P. Mazzotta - Academia.edu (original) (raw)

Papers by P. Mazzotta

We present preliminary results from a Chandra X-ray Observatory study of the field X-ray source p... more We present preliminary results from a Chandra X-ray Observatory study of the field X-ray source populations in 3 different fields: two include the two medium-redshift (z~0.5) clusters of galaxies 3C 295 and RXJ003033.2+261819, and the third is a non-cluster field with similar exposure time. Surprisingly, the 0.5 - 2 keV source surface densities (~900 - 1200 sources deg-2 at a

The Astrophysical Journal, 2008

The X-ray measurements of the intra-cluster medium metallicity are becoming more and more frequen... more The X-ray measurements of the intra-cluster medium metallicity are becoming more and more frequent due to the availability of powerful X-ray telescope with excellent spatial and spectral resolutions. The information which can be extracted from the measurements of the α-elements, like Oxygen, Magnesium and Silicon with respect to the Iron abundance is extremely important to better understand the stellar formation and its evolutionary history. In this paper we investigate possible source of bias or systematic effects connected to the plasma physics when recovering metal abundances from X-ray spectra. To do this we analyze 6 simulated galaxy clusters processed through the new version of our X-ray MAp Simulator (X-MAS), which allows to create mock XMM-Newton EPIC MOS1 and MOS2 observations. By comparing the spectroscopic results inferred by the X-ray spectra to the expected values directly obtained from the original simulation we find that: i) the Iron is recovered with high accuracy for both hot (T > 3 keV) and cold (T < 2 keV) systems; at intermediate temperatures, however, we find a systematic overestimate which depends inversely on the number counts; ii) Oxygen is well recovered in cold clusters, while in hot systems the X-ray measurement may overestimate the true value by a factor up to 2-3; iii) Being a weak line, the measurement of Magnesium is always difficult; despite of this, for cold systems (i.e. with T < 2 keV) we do not find any systematic behavior, while for very hot systems (i.e. with T > 5 keV) the spectroscopic measurement may strongly overestimate the true value up to a factor of 4; iv) Silicon is well recovered for all the clusters in our sample. We investigate in detail the nature of the systematic effects and biases found performing XSPEC simulations. We conclude that they are mainly connected with the multi-temperature nature of the projected observed spectra and to the intrinsic limitation of the XMM-Newton-EPIC spectral resolution that does not always allow to disentangle among the emission lines produced by different elements.

Astronomy and Astrophysics, 2008

Aims. Using a newly developed algorithm, we map, to the highest angular resolution allowed by the... more Aims. Using a newly developed algorithm, we map, to the highest angular resolution allowed by the data, the temperature structure of the intra-cluster medium (ICM) within a nearly complete X-ray flux limited sample of galaxy clusters in the redshift range between z = 0.045 and z = 0.096. Our sample contains seven bright clusters of galaxies observed with XMM-Newton: Methods. We use a multi-scale spectral mapping algorithm especially designed to map spectroscopic observables from Xray extended emission of the ICM. By means of a wavelet analysis, this algorithm couples spatially resolved spectroscopy with a structure detection approach. Derived from a former algorithm using Haar wavelets, our algorithm is now implemented with B-spline wavelets in order to perform a more regular analysis of the signal. Compared to other adaptive algorithms, our method has the advantage of analysing spatially the gas temperature structure itself, instead of being primarily driven by the geometry of gas brightness. Results. For the four clusters in our sample that are major mergers, we find a rather complex thermal structure with strong thermal variations consistent with their dynamics. For two of them, A2065 and A2256, we perform a 3-d analysis of cold front-like features evidenced from the gas temperature and brightness maps. Furthermore, we detect a significant non-radial thermal structure outside the cool core region of the other 3 more "regular" clusters, with relative amplitudes of about about 10 % and typical sizes ranging between 2 and 3 arcmin. We investigate possible implications of this thermal structure on the mass estimates, by extracting the surface brightness and temperature profiles from complementary sectors in the "regular" clusters A1795 and A2029, corresponding to hottest and coldest regions in the maps. For A2029, the temperature and surface brightness gradients seem to compensate each other, leading to a consistent mass profile. For A1795, however, the temperature structure leads to a significant mass discrepancy in the innermost cluster region. The third "regular" cluster, A478, is located in a particular sky region characterised by strong variations of neutral hydrogen column density, Nh, even on angular scales smaller than the cluster itself. For this cluster, we derive a spectroscopic Nh map and investigate the origin of Nh structure by discussing its correlation with galactic emission of dust in the infrared.

Astronomy and Astrophysics, 2007

Aims. We present a radio morphological study and spectral analysis for a sample of 13 cD galaxies... more Aims. We present a radio morphological study and spectral analysis for a sample of 13 cD galaxies in rich and poor clusters of galaxies. Methods. Our study is based on new high sensitivity Giant Metrewave Radio Telescope (GMRT) observations at 1.28 GHz, 610 MHz and 235 MHz, and on archival data. From a statistical sample of cluster cD galaxies we selected those sources with little information available in the literature and promising for the detection of aged radio emission. Beyond the high sensitivity images for all 13 radio galaxies, we present also a detailed spectral analysis for 7 of them. Results. We found a variety of morphologies and linear sizes, as typical for radio galaxies in the radio power range sampled here (low to intermediate power radio galaxies). The spectral analysis shows that 10/13 radio galaxies have steep radio spectrum, with spectral index α ≥ 1. In general, the radiative ages and growth velocities are consistent with previous findings that the evolution of radio galaxies at the cluster centres is affected by the dense external medium (i.e. low growth velocities and old ages). We suggest that the dominant galaxies in A 2622 and MKW 03s are dying radio sources, which at present are not fed by nuclear activity. On the other hand, the spectacular source at the centre of A 2372 might be a very interesting example of restarted radio galaxy. For this source we estimated a life cycle of the order of 10 6 yr.

Astronomy and Astrophysics, 2005

We present detailed predictions of the contributions of the various source populations to the cou... more 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 γ-ray burst afterglows are also dealt with. The counts of different populations of star-forming galaxies (normal spirals, starbursts, highz 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.

Astronomy and Astrophysics, 2009

Aims. We present a combined radio, X-ray and optical study of the galaxy cluster RXCJ 2003.5-2323... more Aims. We present a combined radio, X-ray and optical study of the galaxy cluster RXCJ 2003.5-2323. The cluster hosts one of the largest, most powerful and distant giant radio halos known to date, suggesting that it may be undergoing a strong merger process. The aim of our multiwavelength study is to investigate the radio-halo cluster merger scenario. Methods. We studied the radio properties of the giant radio halo in RXCJ 2003.5-2323 by means of new radio data obtained at 1.4 GHz with the Very Large Array, and at 240 MHz with the Giant Metrewave Radio Telescope, in combination with previously published GMRT data at 610 MHz. The dynamical state of the cluster was investigated by means of X-ray Chandra observations and optical ESO-NTT observations. Results. Our study confirms that RXCJ 2003.5-2323 is an unrelaxed cluster. The unusual filamentary and clumpy morphology of the radio halo could be due to a combination of the filamentary structure of the magnetic field and turbulence in the inital stage of a cluster merger.

High-resolution Chandra images of several clusters of galaxies reveal sharp, edge-like discontinu... more High-resolution Chandra images of several clusters of galaxies reveal sharp, edge-like discontinuities in their gas density. The gas temperature is higher in front of the edge where the density is low, corresponding to approximately continuous pressure across the edge. This new phenomenon was called ``cold fronts'', to contrast it to shock fronts that should look similar in X-ray images but where the temperature should jump in the opposite direction. The first cold fronts were discovered in merging clusters, where they appear to delineate the boundaries of dense cool subcluster remnants moving through and being stripped by the surrounding shock-heated gas. Later, Chandra revealed cold fronts in the central regions of several apparently relaxed clusters. To explain the gas bulk motion in these clusters, we propose either a peculiar cluster formation history that resulted in an oscillating core, or gas sloshing (without the involvement of the underlying dark matter peak) caused by past subcluster infall or central AGN activity. We review these observations and discuss their implications for the X-ray cluster mass estimates.