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Date and Time of the Query: 2019-03-21 T08:56:35 PDT
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For refcode 1999ApJ...518...69M:
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1999ApJ...518...69M The Dynamics of Poor Systems of Galaxies ANDISHEH MAHDAVI AND MARGARET J. GELLER Harvard-Smithsonian Center for Astrophysics, Mail Stop 10, 60 Garden Street, Cambridge, MA 02138 HANS BOHRINGER Max-Planck-Institut fur Extraterrestrische Physik MICHAEL J. KURTZ Harvard-Smithsonian Center for Astrophysics AND MASSIMO RAMELLA Osservatorio Astronomico di Trieste Received 1998 October 2; accepted 1999 January 15 ABSTRACT We assemble and observe a sample of poor galaxy systems that is suitable for testing N-body simulations of hierarchical clustering and other dynamical halo models. We (1) determine the parameters of the density profile {rho}(r) and the velocity dispersion profile {sigma}p(R),(2) separate emission-line galaxies from absorption-line galaxies, examining the model parameters and as a function of spectroscopic type, and (3) for the best-behaved subsample, constrain the velocity anisotropy parameter, {beta}, which determines the shapes of the galaxy orbits. Our sample consists of 20 systems, 12 of which have extended X-ray emission in the ROSAT All-Sky Survey. We measure the 877 optical spectra of galaxies brighter than m_R_ ~ 15.4 within 1.5 h^-1^ Mpc of the system centers (we take H_0_ = 100 h km s^-1^ Mpc^-1^). Thus, we sample the system membership to a radius typically three times larger than other recent optical group surveys. The average system population is 30 galaxies, and the average line-of-sight velocity dispersion is ~300 km s-1. The Navarro, Frenk, & White universal profile and the Hernquist model both provide good descriptions of the spatial data. In most cases an isothermal sphere is ruled out. Systems with declining {sigma}_p_(R) are well-matched by theoretical profiles in which the star-forming galaxies have predominantly radial orbits ({beta}>0); many of these galaxies are probably falling in for the first time. There is significant evidence for spatial segregation of the spectroscopic classes regardless of {sigma}_p_(R). Subject headings: galaxies: clusters: general-galaxies: fundamental parameters-X-rays: galaxies
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