* Astronomy

Blobrana · L

RE: Cl 1604 Supercluster

Blobrana · L

Title: Chandra Observations of the Cl1604 Supercluster at z=0.9: Evidence for an Overdensity of Active Galactic Nuclei
Authors: Dale D. Kocevski, Lori M. Lubin, Roy Gal, Brian C. Lemaux, Christopher D. Fassnacht, Gordon K. Squires

We present the results of Chandra observations of the Cl1604 supercluster at z~0.9. The system is the largest structure mapped at redshifts approaching unity, containing at least eight spectroscopically confirmed galaxy clusters and groups. Using two 50-ksec ACIS-I pointings we examine both the X-ray point source population and the diffuse emission from individual clusters in the system. We find a 2.5\sigma excess of point sources detected in the hard band (2-10 keV) relative to the number of sources found in blank fields observed by Chandra. No such excess is observed in the soft band (0.5-2 keV). The hard-band source density is 1.47 times greater than that of a blank field, in agreement with the previously reported correlation between overdensity amplitude and cluster redshift. Using a maximum likelihood technique we have matched 112 of the 161 detected X-ray point sources to optical counterparts and found 15 sources that are associated with the supercluster. All 15 sources have rest-frame luminosities consistent with emission from active galactic nuclei (AGN). We find that the supercluster AGN largely avoid the densest regions of the system and are instead distributed on the outskirts of massive clusters or within poorer clusters and groups. We have also detected diffuse emission from two of the eight clusters and groups in the system, clusters Cl1604+4304 and Cl1604+4314. The systems have bolometric luminosities of 1.43x10^44 and 8.20x10^43 h70^-2 erg s^-1 and gas temperatures of 3.50 (+1.82-1.08) and 1.64 (+0.65-0.45) keV, respectively. Using updated velocity dispersions, we compare the properties of these systems to the cluster scaling relations followed by other X-ray and optically selected galaxy clusters at high redshift.

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Blobrana · L

Title: The Complex Structure of the Cl 1604 Supercluster at z~0.9
Authors: R. R. Gal, B. C. Lemaux, L. M. Lubin, D. Kocevksi, G. K. Squires

The Cl1604 supercluster at z=0.9 is one of a small handful of such structures discovered in the high redshift universe, and is the first target observed as part of the Observations of Redshift Evolution in Large Scale Environments (ORELSE) Survey. To date, Cl1604 is the largest structure mapped at z~1, with the most constituent clusters and the largest number of spectroscopically confirmed member galaxies. In this paper we present the results of a spectroscopic campaign to create a three-dimensional map of Cl1604 and to understand the contamination by fore- and background large scale structures. Combining new Deep Imaging Multi-object Spectrograph observations with previous data yields redshifts for 1,383 extragalactic objects in a ~ 0.08 sq. deg region, 449 of which are supercluster members. We examine the complex three dimensional structure of Cl1604, providing velocity dispersions for eight of the member clusters and groups. Our extensive spectroscopic dataset is used to examine potential biases in cluster velocity dispersion measurements in the presence of overlapping structures and filaments. We also discuss other structures found along the line-of-sight, including a filament at z=0.6 and two serendipitously discovered clusters/groups at z~1.2.

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