We measure the baryons contained in both the stellar and hot-gas components for 12 galaxy clusters and groups at z ∼ 0.1 with M = 1-5 × 10 14 M . This paper improves upon our previous work through the addition of XMM-Newton X-ray data, enabling measurements of the total mass and masses of each major baryonic component-intracluster medium, intracluster stars, and stars in galaxies-for each system. We recover a mean relation for the stellar mass versus halo mass, M ∝ M −0.52±0.04 500, that is 1σ shallower than in our previous result. We confirm that the partitioning of baryons between the stellar and hot-gas components is a strong function of M 500 ; the fractions of total mass in stars and X-ray gas within a sphere of radius r 500 scale as f ∝ M −0.45±0.04 500 and f gas ∝ M 0.26±0.03 500 , respectively. We also confirm that the combination of the brightest cluster galaxy and intracluster stars is an increasingly important contributor to the stellar baryon budget in lower halo masses. Studies that fail to fully account for intracluster stars typically underestimate the normalization of the stellar baryon fraction versus M 500 relation by ∼25%. Our derived stellar baryon fractions are also higher, and the trend with halo mass weaker, than those derived from recent halo occupation distribution and abundance matching analyses. One difference from our previous work is the weak, but statistically significant, dependence here of the total baryon fraction upon halo mass: f bary ∝ M 0.16±0.04 500 . For M 500 2 × 10 14 , the total baryon fractions within r 500 are on average 18% below the universal value from the seven year Wilkinson Microwave Anisotropy Probe (WMAP) analysis, or 7% below for the cosmological parameters from the Planck analysis. In the latter case, the difference between the universal value and cluster baryon fractions is less than the systematic uncertainties associated with the M 500 determinations. The total baryon fractions exhibit significant scatter, particularly at M 500 < 2 × 10 14 M where they range from 60%-90%, or 65%-100%, of the universal value for WMAP7 and Planck, respectively. The ratio of the stellar-to-gas mass within r 500 (M /M gas ), a measure of integrated star-formation efficiency, strongly decreases with increasing M 500 . This relation is tight, with an implied intrinsic scatter of 12%. The fact that this relation remains tight at low mass implies that the larger scatter in the total baryon fractions at these masses arises from either true scatter in the total baryon content or observational scatter in M 500 rather than late-time physical processes such as redistribution of gas to beyond r 500 . If the scatter in the baryon content at low mass is physical, then our results imply that in this mass range, the integrated star-formation efficiency rather than the baryon fraction that is constant at fixed halo mass.

We report the discovery of a galaxy cluster at z=1.62 located in the Spitzer Wide-Area Infrared Extragalactic survey XMM-LSS field. This structure was selected solely as an overdensity of galaxies with red Spitzer/IRAC colors, satisfying ([3.6] − [4.5]) AB > −0.1 mag. Photometric redshifts derived from Subaru XMM Deep Survey (BViz-bands), UKIRT Infrared Deep Survey-Ultra-Deep Survey (UKIDSS-UDS, JK-bands), and from the Spitzer Public UDS survey (3.6-8.0 µm) show that this cluster corresponds to a surface density of galaxies at z ≈ 1.6 that is > 20σ above the mean at this redshift. We obtained optical spectroscopic observations of galaxies in the cluster region using IMACS on the Magellan telescope. We measured redshifts for seven galaxies in the range z=1.62-1.63 within 2.8 arcmin (< 1.4 Mpc) of the astrometric center of the cluster. A posteriori analysis of the XMM data in this field reveal a weak (4σ) detection in the [0.5-2 keV] band compatible with the expected thermal emission from such a cluster. The color-magnitude diagram of the galaxies in this cluster shows a prominent red-sequence, dominated by a population of red galaxies with (z − J) > 1.7 mag. The photometric redshift probability distributions for the red galaxies are strongly peaked at z = 1.62, coincident with the spectroscopically confirmed galaxies. The rest-frame (U − B) color and scatter of galaxies on the redsequence are consistent with a mean luminosity-weighted age of 1.2 ± 0.1 Gyr, yielding a formation redshift z f = 2.35 ± 0.10, and corresponding to the last significant star-formation period in these galaxies.

We present direct imaging observations at wavelengths of 3.3, 3.8 (L ′ band), and 4.8 (M band) µm, for the planetary system surrounding HR 8799. All three planets are detected at L ′ . The c and d component are detected at 3.3 µm, and upper limits are derived from the M band observations. These observations provide useful constraints on warm giant planet atmospheres. We discuss the current age constraints on the HR 8799 system, and show that several potential co-eval objects can be excluded from being co-moving with the star. Comparison of the photometry is made to models for giant planet atmospheres. Models which include non-equilibrium chemistry provide a reasonable match to the colors of c and d. From the observed colors in the thermal infrared we estimate T eff < 960 K for b, and T eff =1300 and 1170 K for c and d, respectively. This provides an independent check on the effective temperatures and thus masses of the objects from the Marois et al. (2008) results.

The Multi-Epoch Nearby Cluster Survey has discovered 23 cluster Type Ia supernovae (SNe Ia) in the 58 X-rayselected galaxy clusters (0.05 z 0.15) surveyed. Four of our SN Ia events have no host galaxy on close inspection, and are likely intracluster SNe. Although one of the candidates, Abell399_3_14_0, appears to be associated in projection with the outskirts of a nearby red sequence galaxy, its velocity offset of ∼1000 km sindicates that it is unbound and therefore an intracluster SN. Another of our candidates, Abell85_6_08_0, has a spectrum consistent with an SN1991bg-like object, suggesting that at least some portion of intracluster stars belong to an old stellar population. Deep image stacks at the location of the candidate intracluster SNe put upper limits on the luminosities of faint hosts, with M r −13.0 mag and M g −12.5 mag in all cases. For such limits, the fraction of the cluster luminosity in faint dwarfs below our detection limit is 0.1%, assuming a standard cluster luminosity function. All four events occurred within ∼600 kpc of the cluster center (projected), as defined by the position of the brightest cluster galaxy, and are more centrally concentrated than the cluster SN Ia population as a whole. After accounting for several observational biases that make intracluster SNe easier to discover and spectroscopically confirm, we calculate an intracluster stellar mass fraction of 0.16 +0.13 −0.09 (68% confidence limit) for all objects within R 200 . If we assume that the intracluster stellar population is exclusively old, and the cluster galaxies themselves have a mix of stellar ages, we derive an upper limit on the intracluster stellar mass fraction of <0.47 (84% one-sided confidence limit). When combined with the intragroup SNe results of McGee & Balogh, we confirm the declining intracluster stellar mass fraction as a function of halo mass reported by Gonzalez and collaborators.

We examine metal and entropy content in galaxy groups having T X ≈ 0.5-2 keV in cosmological hydrodynamic simulations. Our simulations include a well-constrained prescription for galactic outflows following momentum-driven wind scalings, and a sophisticated chemical evolution model. Our simulation with no outflows reproduces observed iron abundances in X-ray emitting gas, but the oxygen abundance is too low; including outflows yields iron and oxygen abundances in good agreement with data. X-ray measures of [O/Fe] primarily reflect metal distribution mechanisms into hot gas, not the ratio of Type Ia to Type II supernovae within the group. Iron abundance increases by ∼ ×2 from z ∼ 1 to 0 independent of group size, consistent with that seen in clusters, while [O/Fe] drops by ∼30 per cent. Core entropy versus temperature is elevated over self-similar predictions regardless of outflows due to radiative cooling removing low-entropy gas, but outflows provide an additional entropy contribution below 1 keV. This results in a noticeable break in the L X -T X relation below ∼1 keV, as observed. Entropy at R 500 is also in good agreement with data, and is unaffected by outflows. Importantly, outflows serve to reduce the stellar content of groups to observed levels. Specific energy injection from outflows drops with group mass, and exceeds the thermal energy for 0.5-keV systems. Radial profiles from simulations are in broad agreement with observations, but there remain non-trivial discrepancies that may reflect an excess of late-time star formation in central group galaxies in our simulations. Our model with outflows suggests a connection between physical processes of galaxy formation and both pre-heating and enrichment in intragroup gas, though more definitive conclusions must await a model that simultaneously suppresses cooling flows as observed.

We present the first high-resolution map of the cold molecular gas distribution, as traced by CO(2-1) emission with ALMA, in a prominent ram pressure stripped tail. The Norma cluster galaxy ESO 137-001 is undergoing a strong interaction with the surrounding intra-cluster medium and is one of the nearest jellyfish galaxies with a long multi-phase tail. We have mapped the full extent of the tail at 1 ′′ (350 pc) angular resolution and found a rich distribution of mostly compact CO regions extending to nearly 60 kpc in length and 25 kpc in width. In total about 10 9 M ⊙ of molecular gas was detected. The CO features are found predominantly at the heads of numerous small-scale (∼ 1.5 kpc) fireballs (i.e., star-forming clouds with linear streams of young stars extending toward the galaxy) but also of largescale (∼ 8 kpc) super-fireballs, and double-sided fireballs that have additional diffuse ionized gas tails extending in the direction opposite to the stellar tails. The new data help to shed light on the origin of the molecular tail -CO filaments oriented in the direction of the tail with only diffuse associated Hα emission are likely young molecular features formed in situ, whereas other large CO features tilted with respect to the tail may have originated from the densest gas complexes that were pushed gradually away from the disk. The ALMA observations of ESO 137-001, together with observations from HST, Chandra and VLT/MUSE, offer the most complete view of a spectacular ram pressure stripped tail to date.

We have discovered a remarkable warm (130 − 160 K) molecular hydrogen tail with a H 2 mass of approximately 4 × 10 7 M ⊙ extending 20 kpc from a cluster spiral galaxy, ESO 137-001, in Abell 3627. At least half of this gas is lost permanently to the intracluster medium, as the tail extends beyond the tidal radius of the galaxy. We also detect a hot (400 − 550 K) component in the tail that is approximately 1% of the mass. The large H 2 line to IR continuum luminosity ratio in the tail indicates that star formation is not a major excitation source and that the gas is possibly shock-heated. This discovery confirms that the galaxy is currently undergoing ram-pressure stripping, as also indicated by its X-ray and Hα tails found previously. We estimate the galaxy is losing its warm H 2 gas at a rate of ∼ 2 − 3 M ⊙ yr −1 . The true mass loss rate is likely higher if we account for cold molecular gas and atomic gas. We predict that the galaxy will lose most of its gas in a single pass through the core and place a strong upper limit on the ram-pressure timescale of 1 Gyr. We also study the starforming properties of the galaxy and its tail. We identify most of the previously discovered external Hα sources within the tail in our 8µm data but not in our 3.6µm data; IRS spectroscopy of the region containing these Hα sources also reveals aromatic features typically associated with star formation. From the positions of these HII regions, it appears that star formation is not occurring throughout the molecular hydrogen tail but only immediately downstream of the galaxy. Some of these HII regions lie outside the tidal radius of the galaxy, indicating that ram-pressure stripping can be a source of intracluster stars.

We present a study of the hot gas and stellar content of 5 optically-selected poor galaxy clusters, including a full accounting of the contribution from intracluster light (ICL) and a combined hot gas and hydrostatic X-ray mass analysis with XMM-Newton observations. We find weighted mean stellar (including ICL), gas and total baryon mass fractions within r 500 of 0.026 ± 0.003, 0.070 ± 0.005 and 0.096 ± 0.006 , respectively, at a corresponding weighted mean M 500 of (1.08 +0.21 −0.18 ) × 10 14 M . Even when accounting for the intracluster stars, 4 out of 5 clusters show evidence for a substantial baryon deficit within r 500 , with baryon fractions (f b ) between 50±6 to 59±8 per cent of the Universal mean level (i.e. Ω b /Ω m ); the remaining cluster having f b = 75±11 per cent. For the 3 clusters where we can trace the hot halo to r 500 we find no evidence for a steepening of the gas density profile in the outskirts with respect to a power law, as seen in more massive clusters. We find that in all cases, the X-ray mass measurements are larger than those originally published on the basis of the galaxy velocity dispersion (σ) and an assumed σ − M 500 relation, by a factor of 1.7-5.7. Despite these increased masses, the stellar fractions (in the range 0.016-0.034, within r 500 ) remain consistent with the trend with mass published by Gonzalez, Zaritsky, & Zabludoff (2007), from which our sample is drawn.