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Proposal Information for 2002A-0286


PI: Marc E. Zimer, Max PlanCk Institute for Astronomy, zimer@mpia.de
Address: Koenigstuhl 17, Heidelberg 69117, Germany

CoI: Ann I. Zabludoff, University of Arizona
CoI: John S. Mulchaey, Carnegie Observatories

Title: The Study of X-Ray Faint Groups of Galaxies

Abstract: Numerical simulations indicate that in the absence of non- gravitational heating, the density profiles of groups and clusters should be nearly identical (Navarro et al 1997). If this is the case, the relationships between X-ray luminosity (L_\rm X), X-ray temperature (T) and optical velocity dispersion (\sigma) are expected to be similar for groups and clusters. Some authors have reported departures from such uniformity which is consistent with significant preheating of the intragroup medium by an early generation of stars (e.g. Ponman et al. 1999; Helsdon & Ponman 2001). However, other studies have found that clusters and groups scale similarly (e.g. Mulchaey & Zabludoff 1998). To adequately compare the properties of groups and clusters requires well-determined X-ray temperatures, X-ray luminosities and optical velocity dispersions. While these quantities generally exist for rich clusters, the properties of groups are often poorly determined. In particular, most group velocity dispersions are based on only 3 or 4 velocity measurements. We have recently completed a large ROSAT survey which has determined accurate X-ray temperatures and luminosities for approximately 50 groups. We propose to use Hydra on WIYN to study a small subset of these groups. We will use the HYDRA data to: 1) significantly increase the membership for a sample of X-ray detected groups 2) determine accurate velocity dispersions for groups with well- known X-ray luminosities and temperatures 3) constrain the scaling relationships for groups and clusters 4) study the importance of preheating in groups and clusters


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