317 research outputs found
Dark matter cores and cusps in spiral galaxies and their explanations
We compare proposed solutions to the core vs cusp issue of spiral galaxies, which has also been framed as a diversity problem, and demonstrate that the cuspiness of dark matter halos is correlated with the stellar surface brightness. We compare the rotation curve fits to the SPARC sample from a self-interacting dark matter (SIDM) model, which self-consistently includes the impact of baryons on the halo profile, and hydrodynamical N-body simulations with cold dark matter (CDM). The SIDM model predicts a strong correlation between the core size and the stellar surface density, and it provides the best global fit to the data. The CDM simulations without strong baryonic feedback effects fail to explain the large dark matter cores seen in low surface brightness galaxies. On the other hand, with strong feedback, CDM simulations do not produce galaxy analogs with high stellar and dark matter densities, and therefore they have trouble in explaining the rotation curves of high surface brightness galaxies. This implies that current feedback implementations need to be modified. We also explicitly show how the concentration-mass and stellar-to-halo mass relations together lead to a radial acceleration relation (RAR) in an averaged sense, and reiterate the point that the RAR does not capture the diversity of galaxy rotation curves in the inner regions. These results make a strong case for SIDM as the explanation for the cores and cusps of field galaxies
Cosmological Information from Lensed CMB Power Spectra
Gravitational lensing distorts the cosmic microwave background (CMB)
temperature and polarization fields and encodes valuable information on
distances and growth rates at intermediate redshifts into the lensed power
spectra. The non-Gaussian bandpower covariance induced by the lenses is
negligible to l=2000 for all but the B polarization field where it increases
the net variance by up to a factor of 10 and favors an observing strategy with
3 times more area than if it were Gaussian. To quantify the cosmological
information, we introduce two lensing observables, characterizing nearly all of
the information, which simplify the study of non-Gaussian impact, parameter
degeneracies, dark energy models, and complementarity with other cosmological
probes. Information on the intermediate redshift parameters rapidly becomes
limited by constraints on the cold dark matter density and initial amplitude of
fluctuations as observations improve. Extraction of this information requires
deep polarization measurements on only 5-10% of the sky, and can improve Planck
lensing constraints by a factor of ~2-3 on any one of the parameters w_0, w_a,
Omega_K, sum(m_nu) with the others fixed. Sensitivity to the curvature and
neutrino mass are the highest due to the high redshift weight of CMB lensing
but degeneracies between the parameters must be broken externally.Comment: 19 pages, 16 figures, submitted to PR
Precision Cosmology and the Density of Baryons in the Universe
Big-bang Nucleosynthesis (BBN) and Cosmic Microwave Background (CMB) anisotropy measurements give independent, accurate measurements of the baryon density and can test the framework of the standard cosmology. Early CMB data are consistent with the longstanding conclusion from BBN that baryons constitute a small fraction of matter in the Universe. We clarify precisely what the two methods determine, and point out that differing values for the baryon density need not indicate inconsistency if the entropy has changed since BBN. Such an entropy change has a clear signature in the CMB anisotropy
Are Light Sterile Neutrinos Preferred or Disfavored by Cosmology?
We find that the viability of a cosmological model that incorporates 2
sterile neutrinos with masses around 1 eV each, as favored by global neutrino
oscillation analyses including short baseline results, is significantly
dependent on the choice of datasets included in the analysis and the ability to
control the systematic uncertainties associated with these datasets. Our
analysis includes a variety of cosmological probes including the cosmic
microwave background (WMAP7+SPT), Hubble constant (HST), galaxy power spectrum
(SDSS-DR7), and supernova distances (SDSS and Union2 compilations). In the
joint observational analysis, our sterile neutrino model is equally favored as
a LCDM model when using the MLCS light curve fitter for the supernova
measurements, and strongly disfavored by the data at \Delta\chi^2 ~ 18 when
using the SALT2 fitter. When excluding the supernova measurements, the sterile
neutrino model is disfavored by the other datasets at \Delta\chi^2 ~ 12, and at
best becomes mildly disfavored at \Delta\chi^2 ~ 3 when allowing for curvature,
evolving dark energy, additional relativistic species, running of the spectral
index, and freedom in the primordial helium abundance. No single additional
parameter accounts for most of this effect. Therefore, if laboratory
experiments continue to favor a scenario with roughly eV mass sterile
neutrinos, and if this becomes decisively disfavored by cosmology, then a more
exotic cosmological model than explored here may become necessary.Comment: 10 pages, 3 figures. Minor refinements, reflects version accepted for
publication in PR
Strong Evidence that the Galactic Bulge is Shining in Gamma Rays
There is growing evidence that the Galactic Center Excess identified in the
-LAT gamma-ray data arises from a population of faint
astrophysical sources. We provide compelling supporting evidence by showing
that the morphology of the excess traces the stellar over-density of the
Galactic bulge. By adopting a template of the bulge stars obtained from a
triaxial 3D fit to the diffuse near-infrared emission, we show that it is
detected at high significance. The significance deteriorates when either the
position or the orientation of the template is artificially shifted, supporting
the correlation of the gamma-ray data with the Galactic bulge. In deriving
these results, we have used more sophisticated templates at low-latitudes for
the bubbles compared to previous work and the
three-dimensional Inverse Compton (IC) maps recently released by the team. Our results provide strong constraints on Millisecond Pulsar
(MSP) formation scenarios proposed to explain the excess. We find that an
scenario, in which some of the relevant binaries
are and the rest are formed , is
preferred over a primordial-only formation scenario at confidence
level. Our detailed morphological analysis also disfavors models of the
disrupted globular clusters scenario that predict a spherically symmetric
distribution of MSPs in the Galactic bulge. For the first time, we report
evidence of a high energy tail in the nuclear bulge spectrum that could be the
result of IC emission from electrons and positrons injected by a population of
MSPs and star formation activity from the same site.Comment: 21 pages, 13 figures, V2: Minor changes to match submitted version,
V3: matches JCAP published versio
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