arXiv subjects

Pasquale Mazzotta

Publications and source records attributed to Pasquale Mazzotta.

43 records · Page 3Linked to original sources

arXiv2004

Predictions for high-frequency radio surveys of extragalactic sources

We present detailed predictions of the contributions of the various source populations to the counts at frequencies of tens of GHz. New evolutionary models are worked out for flat-spectrum radio quasars, BL Lac objects, and steep-spectrum sources. Source populations characterized by spectra peaking at high radio frequencies, such as extreme GPS sources, ADAF/ADIOS sources and early phases of gamma-ray burst afterglows are also dealt with. The counts of different populations of star-forming galaxies (normal spirals, starbursts, high-z galaxies detected by SCUBA and MAMBO surveys, interpreted as proto-spheroidal galaxies) are estimated taking into account both synchrotron and free-free emission, and dust re-radiation. Our analysis is completed by updated counts of Sunyaev-Zeldovich effects in clusters of galaxies and by a preliminary estimate of galactic-scale Sunyaev-Zeldovich signals associated to proto-galactic plasma.

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arXiv2004

Quenching Cluster Cooling Flows with Recurrent Hot Plasma Bubbles

The observed cooling rate of hot gas in clusters is much lower than that inferred from the gas density profiles. This suggests that the gas is being heated by some source. We use an adaptive-mesh refinement code (FLASH) to simulate the effect of multiple, randomly positioned, injections of thermal energy within 50 kpc of the centre of an initially isothermal cluster with mass M_200=3x10^(14) Msol and kT=3.1 keV. We have performed eight simulations with spherical bubbles of energy generated every 10^8 years, over a total of 1.5 Gyr. Each bubble is created by injecting thermal energy steadily for 10^7 years; the total energy of each bubble ranges from 0.1--3x10^(60) erg, depending on the simulation. We find that 2x10^(60) erg per bubble (corresponding to a average power of 6.3x10^(44) erg/s) effectively balances energy loss in the cluster and prevents the accumulation of gas below kT=1 keV from exceeding the observational limits of 30 Msol/yr. This injection rate is comparable to the radiated luminosity of the cluster, and the required energy and periodic timescale of events are consistent with observations of bubbles produced by central AGN in clusters. The effectiveness of this process depends primarily on the total amount of injected energy and the initial location of the bubbles, but is relatively insensitive to the exact duty cycle of events.

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arXiv2004

A Hubble Space Telescope Lensing Survey of X-ray Luminous Galaxy Clusters: IV. Mass, Structure and Thermodynamics of Cluster Cores at z=0.2

We present a comprehensive space-based study of ten X-ray luminous galaxy clusters (L_X>=8e44erg/s[0.1-2.4keV]) at z=0.2. Hubble Space Telescope observations reveal numerous gravitationally-lensed arcs for which we present four new spectroscopic redshifts, bringing the total to thirteen confirmed arcs in this cluster sample. We combine the multiple-image systems with the weakly-sheared background galaxies to model the total mass distribution in the cluster cores (R<=500kpc). These models are complemented by high-resolution X-ray data from Chandra and used to develop quantitative criteria to classify the clusters as relaxed or unrelaxed. Formally, (30+/-20)% of the clusters form a homogeneous sub-sample of relaxed clusters; the remaining (70+/-20)% are unrelaxed and are a much more diverse population. Most of the clusters therefore appear to be experiencing a cluster-cluster merger, or relaxing after such an event. We also study the normalization and scatter of scaling relations between cluster mass, luminosity and temperature. The scatter in these relations is dominated by the unrelaxed clusters and is typically sigma~0.4. Most notably, we detect 2-3 times more scatter in the mass-temperature relation than theoretical simulations and models predict. The observed scatter is also asymmetric - the unrelaxed systems are systematically 40% hotter than the relaxed clusters at 2.5 sigma significance. This structural segregation should be a major concern for experiments designed to constrain cosmological parameters using galaxy clusters. Overall our results are consistent with a scenario of cluster-cluster merger induced boosts to cluster X-ray luminosities and temperatures. [Abridged]

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arXiv2004

The faint X-ray Source Population near 3C 295

We present a statistical analysis of the Chandra observation of the source field around the 3C 295 galaxy cluster (z=0.46) aimed at the search for clustering of X-ray sources. We applied three different methods of analysis, all suggesting a strong clustering in the field on scales of a few arcmin. In particular 1) the logN-logS computed separately for the four ACIS-I chips reveals that there is a significant (3.2 sigma in the 0.5-2 keV, 3.3 sigma in the 2-10 keV and 4.0 sigma in the 0.5-10 keV band) excess of sources to the North-North East and a void to the South of the central cluster. 2) the two point, two-dimensional Kolmogorov-Smirnov (KS) test, shows the probability that the sources are uniformly distributed is only a few percent. 3) a strong spatial correlation emerges from the study of the angular correlation function of the field: the angular correlation function (ACF) shows a clear signal on scales of 0.5 - 5 arcmin, correlation angle in the 0.5-7 keV band theta = 8.5^{+6.5}_{-4.5}, 90% confidence limit (assuming a power law ACF with slope gamma=1.8). This correlation angle is 2 times higher than that of a sample of 8 ACIS-I field at the 2.5 sigma confidence level. The above scales translate to 0.2 - 2 Mpc at the cluster redshift, higher than the typical cluster core radius, and more similar to the size of a ``filament'' of the large scale structure.

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arXiv2003

A Chandra Study of the Complex Structure in the Core of 2A 0335+096

We present a Chandra observation of the central (r< 200kpc) region of the cluster of galaxies 2A 0335+096, rich in interesting phenomena. On large scales (r> 40kpc), the X-ray surface brightness is symmetric and slightly elliptical. The cluster has a cool dense core; the radial temperature gradient varies with position angle. The radial metallicity profile shows a pronounced central drop and an off-center peak. Similarly to many clusters with dense cores, 2A 0335+096 hosts a cold front at r\approx 40kpc south of the center. The gas pressure across the front is discontinuous by a factor A_P=1.6\pm 0.3, indicating that the cool core is moving with respect to the ambient gas with a Mach number M\approx 0.75\pm 0.2. The central dense region inside the cold front shows an unusual X-ray morphology, which consists of a number of X-ray blobs and/or filaments on scales \gtrsim 3kpc, along with two prominent X-ray cavities. The X-ray blobs are not correlated with either the optical line emission (Hα+[NII]), member galaxies or radio emission. Deprojected temperature of the dense blobs is consistent with that of the less dense ambient gas, so these gas phases do not appear to be in thermal pressure equilibrium. An interesting possibility is a significant, unseen non-thermal pressure component in the inter-blob gas, possibly arising from the activity of the central AGN. We discuss two models for the origin of the gas blobs -- hydrodynamic instabilities caused by the observed motion of the gas core, or ``bubbling'' of the core caused by multiple outbursts of the central AGN.

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arXiv2002

Chandra Observation of a 300 kpc Hydrodynamic Instability in the Intergalactic Medium of the Merging Cluster of Galaxies A3667

We present results from the combination of two Chandra pointings of the central region of the cluster of galaxies A3667. From the data analysis of the first pointing Vikhlinin et al. reported the discovery of a prominent cold front which is interpreted as the boundary of a cool gas cloud moving through the hotter ambient gas. Vikhlinin et al. discussed the role of the magnetic fields in maintaining the apparent dynamical stability of the cold front over a wide sector at the forward edge of the moving cloud and suppressing transport processes across the front. In this Letter, we identify two new features in the X-ray image of A3667: i) a 300 kpc arc-like filamentary X-ray excess extending from the cold gas cloud border into the hotter ambient gas; ii) a similar arc-like filamentary X-ray depression that develops inside the gas cloud. The temperature map suggests that the temperature of the filamentary excess is consistent with that inside the gas cloud while the temperature of the depression is consistent with that of the ambient gas. We suggest that the observed features represent the first evidence for the development of a large scale hydrodynamic instability in the cluster atmosphere resulting from a major merger. This result confirms previous claims for the presence of a moving cold gas cloud into the hotter ambient gas. Moreover it shows that, although the gas mixing is suppressed at the leading edge of the subcluster due to its magnetic structure, strong turbulent mixing occurs at larger angles to the direction of motion. We show that this mixing process may favor the deposition of a nonnegligible quantity of thermal energy right in the cluster center, affecting the development of the central cooling flow.

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arXiv2002

Development of Hydrodynamic Instability in the Intergalactic Medium of the Merging Cluster of Galaxies A3667

A3667, a spectacular merger cluster, was observed by Chandra twice. In this paper we review the main results of the analysis of these observations. In particular we show evidence for the presence in the cluster of a 300 kpc Kelvin-Helmholtz hydrodynamic instability. We discuss the development of such instability and the structure of the intracluster magnetic filed in light of a self-consistent cluster dynamical model.

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