3,993 research outputs found
Disk Evolution and Bar Triggering Driven by Interactions with Dark Matter Substructure
We study formation and evolution of bar-disk systems in fully self-consistent
cosmological simulations of galaxy formation in the LCDM WMAP3 Universe. In a
representative model we find that the first generation of bars form in response
to the asymmetric dark matter (DM) distribution (i.e., DM filament) and quickly
decay. Subsequent bar generations form and are destroyed during the major
merger epoch permeated by interactions with a DM substructure (subhalos). A
long-lived bar is triggered by a tide from a subhalo and survives for ~10 Gyr.
The evolution of this bar is followed during the subsequent numerous minor
mergers and interactions with the substructure. Together with intrinsic
factors, these interactions largely determine the stellar bar evolution. The
bar strength and its pattern speed anticorrelate, except during interactions
and when the secondary (nuclear) bar is present. For about 5 Gyr bar pattern
speed increases substantially despite the loss of angular momentum to stars and
cuspy DM halo. We analyze the evolution of stellar populations in the bar-disk
and relate them to the underlying dynamics. While the bar is made mainly of an
intermediate age, ~5-6 Gyr, disk stars at z=0, a secondary nuclear bar which
surfaces at z~0.1 is made of younger, ~1-3 Gyr stars.Comment: 5 pages, 5 figures, accepted for publication in ApJ Letter
The Dark Side of QSO Formation at High Redshifts
Observed high-redshift QSOs, at z~6, may reside in massive dark matter (DM)
halos of more than 10^{12} Msun and are thus expected to be surrounded by
overdense regions. In a series of 10 constrained simulations, we have tested
the environment of such QSOs. Comparing the computed overdensities with respect
to the unconstrained simulations of regions empty of QSOs, assuming there is no
bias between the DM and baryon distributions, and invoking an
observationally-constrained duty-cycle for Lyman Break Galaxies, we have
obtained the galaxy count number for the QSO environment. We find that a clear
discrepancy exists between the computed and observed galaxy counts in the Kim
et al. (2009) samples. Our simulations predict that on average eight z~6
galaxies per QSO field should have been observed, while Kim et al. detect on
average four galaxies per QSO field compared to an average of three galaxies in
a control sample (GOODS fields). While we cannot rule out a small number
statistics for the observed fields to high confidence, the discrepancy suggests
that galaxy formation in the QSO neighborhood proceeds differently than in the
field. We also find that QSO halos are the most massive of the simulated volume
at z~6 but this is no longer true at z~3. This implies that QSO halos, even in
the case they are the most massive ones at high redshifts, do not evolve into
most massive galaxy clusters at z=0.Comment: 12 pages, 7 figures, revised after the referee comments, to be
published by the Astrophysical Journa
Observational Properties of Simulated Galaxies in Overdense and Average Regions at High Redshifts z= 6-12
We use high-resolution zoom-in cosmological simulations of galaxies of
Romano-Diaz et al., post-processing them with a panchromatic three-dimensional
radiation transfer code to obtain the galaxy UV luminosity function (LF) at z ~
6-12. The galaxies are followed in a rare, heavily overdense region within a ~
5-sigma density peak, which can host high-z quasars, and in an average density
region, down to the stellar mass of M_star ~ 4* 10^7 Msun. We find that the
overdense regions evolve at a substantially accelerated pace --- the most
massive galaxy has grown to M_star ~ 8.4*10^10 Msun by z = 6.3, contains dust
of M_dust~ 4.1*10^8 Msun, and is associated with a very high star formation
rate, SFR ~ 745 Msun/yr.The attained SFR-M_star correlation results in the
specific SFR slowly increasing with M_star. Most of the UV radiation in massive
galaxies is absorbed by the dust, its escape fraction f_esc is low, increasing
slowly with time. Galaxies in the average region have less dust, and agree with
the observed UV LF. The LF of the overdense region is substantially higher, and
contains much brighter galaxies. The massive galaxies are bright in the
infrared (IR) due to the dust thermal emission, with L_IR~ 3.7*10^12 Lsun at z
= 6.3, while L_IR < 10^11 Lsun for the low-mass galaxies. Therefore, ALMA can
probe massive galaxies in the overdense region up to z ~ 10 with a reasonable
integration time. The UV spectral properties of disky galaxies depend
significantly upon the viewing angle.The stellar and dust masses of the most
massive galaxy in the overdense region are comparable to those of the
sub-millimetre galaxy (SMG) found by Riechers et al. at z = 6.3, while the
modelled SFR and the sub-millimetre flux fall slightly below the observed one.
Statistical significance of these similarities and differences will only become
clear with the upcoming ALMA observations.Comment: 17 pages, 13 figures, accepted for publication in MNRA
Erasing Dark Matter Cusps in Cosmological Galactic Halos with Baryons
We study the central dark matter (DM) cusp evolution in cosmological galactic
halos. Models with and without baryons (baryons+DM, hereafter BDM model, and
pure DM, PDM model, respectively) are advanced from identical initial
conditions. The DM cusp properties are contrasted by a direct comparison of
pure DM and baryonic models. We find a divergent evolution between the PDM and
BDM models within the inner ~10 kpc region. The PDM model forms a R^{-1} cusp
as expected, while the DM in the BDM model forms a larger isothermal cusp
R^{-2} instead. The isothermal cusp is stable until z~1 when it gradually
levels off. This leveling proceeds from inside out and the final density slope
is shallower than -1 within the central 3 kpc (i.e., expected size of the
R^{-1} cusp), tending to a flat core within ~2 kpc. This effect cannot be
explained by a finite resolution of our code which produces only a 5%
difference between the gravitationally softened force and the exact Newtonian
force of point masses at 1 kpc from the center. Neither is it related to the
energy feedback from stellar evolution or angular momentum transfer from the
bar. Instead it can be associated with the action of DM+baryon subhalos heating
up the cusp region via dynamical friction and forcing the DM in the cusp to
flow out and to `cool' down. The process described here is not limited to low z
and can be efficient at intermediate and even high z.Comment: 4 pages, 4 figures, accepted for publication by the Astrophysical
Journal Letters. Minor corrections following the referee repor
Dissecting Galaxy Formation: II. Comparing Substructure in Pure Dark Matter and Baryonic Models
We compare the substructure evolution in pure dark matter (DM) halos with
those in the presence of baryons (PDM and BDM). The prime halos have been
analyzed by Romano-Diaz et al (2009). Models have been evolved from identical
initial conditions using Constrained Realizations, including star formation and
feedback. A comprehensive catalog of subhalos has been compiled and properties
of subhalos analyzed in the mass range of 10^8 Mo - 10^11 Mo. We find that
subhalo mass functions are consistent with a single power law, M_sbh^{alpha},
but detect a nonnegligible shift between these functions, alpha -0.86 for the
PDM, and -0.98 for the BDM. Overall, alpha const. in time with variations of
+-15%. Second, we find that the radial mass distribution of subhalos can be
approximated by a power law, R^{gamma} with a steepening around the radius of a
maximal circular velocity, Rvmax, in the prime halos. Gamma ~-1.5 for the PDM
and -1 for the BDM, inside Rvmax, and is steeper outside. We detect little
spatial bias between the subhalo populations and the DM of the main halos. The
subhalo population exhibits much less triaxiality with baryons, in tandem with
the prime halo. Finally, we find that, counter-intuitively, the BDM population
is depleted at a faster rate than the PDM one within the central 30kpc of the
prime. Although the baryons provide a substantial glue to the subhalos, the
main halos exhibit the same trend. This assures a more efficient tidal
disruption of the BDM subhalos. This effect can be reversed for a more
efficient feedback from stellar evolution and supermassive black holes, which
will expel baryons from the center and decrease the concentration of the prime
halo. We compare our results with via Lactea and Aquarius simulations and other
published results.Comment: 12 pages, 9 figures, to be published by the Astrophysical Journa
Weak lensing evidence for a filament between A222/A223
We present a weak lensing analysis and comparison to optical and X-ray maps
of the close pair of massive clusters A222/223. Indications for a filamentary
connection between the clusters are found and discussed.Comment: 6 pages, 1 figure. To appear in Proc. IAU Colloquium 195: Outskirts
of Galaxy Clusters - Intense Life in the Suburbs. Version with higher
resolution available at
http://www.astro.uni-bonn.de/~dietrich/torino_proc.ps.g
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