1,293 research outputs found
Thermodynamical properties of the ICM from hydrodynamical simulations
Modern hydrodynamical simulations offer nowadays a powerful means to trace
the evolution of the X-ray properties of the intra-cluster medium (ICM) during
the cosmological history of the hierarchical build up of galaxy clusters. In
this paper we review the current status of these simulations and how their
predictions fare in reproducing the most recent X-ray observations of clusters.
After briefly discussing the shortcomings of the self-similar model, based on
assuming that gravity only drives the evolution of the ICM, we discuss how the
processes of gas cooling and non-gravitational heating are expected to bring
model predictions into better agreement with observational data. We then
present results from the hydrodynamical simulations, performed by different
groups, and how they compare with observational data. As terms of comparison,
we use X-ray scaling relations between mass, luminosity, temperature and
pressure, as well as the profiles of temperature and entropy. The results of
this comparison can be summarised as follows: (a) simulations, which include
gas cooling, star formation and supernova feedback, are generally successful in
reproducing the X-ray properties of the ICM outside the core regions; (b)
simulations generally fail in reproducing the observed ``cool core'' structure,
in that they have serious difficulties in regulating overcooling, thereby
producing steep negative central temperature profiles. This discrepancy calls
for the need of introducing other physical processes, such as energy feedback
from active galactic nuclei, which should compensate the radiative losses of
the gas with high density, low entropy and short cooling time, which is
observed to reside in the innermost regions of galaxy clusters.Comment: 26 pages, 12 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 13; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
The effect of AGN feedback on the halo mass function
[Abridged.] We investigate baryon effects on the halo mass function (HMF),
with emphasis on the role played by AGN feedback. Halos are identified with
both Friends-of-Friends (FoF) and Spherical Overdensity (SO) algorithms. We
embed the standard SO algorithm into a memory-controlled frame program and
present the {\bf P}ython spher{\bf I}c{\bf A}l {\bf O}verdensity code ---
{\small PIAO}.
For both FoF and SO halos, the effect of AGN feedback is that of suppressing
the HMFs to a level even below that of Dark Matter simulations. The ratio
between the HMFs in the AGN and in the DM simulations is at
overdensity , a difference that increases at higher overdensity
, with no significant redshift and mass dependence. A decrease
of the halo masses ratio with respect to the DM case induces the decrease of
the HMF in the AGN simulation. The shallower inner density profiles of halos in
the AGN simulation witnesses that mass reduction is induced by the sudden
displacement of gas induced by thermal AGN feedback. We provide fitting
functions to describe halo mass variations at different overdensities, which
can recover the HMFs with a residual random scatter per cent for halo
masses larger than .Comment: 16 pages, 11 figures. Matches to MNRAS published version, typo
corrected in the fitting functio
The baryon fraction in hydrodynamical simulations of galaxy clusters
We study the baryon mass fraction in a set of hydrodynamical simulations of
galaxy clusters performed using the Tree+SPH code GADGET-2. We investigate the
dependence of the baryon fraction upon the radiative cooling, star formation,
feedback through galactic winds, conduction and redshift. Both the cold stellar
component and the hot X-ray emitting gas have narrow distributions that, at
large cluster-centric distances r>R500, are nearly independent of the physics
included in the simulations. Only the non-radiative runs reproduce the gas
fraction inferred from observations of the inner regions (r ~ R2500) of massive
clusters. When cooling is turned on, the excess star formation is mitigated by
the action of galactic winds, but yet not by the amount required by
observational data. The baryon fraction within a fixed overdensity increases
slightly with redshift, independent of the physical processes involved in the
accumulation of baryons in the cluster potential well. In runs with cooling and
feedback, the increase in baryons is associated with a larger stellar mass
fraction that arises at high redshift as a consequence of more efficient gas
cooling. For the same reason, the gas fraction appears less concentrated at
higher redshift. We discuss the possible cosmological implications of our
results and find that two assumptions generally adopted, (1) mean value of Yb =
fb / (Omega_b/Omega_m) not evolving with redshift, and (2) a fixed ratio
between f_star and f_gas independent of radius and redshift, might not be
valid. In the estimate of the cosmic matter density parameter, this implies
some systematic effects of the order of Delta Omega_m/Omega_m < +0.15 for
non-radiative runs and Delta Omega_m/Omega_m ~ +0.05 and < -0.05 for radiative
simulations.Comment: 10 pages, to appear in MNRA
Radiative feedback and cosmic molecular gas: the role of different radiative sources
We present results from multifrequency radiative hydrodynamical chemistry
simulations addressing primordial star formation and related stellar feedback
from various populations of stars, stellar energy distributions (SEDs) and
initial mass functions. Spectra for massive stars, intermediate-mass stars and
regular solar-like stars are adopted over a grid of 150 frequency bins and
consistently coupled with hydrodynamics, heavy-element pollution and
non-equilibrium species calculations. Powerful massive population III stars are
found to be able to largely ionize H and, subsequently, He and He, causing
an inversion of the equation of state and a boost of the Jeans masses in the
early intergalactic medium. Radiative effects on star formation rates are
between a factor of a few and 1 dex, depending on the SED. Radiative processes
are responsible for gas heating and photoevaporation, although emission from
soft SEDs has minor impacts. These findings have implications for cosmic gas
preheating, primordial direct-collapse black holes, the build-up of "cosmic
fossils" such as low-mass dwarf galaxies, the role of AGNi during reionization,
the early formation of extended disks and angular-momentum catastrophe.Comment: 19 pages on MNRA
- …