No Evolution in the X-ray Cluster Luminosity Function out to z=0.7
In contrast to claims of strong negative evolution by other groups, we find no evidence for evolution of the X-ray cluster luminosity function out to z=0.7
astro-ph↗
arXiv subjects
M. P. Ulmer
Publications and source records attributed to M. P. Ulmer.
Evolution in the X-ray Cluster Luminosity Function Revisited
(Shortened Abstract) We present new X-ray data taken from the ROSAT PSPC pointing archive for 21 clusters in the Einstein Extended Medium Sensitivity Survey (EMSS). We have supplemented these data with new optical follow-up observations found in the literature and overall, 32 of the original 67 z>0.14 EMSS clusters now have new information. Using this improved EMSS sample, we have re-determined the EMSS X-ray Cluster Luminosity Function as a function of redshift. We have removed potential mis-classifications and included our new measurements of the clusters X-ray luminosities and redshifts. We find similar luminosity functions to those originally presented by Henry etal (1992); albeit with two important differences. First, we show that the original low redshift EMSS luminosity function is insufficiently constrained. Secondly, the power law shape of our new determination of the high redshift EMSS luminosity function (z=0.3 to 0.6) has a shallower slope than that seen by Henry etal. We have quantified the degree of evolution seen in the X-ray cluster luminosity using several statistical tests. The most restrictive analysis indicates that our low and high redshift EMSS luminosity functions are statistically different at only the 95% level. However, other tests indicate that these luminosity functions differ by as little as one sigma. These data are therefore, consistent with no evolution in the X-ray cluster luminosity function out to z=0.5.
astro-ph↗
Low Surface Brightness Galaxies in the Core of the Coma Cluster
We present the results of a search for low surface brightness galaxies (hereafter LSBs) in the Coma cluster. Bernstein et al. report on deep CCD observations in R of a 7.5 by 7.5 arcminute region in the core of the Coma cluster, and we extend this work by finding and measuring 36 LSBs within this field. We report both R and Bj results. The average magnitude based on the best fit exponential to the images is 22.5 (R) and the typical exponential scale is 1.3 arcseconds. The range of exponential scales is 0.4 to 1.2 kpc (distance modulus 34.89), and the range of central surface brightnesses is 24 to 27.4 R magnitudes per square arcsecond. Many of these objects are similar in terms of scale length and central surface brightness to those found by others in nearby clusters such as Fornax (Bothun, Impey and Malin), as well as in the low luminosity end of the dwarfs cataloged in the review by Ferguson and Binggeli. We find no evidence for a dependence of color on central surface brightness or on distance from the D galaxies or the X-ray center of Coma. We also find that these LSBs make a small contribution to the overall mass of the cluster. We discuss these results in terms of possible scenarios of LSB formation and evolution.
astro-ph↗
A search for distant X-ray galaxy clusters
We report on the progress of our search for serendipitous distant X-ray galaxy clusters in the ROSAT PSPC pointed observations archive. The initial aim of our work is to measure the X-ray luminosity function of clusters down to 4 x 10^-14 erg cm^-2 s^-1 and so test the claims of cluster evolution at moderate redshifts. We have R band images and spectroscopy for 45 extended sources detected in 50 of the 100 deepest southern fields. A preliminary analysis suggests we cover a range of distances, from nearby clusters to possible distant clusters, z \simeq 1.0.
astro-ph↗
The Luminosity Function of the Coma Cluster Core for -25<M_R<-11
We determine the luminosity function (LF) of galaxies in the core of the Coma cluster for M_R<=-11.4 (assuming H_0=75 km/s/Mpc), a magnitude regime previously explored only in the Local Group. Objects are counted in a deep CCD image of Coma having RMS noise of 27.7 R mag~arcsec$^{-2}$. A correction for objects in the foreground or background of the Coma cluster---and the uncertainty in this correction---are determined from images of five other high-latitude fields, carefully matched to the Coma image in both resolution and noise level. Accurate counts of Coma cluster members are obtained as faint as R=25.5, or M_R=-9.4. The LF for galaxies is well fit by a power law dN/dL\propto L^α, with α=-1.42\pm0.05, over the range -19.4<M_R<-11.4; faintward of this range, the galaxies are unresolved and indistinguishable from globular clusters, but the data are consistent with an extrapolation of the power law. Surface brightness biases are minimized since galaxies are not subjected to morphological selection, and the limiting detection isophote is 27.6 R mag~arcsec$^{-2}$. We find the typical $M_R\approx-12$ Coma cluster galaxy to have an exponential scale length $\approx200$~pc, similar to Local Group galaxies of comparable magnitude. These extreme dwarf galaxies show a surface density increasing towards the giant elliptical NGC~4874 as $r^{-1.3}$, similar to the diffuse light and globular cluster distributions. The luminosity in the detected dwarf galaxies is at most a few percent of the total diffuse light of the giant galaxies in the cluster, and the contribution of the dwarfs to the mass of the cluster is likely negligible as well.
astro-ph↗
A Search for X-Ray Bright Distant Clusters of Galaxies
We present the results of a search for X--ray luminous distant clusters of galaxies. We found extended X--ray emission characteristic of a cluster towards two of our candidate clusters of galaxies. They both have a luminosity in the ROSAT bandpass of $\simeq10^{44}{\rm \,erg\,s^{-1}}$ and a redshift of $>0.5$; thus making them two of the most distant X--ray clusters ever observed. Furthermore, we show that both clusters are optically rich and have a known radio source associated with them. We compare our result with other recent searches for distant X--ray luminous clusters and present a lower limit of $1.2\times10^{-7}\,{\rm Mpc^{-3}}$ for the number density of such high redshift clusters. This limit is consistent with the expected abundance of such clusters in a standard (b=2) Cold Dark Matter Universe. Finally, our clusters provide important high redshift targets for further study into the origin and evolution of massive clusters of galaxies. Accepted for publication in the 10th September 1994 issue of ApJ.
astro-ph↗