arXiv subjects

R. G. Morris

Publications and source records attributed to R. G. Morris.

23 records · Page 2Linked to original sources

arXiv2012

X-ray Bright Active Galactic Nuclei in Massive Galaxy Clusters I: Number Counts and Spatial Distribution

We present an analysis of the X-ray bright point source population in 43 massive clusters of galaxies observed with the Chandra X-ray Observatory. We have constructed a catalog of 4210 rigorously selected X-ray point sources in these fields, which span a survey area of 4.2 square degrees. This catalog reveals a clear excess of sources when compared to deep blank-field surveys, which amounts to roughly 1 additional source per cluster, likely Active Galactic Nuclei (AGN) associated with the clusters. The excess sources are concentrated within the virial radii of the clusters, with the largest excess observed near the cluster centers. The average radial profile of the excess X-ray sources of the cluster are well described by a power law (N(r) ~ r^β) with an index of β~ -0.5. An initial analysis using literature results on the mean profile of member galaxies in massive X-ray selected clusters indicates that the fraction of galaxies hosting X-ray AGN rises with increasing clustercentric radius, being approximately 5 to 10 times higher near the virial radius than in the central regions. This trend is qualitatively similar to that observed for star formation in cluster member galaxies.

astro-ph.CO↗

arXiv2008

Cool X-ray emitting gas in the core of the Centaurus cluster of galaxies

We use a deep XMM-Newton Reflection Grating Spectrometer observation to examine the X-ray emission from the core of the Centaurus cluster of galaxies. We clearly detect Fe-XVII emission at four separate wavelengths, indicating the presence of cool X-ray emitting gas in the core of the cluster. Fe ions from Fe-XVII to XXIV are observed. The ratio of the Fe-XVII 17.1A lines to 15.0A line and limits on O-VII emission indicate a lowest detected temperature in the emitting region of 0.3 to 0.45 keV (3.5 to 5.2x10^6 K). The cluster also exhibits strong N-VII emission, making it apparent that the N abundance is supersolar in its very central regions. Comparison of the strength of the Fe-XVII lines with a Solar metallicity cooling flow model in the inner 17 kpc radius gives mass deposition rates in the absence of heating of 1.6-3 Msun/yr. Spectral fitting implies an upper limit of 0.8 Msun/yr below 0.4 keV, 4 Msun/yr below 0.8 keV and 8 Msun/yr below 1.6 keV. The cluster contains X-ray emitting gas over at least the range of 0.35 to 3.7 keV, a factor of more than 10 in temperature. We find that the best fitting metallicity of the cooler components is smaller than the hotter ones, confirming that the apparent metallicity does decline within the inner 1 arcmin radius.

astro-ph↗

arXiv2006

Tracing gas motions in the Centaurus Cluster

We apply the stochastic model of iron transport developed by Rebusco et. al. (2005) to the Centaurus cluster. Using this model, we find that an effective diffusion coefficient D in the range 2x10^28 - 4x10^28 cm^2 s^-1 can approximately reproduce the observed abundance distribution. Reproducing the flat central profile and sharp drop around 30-70 kpc, however, requires a diffusion coefficient that drops rapidly with radius so that D > 4x10^28 cm^2 s^-1 only inside about 25 kpc. Assuming that all transport is due to fully-developed turbulence, which is also responsible for offsetting cooling in the cluster core, we calculate the length and velocity scales of energy injection. These length scales are found to be up to a factor of ~ 10 larger than expected if the turbulence is due to the inflation and rising of a bubble. We also calculate the turbulent thermal conductivity and find it is unlikely to be significant in preventing cooling.

astro-ph↗

arXiv2004

The Galaxy Cluster Abell 3581 as seen by Chandra

We present results from an analysis of a Chandra observation of the cluster of galaxies Abell 3581. We discover the presence of a point-source in the central dominant galaxy which is coincident with the core of the radio source PKS 1404-267. The emission from the intracluster medium is analysed, both as seen in projection on the sky, and after correcting for projection effects, to determine the spatial distribution of gas temperature, density and metallicity. We find that the cluster, despite hosting a moderately powerful radio source, shows a temperature decline to around 0.4Tmax within the central 5 kpc. The cluster is notable for the low entropy within its core. We test and validate the xspec projct model for determining the intrinsic cluster gas properties.

astro-ph↗

arXiv2002

On conduction, cooling flows and galaxy formation

On the basis of the universal gas fraction in clusters of galaxies, we estimate that the effective thermal conductivity required to balance radiative cooling in the cores, where the gas temperature is 3-10keV, is about one tenth of the Spitzer rate. This confirms that thermal conduction can be important for the energy balance provided that it is not highly suppressed by magnetic fields in the gas. We determine the global effective conductivity in a sample of 29 clusters using published X-ray data on the inferred cooling rates and show that most lie between one and one tenth of the Spitzer rate. More work on the profiles in cooling flow clusters is required to test the conduction hypothesis further. We examine the possibility that conduction operates during galaxy formation, and show that it provides a simple explanation for the upper-mass cutoff in galaxy masses.

astro-ph↗