Southern Abell Clusters Research Articles

A radio survey of seven southern X-ray luminous clusters of galaxies

The Australia Telescope Compact Array (ATCA) has been used at 1.38 and 2.38 GHz to survey seven southern Abell clusters of galaxies with high X-ray luminosities: A2746, A2837, A3126, A3216, A3230, A3827 and A3836. The clusters have also been surveyed at 0.843 GHz with the Molonglo Observatory Synthesis Telescope (MOST). We have listed a complete 1.38-GHz sample of 149 radio sources within the Abell circles centred on their X-ray centroids. We compare their identification fractions, emitted 1.38-GHz and optical powers, radio spectral indices and radial variation in projected source density with those of the radio-selected samples of Slee et al. (1998). We compare our fractional radio luminosity function with that of the radio-selected samples of Ledlow and Owen (1996) and Slee et al. (1998). Three significant differences are noted between X-ray and radio-selected samples of clusters; (1) the X-ray sample has an excess of flat-spectrum radio sources; (2) the fractional radio luminosity function for the FR I sources in the X-ray selected sample is much steeper, implying that fewer of their cluster galaxies become hosts for the stronger FR I radio galaxies; (3) a complete absence of FR II radio galaxies in the X-ray selected sample. The average excess projected density of radio sources near our cluster centres is approx. 5 times the background source density.

Photometric Observations of Southern Abell Cluster Redshifts Survey Clusters: Structure of Galaxies in the Inner Region of Clusters of Galaxies

We analyze photometric properties of 1384 cluster galaxies as a function of the normalized distance to cluster center. These galaxies were selected in the central region ($r/r_{200} \leq$ 0.8) of 14 southern Abell clusters chosen from the Southern Abell Cluster Redshifts Survey (SARS). For 507 of these galaxies we also obtained their luminosity profiles. We have studied the morphology-clustercentric distance relation on the basis of the shape parameter $n$ of the S\'ersic's law. We also have analyzed the presence of a possible segregation in magnitude for both, the galaxy total luminosity and that of their components (i.e. the bulge and the disk). Results show a marginal ($2\sigma$ level) decrease of the total luminosity as a function of normalized radius. However, when bulges are analyzed separately, a significant luminosity segregation is found ($3\sigma$ and $2\sigma$ for galaxies in projection and member galaxies respectively). The fraction of bulges brighter than $M_B \leq -22$ is three times larger in the core of clusters than in the outer region. Our analysis of the disk component suggests that disks are, on average, less luminous in the cluster core than at $r/r_{200} \sim 0.8$. In addition, we found that the magnitude-size relation as a function of $r/r_{200}$ indicates (at $2\sigma$ level) that disks are smaller and centrally brighter in the core of clusters. However, the Kormendy relation (the bulge magnitude-size relation) appears to be independent of environment.

Mass distribution and Dynamical State of Galaxy Clusters in the LZLS Sample

We use the weak gravitational lensing effect to study the mass distribution of a sample of 50 southern Abell clusters (0.05 z L X > 5 × 10 44 erg s -1 observed with ESO-VLT under uniform sky conditions and subarsecond (0.6 '' ) image quality. Their dynamical equibrium is assesed through comparison of the clusters mass estimates made by weak-lensing, velocity-dispersions and X-ray techniques. So far, for 24 clusters (Cypriano et al. 2004), we find: a) the center of their mass and light distributions are coincident for 77% of the sample; b) the elongations of the fitted mass profiles and of the light of the cD galaxies generally match with each other; c) although most of the clusters are found to be in dynamical equilibrium, those with T X ≥ 8 keV (or σ v ≥ 1120 km s -1 ) are the discordant ones. The preliminary bright arc statistics for our whole sample (LZLS) suggests the presence of a cut-off at z ~ 0.07 which is qualitatively consistent with predictions done in a ΛCDM cosmology (Meneghetti et al. 2003).

Photometric Observations of Southern Abell Clusters Redshifts Survey Clusters: Galaxy Luminosity Profiles

We have analyzed CCD images of 14 Abell clusters in the R filter of the Southern Abell Clusters Redshifts Survey (SARS) with cz < 40,000 km s-1. We have obtained the luminosity profiles for 507 galaxies, of which 232 (46%) have known redshifts. In order to fit the luminosity profiles, we used the de Vaucouleurs law for bulge systems and an exponential profile for disk systems, and we also fitted the Sersic's law (rn) to all galaxy profiles. We have found that 162 galaxies (32%) in the sample have pure r1/4 profiles, 168 (33%) have pure exponential profiles, and 93 (18%) have luminosity profiles that are well fitted by a combination of bulge and disk profiles. On the other hand, we could not fit the classical bulge + disk profile to the remaining 84 galaxies (17%) of the sample. For such cases we have used only the Sersic law. We have also analyzed how seeing and sky cleaning affect the structural and photometric parameters obtained through profile fitting. In addition, we have studied several relations between these parameters. We have found that bulges and disks show consistency with a unique relation in the μe– log re plane. We also found that bulges and disks obey a magnitude-size relation in the sense that large bulges and disks (large re values) have high luminosities. On the other hand, Sersic-law fitting parameters n, rs, and μs show a strong correlation, in agreement with the findings of other authors, suggesting that not only elliptical galaxies but all galaxies are likely to be understood as a one-parameter family.

Results of the Mount Stromlo Abell cluster supernova search

We report the results of the Mount Stromlo Abell cluster supernova search, a three-year project to find supernovae (SNe) in a well-defined sample of high-density, southern Abell clusters with redshifts 0.02 ≥ z ≥ 0.08. The search discovered 48 SNe, 23 of which were consistent with SNe of type Ia (SNIa). Of these, 15 were spectroscopically classified SNIa, with the remaining 8 SNe tentatively classified as SNIa via the goodness of fit of the template light curves. This paper describes the methods employed to produce the light curves for the SNe discovered during the Mount Stromlo Abell cluster supernova search. We derive the redshift-independent distances to the SNIa from the search, as well as a large sample of other well-observed SNIa taken from the literature via a modified Δm15 template light curve fitting technique. This technique and the problems encountered in using it are described in detail. We construct a Hubble diagram for SNIa and show that our data with z < 0.2 are consistent with an accelerating universe. Using current Cepheid HST calibrations, we estimate that the value of the Hubble constant lies between 53 < H0 < 83 km-1 s-1 Mpc-1, with the large spread almost entirely due to possible systematic errors in the Cepheid calibration.

Velocity Dispersions and Cluster Properties in the Southern Abell Redshift Survey Clusters. II.

We report an analysis of the dynamical structure of clusters of galaxies from a survey of photometric and spectroscopic observations in the fields of southern Abell clusters. We analyze the galaxy velocity field in extended regions up to 7 h-1 Mpc from cluster centers, and we estimate mean velocity dispersions and their radial dependence. Only one from a total of 41 Abell clusters does not correspond to a dynamically bound system. However, four of these bound objects are double clusters. We estimate that 20% (seven clusters) of the 35 remaining are subject to serious projection effects. Normalizing the clustercentric distances by means of the overdensity radius r200, and the velocity dispersion profiles (VDPs) by the corresponding mean cluster velocity dispersion, we computed the average VDP. Our results indicate a flat behavior of the mean VDP at large distances from the cluster center. Nevertheless, we found that for the inner part of the clusters (r/r200 ≤ 1) the VDP is up to 10% smaller than at larger radii.

Extreme Relic Radio Sources in Four Southern Clusters

We describe the highest-resolution radio observations yet made of relic radio sources. These relics have extremely steep (α ≤ −2.5) spectra and are located in four southern Abell clusters (A 13, A 85, A133, A 4038). VLA images at 1.4 GHz and ∼4″ resolution show a remarkable variety of fine structure like arcs, wisps, plumes, and loops. Integrated polarization fractions range from 2.3% to 16.8%. Deep red CCD images do not reveal any optical object with a brightness and/or position typical of a radio host galaxy. The X-ray centroids in ROSAT images tend to be displaced from the cluster potential wells in the direction of the relics in A85, A133 and A4038, suggesting that some of the X-rays may be inverse Compton or excess thermal emission from the relic itself.

Photometry of the Central Regions in a Complete Sample of High Bautz‐Morgan–Type Abell Clusters. I. Observations and Data Calibration

We present CCD photometry of 209 southern Abell clusters selected according to Bautz-Morgan type I, I-II, and II. We have performed total photometry in the Gunn r bandpass, classified stars and galaxies, and obtained structural parameters for the images. To estimate the photometric and structural errors on the CCD images and the completeness limits of our photometry, we performed realistic simulations of stars and galaxies and ran our classification algorithms. Here, we present central galaxy counts and metric photometry of the brightest cluster members, for which we give accurate positions, and compare this photometry with values in the literature. A linear magnitude-redshift relation has been derived from the tenth-ranked galaxy in each cluster. Photometric redshifts have been estimated for 57 clusters. We provide either spectroscopic or photometric redshifts for all the clusters in our sample. Further analysis of these data will be presented in further publications.

The Mount Stromlo Abell Cluster Supernova Search

We have initiated a 3 year project to find supernovae in a well-defined sample of high-density southern Abell clusters with redshifts z ≤ 0.08. These observations will provide a volume-limited sample of Type Ia supernovae (SNe Ia) to more than a magnitude below their peak brightness and will enable us to (1) measure the luminosity function of SNe, (2) further explore the correlation of light-curve shape with the absolute luminosity of SNe Ia to better understand SNe Ia as distance indicators, (3) measure SN rates, (4) measure the bulk motion of the Local Group using SNe Ia, and (5) directly compare SN Ia distances with brightest cluster galaxy distances. We use the MACHO wide-field two-color imager on the 1.3 m telescope at Mount Stromlo to routinely monitor ∼12 clusters per week. We describe our technique for target selection and scheduling search observations, and for finding and identifying SN candidates. We also describe the results from the first year of our program, including the detection of 19 SNe, several RR Lyrae variables, and hundreds of asteroids.

On the distribution of radio sources in rich galaxy clusters

The radial surface density distribution of Molongo radiosources in rich southern Abell clusters reported by Robertson J. G. and Roach G. J. (1990, Mon. Not. R. ast. Soc., 247) is shown to follow very precisely over a three dex range the r 1/4 law with an effectif radius of 100 kpc and an effective surface density of 0.333 radio source Mpc -2 . There is no need to postulate a two-component distribution. Comparison with the known effective radii of a few rich northern clusters suggest that the radio source distribution is much more concentrated to the cluster centres than the radio-quiet members.

REDSHIFTS OF FOUR SOUTHERN ABELL CLUSTERS.

ABSTRACT Redshifts have been measured for galaxies in four southern Abell clusters: A266, A2361, A2362, and A2661. Their average heliocentric values are: 28473, 18418, 18127, and 19060 km/s, respectively. A2361 and A2362 have a projected separation of just 1.3/h Mpc, which would make them among the tightest known binary clusters. Unless the single galaxy measured is in the foreground, A2661 is much closer than its D = 6 classification suggests. This casts further doubt on the reality of the putative association of distant rich clusters of which it was thought to be a member.