Galaxy And Mass Assembly: search for a population of high-entropy galaxy groups

Abstract

Observations with the Chandra X-ray Observatory are used to examine the hot gas properties within a sample of 10 galaxy groups selected from the Galaxy And Mass Assembly survey's optical friends-of-friends group catalogue. Our groups have been screened to eliminate spurious and unrelaxed systems, and the effectiveness of this procedure is demonstrated by the detection of intergalactic hot gas in 80 per cent of our sample. However we find that 9 of the 10 are X-ray underluminous by a mean factor ∼ 4 compared to typical X-ray selected samples. Consistent with this, the majority of our groups have gas fractions which are lower and gas entropies somewhat higher than those seen in typical X-ray selected samples. Two groups, which have high 2σ lower limits on their gas entropy, are candidates for the population of high entropy groups predicted by some AGN feedback models.