220 research outputs found
High-Resolution Simulation on Structure Formation with Extremely Light Bosonic Dark Matter
An alternative bosonic dark matter model is examined in detail via
high-resolution simulations. These bosons have particle mass of order
and are non-interacting. If they do exist and can account for
structure formation, these bosons must be condensed into the Bose-Einstein
state and described by a coherent wave function. This matter, also known as
Fuzzy Dark Matter (Hu, Barkana & Gruzinov 2000),, is speculated to be able,
first, to eliminate the sub-galactic halos to solve the problem of
over-abundance of dwarf galaxies, and, second, to produce flat halo cores in
galaxies suggested by some observations. Our simulation results show that
although this extremely light bosonic dark matter indeed suppresses low-mass
halos, it can, to the contrary of expectation, yield singular halo cores. The
density profile of the singular halo is almost identical to the halo profile of
Navarro, Frenk & White (1997). Such a profile seems to be universal, in that it
can be produced via either accretion or merger.Comment: 21 pages, 10 figure
Recovering cores and cusps in dark matter haloes using mock velocity field observations
We present mock DensePak Integral Field Unit (IFU) velocity fields, rotation curves and halo fits for disc galaxies formed in spherical and triaxial cuspy dark matter haloes and spherical cored dark matter haloes. The simulated galaxies are ‘observed' under a variety of realistic conditions to determine how well the underlying dark matter halo can be recovered and to test the hypothesis that cuspy haloes can be mistaken for cored haloes. We find that the appearance of the velocity field is distinctly different depending on the underlying halo type. We also find that we can successfully recover the parameters of the underlying dark matter halo. Cuspy haloes appear cuspy in the data and cored haloes appear cored. Our results suggest that the cores observed using high-resolution velocity fields in real dark matter dominated galaxies are genuine and cannot be ascribed to systematic errors, halo triaxiality or non-circular motion
The Case Against Warm or Self-Interacting Dark Matter as Explanations for Cores in Low Surface Brightness Galaxies
Warm dark matter (WDM) and self-interacting dark matter (SIDM) are often
motivated by the inferred cores in the dark matter halos of low surface
brightness (LSB) galaxies. We test thermal WDM, non-thermal WDM, and SIDM using
high-resolution rotation curves of nine LSB galaxies. We fit these dark matter
models to the data and determine the halo core radii and central densities.
While the minimum core size in WDM models is predicted to decrease with halo
mass, we find that the inferred core radii increase with halo mass and also
cannot be explained with a single value of the primordial phase space density.
Moreover, if the core size is set by WDM particle properties, then even the
smallest cores we infer would require primordial phase space density values
that are orders of magnitude smaller than lower limits obtained from the Lyman
alpha forest power spectra. We also find that the dark matter halo core
densities vary by a factor of about 30 from system to system while showing no
systematic trend with the maximum rotation velocity of the galaxy. This
strongly argues against the core size being directly set by large
self-interactions (scattering or annihilation) of dark matter. We therefore
conclude that the inferred cores do not provide motivation to prefer WDM or
SIDM over other dark matter models.Comment: Accepted to ApJL; additions to Figs 3 and 4; minor changes to tex
Comparing the Dark Matter Halos of Spiral, Low Surface Brightness and Dwarf Spheroidal Galaxies
We consider dark masses measured from kinematic tracers at discrete radii in
galaxies for which baryonic contributions to overall potentials are either
subtracted or negligible. Recent work indicates that rotation curves due to
dark matter (DM) halos at intermediate radii in spiral galaxies are remarkably
similar, with a mean rotation curve given by
. Independent
studies show that while estimates of the dark mass of a given dwarf spheroidal
(dSph) galaxy are robust only near the half-light radius, data from the Milky
Way's (MW's) dSph satellites are consistent with a narrow range of mass
profiles. Here we combine published constraints on the dark halo masses of
spirals and dSphs and include available measurements of low surface brightness
galaxies for additional comparison. We find that most measured MW dSphs lie on
the extrapolation of the mean rotation curve due to DM in spirals. The union of
MW-dSph and spiral data appears to follow a mass-radius relation of the form
, or
equivalently a constant acceleration , spanning 0.02\la r \la 75 kpc. Evaluation at
specific radii immediately generates two results from the recent literature: a
common mass for MW dSphs at fixed radius and a constant DM central surface
density for galaxies ranging from MW dSphs to spirals. However, recent
kinematic measurements indicate that M31's dSph satellites are systematically
less massive than MW dSphs of similar size. Such deviations from what is
otherwise a surprisingly uniform halo relation presumably hold clues to
individual formation and evolutionary histories.Comment: ApJL in press (minor edits to text in order to match version in
press
High Resolution Optical Velocity Fields of Low Surface Brightness Galaxies and the Density Profiles of Dark Matter Halos
This dissertation investigates the behavior of cold dark matter (CDM) on galaxy scales. We present well-resolved Halpha velocity fields of the central regions of 17 dark matter-dominated low surface brightness (LSB) and dwarf galaxies observed with the DensePak Integrated Field Unit. We derive rotation curves from the two-dimensional data and compare them to published long-slit and HI rotation curves. We find broad consistency between the independent data sets. Under several assumptions about the velocity contribution from the baryons, we fit the dark matter component with cuspy NFW and cored pseudoisothermal halos. We find the data to be better described by cored dark matter halos. For the majority of galaxies, NFW halo fits either cannot be made or the implied concentrations are too low for LCDM. The shapes of the NFW rotation curves are also inconsistent with the galaxy rotation curves. We find that CDM predicts a substantial cusp mass excess near the centers of the galaxies and that the ratio of predicted to observed dark matter increases as baryons become more important. We investigate claims that systematic effects including beam smearing, slit misplacement and noncircular motions are responsible for slowly rising long-slit and HI rotation curves. We find the DensePak rotation curves to also be slowly rising, supporting the idea that this is an intrinsic feature of LSB rotation curves. We also model the two-dimensional NFW halo and test several modifications to the potential in an attempt to simultaneously reconcile both the NFW velocity field and rotation curve with observed galaxy data. We present mock DensePak velocity fields and rotation curves of axisymmetric and non-axisymmetric potentials. We find that a non-axisymmetric NFW potential with a constant axis ratio can reduce the cusp mass excess in the observed galaxy data, but the observer's line-of-sight must be along the minor axis of the potential, and the NFW pinch is not erased from the velocity field. We find that a non-axisymmetric NFW potential with a radially varying axis ratio tends to wash out the NFW pinch but introduces a twist to the velocity field
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