110 research outputs found
The Caterpillar Project: A Large Suite of Milky Way Sized Halos
We present the largest number of Milky Way sized dark matter halos simulated
at very high mass ( M/particle) and temporal resolution
(5 Myrs/snapshot) done to date, quadrupling what is currently available
in the literature. This initial suite consists of the first 24 halos of the
(www.caterpillarproject.org) whose project goal of 60 -
70 halos will be made public when complete. We resolve 20,000
gravitationally bound subhalos within the virial radius of each host halo. Over
the ranges set by our spatial resolution our convergence is excellent and
improvements were made upon current state-of-the-art halo finders to better
identify substructure at such high resolutions (e.g., on average we recover
4 subhalos in each host halo above 10 M which would have
otherwise not been found using conventional methods). For our relaxed halos,
the inner profiles are reasonably fit by Einasto profiles ( = 0.169
0.023) though this depends on the relaxed nature and assembly history of
a given halo. Averaging over all halos, the substructure mass fraction is
, and mass function slope is d/d though we find scatter in the normalizations for fixed halo
mass due to more concentrated hosts having less subhalos at fixed subhalo mass.
There are no biases stemming from Lagrangian volume selection as all Lagrangian
volume types are included in our sample. Our detailed contamination study of
264 low resolution halos has resulted in obtaining very large and
unprecedented, high-resolution regions around our host halos for our target
resolution (sphere of radius Mpc) allowing for accurate
studies of low mass dwarf galaxies at large galactocentric radii and the very
first stellar systems at high redshift ( 10).Comment: 19 pages; 14 figures; 6 tables; Received September 3, 2015; Accepted
November 15, 2015; Published February 2, 201
The Supersonic Project: SIGOs, A Proposed Progenitor to Globular Clusters, and Their Connections to Gravitational-wave Anisotropies
Supersonically induced gas objects (SIGOs), are structures with little to no dark-matter component predicted to exist in regions of the universe with large relative velocities between baryons and dark matter at the time of recombination. They have been suggested to be the progenitors of present-day globular clusters. Using simulations, SIGOs have been studied on small scales (around 2 Mpc) where these relative velocities are coherent. However, it is challenging to study SIGOs using simulations on large scales due to the varying relative velocities at scales larger than a few Mpc. Here, we study SIGO abundances semi-analytically: using perturbation theory, we predict the number density of SIGOs analytically, and compare these results to small-box numerical simulations. We use the agreement between the numerical and analytic calculations to extrapolate the large-scale variation of SIGO abundances over different stream velocities. As a result, we predict similar large-scale variations of objects with high gas densities before reionization that could possibly be observed by JWST. If indeed SIGOs are progenitors of globular clusters, then we expect a similar variation of globular cluster abundances over large scales. Significantly, we find that the expected number density of SIGOs is consistent with observed globular cluster number densities. As a proof-of-concept, and because globular clusters were proposed to be natural formation sites for gravitational wave sources from binary black-hole mergers, we show that SIGOs should imprint an anisotropy on the gravitational wave signal on the sky, consistent with their distribution
X-ray morphology of cluster-mass haloes in self-interacting dark matter
We perform cosmological zoom-in simulations of relaxed cluster-mass
haloes with the inclusion of adiabatic gas in the cold dark matter (CDM) and
self-interacting dark matter (SIDM) models. These clusters are selected as
dynamically relaxed clusters from a parent simulation with . Both the dark matter and
the intracluster gas distributions in SIDM appear more spherical than their CDM
counterparts. Mock X-ray images are generated based on the simulations and are
compared to the real X-ray images of relaxed clusters selected from the
Chandra and ROSAT archives. We perform ellipse fitting for the isophotes of
mock and real X-ray images and obtain the ellipticities at cluster-centric
radii of . The X-ray isophotes in
SIDM models with increasing cross-sections are rounder than their CDM
counterparts, which manifests as a systematic shift in the distribution
function of ellipticities. Unexpectedly, the X-ray morphology of the observed
non-cool-core clusters agrees better with SIDM models with cross-section
than CDM and SIDM with
. Our statistical analysis indicates that
the latter two models are disfavored at the confidence level (as
conservative estimates). This conclusion is not altered by shifting the radial
range of measurements or applying temperature selection criterion. However, the
primary uncertainty originates from the lack of baryonic physics in the
adiabatic model, such as cooling, star formation and feedback effects, which
still have the potential to reconcile CDM simulations with observations.Comment: Accepted by MNRA
Local dark matter searches with LISA
The drag-free satellites of LISA will maintain the test masses in geodesic
motion over many years with residual accelerations at unprecedented small
levels and time delay interferometry (TDI) will keep track of their
differential positions at level of picometers. This may allow investigations of
fine details of the gravitational field in the Solar System previously
inaccessible. In this spirit, we present the concept of a method to measure
directly the gravitational effect of the density of diffuse Local Dark Matter
(LDM) with a constellation of a few drag-free satellites, by exploiting how
peculiarly it would affect their relative motion. Using as test bed an
idealized LISA with rigid arms, we find that the separation in time between the
test masses is uniquely perturbed by the LDM, so that they acquire a
differential breathing mode. Such a LDM signal is related to the LDM density
within the orbits and has characteristic spectral components, with amplitudes
increasing in time, at various frequencies of the dynamics of the
constellation. This is the relevant result, in that the LDM signal is brought
to non-zero frequencies.Comment: 8 pages, 1 figure; v2: minor changes to match the version in press on
Classical and Quantum Gravity (special issue for the 7th International LISA
Symposium proceedings
The Supersonic Project: The Early Evolutionary Path of Supersonically Induced Gas Objects
Supersonically induced gas objects (SIGOs) are a class of early universe objects that have gained attention as a potential formation route for globular clusters. SIGOs have recently begun to be studied in the context of molecular hydrogen cooling, which is key to characterizing their structure and evolution. Studying the population-level properties of SIGOs with molecular cooling is important for understanding their potential for collapse and star formation, and for addressing whether SIGOs can survive to the present epoch. Here, we investigate the evolution of SIGOs before they form stars, using a combination of numerical and analytical analysis. We study timescales important to the evolution of SIGOs at a population level in the presence of molecular cooling. Revising the previous formulation for the critical density of collapse for SIGOs allows us to show that their prolateness tends to act as an inhibiting factor to collapse. We find that simulated SIGOs are limited by artificial two-body relaxation effects that tend to disperse them. We expect that SIGOs in nature will be longer lived compared to our simulations. Further, the fall-back timescale on which SIGOs fall into nearby dark matter halos, potentially producing a globular-cluster-like system, is frequently longer than their cooling timescale and the collapse timescale on which they shrink through gravity. Therefore, some SIGOs have time to cool and collapse outside of halos despite initially failing to exceed the critical density. From this analysis we conclude that SIGOs should form stars outside of halos in nonnegligible stream velocity patches in the universe
Understanding Dwarf Galaxies in order to Understand Dark Matter
Much progress has been made in recent years by the galaxy simulation
community in making realistic galaxies, mostly by more accurately capturing the
effects of baryons on the structural evolution of dark matter halos at high
resolutions. This progress has altered theoretical expectations for galaxy
evolution within a Cold Dark Matter (CDM) model, reconciling many earlier
discrepancies between theory and observations. Despite this reconciliation, CDM
may not be an accurate model for our Universe. Much more work must be done to
understand the predictions for galaxy formation within alternative dark matter
models.Comment: Refereed contribution to the Proceedings of the Simons Symposium on
Illuminating Dark Matter, to be published by Springe
DDO 216-A1: A Central Globular Cluster in a Low-luminosity Transition-type Galaxy
United States. National Aeronautics and Space Administration (HST GO-13768)United States. National Aeronautics and Space Administration (AST-1517226)United States. National Aeronautics and Space Administration (HST-AR-12836)United States. National Aeronautics and Space Administration (HST-AR-13888)United States. National Aeronautics and Space Administration (HST-AR-13896
The detection of sub-solar mass dark matter halos
Dark matter halos of sub-solar mass are the first bound objects to form in
cold dark matter theories. In this article, I discuss the present understanding
of "microhalos'', their role in structure formation, and the implications of
their potential presence, in the interpretation of dark matter experiments.Comment: 18 pages, 7 figures. Invited contribution to NJP Focus Issue on "Dark
Matter and Particle Physics
Star formation at the edge of the Local Group: a rising star formation history in the isolated galaxy WLM
We present the star formation history (SFH) of the isolated (D~970 kpc) Local
Group dwarf galaxy WLM measured from color-magnitude diagrams constructed from
deep Hubble Space Telescope imaging. Our observations include a central (0.5
) and outer field (0.7 ) that reach below the oldest main sequence
turnoff. WLM has no early dominant episode of star formation: 20% of its
stellar mass formed by ~12.5 Gyr ago (z~5). It also has an SFR that rises to
the present with 50% of the stellar mass within the most recent 5 Gyr (z<0.7).
There is evidence of a strong age gradient: the mean age of the outer field is
5 Gyr older than the inner field despite being only 0.4 kpc apart. Some models
suggest such steep gradients are associated with strong stellar feedback and
dark matter core creation. The SFHs of real isolated dwarf galaxies and those
from the the Feedback In Realistic Environment suite are in good agreement for
, but in worse agreement at lower
masses (). These differences may be
explainable by systematics in the models (e.g., reionization model) and/or
observations (HST field placement). We suggest that a coordinated effort to get
deep CMDs between HST/JWST (crowded central fields) and WFIRST (wide-area halo
coverage) is the optimal path for measuring global SFHs of isolated dwarf
galaxies.Comment: 13 pages, 13 Figures, 4 Tables. Re-submitted to MNRAS after
addressing the referee's comment
Antimatter and Gamma-rays from Dark Matter Annihilation
A brief review of the indirect detection signatures of dark matter is given.
In particular, detection methods of dark matter particle annihilation to
antimatter and gamma-rays are reviewed. With the GLAST satellite soon to be
launched, a crucial window in the energy range of a few GeV up to 300 GeV will
open. The good angular and energy resolution of the instrument means that
structures predicted by cold dark matter models can be searched for. Large,
currently planned ground-based imaging Cherenkov telescope arrays, may further
improve the limits, or discover a signal, if the current understanding of halo
dark matter structure is correct.Comment: 7p, one fig., invited talk at TAUP 2007, Sendai, Japan, to appear in
the Proceeding
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