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Register a new userBeppoSAX observation of the rich cluster of galaxies Abell 85
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Added by
Gastao B. Lima Neto
Publication date
2001
fields
Physics
and research's language is
English
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We report the observation of the Intra-Cluster Medium (ICM) of Abell 85 by the X-ray satellite BeppoSAX. We have both analysed the spectrum obtained in the central 8 arcmin circular region centred on the Very Steep Spectrum Radio Source (VSSRS) and the spectra from a number of sub-regions. Analysis of the spectra allowed us to independently obtain new estimates of the temperature, metallicity and line-of-sight hydrogen density column, both globally (T=6.6pm0.3 keV, Z = 0.38pm0.06 Z_odot and N_H = 5.5^+0.9_-0.7 10^20 cm^-2) and locally. These measures are in good agreement with previous measures based on ROSAT and ASCA data. In the region of the VSRSS, we have tried to disentangle the thermal from the non-thermal X-ray emission. Although we could not do this unambiguously, we have nonetheless estimated the extended magnetic field using the radio spectrum available for this region. We obtain a lower limit intensity of 0.9 mu G, consistent with our previous estimate. We also derive alpha-elements/iron abundance ratios that turn out to be higher than 1. Such a result tends to support the burst model for elliptical galaxies, where a strong galactic wind develops early in the galaxy history and type II supernovae (SN) may have the main role in the enrichment of the ICM. A two-temperature ICM model was fitted in the central region yielding a main component with roughly the mean cluster temperature and a cooler component with temperature less than 0.1 keV.
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We report new results on the cluster of galaxies Abell 970 obtained from X-ray observation with BeppoSAX. Our analysis of the BeppoSAX MECS and LECS data in the range [0.15-10] keV reveals a mean cluster gas temperature of kT = 4.46_{-0.15}^{+0.14}, a metallicity of Z = 0.31_{-0.04}^{+0.05} Z_odot, and an interstellar hydrogen absorption density column of N_H = 6.05_{-0.97}^{+1.29} 10^20 cm^-2. Moreover, we obtained azimuthally averaged radial profiles of these quantities. Our results are consistent with the hypothesis that Abell 970 has been disturbed by a past merger or by the ongoing merger process of a substructure, that put the cluster out of equilibrium. This is also demonstrated by the offset between the gas and galaxy distributions. Combining the X-ray data with a recently published analysis of new galaxy radial velocities, we conclude that a subcluster 8 arcmin to the NW is falling into Abell 970 and will merge in a few Gigayears, thus disturbing Abell 970s newly acquired equilibrium. The high alpha-elements/iron ratio that we derive for this cluster supports the hypothesis of early intracluster medium enrichment by Type II supernovae.
We present results from a BeppoSAX observation of the rich cluster Abell 3266. The broad band spectrum (2-50 keV) of the cluster, when fitted with an optically thin thermal emission model, yields a temperature of 8.1 +/- 0.2 keV and a metal abundance of 0.17 +/- 0.02 in solar units, and with no evidence of a hard X-ray excess in the PDS spectrum. By performing a spatially resolved spectral analysis we find that the projected temperature drops with increasing radius, going from ~ 10 keV at the cluster core to ~ 5 keV at about 1.5 Mpc. Our BeppoSAX temperature profile is in good agreement with the ASCA temperature profile of Markevitch et al. (1998). From our two-dimensional temperature map we find that the gradient is observed in all azimuthal directions. The temperature gradient may have been caused by a recent merger event also responsible for a velocity dispersion gradient measured in the optical band. The projected metal abundance profile and two-dimensional map are both consistent with being constant.
Based on a VLA HI-imaging through the total volume of the cluster Abell 85, we compare the distribution of HI-rich and HI deficient late type galaxies with the intra cluster medium (ICM) drawn by the X-ray emission.
For the first time, we explore the dynamics of the central region of a galaxy cluster within $r_{500}sim 600h^{-1}$~kpc from its center by combining optical and X-ray spectroscopy. We use (1) the caustic technique that identifies the cluster substructures and their galaxy members with optical spectroscopic data, and (2) the X-ray redshift fitting procedure that estimates the redshift distribution of the intracluster medium (ICM). We use the spatial and redshift distributions of the galaxies and of the X-ray emitting gas to associate the optical substructures to the X-ray regions. When we apply this approach to Abell 85 (A85), a complex dynamical structure of A85 emerges from our analysis: a galaxy group, with redshift $z=0.0509 pm 0.0021$ is passing through the cluster center along the line of sight dragging part of the ICM present in the cluster core; two additional groups, at redshift $z=0.0547 pm 0.0022$ and $z=0.0570 pm 0.0020$, are going through the cluster in opposite directions, almost perpendicularly to the line of sight, and have substantially perturbed the dynamics of the ICM. An additional group in the outskirts of A85, at redshift $z=0.0561 pm 0.0023$, is associated to a secondary peak of the X-ray emission, at redshift $z=0.0583^{+0.0039}_{-0.0047}$. Although our analysis and results on A85 need to be confirmed by high-resolution spectroscopy, they demonstrate how our new approach can be a powerful tool to constrain the formation history of galaxy clusters by unveiling their central and surrounding structures.
We present results from the XMM-Newton observation of the non-cooling flow cluster A1060. Large effective area of XMM-Newton enables us to investigate the nature of this cluster in unprecedented detail. From the observed surface brightness distribution, we have found that the gravitational mass distribution is well described by the NFW profile but with a central density slope of ~1.5. We have undoubtedly detected a radial temperature decrease of as large as ~30% from the center to the outer region (r ~13), which seems much larger than that expected from the temperature profile averaged over nearby clusters. We have established that the temperature of the region ~7 southeast of the center is higher than the azimuthally averaged temperature of the same radius by ~20%. Since the pressure of this region already reaches equilibrium with the environment, the temperature structure can be interpreted as having been produced between 4*10^7 yr (the sound-crossing time) and 3*10^8 yr (the thermal conduction time) ago. We have found that the high-metallicity blob located at ~1.5 northeast of NGC 3311 is more extended and its iron mass of 1.9*10^7 M_solar is larger by an order of magnitude than estimated from our Chandra observation. The amount of iron can still be considered as being injected solely from the elliptical galaxy NGC3311.
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