X-ray/optical image of the galaxy group LGG 402, showing the hot, X-ray emitting plasma of the group halo centred on the elliptical galaxy NGC 5982.
X-ray/optical image of CLoGS group
LGG 402. Mouseover to remove X-ray

The CLoGS project aims to be be the first statistically complete survey of galaxy groups observed in the X-ray, optical and radio wavebands. Since >50% of galaxies in the local volume reside in groups, they are a key environment for studies of galaxy evolution. As the locus of much of the mass in the nearby Universe, and the environment in which the hot, X-ray emitting intergalactic medium first becomes important, groups are also fundamental to our understanding of AGN feedback and structure formation. Our main science goals include:

The CLoGS sample consists of 53 candidate groups in the local Universe (<80 Mpc), so high-quality optical data are already available (from, e.g., LEDA). About 45% have archival X-ray data available, and we are using the Chandra and XMM-Newton X-ray observatories to complete the richer half of the sample. As low-frequency radio data provide the best chance of detecting older, fading radio galaxies, we are using the Giant Metrewave Radio Telescope to observe our groups at 610 and 235 MHz. The sample has also been selected to be within the coverage of the NVSS 1.4 GHz and TGSS 150 MHz surveys.

CLoGS has already been granted 50 ks of Chandra guaranteed time, 279 ks of XMM-Newton time, and 208 hours of observations on the GMRT. X-ray observations of the 26-group high-richness subsample, and radio observations of the full 53-group sample are now complete. CLoGS paper I describes the sample and the X-ray properties of the high-richness subsample.

In parallel with the main X-ray and radio surveys, the CHANGES (Complete H-alpha imaging of Nearby Group EnvironmentsS) survey aims to image all 53-groups in broadband optical and Hα, with the goal of examining the impact of the group environment on star formation. Roughly half the sample has been observed so far.