paper

CHANDRA observations of the NGC 1550 galaxy group -- implication for the temperature and entropy profiles of 1 keV galaxy groups

arXiv:astro-ph/0308037 · doi:10.1086/378887

Abstract

We present a detailed \chandra study of the galaxy group NGC 1550. For its temperature (1.370.01 keV) and velocity dispersion ( 300 km s), the NGC 1550 group is one of the most luminous known galaxy groups (L = 1.65 erg s within 200 kpc, or 0.2 \rv). We find that within kpc, where the gas cooling time is less than a Hubble time, the gas temperature decreases continuously toward the center, implying the existence of a cooling core. The temperature also declines beyond 100 kpc (or 0.1 \rv). There is a remarkable similarity of the temperature profile of NGC 1550 with those of two other 1 keV groups with accurate temperature determination. The temperature begins to decline at 0.07 - 0.1 \rv, while in hot clusters the decline begins at or beyond 0.2 \rv. Thus, there are at least some 1 keV groups that have significantly different temperature profiles from those of hot clusters, which may reflect the role of non-gravitational processes in ICM/IGM evolution. NGC 1550 has no isentropic core in its entropy profile, in contrast to the predictions of `entropy-floor' simulations. We compare the scaled entropy profiles of three 1 keV groups (including NGC 1550) and three 2 - 3 keV groups. The scaled entropy profiles of 1 keV groups show much larger scatter than those of hotter systems, which implies varied pre-heating levels. We also discuss the mass content of the NGC 1550 group and the abundance profile of heavy elements.

arXiv commentemulateapj5.sty, 18 pages, 11 figures (including 4 color), to appear in ApJ, v598, n1, 20 Nov 2003

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