The galaxy populations of X-ray-detected, poor groups

Kim Vy H. Tran, Luc Simard, Ann I. Zabludoff, John S. Mulchaey

Research output: Contribution to journalArticlepeer-review

87 Scopus citations


We determine the quantitative morphology and star formation properties of galaxies in six nearby X-ray-detected, poor groups using multiobject spectroscopy and wide-field R imaging. The mean recessional velocities of the galaxy groups range from 2843 to 7558 km s-1. Each group has 15-38 confirmed members ranging in luminosity from dwarfs to giants (-13.7 ≥ MR - 5 log h ≥ - 21.9). We measure structural parameters for each galaxy by fitting a PSF-convolved, two-component model to their surface brightness profiles. To compare the samples directly, we fade, smooth, and rebin each galaxy image so that we effectively observe each galaxy at the same redshift (9000 km s-1) and physical resolution (0.87 h-1 kpc). The structural parameters are combined with [O II] measurements to test for correlations between morphological characteristics and current star formation in these galaxies. We compare results for the groups to a sample of field galaxies. We find that: (1) Galaxies spanning a wide range in morphological type and luminosity are fit well by a de Vaucouleurs bulge with exponential disk profile. (2) Morphologically classifying these nearby group galaxies by their bulge fraction (B/T) is fairly robust on average, even when their redshift has increased by up to a factor of 4 and the effective resolution of the images is degraded by up to a factor of 5. (3) The fraction of bulge-dominated systems in these groups is higher than in the field (∼ 50% versus ∼ 20%). (4) The fraction of bulge-dominated systems in groups decreases with increasing radius, similar to the morphology-radius (∼ density) relation observed in galaxy clusters. (5) Current star formation in group galaxies is correlated with significant morphological asymmetry for disk-dominated systems (B/T < 0.4). (6) The group galaxies that are most disk dominated (B/T < 0.2) are less star forming and asymmetric on average than their counterparts in the field.

Original languageEnglish (US)
Pages (from-to)172-191
Number of pages20
JournalAstrophysical Journal
Issue number1 PART 1
StatePublished - Mar 1 2001


  • Galaxies : fundamental parameters
  • Galaxies : structure
  • Galaxies: clusters: general
  • Galaxies: evolution

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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