69 research outputs found
Non-universality of halo profiles and implications for dark matter experiments
We explore the cosmological halo-to-halo scatter of the distribution of mass within dark matter haloes utilizing a well-resolved statistical sample of clusters from the cosmological Millennium Simulation. We find that at any radius, the spherically averaged dark matter density of a halo (corresponding to the ‘smooth component') and its logarithmic slope are well described by a Gaussian probability distribution. At small radii (within the scale radius), the density distribution is fully determined by the measured Gaussian distribution in halo concentrations. The variance in the radial distribution of mass in dark matter haloes is important for the interpretation of direct and indirect dark matter detection efforts. The scatter in mass profiles imparts approximately a 25 per cent cosmological uncertainty in the dark matter density at the Solar neighbourhood and a factor of ∼3 uncertainty in the expected Galactic dark matter annihilation flux. The aggregate effect of halo-to-halo profile scatter leads to a small (few per cent) enhancement in dark matter annihilation background if the Gaussian concentration distribution holds for all halo masses versus a 10 per cent enhancement under the assumption of a lognormal concentration distribution. The Gaussian nature of the cluster profile scatter implies that the technique of ‘stacking' haloes to improve signal-to-noise ratio should not suffer from bia
Dark matter annihilation and decay profiles for the Reticulum II dwarf spheroidal galaxy
The dwarf spheroidal galaxies (dSph) of the Milky Way are among the most
attractive targets for indirect searches of dark matter. In this work, we
reconstruct the dark matter annihilation (J-factor) and decay profiles for the
newly discovered dSph Reticulum II. Using an optimized spherical Jeans analysis
of kinematic data obtained from the Michigan/Magellan Fiber System (M2FS), we
find Reticulum II's J-factor to be among the largest of any Milky Way dSph. We
have checked the robustness of this result against several ingredients of the
analysis. Unless it suffers from tidal disruption or significant inflation of
its velocity dispersion from binary stars, Reticulum II may provide a unique
window on dark matter particle properties.Comment: 5 pages, 4 figures. Match the ApJL accepted versio
Testing general relativity and probing the merger history of massive black holes with LISA
Observations of binary inspirals with LISA will allow us to place bounds on
alternative theories of gravity and to study the merger history of massive
black holes (MBH). These possibilities rely on LISA's parameter estimation
accuracy. We update previous studies of parameter estimation including
non-precessional spin effects. We work both in Einstein's theory and in
alternative theories of gravity of the scalar-tensor and massive-graviton
types. Inclusion of non-precessional spin terms in MBH binaries has little
effect on the angular resolution or on distance determination accuracy, but it
degrades the estimation of the chirp mass and reduced mass by between one and
two orders of magnitude. The bound on the coupling parameter of scalar-tensor
gravity is significantly reduced by the presence of spin couplings, while the
reduction in the graviton-mass bound is milder. LISA will measure the
luminosity distance of MBHs to better than ~10% out to z~4 for a (10^6+10^6)
Msun binary, and out to z~2 for a (10^7+10^7) Msun binary. The chirp mass of a
MBH binary can always be determined with excellent accuracy. Ignoring spin
effects, the reduced mass can be measured within ~1% out to z=10 and beyond for
a (10^6+10^6) Msun binary, but only out to z~2 for a (10^7+10^7) Msun binary.
Present-day MBH coalescence rate calculations indicate that most detectable
events should originate at z~2-6: at these redshifts LISA can be used to
measure the two black hole masses and their luminosity distance with sufficient
accuracy to probe the merger history of MBHs. If the low-frequency LISA noise
can only be trusted down to 10^-4 Hz, parameter estimation for MBHs (and LISA's
ability to perform reliable cosmological observations) will be significantly
degraded.Comment: 13 pages, 4 figures. Proceedings of GWDAW 9. Matches version accepted
in Classical and Quantum Gravit
The most dark-matter-dominated galaxies : predicted gamma-ray signals from the faintest milky way dwarfs
We use kinematic data from three new nearby, extremely low luminosity Milky Way dwarf galaxies (Ursa Major II, Willman 1, and Coma Berenices) to constrain the properties of their dark matter halos, and from these we make predictions for the γ-ray flux from annihilation of dark matter particles in these halos. We show that these ~10^3 L⊙ dwarfs are the most dark-matter-dominated galaxies known, with total masses within 100 pc that are in excess of 10^6 M⊙. Coupled with their relative proximity, their large masses imply that they should have mean γ-ray fluxes that are comparable to or greater than those of any other known satellite galaxy of the Milky Way. Our results are robust to both variations of the inner slope of the density profile and the effect of tidal interactions. The fluxes could be boosted by up to 2 orders of magnitude if we include the density enhancements caused by surviving dark matter substructure
Section on Prospects for Dark Matter Detection of the White Paper on the Status and Future of Ground-Based TeV Gamma-Ray Astronomy
This is a report on the findings of the dark matter science working group for
the white paper on the status and future of TeV gamma-ray astronomy. The white
paper was commissioned by the American Physical Society, and the full white
paper can be found on astro-ph (arXiv:0810.0444). This detailed section
discusses the prospects for dark matter detection with future gamma-ray
experiments, and the complementarity of gamma-ray measurements with other
indirect, direct or accelerator-based searches. We conclude that any
comprehensive search for dark matter should include gamma-ray observations,
both to identify the dark matter particle (through the charac- teristics of the
gamma-ray spectrum) and to measure the distribution of dark matter in galactic
halos.Comment: Report from the Dark Matter Science Working group of the APS
commissioned White paper on ground-based TeV gamma ray astronomy (19 pages, 9
figures
Exploring the effects of pressure on the radial accretion of dark matter by a Schwarzschild supermassive black hole
Based on the numerical solution of the time-dependent relativistic Euler
equations onto a fixed Schwarzschild background space-time, we estimate the
accretion rate of radial flow toward the horizon of a test perfect fluid
obeying an ideal gas equation of state. We explore the accretion rate in terms
of the initial density of the fluid for various values of the inflow velocity
in order to investigate whether or not sufficiently arbitrary initial
conditions allow a steady state accretion process depending on the values of
the pressure. We extrapolate our results to the case where the fluid
corresponds to dark matter and the black hole is a supermassive black hole
seed. Then we estimate the equation of state parameters that provide a steady
state accretion process. We found that when the pressure of the dark matter is
zero, the black hole's mass grows up to values that are orders of magnitude
above during a lapse of 10Gyr, whereas in the case of the
accretion of the ideal gas dark matter with non zero pressure the accreted mass
can be of the order of for black holes of
. This would imply that if dark matter near a supermassive
black hole acquires an equation of state with non trivial pressure, the
contribution of accreted dark matter to the supermassive black hole growth
could be small, even though only radial accretion is considered.Comment: 9 pages, 24 eps figures, 2 tables. Accepted for publication in MNRA
Non-universality of halo profiles and implications for dark matter experiments
We explore the cosmological halo-to-halo scatter of the distribution of mass
within dark matter halos utilizing a well-resolved statistical sample of
clusters from the cosmological Millennium simulation. We find that at any
radius, the spherically-averaged dark matter density of a halo (corresponding
to the "smooth-component") and its logarithmic slope are well-described by a
Gaussian probability distribution. At small radii (within the scale radius),
the density distribution is fully determined by the measured Gaussian
distribution in halo concentrations. The variance in the radial distribution of
mass in dark matter halos is important for the interpretation of direct and
indirect dark matter detection efforts. The scatter in mass profiles imparts
approximately a 25 percent cosmological uncertainty in the dark matter density
at the Solar neighborhood and a factor of ~3 uncertainty in the expected
Galactic dark matter annihilation flux. The aggregate effect of halo-to-halo
profile scatter leads to a small (few percent) enhancement in dark matter
annihilation background if the Gaussian concentration distribution holds for
all halo masses versus a 10 percent enhancement under the assumption of a
log-normal concentration distribution. The Gaussian nature of the cluster
profile scatter implies that the technique of "stacking" halos to improve
signal to noise should not suffer from bias.Comment: replaced with accepted mnras versio
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