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tokens: They used an automated search, applying a ‘friends-of- friends’ algorithm to find groups in the magnitude-limited Center for Astrophysics 2 redshift survey (CfA2; de Lapparent, Geller Huchra 1986 ) and Southern Sky Redshift Survey (SSRS2; da Costa et al. 1991 ) catalogues. This algorithm used projected distances between galaxies (ΔD ≤ 50 kpc), and their line-of-sight velocity differences (Δv ≤ 1000 km s −1 ) to determine whether two galaxies belong to a group. This methodology was adopted in order to eliminate biases as a function of distance which are introduced by visually selecting groups, as Hickson ( 1982 ) had done. Selecting CGs based on their redshift reduces the possibility of chance projections, however the isolation criterion was not rigorously satisfied and therefore many RSCGs are actually components of larger structures. Because of this, RSCGs 21, 67 and 68 are excluded from our analysis as they are part of clusters, thus reducing our sample to 46 CGs (Walker et al. 2012 ). The RSCGs in our sample were therefore selected to have properties similar to HCGs. In addition, Walker et al. ( 2010 ) chose to include only CGs that are at a sufficiently low redshift ( z 0.035) that the polycyclic aromatic hydrocarbon features do not shift out of their rest-frame IRAC bands to maintain their rest-frame positions in mid-IR colour space. The 46 remaining CGs in our sample satisfy this requirement. The coordinates and group velocities of each CG are given in Table 1 , as well as the breakdown of group properties such as group H i content. Table 1. HCG and RSCG sample. Notes . a Position data taken from Hickson ( 1982 ) for HCG sample. b Position data taken from Barton et al. ( 1996 ) for RSCG sample. c Velocities corrected to CMB taken from http://ned.ipac.caltech.edu/ for all CGs in our sample. d CMB corrected values from http://ned.ipac.caltech.edu/ with a cosmology of H 0 = 70 kms −1 Mpc −1 , Ω M = 0.3, Ω Λ = 0.7. e Values taken from http://ned.ipac.caltech.edu/ with a cosmology of H 0 = 70 kms −1 Mpc −1 , Ω M = 0.3, Ω Λ = 0.7. f SDSS Optical r -band Data from Walker et al. ( 2013 ). g Group types as defined by J07 . h Walker et al. (submitted). i These CGs are part of clusters. Their photometry is presented in Table 5 , but they are not included in the subsequent analysis. 2.2 UV data Swift is a multiwavelength observatory (Gehrels et al. 2004 ) whose primary goal is to study gamma-ray bursts. When Swift is not following gamma-ray burst targets, there is a fill-in program of other observations. The UVOT (Roming et al. 2005 ) instrument is a 30 cm telescope with a 17 × 17 arcmin 2 field of view that provides UV and optical coverage (1600–8000 Å) with a spatial resolution of ∼ 2.5 arcsec. It uses a micro-channel-plate, intensified photon- counting CCD detector. It has 256 × 256 active pixels, each of which is subdivided into 8 × 8 pixels using a centroiding algorithm (Breeveld et al. 2010 ). The data used in this study originated from