Deep Optical Observations of Compact Groups of Galaxies

Abstract

Compact groups of galaxies appear to be extremely dense, making them likely sites of intense galaxy interaction, while their small populations make them relatively simple to analyze. In order to search for optical interaction tracers such as diffuse light and galaxy tidal features in Hickson compact groups (HCGs), we carried out deep photometry in three filters on a sample of HCGs with $ROSAT$ observations. Using a modeling procedure to subtract the light of bright early-type galaxies, we found shell systems and extended envelopes around many, but not all, of those galaxies. Only one group in our sample, HCG 94, has diffuse light in the group potential (with a luminosity of 7 L${}^{\ast }$); the other groups do not contain more than 1/3 L${}^{\ast }$ in diffuse light. With the exception of HCG 94 (which is the most X-ray--luminous HCG), we found no correlation between the presence of shells or other tidal features and the X-ray luminosity of a group. Better predictors of detectable group X-ray emission are a low spiral fraction and belonging to a larger galaxy condensation---neither of which are correlated with optical disturbances in the group galaxies. Two elliptical galaxies that are extremely optically luminous but X-ray--faint are found to have shells and very complex color structures. This is likely due to recent infall of gas-rich material into the galaxies, which would produce both the disruption of stellar orbits and a significant amount of star formation.

24 pages, to appear in October 1995 Astronomical Journal; postscript text and figures (low resolution scans, tar'ed and compressed) available at ftp://astro.lsa.umich.edu/pub/get/pildis2

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• The Dynamics of Poor Systems of Galaxies
• Intragroup diffuse light in compact groups of galaxies II. HCG 15, 35 and 51
• On the Influence of the Environment in the Star Formation Rates of a Sample of Galaxies in Nearby Compact Groups
• Evidence for tidal interaction and merger as the origin of galaxy morphology evolution in compact groups
• HCG 16: A High Concentration of Active Galaxies in the Nearby Universe
• Does the virial mass drive the intra-cluster light? The relationship between the ICL and M${}_{vir}$ from VEGAS
• VEGAS: A VST Early-type GAlaxy Survey.VI. The diffuse light in HCG 86 from the ultra-deep VEGAS images
• Hierarchical Structure Formation and Modes of Star Formation in Hickson Compact Group 31
• Diffuse Light in Hickson Compact Groups: The Dynamically Young System HCG 44
• Seyfert's Sextet: A Slowly Dissolving Stephan's Quintet?
• Quantified diffuse light in compact groups of galaxies
• Gas Kinematics of Three Hickson Compact Groups: The Data
• Is the Fast Evolution Scenario for Virialized Compact Groups Really Compelling? The Role of a Dark Massive Group Halo
• The ASTRID Simulation at z=0: From Massive Black Holes to Large-scale Structure
• H_αLuminosity and Star Formation of Galaxies in HCGs
• Galaxy groups in the 2dF galaxy redshift survey: A Compactness Analysis of Groups
• MeerKAT view of Hickson Compact Groups:I. Data description and release
• Compact Groups in GDM Cosmological Simulations