We present a new method for photometering objects in galaxy clusters. We introduce a mode-filtering technique for removing spatially variable backgrounds, improving both detection and photometric accuracy (roughly halving the scatter in the red sequence compared to previous catalogs of the same clusters). This method is based on robustly determining the distribution of background pixel values and should provide comparable improvement in photometric analysis of any crowded fields. We produce new multiwavelength catalogs for the 25 CLASH cluster fields in all 16 bandpasses from the UV through the near-IR, as well as rest-frame magnitudes. A comparison with spectroscopic values from the literature finds a similar to 30% decrease in the redshift deviation from previously released CLASH photometry. This improvement in redshift precision, in combination with a detection scheme designed to maximize purity, yields a substantial upgrade in cluster member identification over the previous CLASH galaxy catalog. We construct luminosity functions for each cluster, reliably reaching depths of at least 4.5 mag below M* in every case, and deeper still in several clusters. We measure M*, a, and their redshift evolution, assuming the cluster populations are coeval, and find little to no evolution of alpha, -0.9 less than or similar to less than or similar to -0.8, and M* values consistent with passive evolution. We present a catalog of galaxy photometry, photometric and spectroscopic redshifts, and rest-frame photometry for the full fields of view of all 25 CLASH clusters. Not only will our new photometric catalogs enable new studies of the properties of CLASH clusters, but mode-filtering techniques, such as those presented here, should greatly enhance the data quality of future photometric surveys of crowded fields.

We present new observations of the late-stage merger galaxy NGC. 7727, including Hubble Space Telescope/WFPC2 images and long-slit spectra obtained with the Clay telescope. NGC. 7727 is relatively luminous (M-V = -21.7) and features two unequal tidal tails, various bluish arcs and star clusters, and two bright nuclei 480. pc apart in projection. These two nuclei have nearly identical redshifts, yet are strikingly different. The primary nucleus, hereafter Nucleus 1, fits smoothly into the central luminosity profile of the galaxy and appears-at various wavelengths-"red and dead." In contrast, Nucleus 2 is very compact, has a tidal radius of 103 pc, and exhibits three signs of recent activity: a post-starburst spectrum, an [O III] emission line, and a central X-ray point source. Its emission-line ratios place it among Seyfert nuclei. A comparison of Nucleus 2 (M-V = -15.5) with ultracompact dwarf galaxies (UCDs) suggests that it may be the best case yet for a massive UCD having formed through tidal stripping of a gas-rich disk galaxy. Evidence for this comes from its extended star formation history, long blue tidal stream, and elevated dynamical-to-stellar-mass ratio. While the majority of its stars formed greater than or similar to 10 Gyr ago, similar to 1/3 formed during starbursts in the past 2 Gyr. Its weak active galactic nucleus activity is likely driven by a black hole of mass 3 x 10(6-8) M-circle dot. We estimate that the former companion's initial mass was less than half that of then NGC. 7727, implying a minor merger. By now this former companion has been largely shredded, leaving behind Nucleus 2 as a freshly minted UCD that probably moves on a highly eccentric orbit.

We introduce Project MEGaSaURA: the Magellan Evolution of Galaxies Spectroscopic and Ultraviolet Reference Atlas. MEGaSaURA comprises medium-resolution, rest-frame ultraviolet spectroscopy of N = 15 bright gravitationally lensed galaxies at redshifts of 1.68 < z < 3.6, obtained with the MagE spectrograph on the Magellan telescopes. The spectra cover the observed-frame wavelength range 3200 < lambda(o) < 8280 angstrom; the average spectral resolving power is R = 3300. The median spectrum has a signal-to-noise ratio (S/N) = 21 per resolution element at 5000 angstrom. As such, the MEGaSaURA spectra have superior S/N and wavelength coverage compared to what COS/HST provides for starburst galaxies in the local universe. This paper describes the sample, the observations, and the data reduction. We compare the measured redshifts for the stars, the ionized gas as traced by nebular lines, and the neutral gas as traced by absorption lines; we find the expected bulk outflow of the neutral gas, and no systemic offset between the redshifts measured from nebular lines and the redshifts measured from the stellar continuum. We provide the MEGaSaURA spectra to the astronomical community through a data release.

We have selected a sample of 11 massive clusters of galaxies observed by the Hubble Space Telescope in order to study the impact of the dynamical state on the intracluster light (ICL) fraction, the ratio of total integrated ICL to the total galaxy member light. With the exception of the Bullet cluster, the sample is drawn from the Cluster Lensing and Supernova Survey and the Frontier Fields program, containing five relaxed and six merging clusters. The ICL fraction is calculated in three optical filters using the CHEFs ICL estimator, a robust and accurate algorithm free of a priori assumptions. We find that the ICL fraction in the three bands is, on average, higher for the merging clusters, ranging between similar to 7% and 23%, compared with the similar to 2%-11% found for the relaxed systems. We observe a nearly constant value (within the error bars) in the ICL fraction of the regular clusters at the three wavelengths considered, which would indicate that the colors of the ICL and the cluster galaxies are, on average, coincident and, thus, so are their stellar populations. However, we find a higher ICL fraction in the F606W filter for the merging clusters, consistent with an excess of lower-metallicity/younger stars in the ICL, which could have migrated violently from the outskirts of the infalling galaxies during the merger event.

We present an X-ray point-source catalogue from the XMM-Large Scale Structure (XMMLSS) survey region, one of the XMM-Spitzer Extragalactic Representative Volume Survey (XMM-SERVS) fields. We target the XMM-LSS region with 1.3 Ms of new XMM-Newton AO-15 observations, transforming the archival X-ray coverage in this region into a 5.3 deg(2) contiguous field with uniform X-ray coverage totaling 2.7 Ms of flare-filtered exposure, with a 46 ks median PN exposure time. We provide an X-ray catalogue of 5242 sources detected in the soft (0.5-2 keV), hard (2-10 keV), and/or full (0.5-10 keV) bands with a 1 per cent expected spurious fraction determined from simulations. A total of 2381 new X-ray sources are detected compared to previous source catalogues in the same area. Our survey has flux limits of 1.7 x 10(-15), 1.3 x 10(-14),and 6.5 x 10(-15) erg cm(-2) s(-1) over 90 per cent of its area in the soft, hard, and full bands, respectively, which is comparable to those of the XMM- COSMOS survey. We identify multiwavelength counterpart candidates for 99.9 per cent of the X-ray sources, of which 93 per cent are considered as reliable based on their matching likelihood ratios. The reliabilities of these high-likelihood-ratio counterparts are further confirmed to be approximate to 97 per cent reliable based on deep Chandra coverage over approximate to 5 per cent of the XMM-LSS region. Results of multiwavelength identifications are also included in the source catalogue, along with basic optical-to-infrared photometry and spectroscopic redshifts from publicly available surveys. We compute photometric redshifts for X-ray sources in 4.5 deg2 of our field where forced-aperture multiband photometry is available; > 70 per cent of the X-ray sources in this subfield have either spectroscopic or high-quality photometric redshifts.

Filaments of the cosmic web have long been associated with the threadlike structures seen in galaxy redshift surveys. However, despite their baryon content being dominated by hot gas, these filaments have been an elusive target for X-ray observations. Recently, detections of filaments in very deep (2.4 Ms) observations with Chandra were reported around Abell 133 (z = 0.0559). To verify these claims, we conducted a multiobject spectrographic campaign on the Baade 6.5 m telescope around Abell 133; this resulted in a catalog of similar to 3000 new redshift measurements, of which 254 are of galaxies near the cluster. We investigate the kinematic state of Abell 133 and identify the physical locations of filamentary structure in the galaxy distribution. Contrary to previous studies, we see no evidence that Abell 133 is dynamically disturbed; we reject the hypothesis that there is a kinematically distinct subgroup (p = 0.28) and find no velocity offset between the central galaxy and the cluster (Z(score) = 0.0411(-0.106)(+0.111)Mb. The spatial distribution of galaxies traces the X-ray filaments, as confirmed by angular cross-correlation with a significance of similar to 5 sigma. A similar agreement is found in the angular density distribution, where two X-ray structures have corresponding galaxy enhancements. We also identify filaments in the large-scale structure of galaxies; these filaments approach the cluster from the direction the X-ray structures are seen. While more members between R(200)( )and 2 x R-200 are required to clarify which large-scale filaments connect to the X-ray gas, we argue that this is compelling evidence that the X-ray emission is indeed associated with cosmic filaments.

Using the PROSPECTOR spectral energy distribution (SED) fitting code, we analyze the properties of 19 extreme emission-line galaxies (EELGs) identified in the bluest composite SED in the ZFOURGE survey at 2.5 <= z <= 4. PROSPECTOR includes a physical model for nebular emission and returns probability distributions for stellar mass, stellar metallicity, dust attenuation, and nonparametric star formation history (SFH). The EELGs show evidence of a starburst in the most recent 50 Myr, with the median EELG having a specific star formation rate (sSFR) of 4.6 Gyr(-1) and forming 15% of its mass in this short time. For a sample of more typical star-forming galaxies (SFGs) at the same redshifts, the median SFG has an sSFR of 1.1 Gyr(-1) and forms only 4% of its mass in the last 50 Myr. We find that virtually all of our EELGs have rising SFHs, while most of our SFGs do not. From our analysis, we hypothesize that many, if not most, SFGs at z >= 2.5 undergo an extreme H beta+[O III] emission-line phase early in their lifetimes. In a companion paper, we obtain spectroscopic confirmation of the EELGs as part of our MOSEL survey. In the future, explorations of uncertainties in modeling the UV slope for galaxies at z > 2 are needed to better constrain their properties, e.g., stellar metallicities.

Late bloomers (LBs) are massive (M-* > 10(10) M-circle dot) galaxies at z < 1 that formed the majority of their stars within similar to 2 Gyr of the epoch of observation. Our improved methodology for deriving star formation histories (SFHs) of galaxies at redshifts 0.45 < z < 0.75 from the Carnegie-Spitzer-IMACS Survey includes confidence intervals that robustly distinguish LBs from "old" galaxies. We use simulated SFHs to test for "false positives" and contamination from old galaxies to demonstrate that the late-bloomer population is not an artifact of our template modeling technique. We show that LBs account for similar to 20% of z similar to 0.6 galaxies with masses of the modern Milky Way, with a moderate dependence on mass. We take advantage of a 1% overlap of our sample with HST (CANDELS) imaging to construct a "gold standard" catalog of 74 galaxies with high-confidence SFHs, SEDs, basic data, and HST images to facilitate comparison with future studies by others. This small subset suggests that galaxies with both old and young SFHs cover the full range of morphology and environment (excluding rich groups or clusters), albeit with a mild but suggestive correlation with the local environment. We begin the investigation of whether LBs of sufficient mass and frequency are produced in current-generation.CDM-based semianalytic models of galaxy formation. In terms of halo growth, we find a late-assembling halo fraction within a factor of two of our late bloomer fraction. However, sufficiently delaying star formation in such halos may be a challenge for the baryon component of such models.

In clusters of galaxies, the red sequence is believed to be a consequence of a correlation between stellar mass and chemical abundances, with more massive galaxies being more metal-rich and, as a consequence, redder. However, there is a color scatter around the red sequence that holds even with precision photometry, implying that the galaxy population is more complicated than as described by a mass-metallicity relation. We use precision photometry from the Cluster Lensing and Supernova survey with Hubble (CLASH) to investigate what drives this scatter. In four CLASH clusters at z = 0.355 +/- 0.007, we find that the optical-IR galaxy colors confirm the previously known trend of metallicity along the red sequence but also show a strong connection between stellar age and red sequence offset, with ages ranging from 3 to 8 Gyr. Starting with fixed-age color-magnitude relations motivated by the mass-metallicity correlations of CLASH cluster galaxies, and by adjusting galaxy colors through stellar population models to put them all at the age of our red sequence, we are able to reduce the, e.g., F625W-F814W scatter from 0.051 to 0.026 mag with median photometric errors of 0.029 mag. While we will extend this analysis to the full CLASH sample, in four clusters our technique already provides a color precision in near-total-light apertures to resolve the spread in stellar population formation ages that drives the scatter in the red sequence.