VEGAS: A VST Early-type GAlaxy Survey

Abstract

Context. In this paper, we present ultra-deep images of the compact group of galaxies HCG 86 as part of the VEGAS survey. Aims. Our main goals are to estimate the amount of intra-group light (IGL) as well as to study the light and colour distributions in order to address the main formation process of the IGL component in groups of galaxies. Methods. We derived the azimuthally averaged surface brightness profiles in the g, r, and i bands with g − r and r − i average colours and colour profiles for all group members. By fitting the light distribution, we extrapolated the contribution of the stellar halos plus the diffuse light from the brightest component of each galaxy. The results are compared with theoretical predictions. Results. The long integration time and wide area covered make our data reach deeper than previous literature studies of the IGL in compact groups of galaxies and allow us to produce an extended (∼160 kpc) map of the IGL, down to a surface brightness level of ∼30 mag arcsec−2 in the g band. The IGL in HCG 86 is mainly in diffuse form and has average colours of g − r ∼ 0.8 mag and r − i ∼ 0.4 mag. The fraction of IGL in HCG 86 is ∼16% of the total luminosity of the group, and this is consistent with estimates available for other compact groups and loose groups of galaxies of similar virial masses. A weak trend is present between the amount of IGL and the early-type to late-type galaxy ratio. A lack of a clear correlation is found between the amount of diffuse light and the cluster or group virial mass. Conclusions. By comparing the IGL fraction and colours with those predicted by simulations, the amount of IGL in HCG 86 would be the result of the disruption of satellites at an epoch of z ∼ 0.4. At this redshift, the observed colours are consistent with the scenario where the main contribution to the mass of the IGL comes from the intermediate-to-massive galaxies (1010 ≤ M* ≤ 1011 M⊙).