We constrain the evolution of the brightest cluster galaxy plus intracluster light (BCG + ICL) using an ensemble of 42 galaxy groups and clusters that span redshifts of z = 0.05-1.75 and masses of M-500,M-c = 2 x 10(13)-10(15) M-circle dot. Specifically, we measure the relationship between the BCG + ICL stellar mass M-star and M-500,M-c at projected radii 10 < r < 100 kpc for three different epochs. At intermediate redshift ((z) over bar = 0.40), where we have the best data, we find M-star M-500,c(0.48 +/- 0.06). Fixing the exponent of this power law for all redshifts, we constrain the normalization of this relation to be 2.08 +/- 0.21 times higher at (z) over bar = 0.40 than at high redshift ((z) over bar = 1.55). We find no change in the relation from intermediate to low redshift ((z) over bar = 0.10). In other words, for fixed M-500,M-c, M-star at 10 < r < 100 kpc increases from (z) over bar = 1.55 to (z) over bar = 0.40 and not significantly thereafter. Theoretical models predict that the physical mass growth of the cluster from z = 1.5 to z = 0 within r(500,c) is 1.4x, excluding evolution due to definition of r(500,c). We find that M-star within the central 100 kpc increases by similar to 3.8x over the same period. Thus, the growth of M-star in this central region is more than a factor of 2 greater than the physical mass growth of the cluster as a whole. Furthermore, the concentration of the BCG + ICL stellar mass, defined by the ratio of stellar mass within 10 kpc to the total stellar mass within 100 kpc, decreases with increasing M-500,M-c at all z. We interpret this result as evidence for inside-out growth of the BCG + ICL over the past 10 Gyr, with stellar mass assembly occurring at larger radii at later times.

Quasars at early redshifts (z > 6) with companion galaxies offer unique insights into the growth and evolution of the first supermassive black holes. Here, we report on a 150 ks Chandra observation of PSO.J308.0416-21.2339, a z = 6.23 quasar with a merging companion galaxy identified in [C II] and rest-frame UV emission. With 72.3(-8.6)(+9.6) net counts, we find that PSO.J308.0416-21.2339 is powerful (L-X = 2.31(-0.76)(+1.14) x 10(45) erg s(-1) cm(-2) in rest-frame 2.0-10.0 keV) yet soft (spectral power-law index Gamma = 2.39(-0.36)(+0.37) and optical-to-X-ray slope alpha(OX) = -1.41 +/- 0.11). In addition, we detect three hard-energy photons 2 ''.0 to the west of the main quasar, cospatial with the brightest UV emission of the merging companion. As no soft-energy photons are detected in the same area, this is potentially indicative of a highly obscured source. With conservative assumptions, and accounting for both background fluctuations and the extended wings of the quasar's emission, these photons only have a probability P = 0.021 of happening by chance. If confirmed by deeper observations, this system is the first high-redshift quasar and companion individually detected in X-rays and is likely a dual active galactic nucleus.

The relationship between galaxies and the state/chemical enrichment of the warm-hot intergalactic medium (WHIM) expected to dominate the baryon budget at low-z provides sensitive constraints on structure formation and galaxy evolution models. We present a deep redshift survey in the field of 1ES1553+113, a blazar with a unique combination of ultraviolet (UV)+X-ray spectra for surveys of the circumgalactic/intergalactic medium (CGM/IGM). Nicastro et al. reported the detection of two O VII WHIM absorbers at z = 0.4339 and 0.3551 in its spectrum, suggesting that the WHIM is metal rich and sufficient to close the missing baryons problem. Our survey indicates that the blazar is a member of a z = 0.433 group and that the higher-z O VII candidate arises from its intragroup medium. The resulting bias precludes its use in baryon censuses. The z = 0.3551 candidate occurs in an isolated environment 630 kpc from the nearest galaxy (with stellar mass log M-*/M-circle dot approximate to 9.7), which we show is unexpected for the WHIM. Finally, we characterize the galactic environments of broad H I Ly alpha absorbers (Doppler widths of b = 40-80 km s(-1); T less than or similar to 4 x10(5) K) that provide metallicity-independent WHIM probes. On average, broad Ly alpha absorbers are approximate to 2x closer to the nearest luminous (L > 0.25L(*)) galaxy (700 kpc) than narrow (b < 30 km s(-1); T less than or similar to 4 x 10(5) K) ones (1300 kpc) but approximate to 2x further than O VI absorbers (350 kpc). These observations suggest that gravitational collapse heats portions of the IGM to form the WHIM, but with feedback that does not enrich the IGM far beyond galaxy/group halos to levels currently observable in UV/X-ray metal lines.

We present the analysis of deep optical imaging of the galaxy cluster A133 with the IMACS instrument on Magellan. Our multi-band photometry enables stellar-mass measurements in the cluster member galaxies down to a mass limit of M = 3 x 108 M (0.1 of the Large Magellanic Cloud stellar mass). We observe a clear difference in the spatial distribution of large and dwarf galaxies within the cluster. Modeling these galaxy populations separately, we can confidently track the distribution of stellar mass locked in the galaxies to the cluster's virial radius. The extended envelope of the cluster's brightest galaxy can be tracked to 200 kpc. The central galaxy contributes 1/3 of the total cluster stellar mass within the radius r(500c).

Despite significant progress both observationally and theoretically, the origin of high-ionization nebular He If emission in galaxies dominated by stellar photoionization remains unclear. Accretion-powered radiation from high-mass X-ray binaries (HMXBs) is still one of the leading proposed explanations for the missing He-ionizing photons, but this scenario has yet to be conclusively tested. In this paper, we present nebular line predictions from a grid of photoionization models with input spectral energy distributions containing the joint contribution of both stellar atmospheres and a multicolour disc model for HMXBs. This grid demonstrates that HMXBs are inefficient producers of the photons necessary to power He II, and can only boost this line substantially in galaxies with HMXB populations large enough to power X-ray luminosities of 10(42) erg s(-1) per unit star formation rate (SFR). To test this, we assemble a sample of 11 low-redshift star-forming galaxies with high-quality constraints on both X-ray emission from Chandra and He II emission from deep optical spectra, including new observations with the MMT. These data reveal that the HMXB populations of these nearby systems are insufficient to account for the observed He It strengths, with typical X-ray luminosities or upper limits thereon of only 10(40)-10(41) erg s(-1) per SFR. This indicates that HMXBs are not the dominant source of He+ ionization in these metal-poor star-forming galaxies. We suggest that the solution may instead reside in revisions to stellar wind predictions, softer X-ray sources, or very hot products of binary evolution at low metallicity.

We present an analysis of 10 ks snapshot Chandra observations of 12 shocked post-starburst galaxies, which provide a window into the unresolved question of active galactic nuclei (AGN) activity in post-starburst galaxies and its role in the transition of galaxies from active star formation to quiescence. While seven of the 12 galaxies have statistically significant detections (with two more marginal detections), the brightest only obtained 10 photons. Given the wide variety of hardness ratios in this sample, we chose to pursue a forward-modeling approach to constrain the intrinsic luminosity and obscuration of these galaxies, rather than stacking. We constrain the intrinsic luminosity of obscured power laws based on the total number of counts and spectral shape, itself mostly set by the obscuration, with hardness ratios consistent with the data. We also tested thermal models. While all the galaxies have power-law models consistent with their observations, a third of the galaxies are better fit as an obscured power law and another third are better fit as thermal emission. If these post-starburst galaxies, early in their transition, contain AGNs, then these are mostly confined to lower obscuration (N ( H ) <= 10(23) cm(-2)) and lower luminosity (L (2-10 keV) <= 10(42) erg s(-1)). Two galaxies, however, are clearly best fit as significantly obscured AGNs. At least half of this sample shows evidence of at least low-luminosity AGN activity, though none could radiatively drive out the remaining molecular gas reservoirs. Therefore, these AGNs are more likely along for the ride, having been fed gas by the same processes driving the transition.

WISE J104915.57-531906.1 is a L/T brown dwarf binary located 2 pc from the Sun. The pair contains the closest known brown dwarfs and is the third closest known system, stellar or sub-stellar. We report comprehensive follow-up observations of this newly uncovered system. We have determined the spectral types of both components (L8 +/- 1, for the primary, agreeing with the discovery paper; T1.5 +/- 2 for the secondary, which was lacking spectroscopic type determination in the discovery paper) and, for the first time, their radial velocities (V-rad similar to 23.1, 19.5 km s(-1)) using optical spectra obtained at the Southern African Large Telescope and other facilities located at the South African Astronomical Observatory (SAAO). The relative radial velocity of the two components is smaller than the range of orbital velocities for theoretically predicted masses, implying that they form a gravitationally bound system. We report resolved near-infrared JHK(S) photometry from the Infrared Survey Facility telescope at the SAAO which yields colors consistent with the spectroscopically derived spectral types. The available kinematic and photometric information excludes the possibility that the object belongs to any of the known nearby young moving groups or associations. Simultaneous optical polarimetry observations taken at the SAAO 1.9 m give a non-detection with an upper limit of 0.07%. For the given spectral types and absolute magnitudes, 1 Gyr theoretical models predict masses of 0.04-0.05 M-circle dot for the primary, and 0.03-0.05 M-circle dot for the secondary.

New photometric material is presented for six outer disc supposedly old, Galactic star clusters: Berkeley 76, Haffner 4, Ruprecht 10, Haffner 7, Haffner 11 and Haffner 15, which are projected against the rich and complex Canis Major overdensity at 225 degrees <= l <= 248 degrees, -7 degrees <= b <= -2 degrees. This CCD data set, in the UBVI passbands, is used to derive their fundamental parameters, in particular age and distance. Four of the program clusters turn out to be older than 1 Gyr. This fact makes them ideal targets for future spectroscopic campaigns aiming at deriving their metal abundances. This, in turn, contributes to increase the number of well-studied outer disc old open clusters. Only Haffner 15, previously considered an old cluster, is found to be a young, significantly reddened cluster, member of the Perseus arm in the third Galactic quadrant. As for Haffner 4, we suggest an age of about half a Gyr. The most interesting result we found is that Berkeley 76 is probably located at more than 17 kpc from the Galactic centre, and therefore is among the most peripherical old open clusters so far detected. Besides, for Ruprecht 10 and Haffner 7, which were never studied before, we propose ages larger than 1 Gyr.