The Moderate Cooling Flow Model and Feedback in Galaxy Formation

For the recent four years we have been studying feedback heating in cooling flow (CF) clusters by AGN activity that inflate bubbles by jets; this short contribution to a meeting summarizes our main results. To achieve our results we had to self-consistently inflate the bubbles with jets, rather than inject them artificially. Our main results are as follows (1) Feedback mechanisms that are based on Bondi accretion fail. Instead, the accretion to the central super-massive black hole (SMBH) is in the form of cold dense blobs that fall-in from an extended region. (2) Slow massive wide (SMW) jets, or rapidly precessing jets, can inflate bubbles similar to those observed in CF clusters. (3) Contrary to some claims in the literature, the inflated bubbles are stable for a relatively long time, becoming unstable only at later times. (4) A single bubble inflation episode excites multiple sound waves and shocks. These can then heat the intracluster medium (ICM). (5) Mixing of the bubble material to the ICM is efficient, and can serve as a main heating channel. (6) The heating processes work in all directions, and can explain the heating of the ICM in CF in clusters and in galaxies.Comment: To appear in proceedings of "The Monster's Fiery Breath", Eds. Sebastian Heinz & Eric Wilcots (AIP conference series

Feedback Heating with Slow Jets in Cooling Flow Clusters

We propose a scenario in which a large fraction, or even most, of the gas cooling to low temperatures of T<10^4 K in cooling flow clusters, directly gains energy from the central black hole. Most of the cool gas is accelerated to non-relativistic high velocities, v ~ 10^3-10^4 km/sec, after flowing through, or close to, an accretion disk around the central black hole. A poorly collimated wind (or double not-well collimated opposite jets) is formed. According to the proposed scenario, this gas inflates some of the X-ray deficient bubbles, such that the average gas temperature inside these bubbles (cavities) in cooling flow clusters is kT_b ~< 100 keV. A large fraction of these bubbles will be very faint, or not detectable, in the radio. The bright rims of these weak smaller bubbles will appear as ripples. We suggest that the X-ray ripples observed in the Perseus cluster, for example, are not sound waves, but rather the rims of radio-faint weak bubbles which are only slightly hotter than their environment. This scenario is incorporated into the moderate cooling flow model; although not a necessary ingredient in that model, it brings it to better agreement with observations. In the moderate cooling flow model a cooling flow does exist, but the mass cooling rate is ~<10% of that in old versions of cooling flow models.Comment: The Astrophysical Journal, in pres

Spin and magnetism in old neutron stars

The thermal, spin and magnetic evolution of neutron stars in the old low mass binaries is first explored. Recycled to very short periods via accretion torques, the neutron stars lose their magnetism progressively. If accretion proceeds undisturbed for 100 Myrs these stars can rotate close to break up with periods far below the minimum observed of 1.558 ms. We investigate their histories using population synthesis models to show that a tail should exist in the period distribution below 1.558 ms. The search of these ultrafastly spinning neutron stars as pulsars can help discriminating among the various equations of state for nuclear matter, and can shed light into the physics of binary evolution. The evolution of isolated neutron stars in the Galaxy is explored beyond the pulsar phase. Moving through the tenuous interstellar medium, these old solitary neutron stars lose their rotational energy. Whether also their magnetism fades is still a mystery. A population synthesis model has revealed that only a tiny fraction of them is able to accrete from the interstellar medium, shining in the X-rays. There is the hope that these solitary stars will eventually appear as faint sources in the Chandra sky survey. This might give insight on the long term evolution of the magnetic field in isolated objects.Comment: 28 pages, 11 PostScript figures. To be published in "Physics of Neutron Star Interiors" (Lecture Notes in Physics), ed. D. Blaschke, N.K. Glendenning and A. Sedrakian (Springer, 2001

The population of ULXs in the spiral galaxy NGC 2276

We present results for X-ray point sources in the Sc galaxy NGC 2276, obtained by analyzing Chandra data. The galaxy is known to be very active in many wavelengths, possibly due to gravitational interaction with the central elliptical of the group, NGC 2300. However, previous XMM-Newton observations resulted in the detection of only one bright ULX and extended hot gas emission. We present here the X-ray population in NGC 2276 which comprises 17 sources. We found that 6 of them are new ULX sources in this spiral galaxy resolved for the first time by Chandra. We constructed the Luminosity Function that can be interpreted as mainly due of High Mass X-ray binaries, and estimate the Star Formation rate (SFR) to be SFR ~ 5-10 M_sun/yr.Comment: 4 pages, 4 figures, Proceedings of the meeting 'Ultra-Luminous X-ray sources and Middle Weight Black Holes', ESAC, Madrid, Spain, May 201

SMAUG: a new technique for the deprojection of galaxy clusters

This paper presents a new technique for reconstructing the spatial distributions of hydrogen, temperature and metal abundance of a galaxy cluster. These quantities are worked out from the X-ray spectrum, modeled starting from few analytical functions describing their spatial distributions. These functions depend upon some parameters, determined by fitting the model to the observed spectrum. We have implemented this technique as a new model in the XSPEC software analysis package. We describe the details of the method, and apply it to work out the structure of the cluster A1795. We combine the observation of three satellites, exploiting the high spatial resolution of Chandra for the cluster core, the wide collecting area of XMM-Newton for the intermediate regions and the large field of view of Beppo-SAX for the outer regions. We also test the validity and precision of our method by i) comparing its results with those from a geometrical deprojection, ii) examining the spectral residuals at different radii of the cluster and iii) reprojecting the unfolded profiles and comparing them directly to the measured quantities. Our analytical method yields the parameters defining the spatial functions directly from the spectra. Their explicit knowledge allows a straightforward derivation of other indirect physical quantities like the gravitating mass, as well as a fast and easy estimate of the profiles uncertainties.Comment: 24 pages, 11 figures, 3 tables; emulateapj; accepted for publication in the Astrophysical Journa

Inflating Fat Bubbles in Clusters of Galaxies by Wide Jets

We conduct two-dimensional hydrodynamical simulations of jets expanding in the intra-cluster medium (ICM). We find that for a fat, i.e. more or less spherical, bubble attached to the center to be formed the jet should have high momentum flux and a large opening angle. Typically, the half opening angle should be >50 degrees, and the large momentum flux requires a jet speed of \~10,000 km/sec. The inflation process involves vortices and local instabilities which mix some ICM with the hot bubble. These results predict that most of the gas inside the bubble has a temperature of 3x10^8<T<3x10^9 K, and that large quantities of the cooling gas in cooling flow clusters are expelled back to the intra-cluster medium, and heated up. The magnetic fields and relativistic electrons that produce the synchrotron radio emission might be formed in the shock wave of the jet.Comment: Submitted to ApJ Letter