2 research outputs found
Halo mass - concentration relation from weak lensing
We perform a statistical weak lensing analysis of dark matter profiles around
tracers of halo mass from galactic- to cluster-size halos. In this analysis we
use 170,640 isolated ~L* galaxies split into ellipticals and spirals, 38,236
groups traced by isolated spectroscopic Luminous Red Galaxies (LRGs) and 13,823
MaxBCG clusters from the Sloan Digital Sky Survey (SDSS) covering a wide range
of richness. Together these three samples allow a determination of the density
profiles of dark matter halos over three orders of magnitude in mass, from
10^{12} M_{sun} to 10^{15} M_{sun}. The resulting lensing signal is consistent
with an NFW or Einasto profile on scales outside the central region. We find
that the NFW concentration parameter c_{200b} decreases with halo mass, from
around 10 for galactic halos to 4 for cluster halos. Assuming its dependence on
halo mass in the form of c_{200b} = c_0 [M/(10^{14}M_{sun}/h)]^{\beta}, we find
c_0=4.6 +/- 0.7 (at z=0.22) and \beta=0.13 +/- 0.07, with very similar results
for the Einasto profile. The slope (\beta) is in agreement with theoretical
predictions, while the amplitude is about two standard deviations below the
predictions for this mass and redshift, but we note that the published values
in the literature differ at a level of 10-20% and that for a proper comparison
our analysis should be repeated in simulations. We discuss the implications of
our results for the baryonic effects on the shear power spectrum: since these
are expected to increase the halo concentration, the fact that we see no
evidence of high concentrations on scales above 20% of the virial radius
suggests that baryonic effects are limited to small scales, and are not a
significant source of uncertainty for the current weak lensing measurements of
the dark matter power spectrum. [ABRIDGED]Comment: 17 pages, 5 figures, accepted to JCAP pending minor revisions that
are included in v2 here on arXi
The impact of baryons on the spins and shapes of dark matter haloes
We use numerical simulations to investigate how the statistical properties of
dark matter (DM) haloes are affected by the baryonic processes associated with
galaxy formation. We focus on how these processes influence the spin and shape
of a large number of DM haloes covering a wide range of mass scales, from
galaxies to clusters at redshifts zero and one, extending to dwarf galaxies at
redshift two. The haloes are extracted from the OverWhelmingly Large
Simulations, a suite of state-of-the-art high-resolution cosmological
simulations run with a range of feedback prescriptions. We find that the median
spin parameter in DM-only simulations is independent of mass, redshift and
cosmology. At z=0 baryons increase the spin of the DM in the central region
(<=0.25 r_200) by up to 30 per cent when feedback is weak or absent. This
increase can be attributed to the transfer of angular momentum from baryons to
the DM, but is no longer present at z=2. We also present fits to the mass
dependence of the DM halo shape at both low and high redshift. At z=0 the
sphericity (triaxiality) is negatively (positively) correlated with halo mass
and both results are independent of cosmology. Interestingly, these
mass-dependent trends are markedly weaker at z=2. While the cooling of baryons
acts to make the overall DM halo more spherical, stronger feedback
prescriptions tend to reduce the impact of baryons by reducing the central halo
mass concentration. More generally, we demonstrate a strongly positive
(negative) correlation between halo sphericity (triaxiality) and galaxy
formation efficiency, with the latter measured using the central halo baryon
fraction. In conclusion, our results suggest that the effects of baryons on the
DM halo spin and shape are minor when the effects of cooling are mitigated, as
required by realistic models of galaxy formation, although they remain
significant for the inner halo.Comment: 15 pages, 8 figures; accepted for publication in MNRA