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تسجيل مستخدم جديدLooking for the S-Z Effect towards Distant ROSAT Clusters of Galaxies
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We report on observations of the Sunyaev-Zeldovich effect towards X-ray ROSAT clusters taken with a double channel (1.2 and 2 mm) photometer installed at the focus of the 15m SEST antenna in Chile. This paper describes the first results obtained for the high-z clusters S1077, A2744 and S295. Marginal detections were found for A2744 and at 1 mm for S1077. We discuss these data in terms of contamination of sources along the line of sight and give a constraint on the amplitude of the kinematic effect.
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An observing campaign was devoted to the search for the Sunyaev-Zeldovich (S-Z) effect towards X-ray ROSAT Clusters in the millimetric spectral domain. A double channel (1.2 and 2 {it mm}) photometer was installed at the focus of the 15m Swedish ESO
Submillimeter Telescope (SEST) in Chile in september 1994 and 1995 and observations of the targets S1077, A2744, S295 and RXJ0658-5557 were gathered. Detections were found for A2744 at 1 {it mm} and in both channels (at 1.2 and 2 {it mm}) towards RXJ0658-5557. For the first time there is evidence for the S-Z enhancement and both the latter and the decrement were detected on the same source. We discuss astrophysical and systematic effects which could give origin to these signals.
We summarize the main results obtained recently by our group on the identification and study of very high-z galaxies (z>7) using lensing clusters as natural gravitational telescopes. A description of our pilot survey with ISAAC/VLT is presented, aime
d at the spectroscopic confirmation of z>7 candidate galaxies photometrically selected from deep near-IR, HST and optical ground-based imaging. The first results issued from this survey are discussed, in particular the global photometric properties of our high-z candidates, and the implications for the global star formation rate at very high-z.
We investigate the relationship between environment and galaxy evolution in the redshift range $0.5 < z < 1.0$. Galaxy overdensities are selected using a Friends-of-Friends algorithm, applied to deep photometric data in the Ultra-Deep Survey (UDS) fi
eld. A study of the resulting stellar mass functions reveals clear differences between cluster and field environments, with a strong excess of low-mass rapidly quenched galaxies in cluster environments compared to the field. Cluster environments also show a corresponding deficit of young, low-mass star-forming galaxies, which show a sharp radial decline towards cluster centres. By comparing mass functions and radial distributions, we conclude that young star-forming galaxies are rapidly quenched as they enter overdense environments, becoming post-starburst galaxies before joining the red sequence. Our results also point to the existence of two environmental quenching pathways operating in galaxy clusters, operating on different timescales. Fast quenching acts on galaxies with high specific star-formation rates, operating on timescales shorter than the cluster dynamical time ($ < 1$ Gyr). In contrast, slow quenching affects galaxies with moderate specific star-formation rates, regardless of their stellar mass, and acts on longer timescales ($gtrsim 1$ Gyr). Of the cluster galaxies in the stellar mass range $9.0 < log(M_{*}/M_{odot}) < 10.5$ quenched during this epoch, we find that 73% were transformed through fast quenching, while the remaining 27% followed the slow quenching route.
The results of a search for distant clusters of galaxies performed using the I-band data obtained by the ESO Imaging Survey (EIS) are presented. Cluster candidates are identified using a matched filter algorithm, that provides not only an objective d
etection criterion, but also the means to estimate the cluster redshift and richness. A preliminary sample of distant clusters has been obtained, containing 252 cluster candidates with estimated redshift in the interval 0.2 < z < 1.3 (median redshift z_med ~ 0.4) over an area of approximately 14 square degrees. The adopted selection criteria for the inclusion of cluster candidates in this sample has been in general conservative, as the primary concern has been the reliability of the candidates rather than the completeness of the sample.
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 $1.2times10^{-7},{rm Mpc^{-3}}$ 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.
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