4,828 research outputs found
Probing the Mass Distribution with IRAS Galaxies
We present the results of three independent analyses in which we show that
IRAS galaxies faithfully trace the underlying distribution the mass in the
local universe. In the first analysis we compare the mass and the galaxy
density fields and show that they are consistent within 60 Mpc. In the
second one we show that the tidal velocity field of the Mark III catalog is
consistent with the tidal velocity field predicted from the distribution of
IRAS galaxies, hence indicating that IRAS galaxies trace the mass distribution
well beyond 60 Mpc. Finally, a third analysis aimed at determining the
mean biasing relation of IRAS galaxies showed no appreciable deviations from
the linear biasing prescription.Comment: 5 pages including 4 Figures + 1 LaTex macro. Contribution to
``Where's the Matter? Tracing Dark and Bright Matter with the New Generation
of Large Scale Surveys'', June 2001, Treyer & Tresse Eds, Frontier Grou
-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
Testing the Least Action Principle in an Omega_0=1 Universe
The least action principle (LAP) is a dynamically rigorous method for
deriving the history of galaxy orbits. In particular it is an Omega_0 test,
predicting current epoch galaxy velocities as a function of position and of the
cosmological background. It is most usefully applied to in--falling structures,
such as the local group, where its application indicates that the preferred
cosmological model is Omega_0 = 0.1 and h=0.75 (h is the Hubble parameter in
units of 100 Km s^-1 Mpc^-1). The method assumes that all the mass acts as if
it were distributed as the visible galaxies. We test the reliability of the LAP
to Local Group-like systems extracted from Omega_0=1 N--body simulations. While
the orbits of the galaxies are qualitatively well reconstructed, the LAP
systematically underestimates the mass of the system. This failure is
attributed to the presence of extended halos weakly clustered around visible
galaxies which prevent a large fraction of the group mass from being detected
by the LAP technique. We conclude that the LAP method cannot rule out an
Omega_0=1 value on the Local Group scale. Better constraints on Omega_0 may be
obtained by applying this technique to in--falling systems, such as clusters,
containing objects with separations large compared to galaxy sizes.Comment: accepted by APJ, uuencoded-compressed-tarred PostScript file
including figures. SISSA Ref. 56/94/
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
- …