1. First X-Ray Results from the Optically Selected Red Sequence Cluster Survey (RCS) at Z ~ 1 Amalia K. Hicks, Erica Ellingson, Howard Yee, Tesla Jeltema, Mark Bautz, Mike Gladders, Gordon Garmire Studies of clusters of galaxies at high redshift have had a sizeable impact on the cosmological community, yet most of our knowledge of clusters is derived from X- ray selected surveys. By their very nature these surveys preferentially select rich clusters with deep potential wells and/or cooling cores. These objects may primarily represent a high X-ray luminosity tail of the cluster distribution, and therefore might not be representative of clusters as a whole. The Red Sequence Cluster Survey (RCS) has provided an optically selected sample of high redshift clusters (to z ~1.2). Preliminary results from X-ray follow-up observations taken with Chandra indicate that these clusters are indeed less luminous than their similarly rich, X-ray selected counterparts. Here we present and discuss the implications of the first X-ray observations of RCS clusters. Abstract RCS 0224-0002 RCS 0439.6-2905 RCS 1419+5326 RCS 1620+2929 The RCS Survey High redshift clusters detected via color-magnitude relation (Gladders & Yee, 2000). 1 st RCS survey spans 100 deg 2 RCS-2 (1000 deg 2 ) underway The goal: to obtain cosmological constraints via calibration of the link between optical richness (B gc ) and mass RESULTS References All RCS clusters observed with Chandra were detected in X-rays X-ray luminosities are systematically low compared to those of the X-ray selected CNOC sample Surface brightness profiles indicate that the ICM of RCS clusters may be more diffuse than that of their X- ray selected counterparts The L x -B gc relation falls closer to expectations when only red-sequence galaxies are included in the calculation of B gc RCS clusters which exhibit strong gravitational lensing lie closer to the expected L x -B gc relation Evaluation of the efficacy of optical richness as a mass indicator requires additional X-ray data (primarily the determination of T x ) as well as a more detailed understanding of galaxy populations in high-z clusters Z = 0.951 Z = 0.773 Z = 0.64 RCS 0224-0002 ImagesRCS 1419+5326 Images RCS 0439-2905 Images Figure 1: top – optical image of RCS 0439, bottom – 5 pixel FWHM Gaussian smoothed 0.29-7.0 keV Chandra flux image The L x -B gc Relationship Figure 4: Unabsorbed bolometric X-ray luminosities were calculated with PIMMS after obtaining background subtracted count rates within a 500 kpc radius in the 0.3-8.0 keV band. Temperatures for RCS clusters were taken to be 5 keV. Errors were calculated using both photon statistics and temperature uncertainty, with a high temperature estimated from the T x -B gc relationship (Yee & Ellingson, 2003), and a low temperature of 3 keV. References RCS Surface Brightness Profiles and  Fits Figure 5: Surface brightnesses were calculated for the 0.29-7.0 keV band in 2” radial bins (with the exception of RCS 1419, which was extracted in 1” bins). The orange line represents the best fitting  model, while the horizontal and vertical dotted lines indicate the fit-determined background value and the fit range, respectively. Figure 2: top – HST image of RCS 0224-0002. The outer gravitational lensing arc has been spectroscopically confirmed at a redshift of z = 4.87, with the others expected to fall within the range z = 1.8 - 3.6, bottom - HST image of RCS 0224 with overlaid X-ray contours. 5 linearly spaced contours indicating values between 9.4 x 10 -6 and 2.1 x 10 -5 counts/pix 2 /sec were created in DS9 using a Gaussian smoothed (5 pixel FWHM) 0.29- 7.0 keV binned (by 4) Chandra flux image. Figure 3: top – optical image of RCS 1419, note the gravitational lensing arcs, bottom – 5 pixel FWHM Gaussian smoothed 0.29-7.0 keV Chandra flux image.