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A. C. Edge

Publications and source records attributed to A. C. Edge.

176 records · Page 10Linked to original sources
arXiv1999

The REFLEX Cluster Survey: Observing Strategy and First Results on Large-Scale Structure

We give a general description of the optical observing strategy of the ROSAT-ESO Flux-Limited X-ray (REFLEX) cluster survey. This presently includes 460 clusters of galaxies selected from the ROSAT All-Sky Survey in the Southern hemisphere, to a flux limit of 3 10^{-12} erg s^{-1} cm^{-2}. Redshifts are now measured for 95% of this sample. Work is in progress to complete this coverage, and then extend the sample to fainter fluxes. A few highlights on the large-scale distribution of REFLEX clusters and their clustering properties are also discussed.

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arXiv1999

The ROSAT Brightest Cluster Sample (BCS): -- III. Optical spectra of the central cluster galaxies

We present new spectra of dominant galaxies in X-ray selected clusters, which combine with our previously published spectra to form a sample of 256 dominant galaxies in 215 clusters; 177 of these are members of the ROSAT Brightest Cluster Sample. 27% of the central dominant galaxies have emission-line spectra, all but 5 with line intensity ratios typical of cooling flow nebulae. A further 6% show only [NII] with H-alpha in absorption. We find no evidence for an increase in the frequency of line emission with X-ray luminosity. Purely X-ray selected clusters at low redshift have a higher probability of containing line emission. The more H-alpha luminous galaxies have larger emission-line regions and show a higher ratio of Balmer to forbidden line emission, although there is a continuous trend of ionization behaviour across four decades in H-alpha luminosity. Galaxies with the more luminous line emission show a significantly bluer continuum, whereas lower-luminosity and [NII]-only line emitters have continua that differ little from those of non-line emitting dominant galaxies. Values of the Balmer decrement in the more luminous systems commonly imply intrinsic reddening of E(B-V)~0.3, and when this is corrected for, the excess blue light can be characterized by a population of massive young stars, which can also provide sufficient photoionization to produce the observed H-alpha luminosity. The lower H-alpha luminosity systems show a higher ionization state and few massive stars, requiring instead the introduction of a harder source of photoionization.

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arXiv1999

X-ray and lensing results on the cluster around the powerful radio galaxy 4C+55.16

We present results from ASCA and ROSAT HRI observations of the powerful radio galaxy 4C+55.16 at redshift 0.24. Extended soft X-ray emission is imaged by the ROSAT HRI. The X-ray brightness profile is sharply peaked on the radio galaxy, characteristic of a strong cooling flow. The X-ray spectrum obtained from ASCA is consistent with multi-phase intracluster gas. There is evidence for an absorbed cool component as well as ambient cluster medium in the ASCA spectrum. A spectral fit, taking a cooling-flow component into account, gives a temperature of kT=5.4(+1.4/-0.9) keV, metal abundance 0.5(+/-0.1)Zsun, excess absorption on the cool component, nH=4.9(+3.4/-1.3)E+21 cm-2, and an absorption-corrected bolometric luminosity of 2.2E+45 erg/s (H0=50km/s/Mpc, q0=0.5). The mass deposition rate is estimated to be about 1100 Msun/yr from the spectral analysis, in good agreement with that derived from imaging analysis of the ROSAT data when corrected for absorption. We tentatively identify a blue feature, seen about 15 arcsec from the centre of the radio galaxy in a published optical image, as a gravitationally-lensed arc. The inferred lensing mass is consistent with the gravitational mass derived from the X-ray data. The best-estimate of the redshift of the lensed object is 1.5(>0.7). All the observed properties suggest that the environment of 4C+55.16 is similar to known massive cooling flow clusters. This is the first massive cooling flow to be found around a powerful, radio source with a compact, GHz-peaked spectrum core.

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arXiv1999

The Detection of Dust in the Central Galaxies of Distant Cooling-Flow Clusters

We present 850-um observations with the SCUBA submillimetre (sub-mm) camera of the central galaxies in seven concentrated clusters of galaxies at redshifts between 0.19 and 0.41. We detect sub-mm emission from the central galaxies in the rich clusters A1835 and A2390, and present upper limits for the central galaxies in the remaining five clusters. The two galaxies which we detect both exhibit unusually blue UV-optical colours and lie in clusters which contain massive cooling flows, >1000 Mo/yr. Moreover, both galaxies host relatively strong radio sources. Focusing on these two systems, we present new and archival radio-optical observations to provide a detailed view of their spectral energy distributions. Our analysis indicates that sub-mm emission from the central galaxy of A1835 can be best understood as arising from dust, heated either by vigorous star formation or an obscured active galactic nucleus. For the central galaxy of A2390, the sub-mm flux is marginally consistent with an extrapolation of the centimetre-millimetre emission from the luminous radio source that lies in its core; although we cannot rule out an excess flux density from dust emission comparable to that seen in A1835. We present details of our multi-wavelength observations and discuss the implications of these data for the interpretation of star formation in cooling-flow galaxies.

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arXiv1998

The ROSAT Brightest Cluster Sample (BCS) - I. The compilation of the sample and the cluster log N-log S distribution

We present a 90 per cent flux-complete sample of the 201 X-ray brightest clusters of galaxies in the northern hemisphere (dec > 0 deg), at high Galactic latitudes (|b| > 20 deg), with measured redshifts z < 0.3 and fluxes higher than 4.4 x 10^(-12) erg cm^(-2) s^{-1) in the 0.1-2.4 keV band. The sample, called the ROSAT Brightest Cluster Sample (BCS), is selected from ROSAT All-Sky Survey data and is the largest X-ray selected cluster sample compiled to date. In addition to Abell clusters, which form the bulk of the sample, the BCS also contains the X-ray brightest Zwicky clusters and other clusters selected from their X-ray properties alone. Effort has been made to ensure the highest possible completeness of the sample and the smallest possible contamination by non-cluster X-ray sources. X-ray fluxes are computed using an algorithm tailored for the detection and characterization of X-ray emission from galaxy clusters. These fluxes are accurate to better than 15 per cent (mean 1 sigma error). We find the cumulative log N-log S distribution of clusters to follow a power law k S^(-alpha) with alpha=1.31 (+0.06)(-0.03) (errors are the 10th and 90th percentiles) down to fluxes of 2 x 10^(-12) erg cm^(-2) s^(-1), i.e. considerably below the BCS flux limit. Although our best-fitting slope disagrees formally with the canonical value of -1.5 for a Euclidean distribution, the BCS log N-log S distribution is consistent with a non-evolving cluster population if cosmological effects are taken into account.

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arXiv1998

Results from the REFLEX Cluster Survey

Based on the ROSAT All-Sky Survey we have conducted a large redshift survey as an ESO key programme to identify and secure redshifts for the X-ray brightest clusters found in the southern hemisphere. We present first results for a highly controlled sample for a flux limit of 3 10-12 erg/s/cm+2 comprising 475 clusters (87% with redshifts). The logN-logS function of the sample shows an almost perfect Euclidian slope and a preliminary X-ray luminosity function is presented.

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arXiv1998

A ROSAT study of the cores of clusters of galaxies - I. Cooling flows in an X-ray flux-limited sample

This is the first part of a study of the detailed X-ray properties of the cores of nearby clusters. We have used the flux-limited sample of 55 clusters of Edge et al. (1990) and archival and proprietary data from the {\it ROSAT} observatory. In this paper an X-ray spatial analysis based on the surface-brightness-deprojection technique is applied to the clusters in the sample with the aim of studying their cooling flow properties. We determine the fraction of cooling flows in this sample to be 70-90 percent and estimate the contribution of the flow region to the cluster X-ray luminosity. We show that the luminosity within a strong cooling flow can account for up to 70 percent of a cluster X-ray bolometric luminosity. Our analysis indicates that about 40 percent of the clusters in the sample have flows depositing more than 100 \Msunpyr throughout the cooling region and that these possibly have been undisturbed for many Gyr, confirming that cooling flows are the natural state of cluster cores. New cooling flows in the sample are presented and previously ambiguous ones are clarified. We have constructed a catalogue of some intracluster medium properties for the clusters in this sample. The profiles of the mass deposited from cooling flows are analyzed and evidence presented for the existence of breaks in some of the profiles. Comparison is made to recent optical and radio data. We cross-correlate our sample with the Green Bank, NVSS and FIRST surveys and to the volume-limited sample of brightest cluster galaxies presented by Lauer and Postman (1994). Although weak trends exist, no strong correlation between optical magnitude or radio power of the brightest cluster galaxy and the strength of the flow is found.

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arXiv1997

The ROSAT Brightest Cluster Sample (BCS): The cluster X-ray luminosity function within z=0.3

We present and discuss the X-ray luminosity function (XLF) of the ROSAT Brightest Cluster sample (BCS), an X-ray flux limited sample of clusters of galaxies in the northern hemisphere compiled from ROSAT All-Sky Survey data. The BCS allows the local cluster XLF to be determined with unprecedented accuracy over almost three decades in X-ray luminosity and provides an important reference for searches for cluster evolution at higher redshifts. We find the significance of evolution in both the XLF amplitude and in the characteristic cluster luminosity L_X^star to be less than 1.8 sigma within the redshift range covered by our sample thereby disproving previous claims of strong evolution within z < 0.2.

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arXiv1996

ASCA and ROSAT observations of distant massive cooling flows

We present the results from a detailed ASCA/ROSAT X-ray study of three distant, massive cooling flows; Zwicky 3146 (z=0.291), Abell 1835 (z=0.252) and E1455+223 (Zwicky 7160; z=0.258). Using multiphase models fitted to the ASCA spectra, we determine values for the temperature, metallicity, luminosity and cooling rates in the clusters. These results are combined with deprojection analyses of the ROSAT images to provide detailed constraints on the mass distributions in the systems, and on the properties of their cooling flows. The spectral and imaging data identify these clusters as the three most-massive cooling flows known, with mass deposition rates of ~ 1400, 2300, and 1500 solar masses per year, respectively. We highlight the need for multiphase models to consistently model the spectral and imaging X-ray data, and discuss the importance of using these models in X-ray determinations of the cluster masses. We also present results from an extensive optical study of the clusters and report the discovery of a gravitational arc in Abell 1835. The lensing data provide an indepenent constraint on the distribution of mass in the cluster, in good agreement with the results from the mutliphase (although not single-phase) X-ray analysis. We present measurements of the galaxy distributions in Abell 1835 and E1455+223 and relate these to the distributions of the total mass. The ASCA spectra place firm constraints on the column density of intrinsic X-ray absorbing material in the clusters. Abell 1835 and E1455+223 exhibit large intrinsic column densities associated with their cooling flows. These clusters also exhibit significant amounts of reddening in the optical spectra of their central galaxies. The data for Zwicky 3146 indicate lower lower levels of X-ray absorption and reddening. All three clusters exhibit excellent alignment

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arXiv1996

Properties of the X-ray brightest Abell-type clusters of galaxies (XBACs) from ROSAT All-Sky Survey data --- I. The sample

We present an essentially complete, all-sky, X-ray flux limited sample of 242 Abell clusters of galaxies (six of which are double) compiled from ROSAT All-Sky Survey data. Our sample is uncontaminated in the sense that systems featuring prominent X-ray point sources such as AGN or foreground stars have been removed. The sample is limited to high Galactic latitudes ($|b| \geq 20^{\circ}$), the nominal redshift range of the ACO catalogue of $z \leq 0.2$, and X-ray fluxes above $5.0 \times 10^{-12}$ erg cm$^{-2}$ s$^{-1}$ in the 0.1 -- 2.4 keV band. Due to the X-ray flux limit, our sample consists, at intermediate and high redshifts, exclusively of very X-ray luminous clusters. Since the latter tend to be also optically rich, the sample is not affected by the optical selection effects and in particular not by the volume incompleteness known to be present in the Abell and ACO catalogues for richness class 0 and 1 clusters. Our sample is the largest X-ray flux limited sample of galaxy clusters compiled to date and will allow investigations of unprecedented statistical quality into the properties and distribution of rich clusters in the local Universe.

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arXiv1995

X-ray evolution in the ROSAT Brightest Cluster Sample

We present the X-ray luminosity function (XLF) of the ROSAT Brightest Cluster Sample (BCS), an X-ray selected, flux limited sample of 172 clusters of galaxies at $z\leq 0.3$ compiled from ROSAT All-Sky Survey data. While the bulk of the BCS consists of Abell clusters, the sample also contains Zwicky clusters and purely X-ray selected systems. The BCS-XLF represents the best determination of the local X-ray luminosity function for galaxy clusters and thus provides an important reference for evolutionary studies. For the BCS itself, we find no convincing evidence for cluster evolution within a redshift of $z=0.3$. This result is not in conflict with the findings of the EMSS study on cluster evolution.

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arXiv1995

Cooling flows, central galaxy--cluster alignments, X-ray absorption and dust

We present the analysis of pointed ROSAT PSPC observations of five of the most luminous, intermediate redshift ($0.1 < z < 0.15$) clusters of galaxies detected in the ROSAT All-Sky Survey. The PSPC data are combined with optical CCD images and spectra to examine the relationship between clusters and their central cluster galaxies (CCGs). Abell 1068, Abell 1361 and Abell 1664 contain three of the most optically line-luminous CCGs known. The PSPC X-ray data show that these galaxies lie at the centres of massive (200 -- 400 solar masses per year) cooling flows. The alignment between CCGs and their host clusters has been investigated. For those clusters with cooling flows, the position angles of the X-ray emission from the clusters and the optical emission from the CCGs agrees within 5 degrees. For the one probable non-cooling flow cluster in the sample, Abell 2208, the alignment is significantly poorer. We examine the evidence for intrinsic X-ray absorption in the clusters. The X-ray spectra for Abell 1068 and Abell 1664 show that the cooling flows in these clusters are intrinsically absorbed by equivalent hydrogen column densities $\geq 10^{21} atom cm$^{-2}$. The optical spectra of the CCGs in these clusters exhibit substantial intrinsic reddening, at levels consistent with the X-ray absorption results if standard dust to gas ratios are assumed.

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arXiv1994

A Giant Arc in a ROSAT Detected Cluster of Galaxies

We report the serendipitous discovery of a giant grvitational arc in the Abell Supplementary cluster S295 during optical follow-up observations of clusters detected in the ROSAT All-Sky Survey. The cluster has a redshift z=0.3007 and a velocity dispersion of about 900 km/sec. This is the first giant arc newly found in a ROSAT Survey cluster, indicating the potential advantage of searching for giant arcs in X-ray selected clusters.

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