67 research outputs found
Formation of Globular Clusters in Hierarchical Cosmology: ART and Science
We test the hypothesis that globular clusters form in supergiant molecular
clouds within high-redshift galaxies. Numerical simulations demonstrate that
such large, dense, and cold gas clouds assemble naturally in current
hierarchical models of galaxy formation. These clouds are enriched with heavy
elements from earlier stars and could produce star clusters in a similar way to
nearby molecular clouds. The masses and sizes of the model clusters are in
excellent agreement with the observations of young massive clusters. Do these
model clusters evolve into globular clusters that we see in our and external
galaxies? In order to study their dynamical evolution, we calculate the orbits
of model clusters using the outputs of the cosmological simulation of a Milky
Way-sized galaxy. We find that at present the orbits are isotropic in the inner
50 kpc of the Galaxy and preferentially radial at larger distances. All
clusters located outside 10 kpc from the center formed in the now-disrupted
satellite galaxies. The spatial distribution of model clusters is spheroidal,
with a power-law density profile consistent with observations. The combination
of two-body scattering, tidal shocks, and stellar evolution results in the
evolution of the cluster mass function from an initial power law to the
observed log-normal distribution. However, not all initial conditions and not
all evolution scenarios are consistent with the observed mass function.Comment: 8 pages, invited review for conference "Globular Clusters, Guide to
Galaxies", 6-10 March 2006, University of Concepcion, Chile, ed. T. Richtler,
et a
Gas rich galaxies from the FIGGS survey
The FIGGS (Faint Irregular Galaxy GMRT Survey) is aimed at creating a
multi-wavelength observational data base for a volume limited sample of the
faintest gas rich galaxies. In this paper we discuss two very gas rich galaxies
that were observed as part of the FIGGS survey, viz. NGC 3741 and And IV. These
galaxies are unusual in that they have extremely extended gas disks and very
high ratios of dark to luminous matter. The very extended HI disks provide an
unique opportunity to trace the extended distribution of dark matter around
faint galaxies. We compare the baryon fraction of these galaxies with a sample
of galaxies with well measured rotation curves and discuss whether extremely
gas rich dwarf galaxies have abnormally small baryon fractions.Comment: 5 Pages, 4 Figures. To be published in the proceedings of "Galaxies
in the Local Volume", ed. B. Koribalski, H. Jerje
Reopening the window on charged dark matter
We reexamine the limits on charged dark matter particles. We show that if
their mass and charge fall in the range 100(q_X/e)^2< m_X < 10^8(q_X/e) TeV,
then magnetic fields prevent particles in the halo from entering the galactic
disk, while those initially trapped inside are accelerated through the Fermi
mechanism and ejected within about 0.1-1 Gyrs. Consequently, previous
constraints on charged dark matter based on terrestrial non-observation are
invalid within that range. Further, we find that charged massive particles may
simultaneously solve several long-standing astrophysical problems, including
the underabundance of dwarf galaxies, the shallow density profiles in the cores
of the LSB galaxies, the absence of cooling flows in the cores of galaxy
clusters, and several others.Comment: 9 pages, 1 figure, accepted for publication in JCA
Strong lens search in the ESO public Survey KiDS
We have started a systematic search of strong lens candidates in the ESO
public survey KiDS based on the visual inspection of massive galaxies in the
redshift range . As a pilot program we have inspected 100 sq. deg.,
which overlap with SDSS and where there are known lenses to use as a control
sample. Taking advantage of the superb image quality of VST/OmegaCAM, the
colour information and accurate model subtracted images, we have found 18 new
lens candidates, for which spectroscopic confirmation will be needed to confirm
their lensing nature and study the mass profile of the lensing galaxies.Comment: 4 pages, 1 figure, to appear on the refereed Proceeding of the "The
Universe of Digital Sky Surveys" conference held at the INAF--OAC, Naples, on
25th-28th november 2014, to be published on Astrophysics and Space Science
Proceedings, edited by Longo, Napolitano, Marconi, Paolillo, Iodic
Neutron star cooling: Theoretical aspects and observational constraints
The cooling theory of isolated neutron stars is reviewed. The main cooling
regulators are discussed, first of all, operation of direct Urca process (or
similar processes in exotic phases of dense matter) and superfluidity in
stellar interiors. The prospects to constrain gross parameters of supranuclear
matter in neutron-star interiors by confronting cooling theory with
observations of isolated neutron stars are outlined. A related problem of
thermal states of transiently accreting neutron stars with deep crustal heating
of accreted matter is discussed in application to soft X-ray transients.Comment: 10 pages, 3 figures, Proceedings of the 34th COSPAR Scientific
Assembly (Adv. Sp. Res., accepted
Non-relativistic limit of Randall-Sundrum model: solutions, applications and constraints
In the Randall-Sundrum model with one brane, we found the approximate and
exact solutions for gravitational potentials and accelerations of test bodies
in these potentials for different geometrical configurations. We applied these
formulas for calculation of the gravitational interaction between two spheres
and found the approximate and exact expressions for the relative force
corrections to the Newton's gravitational force. We demonstrated that the
difference between relative force corrections for the approximate and exact
cases increases with the parameter (for the fixed distance between
centers of the spheres). On the other hand, this difference increases with
decreasing of the distance between the centers of the spheres (for the fixed
curvature scale parameter ). We got the upper limit for the curvature scale
parameter m. For these values of , the difference
between the approximate and exact solutions is negligible.Comment: LaTex 11 pages, 3 figure
Semi-empirical catalog of early-type galaxy-halo systems: dark matter density profiles, halo contraction and dark matter annihilation strength
With SDSS galaxy data and halo data from up-to-date N-body simulations we
construct a semi-empirical catalog (SEC) of early-type systems by making a
self-consistent bivariate statistical match of stellar mass (M_star) and
velocity dispersion (sigma) with halo virial mass (M_vir). We then assign
stellar mass profile and velocity dispersion profile parameters to each system
in the SEC using their observed correlations with M_star and sigma.
Simultaneously, we solve for dark matter density profile of each halo using the
spherical Jeans equation. The resulting dark matter density profiles deviate in
general from the dissipationless profile of NFW or Einasto and their mean inner
density slope and concentration vary systematically with M_vir. Statistical
tests of the distribution of profiles at fixed M_vir rule out the null
hypothesis that it follows the distribution predicted by N-body simulations for
M_vir ~< 10^{13.5-14.5} M_solar. These dark matter profiles imply that dark
matter density is, on average, enhanced significantly in the inner region of
halos with M_vir ~< 10^{13.5-14.5} M_solar supporting halo contraction. The
main characteristics of halo contraction are: (1) the mean dark matter density
within the effective radius has increased by a factor varying systematically up
to ~ 3-4 at M_vir = 10^{12} M_solar, and (2) the inner density slope has a mean
of ~ 1.3 with rho(r) ~ r^{-alpha} and a halo-to-halo rms scatter of
rms(alpha) ~ 0.4-0.5 for 10^{12} M_solar ~< M_vir ~< 10^{13-14} M_solar steeper
than the NFW profile (alpha=1). Based on our results we predict that halos of
nearby elliptical and lenticular galaxies can, in principle, be promising
targets for gamma-ray emission from dark matter annihilation.Comment: 43 pages, 20 figures, JCAP, revised and accepted versio
Star and cluster formation in extreme environments
Current empirical evidence on the star-formation processes in the extreme,
high-pressure environments induced by galaxy encounters (mostly based on
high-resolution Hubble Space Telescope observations) strongly suggests that
star CLUSTER formation is an important and perhaps even the dominant mode of
star formation in such starburst events. The sizes, luminosities, and mass
estimates of the young massive star clusters (YMCs) are entirely consistent
with what is expected for young Milky Way-type globular clusters (GCs). Recent
evidence lends support to the scenario that GCs, which were once thought to be
the oldest building blocks of galaxies, are still forming today. Here, I
present a novel empirical approach to assess the shape of the
initial-to-current YMC mass functions, and hence their possible survival
chances for a Hubble time.Comment: 6 pages, LaTeX with Kluwer style files included; to appear in:
"Starbursts - from 30 Doradus to Lyman break galaxies" (Cambridge UK,
September 2004; talk summary), Astrophysics & Space Science Library, eds. de
Grijs R., Gonzalez Delgado R.M., Kluwer: Dordrech
Gamma Ray Lines from a Universal Extra Dimension
Indirect Dark Matter searches are based on the observation of secondary
particles produced by the annihilation or decay of Dark Matter. Among them,
gamma-rays are perhaps the most promising messengers, as they do not suffer
deflection or absorption on Galactic scales, so their observation would
directly reveal the position and the energy spectrum of the emitting source.
Here, we study the detailed gamma-ray energy spectrum of Kaluza--Klein Dark
Matter in a theory with 5 Universal Extra Dimensions. We focus in particular on
the two body annihilation of Dark Matter particles into a photon and another
particle, which produces monochromatic photons, resulting in a line in the
energy spectrum of gamma rays. Previous calculations in the context of the five
dimensional UED model have computed the line signal from annihilations into
\gamma \gamma, but we extend these results to include \gamma Z and \gamma H
final states. We find that these spectral lines are subdominant compared to the
predicted \gamma \gamma signal, but they would be important as follow-up
signals in the event of the observation of the \gamma \gamma line, in order to
distinguish the 5d UED model from other theoretical scenarios.Comment: 21 pages, 6 figure
A Tentative Gamma-Ray Line from Dark Matter Annihilation at the Fermi Large Area Telescope
The observation of a gamma-ray line in the cosmic-ray fluxes would be a
smoking-gun signature for dark matter annihilation or decay in the Universe. We
present an improved search for such signatures in the data of the Fermi Large
Area Telescope (LAT), concentrating on energies between 20 and 300 GeV. Besides
updating to 43 months of data, we use a new data-driven technique to select
optimized target regions depending on the profile of the Galactic dark matter
halo. In regions close to the Galactic center, we find a 4.6 sigma indication
for a gamma-ray line at 130 GeV. When taking into account the look-elsewhere
effect the significance of the observed excess is 3.2 sigma. If interpreted in
terms of dark matter particles annihilating into a photon pair, the
observations imply a dark matter mass of 129.8\pm2.4^{+7}_{-13} GeV and a
partial annihilation cross-section of = 1.27\pm0.32^{+0.18}_{-0.28}
x 10^-27 cm^3 s^-1 when using the Einasto dark matter profile. The evidence for
the signal is based on about 50 photons; it will take a few years of additional
data to clarify its existence.Comment: 23 pages, 9 figures, 3 tables; extended discussion; matches published
versio
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