1,086 research outputs found
The distribution of annihilation luminosities in dark matter substructure
We calculate the probability distribution function (PDF) of the expected
annihilation luminosities of dark matter subhalos as a function of subhalo mass
and distance from the Galactic center using a semi-analytical model of halo
evolution. We find that the PDF of luminosities is relatively broad, exhibiting
a spread of as much as an order of magnitude at fixed subhalo mass and
halo-centric distance. The luminosity PDF allows for simple construction of
mock samples of gamma-ray luminous subhalos and assessment of the variance in
among predicted gamma-ray signals from dark matter annihilation. Other
applications include quantifying the variance among the expected luminosities
of dwarf spheroidal galaxies, assessing the level at which dark matter
annihilation can be a contaminant in the expected gamma-ray signal from other
astrophysical sources, as well as estimating the level at which nearby subhalos
can contribute to the antimatter flux.Comment: 10 pages, 5 figures. Replaced with version accepted for publication
in Phys. Rev.
Probing the Shape of the Galactic Halo with Hyper-Velocity Stars
Precise proper motion measurements (sigma_mu ~ 10 mkas/yr) of the recently
discovered hyper-velocity star (HVS) SDSS J090745.0+024507 would yield
significant constraints on the axis ratios and orientation of a triaxial model
for the Galactic halo. Triaxiality of dark matter halos is predicted by Cold
Dark Matter models of galaxy formation and may be used to probe the nature of
dark matter. However, unless the distance to this star is determined to better
than 10%, these constraints suffer from one-dimensional degeneracies, which we
quantify. We show how proper motion measurements of several HVSs could
simultaneously resolve the distance degeneracies of all such stars and produce
a detailed picture of the triaxial halo. Additional HVSs may be found from
radial velocity surveys or from parallax/proper-motion data derived from GAIA.
High-precision proper-motion measurements of these stars using the Space
Interferometry Mission (SIM PlanetQuest) would substantially tighten the
constraints they yield on the Galactic potential.Comment: 7 pages, matches printed versio
Dark Matter Halos: Shapes, The Substructure Crisis, and Indirect Detection
In this proceeding, we briefly review three recent results. First, we show
that halos formed in simulations with gas cooling are significantly rounder
than halos formed in dissipationless -body simulations. The increase in
principle axis ratios is in the inner halo and
remains significant at large radii. Second, we discuss the CDM substructure
crisis and demonstrate the sensitivity of the crisis to the spectrum of
primordial density fluctuations on small scales. Third, we assess the ability
of experiments like VERITAS and GLAST to detect -rays from neutralino
dark matter annihilation in dark subhalos about the MW.Comment: 7 Pages, 3 Figures, Review to appear in The Proceedings of the Fifth
International Workshop on the Identification of Dark Matte
Pixel-z: Studying Substructure and Stellar Populations in Galaxies out to z~3 using Pixel Colors I. Systematics
We perform a pixel-by-pixel analysis of 467 galaxies in the GOODS-VIMOS
survey to study systematic effects in extracting properties of stellar
populations (age, dust, metallicity and SFR) from pixel colors using the
pixel-z method. The systematics studied include the effect of the input stellar
population synthesis model, passband limitations and differences between
individual SED fits to pixels and global SED-fitting to a galaxy's colors. We
find that with optical-only colors, the systematic errors due to differences
among the models are well constrained. The largest impact on the age and SFR
e-folding time estimates in the pixels arises from differences between the
Maraston models and the Bruzual&Charlot models, when optical colors are used.
This results in systematic differences larger than the 2{\sigma} uncertainties
in over 10 percent of all pixels in the galaxy sample. The effect of
restricting the available passbands is more severe. In 26 percent of pixels in
the full sample, passband limitations result in systematic biases in the age
estimates which are larger than the 2{\sigma} uncertainties. Systematic effects
from model differences are reexamined using Near-IR colors for a subsample of
46 galaxies in the GOODS-NICMOS survey. For z > 1, the observed optical/NIR
colors span the rest frame UV-optical SED, and the use of different models does
not significantly bias the estimates of the stellar population parameters
compared to using optical-only colors. We then illustrate how pixel-z can be
applied robustly to make detailed studies of substructure in high redshift
galaxies such as (a) radial gradients of age, SFR, sSFR and dust and (b) the
distribution of these properties within subcomponents such as spiral arms and
clumps. Finally, we show preliminary results from the CANDELS survey
illustrating how the new HST/WFC3 data can be exploited to probe substructure
in z~1-3 galaxies.Comment: 37 pages, 21 figures, submitted to Ap
Assembly bias and the dynamical structure of dark matter halos
Based on the Millennium Simulation we examine assembly bias for the halo
properties: shape, triaxiality, concentration, spin, shape of the velocity
ellipsoid and velocity anisotropy. For consistency we determine all these
properties using the same set of particles, namely all gravitationally
self-bound particles belonging to the most massive sub-structure of a given
friends-of-friends halo. We confirm that near-spherical and high-spin halos
show enhanced clustering. The opposite is true for strongly aspherical and
low-spin halos. Further, below the typical collapse mass, M*, more concentrated
halos show stronger clustering whereas less concentrated halos are less
clustered which is reversed for masses above M*. Going beyond earlier work we
show that: (1) oblate halos are more strongly clustered than prolate ones; (2)
the dependence of clustering on the shape of the velocity ellipsoid coincides
with that of the real-space shape, although the signal is stronger; (3) halos
with weak velocity anisotropy are more clustered, whereas radially anisotropic
halos are more weakly clustered; (4) for all highly clustered subsets we find
systematically less radially biased velocity anisotropy profiles. These
findings indicate that the velocity structure of halos is tightly correlated
with environment.Comment: 5 pages, 2 figures, accepted for publication in Ap
Luminous Satellites of Early-Type Galaxies I: Spatial Distribution
We study the spatial distribution of faint satellites of intermediate
redshift (0.1<z<0.8), early-type galaxies, selected from the GOODS fields. We
combine high resolution HST images and state-of-the-art host subtraction
techniques to detect satellites of unprecedented faintness and proximity to
intermediate redshift host galaxies (up to 5.5 magnitudes fainter and as close
as 0."5/2.5 kpc to the host centers). We model the spatial distribution of
objects near the hosts as a combination of an isotropic, homogenous
background/foreground population and a satellite population with a power law
radial profile and an elliptical angular distribution. We detect a significant
population of satellites, Ns =1.7 (+0.9,-0.8) that is comparable to the number
of Milky Way satellites with similar host-satellite contrast.The average
projected radial profile of the satellite distribution is isothermal, gamma_p=
-1.0(+0.3,-0.4), which is consistent with the observed central mass density
profile of massive early-type galaxies. Furthermore, the satellite distribution
is highly anisotropic (isotropy is ruled out at a >99.99% confidence level).
Defining phi to be the offset between the major axis of the satellite spatial
distribution and the major axis of the host light profile, we find a maximum
posterior probability of phi = 0 and |phi| less than 42 degrees at the 68%
confidence level. The alignment of the satellite distribution with the light of
the host is consistent with simulations, assuming that light traces mass for
the host galaxy as observed for lens galaxies. The anisotropy of the satellite
population enhances its ability to produce the flux ratio anomalies observed in
gravitationally lensed quasars.Comment: 21 pages, 16 figures, Accepted for publication in Ap
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