The distance and mass of the galaxy cluster Abell 1995 derived from Sunyaev-Zeldovich effect and X-ray measurements

Sandeep K. Patel, Marshall Joy, John E. Carlstrom, Gilbert P. Holder, Erik D. Reese, Percy L. Gomez, John P. Hughes, Laura Grego, William L. Holzapfel

Research output: Contribution to journalArticlepeer-review


We present multiwavelength observations of the Abell 1995 galaxy cluster. From an analysis of X-ray spectroscopy and imaging data, we derive the electron temperature, cluster core radius, and central electron number density. Using optical spectroscopy of 15 cluster members, we derive an accurate cluster redshift and velocity dispersion. Finally, the interferometric imaging of the Sunyaev-Zeldovich effect toward Abell 1995 at 28.5 GHz provides a measure of the integrated pressure through the cluster. The X-ray and Sunyaev-Zeldovich effect observations are combined to determine the angular diameter distance to the cluster of DA = 1294+294 +438-283 -458 Mpc (statistical followed by systematic uncertainty), implying a Hubble constant of H0 = 52.2+11.4 +18.5-11.9 -17.7 km s-1 Mpc-1 for ΩM = 0.3 and ΩΛ = 0.7. We find a best-fit H0 of 46 km s-1 Mpc-1 for the ΩM = 1 and ΩΛ = 0 cosmology, and 48 km s-1 Mpc-1 for ΩM = 0.3 and ΩΛ = 0.0. The X-ray data are also used to derive a total cluster mass of MHSEtot(r500) = 5.18+0.62-0.48 × 1014 h-1 M; the optical velocity dispersion yields an independent and consistent estimate of Mvirialtot(r500) = 6.35+1.51-1.19 × 1014 h-1 M. Both of the total mass estimates are evaluated at a fiducial radius, r500 = 830 h-1 kpc, where the overdensity is 500 times the critical density. The total cluster mass is then combined with gas mass measurements to determine a cluster gas mass fraction of fg = 0.056+0.010-0.013 h-3/2. In combination with recent baryon density constraints, the measured gas mass fraction yields an upper limit on the mass density parameter of ΩM h1/2 ≤ 0.34+0.06-0.05.

Original languageEnglish (US)
Pages (from-to)37-48
Number of pages12
JournalAstrophysical Journal
Issue number1 PART 1
StatePublished - Sep 20 2000
Externally publishedYes


  • Cosmology: observations
  • Dark matter
  • Distance scale
  • Galaxies: clusters: individual (Abell 1995)
  • X-rays: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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