175 research outputs found
Evolution of the Stellar-to-Dark Matter relation: separating star-forming and passive galaxies from z = 1 to 0
We use measurements of the stellar mass function, galaxy clustering, and galaxy-galaxy lensing within the COSMOS survey to constrain the stellar-to-halo mass relation (SHMR) of star forming and quiescent galaxies over the redshift range z = [0.2, 1.0]. For massive galaxies, M * gsim 1010.6 M ☉, our results indicate that star-forming galaxies grow proportionately as fast as their dark matter halos while quiescent galaxies are outpaced by dark matter growth. At lower masses, there is minimal difference in the SHMRs, implying that the majority low-mass quiescent galaxies have only recently been quenched of their star formation. Our analysis also affords a breakdown of all COSMOS galaxies into the relative numbers of central and satellite galaxies for both populations. At z = 1, satellite galaxies dominate the red sequence below the knee in the stellar mass function. But the number of quiescent satellites exhibits minimal redshift evolution; all evolution in the red sequence is due to low-mass central galaxies being quenched of their star formation. At M * ~ 1010 M ☉, the fraction of central galaxies on the red sequence increases by a factor of 10 over our redshift baseline, while the fraction of quenched satellite galaxies at that mass is constant with redshift. We define a "migration rate" to the red sequence as the time derivative of the passive galaxy abundances. We find that the migration rate of central galaxies to the red sequence increases by nearly an order of magnitude from z = 1 to z = 0. These results imply that the efficiency of quenching star formation for centrals is increasing with cosmic time, while the mechanisms that quench the star formation of satellite galaxies in groups and clusters is losing efficiency
Neutrinos in Non-linear Structure Formation - The Effect on Halo Properties
We use N-body simulations to find the effect of neutrino masses on halo
properties, and investigate how the density profiles of both the neutrino and
the dark matter components change as a function of the neutrino mass. We
compare our neutrino density profiles with results from the N-one-body method
and find good agreement. We also show and explain why the Tremaine-Gunn bound
for the neutrinos is not saturated. Finally we study how the halo mass function
changes as a function of the neutrino mass and compare our results with the
Sheth-Tormen semi-analytic formulae. Our results are important for surveys
which aim at probing cosmological parameters using clusters, as well as future
experiments aiming at measuring the cosmic neutrino background directly.Comment: 20 pages, 8 figure
New constraints on the evolution of the stellar-to-dark matter connection : a combined analysis of galaxy-galaxy lensing, clustering, and stellar mass functions from z = 0.2 to z = 1
Using data from the COSMOS survey, we perform the first joint analysis of galaxy-galaxy weak lensing, galaxy spatial clustering, and galaxy number densities. Carefully accounting for sample variance and for scatter between stellar and halo mass, we model all three observables simultaneously using a novel and self-consistent theoretical framework. Our results provide strong constraints on the shape and redshift evolution of the stellar-to-halo mass relation (SHMR) from z = 0.2 to z = 1. At low stellar mass, we find that halo mass scales as Mh vpropM 0.46 * and that this scaling does not evolve significantly with redshift from z = 0.2 to z = 1. The slope of the SHMR rises sharply at M * > 5 × 1010 M ☉ and as a consequence, the stellar mass of a central galaxy becomes a poor tracer of its parent halo mass. We show that the dark-to-stellar ratio, Mh /M *, varies from low to high masses, reaching a minimum of Mh /M * ~ 27 at M * = 4.5 × 1010 M ☉ and Mh = 1.2 × 1012 M ☉. This minimum is important for models of galaxy formation because it marks the mass at which the accumulated stellar growth of the central galaxy has been the most efficient. We describe the SHMR at this minimum in terms of the "pivot stellar mass," M piv *, the "pivot halo mass," M piv h , and the "pivot ratio," (Mh /M *)piv. Thanks to a homogeneous analysis of a single data set spanning a large redshift range, we report the first detection of mass downsizing trends for both M piv h and M piv *. The pivot stellar mass decreases from M piv * = 5.75 ± 0.13 × 1010 M ☉ at z = 0.88 to M piv * = 3.55 ± 0.17 × 1010 M ☉ at z = 0.37. Intriguingly, however, the corresponding evolution of M piv h leaves the pivot ratio constant with redshift at (Mh /M *)piv ~ 27. We use simple arguments to show how this result raises the possibility that star formation quenching may ultimately depend on Mh /M * and not simply on Mh , as is commonly assumed. We show that simple models with such a dependence naturally lead to downsizing in the sites of star formation. Finally, we discuss the implications of our results in the context of popular quenching models, including disk instabilities and active galactic nucleus feedback
Inflation, cold dark matter, and the central density problem
A problem with high central densities in dark halos has arisen in the context
of LCDM cosmologies with scale-invariant initial power spectra. Although n=1 is
often justified by appealing to the inflation scenario, inflationary models
with mild deviations from scale-invariance are not uncommon and models with
significant running of the spectral index are plausible. Even mild deviations
from scale-invariance can be important because halo collapse times and
densities depend on the relative amount of small-scale power. We choose several
popular models of inflation and work out the ramifications for galaxy central
densities. For each model, we calculate its COBE-normalized power spectrum and
deduce the implied halo densities using a semi-analytic method calibrated
against N-body simulations. We compare our predictions to a sample of dark
matter-dominated galaxies using a non-parametric measure of the density. While
standard n=1, LCDM halos are overdense by a factor of 6, several of our example
inflation+CDM models predict halo densities well within the range preferred by
observations. We also show how the presence of massive (0.5 eV) neutrinos may
help to alleviate the central density problem even with n=1. We conclude that
galaxy central densities may not be as problematic for the CDM paradigm as is
sometimes assumed: rather than telling us something about the nature of the
dark matter, galaxy rotation curves may be telling us something about inflation
and/or neutrinos. An important test of this idea will be an eventual consensus
on the value of sigma_8, the rms overdensity on the scale 8 h^-1 Mpc. Our
successful models have values of sigma_8 approximately 0.75, which is within
the range of recent determinations. Finally, models with n>1 (or sigma_8 > 1)
are highly disfavored.Comment: 13 pages, 6 figures. Minor changes made to reflect referee's
Comments, error in Eq. (18) corrected, references updated and corrected,
conclusions unchanged. Version accepted for publication in Phys. Rev. D,
scheduled for 15 August 200
Understanding Galaxy Formation and Evolution
The old dream of integrating into one the study of micro and macrocosmos is
now a reality. Cosmology, astrophysics, and particle physics intersect in a
scenario (but still not a theory) of cosmic structure formation and evolution
called Lambda Cold Dark Matter (LCDM) model. This scenario emerged mainly to
explain the origin of galaxies. In these lecture notes, I first present a
review of the main galaxy properties, highlighting the questions that any
theory of galaxy formation should explain. Then, the cosmological framework and
the main aspects of primordial perturbation generation and evolution are
pedagogically detached. Next, I focus on the ``dark side'' of galaxy formation,
presenting a review on LCDM halo assembling and properties, and on the main
candidates for non-baryonic dark matter. It is shown how the nature of
elemental particles can influence on the features of galaxies and their
systems. Finally, the complex processes of baryon dissipation inside the
non-linearly evolving CDM halos, formation of disks and spheroids, and
transformation of gas into stars are briefly described, remarking on the
possibility of a few driving factors and parameters able to explain the main
body of galaxy properties. A summary and a discussion of some of the issues and
open problems of the LCDM paradigm are given in the final part of these notes.Comment: 50 pages, 10 low-resolution figures (for normal-resolution, DOWNLOAD
THE PAPER (PDF, 1.9 Mb) FROM http://www.astroscu.unam.mx/~avila/avila.pdf).
Lectures given at the IV Mexican School of Astrophysics, July 18-25, 2005
(submitted to the Editors on March 15, 2006
Unbound Particles in Dark Matter Halos
We investigate unbound dark matter particles in halos by tracing particle
trajectories in a simulation run to the far future (a = 100). We find that the
traditional sum of kinetic and potential energies is a very poor predictor of
which dark matter particles will eventually become unbound from halos. We also
study the mass fraction of unbound particles, which increases strongly towards
the edges of halos, and decreases significantly at higher redshifts. We discuss
implications for dark matter detection experiments, precision calibrations of
the halo mass function, the use of baryon fractions to constrain dark energy,
and searches for intergalactic supernovae.Comment: Significant improvements following referee suggestion
On the reliability of merger-trees and the mass growth histories of dark matter haloes
We have used merger trees realizations to study the formation of dark matter
haloes. The construction of merger-trees is based on three different pictures
about the formation of structures in the Universe. These pictures include: the
spherical collapse (SC), the ellipsoidal collapse (EC) and the non-radial
collapse (NR). The reliability of merger-trees has been examined comparing
their predictions related to the distribution of the number of progenitors, as
well as the distribution of formation times, with the predictions of analytical
relations. The comparison yields a very satisfactory agreement. Subsequently,
>.........Comment: A&SS Accepte
JWST lensed quasar dark matter survey – I. Description and first results
peer reviewedThe flux ratios of gravitationally lensed quasars provide a powerful probe of the nature of dark matter. Importantly, these ratios are sensitive to small-scale structure, irrespective of the presence of baryons. This sensitivity may allow us to study the halo mass function even below the scales where galaxies form observable stars. For accurate measurements, it is essential that the quasar’s light is emitted from a physical region of the quasar with an angular scale of milliarcseconds or larger; this minimizes microlensing effects by stars within the deflector. The warm dust region of quasars fits this criterion, as it has parsec-size physical scales and dominates the spectral energy distribution of quasars at wavelengths greater than 10 μm. The JWST Mid-Infrared Instrument is adept at detecting redshifted light in this wavelength range, offering both the spatial resolution and sensitivity required for accurate gravitational lensing flux ratio measurements. Here, we introduce our survey designed to measure the warm dust flux ratios of 31 lensed quasars. We discuss the flux-ratio measurement technique and present results for the first target, DES J0405-3308. We find that we can measure the quasar warm dust flux ratios with 3 per cent precision. Our simulations suggest that this precision makes it feasible to detect the presence of 107 M dark matter haloes at cosmological distances. Such haloes are expected to be completely dark in cold dark matter models
DES13S2cmm: the first superluminous supernova from the Dark Energy Survey
We present DES13S2cmm, the first spectroscopically-confirmed superluminous
supernova (SLSN) from the Dark Energy Survey (DES). We briefly discuss the data
and search algorithm used to find this event in the first year of DES
operations, and outline the spectroscopic data obtained from the European
Southern Observatory (ESO) Very Large Telescope to confirm its redshift (z =
0.663 +/- 0.001 based on the host-galaxy emission lines) and likely spectral
type (type I). Using this redshift, we find M_U_peak = -21.05 +0.10 -0.09 for
the peak, rest-frame U-band absolute magnitude, and find DES13S2cmm to be
located in a faint, low metallicity (sub-solar), low stellar-mass host galaxy
(log(M/M_sun) = 9.3 +/- 0.3); consistent with what is seen for other SLSNe-I.
We compare the bolometric light curve of DES13S2cmm to fourteen similarly
well-observed SLSNe-I in the literature and find it possesses one of the
slowest declining tails (beyond +30 days rest frame past peak), and is the
faintest at peak. Moreover, we find the bolometric light curves of all SLSNe-I
studied herein possess a dispersion of only 0.2-0.3 magnitudes between +25 and
+30 days after peak (rest frame) depending on redshift range studied; this
could be important for 'standardising' such supernovae, as is done with the
more common type Ia. We fit the bolometric light curve of DES13S2cmm with two
competing models for SLSNe-I - the radioactive decay of 56Ni, and a magnetar -
and find that while the magnetar is formally a better fit, neither model
provides a compelling match to the data. Although we are unable to conclusively
differentiate between these two physical models for this particular SLSN-I,
further DES observations of more SLSNe-I should break this degeneracy,
especially if the light curves of SLSNe-I can be observed beyond 100 days in
the rest frame of the supernova.Comment: Accepted by MNRAS (2015 January 23), 13 pages, 6 figures, 2 table
- …