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Date and Time of the Query: 2018-11-17 T11:06:06 PST
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For refcode 1995ApJ...444L..61O:
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1995ApJ...444L..61O USING X-RAYS TO DETERMINE WHICH COMPACT GROUPS ARE ILLUSORY JEREMIAH P. OSTRIKER AND LORI M. LUBIN Princeton University Observatory, Peyton Hall, Princeton, NJ 08544-0001 AND LARS HERNQUIST Lick Observatory, University of California at Santa Cruz, Santa Cruz CA 95064 Received 1994 November 14; accepted 1995 February 23 ABSTRACT If the large-scale galaxy distribution is filamentary, as suggested by some observations and recent hydrodynamical simulations, then lengthwise views of filaments will apparently produce compact groups (CGs) that are in reality stretched out along the line of sight. This possibility has been advocated recently by Hernquist, Katz:, & Weinberg (1995). Here we propose a test for this hypothesis using X-ray emission from CGs. The observable quantity Q = L_x_a_p_^3^/L_g_^2^T_x_^1/2^ should be proportional to the axis ratio of the group, a/c, where a and c are the short and long axes of a prolate distribution, a_p_ is the radius of the group projected onto the sky, L_x_ is the bolometric X-ray luminosity, L_g_ is the group blue luminosity, and T_x_ is the gas temperature. We find that the distribution of Q is consistent with the notion that many CGs with unusually small values of a/c are frauds, i.e., that the values of Q are anomalously small. Absent other information, it is equally possible that CGs are very gas-poor relative to rich clusters; however, this can be tested using the Sunyaev-Zeldovich effect. If the groups have a close to normal ratio of gas to total mass, but are simply stretched out along the line of sight, a Sunyaev-Zeldovich signal should be detectable. Subject headings: galaxies: compact
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