H. E. Jorgensen

Optically-selected clusters at 0.8 < z < 1.3 in the EIS Cluster Survey

This paper presents preliminary results of a spectroscopic survey being conducted at the VLT of fields with optically-selected cluster candidates identified in the EIS I-band survey. Here we report our findings for three candidates selected for having estimated redshifts in the range z=0.8-1.1. New multi-band optical/infrared data were used to assign photometric redshifts to galaxies in the cluster fields and to select possible cluster members in preparation of the spectroscopic observations. Based on the available spectroscopic data, which includes 147 new redshifts for galaxies with Iab 99%. The detected concentrations include systems with redshifts z=0.81, z=0.95, z=1.14 and the discovery of the first optically-selected cluster at z=1.3. The latter system, with three concordant redshifts, coincides remarkably well with the location of a firm X-ray detection (>5sigma) in a ~80ksec XMM-Newton image taken as part of this program which will be presented in a future paper (Neumann et al. 2002). The z>1 systems presented here are possibly the most distant identified so far by their optical properties alone.

Multi-object spectroscopy of low redshift EIS clusters. II. ⋆

We report the results of the rst multi-object spectroscopic observations at the Danish 1.54 m telescope at La Silla, Chile. Observations of ve cluster candidates from the ESO Imaging Survey Cluster Candidate Catalog are described. From these observations we conrm the reality of the ve clusters with measured redshifts of 0:11 z 0:35. We estimate velocity dispersions in the range 294{621 km s 1 indicating rather poor clusters. This, and the measured cluster redshifts are consistent with the results of the matched lter procedure applied to produce the Cluster Candidate Catalog.

Multi-object spectroscopy of low redshift EIS clusters. III. Properties of optically selected clusters

We have carried out an investigation of the properties of low redshift EIS clusters using both spectroscopy and imaging data. We present new redshifts for 738 galaxies in 21 ESO Imaging Survey (EIS) Cluster fields. We use the gap-technique to search for significant overdensities in redshift space and to identify groups/clusters of galaxies corresponding to the original EIS matched filter cluster candidates. In this way we spectroscopically confirm 20 of the 21 cluster candidates with a matched-filter estimated redshift z MF = 0.2. We have now obtained spectroscopic redshifts for 34 EIS cluster candidates with z MF = 0.2 (see also Hansen et al. 2002, AA Olsen et al. 2003. AA 2) richnesses corresponding to Abell classes R ≤ 1; and 3) concentration indices ranging from C = 0.2 to C = 1.2. From the analysis of the colours of the galaxy populations we find that 60% of the spectroscopically confirmed systems have a significant red sequence. These systems are on average richer and have higher velocity dispersions. We find that the colour of the red sequence galaxies matches passive stellar evolution predictions.

Spectroscopy of high-redshift EIS clusters

We present multi-object spectroscopic observations from FORS1 mounted at the VLT for 5 clusters detected in the ESO Imaging Survey. Together with the results for three other clusters presented previously, we confirm a total of 6 out of 8 clusters with estimated redshift

Optical/Infrared Survey of Galaxy ClustersDeep Fields

z_{MF}\geq0.6

A Deep X-ray Spectroscopic Survey of the ESO Imaging Survey Fields

. The spectroscopic redshifts are in good agreement with the estimated ones. To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

IUE observations of star formation in a cooling flow

In this contribution the ongoing effort to build a statistical sample of clusters of galaxies over a wide range of redshifts to study the evolution of clusters and member galaxies is reviewed. The starting point for this project has been the list of candidate clusters identified from the I-band EIS-WIDE survey data. Since the completion of this survey, new optical/infrared observations have become available and have been used to confirm some of these candidates using the photometric data alone or in combination with the results of follow-up spectroscopic observations. Our preliminary results show that the yield of real physical associations from the original catalog is conservatively >60% and that a large sample of clusters in the southern hemisphere, extending to high-redshifts, is within reach.

IRAS Observations of NGC 4696 — Cooling or Evaporation Flow?

The deepest ROSAT surveys have shown, that, in the energy range 0.5–2.0 keV, QSOs can account for ~ 30 per cent of the Diffuse X-ray Background (DXRB), and Narrow Emission Line Galaxies (NELG) and clusters of galaxies for about 10 per cent each. But, by assuming characteristic spectral behaviour, known from bright archetypes of these classes, the faint ROSAT sources will, due to the hardness of the DXRB spectrum, only give an insignificant contribution at say 10 keV. By exploiting the excellent capability of the SODART telescopes to obtain broad band x-ray spectroscopy at energies > 2 keV, we propose to perform a spectroscopic survey with SODART and push these telescopes to the limit at the high energies. By selecting the four ESO Imaging Survey fields EIS (each 6 deg2) we will take full advantage of the large, systematic effort ESO is putting into the optical survey of these fields. This spectroscopic x-ray survey will provide a large, statistically complete, sample of sources detected at high energies, more than an order of magnitude fainter than obtained by previous missions. The study of these sources will significantly improve our understanding not only of the origin of DXRB, but also provide new insight into the evolution of galaxies, clusters of galaxies and AGNs.

ESO imaging survey: infrared deep public survey

Star formation in cooling flows is usually found to have an initial mass function deficient in massive stars, but the center of the cooling flow in Hydra A has been shown to contain a significant number of early type stars. Here we use UV-spectra obtained with the IUE satellite together with ground based data to constrain the nature of this young population. The data is compatible with a burst of star formation with a Salpeter-like initial mass function, a burst age of about 4 107 yr, and a total mass ≈ 108 M⊙.

On the nature of the EIS candidate clusters: Confirmation of

We have analysed 60 and 100 μm IRAS observations of NGC 4696, the central elliptical galaxy of the Centaurus cluster. Ground-based optical photometry and spectroscopic data as well as ultraviolet (IUE) and X-ray (EINSTEIN) measurements constrain the interpretation of the infrared data. The dust responsible for the infrared emission has a temperature of 24 K, a total mass of 2.5 106 M⨀ and emits a total infrared luminosity of 1.5 109 L ⨀. It is heated by photons from the interstellar radiation field in the elliptical galaxy and by hot electrons from the X-ray gas. About 10 % of the radiating dust mass is located in a small ”horse shoe” shaped dust lane in the centre of NGC 4696. We argue that the other 90 % is distributed over a much larger region (R ≃ 10 kpc) in the galaxy.