7 research outputs found
Entropy "floor" and effervescent heating of intracluster gas
Recent X-ray observations of clusters of galaxies have shown that the entropy
of the intracluster medium (ICM), even at radii as large as half the virial
radius, is higher than that expected from gravitational processes alone. This
is thought to be the result of nongravitational processes influencing the
physical state of the ICM. In this paper, we investigate whether heating by a
central AGN can explain the distribution of excess entropy as a function of
radius. The AGN is assumed to inject buoyant bubbles into the ICM, which heat
the ambient medium by doing pdV work as they rise and expand. Several authors
have suggested that this "effervescent heating" mechanism could allow the
central regions of clusters to avoid the ``cooling catastrophe''. Here we study
the effect of effervescent heating at large radii. Our calculations show that
such a heating mechanism is able to solve the entropy problem. The only free
parameters of the model are the time-averaged luminosity and the AGN lifetime.
The results are mainly sensitive to the total energy injected into the cluster.
Our model predicts that the total energy injected by AGN should be roughly
proportional to the cluster mass. The expected correlation is consistent with a
linear relation between the mass of the central black hole(s) and the mass of
the cluster, which is reminiscent of the Magorrian relation between the black
hole and bulge mass.Comment: accepted for Ap
AGN heating, thermal conduction and Sunyaev-Zeldovich effect in galaxy groups and clusters
(abridged) We investigate in detail the role of active galactic nuclei on the
physical state of the gas in galaxy groups and clusters, and the implications
for anisotropy in the CMB from Sunyaev-Zeldovich effect. We include the effect
of thermal conduction, and find that the resulting profiles of temperature and
entropy are consistent with observations. Unlike previously proposed models,
our model predicts that isentropic cores are not an inevitable consequence of
preheating. The model also reproduces the observational trend for the density
profiles to flatten in lower mass systems. We deduce the energy E_agn required
to explain the entropy observations as a function of mass of groups and
clusters M_cl and show that E_agn is proportional to M_cl^alpha with alpha~1.5.
We demonstrate that the entropy measurements, in conjunction with our model,
can be translated into constraints on the cluster--black hole mass relation.
The inferred relation is nonlinear and has the form M_bh\propto M_cl^alpha.
This scaling is an analog and extension of a similar relation between the black
hole mass and the galactic halo mass that holds on smaller scales. We show that
the central decrement of the CMB temperature is reduced due to the enhanced
entropy of the ICM, and that the decrement predicted from the plausible range
of energy input from the AGN is consistent with available data of SZ decrement.
We show that AGN heating, combined with the observational constraints on
entropy, leads to suppression of higher multipole moments in the angular power
spectrum and we find that this effect is stronger than previously thought.Comment: accepted for publication in The Astrophysical Journa
Impact of Systematic Errors in Sunyaev-Zel'dovich Surveys of Galaxy Clusters
Future high-resolution microwave background measurements hold the promise of
detecting galaxy clusters throughout our Hubble volume through their
Sunyaev-Zel'dovich (SZ) signature, down to a given limiting flux. The number
density of galaxy clusters is highly sensitive to cluster mass through
fluctuations in the matter power spectrum, as well as redshift through the
comoving volume and the growth factor. This sensitivity in principle allows
tight constraints on such quantities as the equation of state of dark energy
and the neutrino mass. We evaluate the ability of future cluster surveys to
measure these quantities simultaneously when combined with PLANCK-like CMB
data. Using a simple effective model for uncertainties in the cluster mass-SZ
flux relation, we evaluate systematic shifts in cosmological constraints from
cluster SZ surveys. We find that a systematic bias of 10% in cluster mass
measurements can give rise to shifts in cosmological parameter estimates at
levels larger than the statistical errors. Systematic errors are
unlikely to be detected from the mass and redshift dependence of cluster number
counts alone; increasing survey size has only a marginal effect. Implications
for upcoming experiments are discussed.Comment: 12 pages, 6 figures; accepted to JCAP; revised to match submitted
versio