Browsing by Author "Mullis, CR"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Cosmological constraints from the evolution of the cluster baryon mass function at z ∼ 0.5
    (2003) Vikhlinin, A; Voevodkin, A; Mullis, CR; VanSpeybroeck, L; Quintana, H; McNamara, BR; Gioia, I; Hornstrup, A; Henry, JP; Forman, WR; Jones, C
    We present a new method for deriving cosmological constraints based on the evolution of the baryon mass function of galaxy clusters and implement it using 17 distant clusters from our 160 deg(2) ROSAT survey. The method uses the cluster baryon mass as a proxy for the total mass, thereby avoiding the large uncertainties of the M-tot-T or M-tot-L-X relations used in all previous studies. Instead, we rely on a well-founded assumption that the M-b/M-tot ratio is a universal quantity, which should result in a much smaller systematic uncertainty. Taking advantage of direct and accurate Chandra measurements of the gas masses for distant clusters, we find strong evolution of the baryon mass function between z > 0.4 and the present. The observed evolution defines a narrow band in the Omega(m)-Lambda plane, Omega(m) + 0.23Lambda = 0.41 +/- 0.10 at 68% confidence, which intersects with constraints from the cosmic microwave background and Type Ia supernovae near Omega(m) = 0.3 and Lambda = 0.7.
  • No Thumbnail Available
    Item
    The 160 Square Degree ROSAT Survey
    (2003) Mullis, CR; McNamara, BR; Quintana, H; Vikhlinin, A; Henry, JP; Gioia, IM; Hornstrup, A; Forman, W; Jones, C
    We present the revised catalog of galaxy clusters detected as extended X-ray sources in the 160 Square Degree ROSAT Survey, including spectroscopic redshifts and X-ray luminosities for 200 of the 201 members. The median redshift is z(median) = 0.25, and the median X-ray luminosity is L-X,L-median = 4.2 x 10(43) h(50)(-2) s(-1) (0.5 - 2.0 keV). This is the largest high-redshift sample of X-ray - selected clusters published to date. There are 73 objects at z > 0.3 and 22 objects at z > 0.5 drawn from a statistically complete flux-limited survey with a median object flux of 1.4 x 10(-13) ergs cm(-2) s(-1). We describe the optical follow-up of these clusters with an emphasis on our spectroscopy, which has yielded 155 cluster redshifts, 110 of which are presented here for the first time. These measurements, combined with 45 from the literature and other sources, provide near-complete spectroscopic coverage for our survey. We discuss the final optical identifications for the extended X-ray sources in the survey region and compare our results to similar X-ray cluster searches.