129 research outputs found
-ray flux from Dark Matter Annihilation in Galactic Caustics
In the frame of indirect dark matter searches we investigate the flux of
high-energy -ray photons produced by annihilation of dark matter in
caustics within our Galaxy under the hypothesis that the bulk of dark matter is
composed of the lightest supersymmetric particles. Unfortunately, the detection
of the caustics annihilation signal with currently available instruments is
rather challenging. Indeed, with realistic assumptions concerning particle
physics and cosmology, the -ray signal from caustics is below the
detection threshold of both erenkov telescopes and
satellite-borne experiments. Nevertheless, we find that this signal is more
prominent than that expected if annihilation only occurs in the smoothed
Galactic halo, with the possible exception of a circle around
the Galactic center if the mass density profile of our Galaxy exhibits a sharp
cusp there. We show that the angular distribution of this -ray flux
changes significantly if DM annihilation preferentially occurs within
virialized sub-halos populating our Galaxy rather than in caustics.Comment: 17 pages, 8 figures. Accepted for publication in JCA
On the detectability of gamma-rays from Dark Matter annihilation in the Local Group with ground-based experiments
Recent studies have suggested the possibility that the lightest
supersymmetric particle is a suitable dark matter candidate. In this
theoretical framework, annihilations in high density environments like the
center of dark matter haloes may produce an intense flux of gamma-rays. In this
paper we discuss the possibility of detecting the signatures of neutralino
annihilation in nearby galaxies with next generation ground-based detectors.Comment: to appear in Proceedings of ICRC 200
Tracing the cosmic velocity field at z ~ 0.1 from galaxy luminosities in the SDSS DR7
Spatial modulations in the distribution of observed luminosities (computed
using redshifts) of ~ 5 10 galaxies from the SDSS Data Release 7,
probe the cosmic peculiar velocity field out to z ~ 0.1. Allowing for
luminosity evolution, the r-band luminosity function, determined via a
spline-based estimator, is well represented by a Schechter form with
M(z) - 5logh = -20.52 - 1.6(z - 0.1) 0.05 and
= -1.1 0.03. Bulk flows and higher velocity moments in
two redshift bins, 0.02 < z < 0.07 and 0.07 < z < 0.22, agree with the
predictions of the CDM model, as obtained from mock galaxy catalogs
designed to match the observations. Assuming a CDM model, we estimate
1.1 0.4 for the amplitude of the linear matter
power spectrum, where the low accuracy is due to the limited number of
galaxies. While the low-z bin is robust against coherent photometric
uncertainties, the bias of results from the second bin is consistent with the ~
1% magnitude tilt reported by the SDSS collaboration. The systematics are
expected to have a significantly lower impact in future datasets with larger
sky coverage and better photometric calibration.Comment: 21 pages, 11 figures, accepted versio
On the recovery of Local Group motion from galaxy redshift surveys
There is a discrepancy between the measured motion of
the Local Group of galaxies (LG) with respect to the CMB and the linear theory
prediction based on the gravitational force field of the large scale structure
in full-sky redshift surveys. We perform a variety of tests which show that the
LG motion cannot be recovered to better than in amplitude
and within a in direction. The tests rely on catalogs of mock
galaxies identified in the Millennium simulation using semi-analytic galaxy
formation models. We compare these results to the Two-Mass Galaxy
Redshift Survey, which provides the deepest, widest and most complete spatial
distribution of galaxies available so far. In our analysis we use a new,
concise relation for deriving the LG motion and bulk flow from the true
distribution of galaxies in redshift space. Our results show that the main
source of uncertainty is the small effective depth of surveys like the 2MRS
that prevents a proper sampling of the large scale structure beyond . Deeper redshift surveys are needed to reach the "convergence
scale" of in a CDM universe. Deeper survey
would also mitigate the impact of the "Kaiser rocket" which, in a survey like
2MRS, remains a significant source of uncertainty. Thanks to the quiet and
moderate density environment of the LG, purely dynamical uncertainties of the
linear predictions are subdominant at the level of .
Finally, we show that deviations from linear galaxy biasing and shot noise
errors provide a minor contribution to the total error budget.Comment: 14 pages, 7 figure
Growth rate of cosmological perturbations at z ~ 0.1 from a new observational test
Spatial variations in the distribution of galaxy luminosities, estimated from
redshifts as distance proxies, are correlated with the peculiar velocity field.
Comparing these variations with the peculiar velocities inferred from galaxy
redshift surveys is a powerful test of gravity and dark energy theories on
cosmological scales. Using ~ 2 10 galaxies from the SDSS Data
Release 7, we perform this test in the framework of gravitational instability
to estimate the normalized growth rate of density perturbations f =
0.37 +/- 0.13 at z ~ 0.1, which is in agreement with the CDM scenario.
This unique measurement is complementary to those obtained with more
traditional methods, including clustering analysis. The estimated accuracy at z
~ 0.1 is competitive with other methods when applied to similar datasets.Comment: 4 pages, 2 figures, matches version accepted for publication in PR
Dark Matter Annihilation in Substructures Revised
Upcoming -ray satellites will search for Dark Matter annihilations in
Milky Way substructures (or 'clumps'). The prospects for detecting these
objects strongly depend on the assumptions made on the distribution of Dark
Matter in substructures, and on the distribution of substructures in the Milky
Way halo. By adopting simplified, yet rather extreme, prescriptions for these
quantities, we compute the number of sources that can be detected with upcoming
experiments such as GLAST, and show that, for the most optimistic particle
physics setup ( GeV and annihilation cross section cm s), the result ranges from zero to
hundred sources, all with mass above . However, for a fiducial DM
candidate with mass GeV and cm s,
at most a handful of large mass substructures can be detected at ,
with a 1-year exposure time, by a GLAST-like experiment. Scenarios where
micro-clumps (i.e. clumps with mass as small as ) can be
detected are severely constrained by the diffuse -ray background
detected by EGRET.Comment: Version accepted for publication in MNRAS. Other subhalos mass
function slopes added. All-sky analysis performed. Boost factors added. High
resolution figures for all models in http://www2.iap.fr/users/bertone/Clumps
Reconstructing Positions \& Peculiar Velocities of Galaxy Clusters within 25000 km/sec: The Bulk Velocity
Using a dynamical 3-D reconstruction procedure we estimate the peculiar
velocities of Abell/ACO galaxy clusters from their measured redshift
within 25000 km/sec. The reconstruction algorithm relies on the linear
gravitational instability hypothesis, assumes linear biasing and requires an
input value of the cluster -parameter (), which we estimated in Branchini \& Plionis (1995)
to be . The resulting cluster velocity field is dominated
by a large scale streaming motion along the Perseus Pisces--Great Attractor
base-line directed towards the Shapley concentration, in qualitative agreement
with the galaxy velocity field on smaller scales. Fitting the predicted cluster
peculiar velocities to a dipole term, in the local group frame and within a
distance of km/sec, we recover extremely well both the local group
velocity and direction, in disagreement with the Lauer \& Postman (1994)
observation. However, we find a probability that their observed
velocity field could be a realization of our corresponding one, if the latter
is convolved with their large distance dependent errors. Our predicted cluster
bulk velocity amplitude agrees well with that deduced by the POTENT and the da
Costa et al. (1995) analyses of observed galaxy motions at
km/sec; it decreases thereafter while at the Lauer \& Postman limiting depth
( km/sec) its amplitude is km/sec, in comfortable
agreement with most cosmological models.Comment: 8 pages, uuencoded compressed tarred postscript file uncluding text
and 3 figures. Accepted in ApJ Letter
Difficulty of detecting minihalos via -rays from dark matter annihilation
Analytical calculations and recent numerical experiments have shown that a
sizable of the mass in our Galaxy is in a form of clumpy, virialized
substructures that, according to \cite{dms:05}, can be as light as 10^{-6}
\msun. In this work we estimate the gamma-rays flux expected from dark matter
annihilation occurring within these minihalos, under the hypothesis that the
bulk of dark matter is composed by neutralinos. We generate mock sky maps
showing the angular distribution of the expected gamma-ray signal. We compare
them with the sensitivities of satellite-borne experiments such as GLAST and
find that a possible detection of minihalos is indeed very challenging.Comment: 4 pages, four color figures. Version published on PR
- …