is a
stellar mass threshold of M_stellar < 1.0x10^9 Msun below which quenched
galaxies do not exist in the field. Below this threshold, we find that none of
the 2951 field dwarf galaxies are quenched; all field dwarf galaxies show
evidence for recent star formation. Correcting for volume effects, this
corresponds to a 1-sigma upper limit on the quenched fraction of 0.06%. In more
dense environments, quenched galaxies account for 23% of the dwarf population
over the same stellar mass range. The majority of quenched dwarf galaxies
(often classified as dwarf elliptical galaxies) are within 2 virial radii of a
massive galaxy, and only a few percent of quenched dwarf galaxies exist beyond
4 virial radii. Thus, for galaxies with stellar mass less than 1.0x10^9 Msun,
ending star-formation requires the presence of a more massive neighbor,
providing a stringent constraint on models of star formation feedback.Comment: 9 pages, 6 figures, accepted to Ap
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