An investigation of cooling flows and general cluster properties from an X-ray image deprojection analysis of 207 clusters of galaxies

Abstract

In this paper we present an X-ray image deprojection analysis of EINSTEIN OBSERVATORY imaging data on 207 clusters of galaxies. The resulting radial profiles for luminosity, temperature, and electron density variations are determined from the cluster surface-brightness profiles according to gravitational potential constraints from average X-ray temperatures and optical velocity dispersions. This enables us to determine cooling-flow and other cluster properties, such as baryon fractions, Sunyaev-Zeldovich microwave decrements, and Thomson depths. From the results, we have compiled a catalogue of the detected cooling flows, and investigated their effects on general cluster properties. To assist in the analysis, we have constructed self-consistent correlations between the cluster X-ray luminosity, temperature, and optical velocity-dispersion, using 'orthogonal distance' regression to account for errors in both dimensions of the data. These fits indicate that, in general, the temperatures of clusters are isothermal and that they have spectral β-values consistent with unity.We find that the X-ray luminosity, temperature, and optical velocity dispersion relations depend significantly on the cooling flow mass-deposition rate, through characteristic differences in the density profiles. Clusters of similar cooling flow mass-deposition rate exhibit self-similar density profiles, with larger cooling flows showing higher central densities. This leads to scatter in the luminosity related correlations within the X-ray luminosity, temperature and optical velocity dispersion plane. The segregation in density also leads to dispersion in other related properties such as 'half-light radii' and baryon fractions. The baryon fraction in the cores of cooling flow clusters appears to be higher, but as the density profiles tend to a similar value at larger radii, irrespective of cooling flow property, so too do the baryon fraction profiles appear to rise to a concordant value of greater than 10 percent at 1 Mpc. Thus, this sample indicates that clusters, as a whole, are inconsistent with primordial nucleosynthesis baryon fraction prediction, for a flat Universe, of 6 percent.

The accretion histories of brightest cluster galaxies from their stellar population gradients

“…For most of the clusters considered here, X-ray imaging is not available, so that we cannot assess whether they host a cool core or not. Only two of our galaxies have been confirmed to be hosted by a non-cooling flow cluster (White et al 1997) and for those we find contradictory results: 2001 is one of the oldest galaxies in our sample, consistent with the cool core hypotheses, however, 1066 shows a young central region and a positive age gradient, suggesting that cool cores are not the explanation for the intermediate ages observed.…”

Thermodynamical Properties of the ICM from Hydrodynamical Simulations

“…This relation has been shown by several independent analyses to have a slope, L X ∝ T α , with α 3 for T 2 keV (e.g., White et al 1997), with indications for a flattening to α 2.5 for the most massive systems (Allen and Fabian 1998). The scatter in this relation is largely contributed by the cool-core emission, so that it significantly decreases when excising the cores (Markevitch 1998) or removing cool-core systems (Arnaud and Evrard 1999).…”

Iron Abundance Profiles of 12 Clusters of Galaxies Observed withBeppoSAX

“…If the density of gas outside the core is greater in cooling-Ñow clusters than in nonÈcooling-Ñow clusters, more metals will be released into the gas phase for the former. A di †erence in density among cooling and nonÈ cooling-Ñow clusters outside of 200 kpc was observed by White et al (1997), who deprojected the surface-brightness proÐles of 207 clusters observed with Einstein Observatory and found that the electron densities of clusters with cooling rates greater than 10 yr~1 were larger than for clusters M _ with cooling rates less than 10 yr~1 out to a radius of 1 M _ Mpc. For a 7 keV cluster, our bin corre-0.075È0.173r virial sponds to 240È560 kpc.…”

“…For a 7 keV cluster, our bin corre-0.075È0.173r virial sponds to 240È560 kpc. At a radius of 450 kpc, White et al (1997) found that the cooling-Ñow clusters had an electron density of D7 ] 10~4 cm~3, whereas the nonÈcooling-Ñow clusters had an electron density of D3 ] 10~4 cm~3. For a grain lifetime of yr (where a is the size of the (2 ] 106)a/n e grain in microns and is the electron density of the hot gas n e in cm~3), grains with a size of around 2 km would survive in nonÈcooling-Ñow clusters for a Hubble time while being sputtered in cooling-Ñow clusters.…”