Isolated compact groups (CGs) of galaxies present a range of dynamical states, group velocity dispersions, and galaxy morphologies with which to study galaxy evolution, particularly the properties of gas both within the galaxies and in the intragroup medium. As part of a large, multiwavelength examination of CGs, we present an archival study of diffuse X-ray emission in a subset of nine Hickson compact groups (HCGs) observed with the Chandra X-Ray Observatory. We find that seven of the groups in our sample exhibit detectable diffuse emission. However, unlike large-scale emission in galaxy clusters, the diffuse features in the majority of the detected groups are linked to the individual galaxies, in the form of both plumes and halos likely as a result of vigourous star formation or activity in the galaxy nucleus, as well as in emission from tidal features. Unlike previous studies from earlier X-ray missions, HCGs 31, 42, 59, and 92 are found to be consistent with the L X -T relationship from clusters within the errors, while HCGs 16 and 31 are consistent with the cluster L X -σ relation, though this is likely coincidental given that the hot gas in these two systems is largely due to star formation. We find that L X increases with decreasing group H i to dynamical-mass ratio with tentative evidence for a dependence in X-ray luminosity on H i morphology whereby systems with intragroup H i indicative of strong interactions are considerably more X-ray luminous than passively evolving groups. We also find a gap in the L X of groups as a function of the total group specific star formation rate. Our findings suggest that the hot gas in these groups is not in hydrostatic equilibrium and these systems are not low-mass analogs of rich groups or clusters, with the possible exception of HCG 62.

We present results from a low-resolution spectroscopic survey for 21 galaxy clusters at 0.4 < z < 0.8 selected from the ESO Distant Cluster Survey (EDisCS). We measured spectra using the Low-Dispersion Prism (LDP) in IMACS on the Magellan Baade telescope and calculate redshifts with a precision of σ z = 0.006. We find 1, 602 galaxies that are brighter than R = 22.6 in the large-scale cluster environs. We identify the galaxies expected to be accreted by the clusters as they evolve to z = 0 using spherical infall models, and find that ∼ 30-70% of the z = 0 cluster population lies outside the virial radius at z ∼ 0.6. For analogous clusters at z = 0, we calculate that the ratio of galaxies that have fallen into the clusters since z ∼ 0.6 to that which were already in the core at that redshift is typically between ∼ 0.3 and 1.5. This wide range of ratios is due to intrinsic scatter and is not a function of velocity dispersion, so a variety of infall histories is to be expected for clusters with current velocity dispersions of 300 < ∼ σ < ∼ 1200 km s −1 . Within the infall regions of z ∼ 0.6 clusters, we find a larger red fraction of galaxies than in the field and greater clustering among red galaxies than blue. We interpret these findings as evidence of "preprocessing", where galaxies in denser local environments have their star formation rates affected prior to their aggregation into massive clusters, although the possibility of backsplash galaxies complicate the interpretation.

Compact groups of galaxies provide insight into the role of low-mass, dense environments in galaxy evolution because the low velocity dispersions and close proximity of galaxy members result in frequent interactions that take place over extended time-scales. We expand the census of star formation in compact group galaxies by Tzanavaris et al. (2010) and collaborators with Swift UVOT, Spitzer IRAC and MIPS 24 µm photometry of a sample of 183 galaxies in 46 compact groups. After correcting luminosities for the contribution from old stellar populations, we estimate the dust-unobscured star formation rate (SFR UV ) using the UVOT uvw2 photometry. Similarly, we use the MIPS 24 µm photometry to estimate the component of the SFR that is obscured by dust (SFR IR ). We find that galaxies which are MIR-active (MIR-'red'), also have bluer UV colours, higher specific SFRs, and tend to lie in H I-rich groups, while galaxies that are MIR-inactive (MIR-'blue') have redder UV colours, lower specific SFRs, and tend to lie in H I-poor groups. We find the SFRs to be continuously distributed with a peak at about 1 M yr −1 , indicating this might be the most common value in compact groups. In contrast, the specific SFR distribution is bimodal, and there is a clear distinction between star-forming and quiescent galaxies. Overall, our results suggest that the specific SFR is the best tracer of gas depletion and galaxy evolution in compact groups.

KA1858+4850 is a narrow-line Seyfert 1 galaxy at redshift 0.078 and is among the brightest active galaxies monitored by the Kepler mission. We have carried out a reverberation mapping campaign designed to measure the broad-line region size and estimate the mass of the black hole in this galaxy. We obtained 74 epochs of spectroscopic data using the Kast Spectrograph at the Lick 3-m telescope from February to November of 2012, and obtained complementary V -band images from five other ground-based telescopes. We measured the Hβ light curve lag with respect to the V -band continuum light curve using both cross-correlation techniques (CCF) and continuum light curve variability modeling with the JAVELIN method, and found rest-frame lags of τ CCF = 13.53 +2.03 −2.32 days and τ JAVELIN = 13.15 +1.08 −1.00 days. The Hβ root-mean-square line profile has a width of σ line = 770 ± 49 km s −1 . Combining these two results and assuming a virial scale factor of f = 5.13, we obtained a virial estimate of M BH = 8.06 +1.59 −1.72 × 10 6 M ⊙ for the mass of the central black hole and an Eddington ratio of L/L Edd ≈ 0.2. We also obtained consistent but slightly shorter emission-line lags with respect to the Kepler light curve. Thanks to the Kepler mission, the light curve of KA1858+4850 has among the highest cadences and signal-to-noise ratios ever measured for an active galactic nucleus; thus, our black hole mass measurement will serve as a reference point for relations between black hole mass and continuum variability characteristics in active galactic nuclei.