We present ACS, NICMOS, and Keck AO-assisted photometry of 20 Type Ia supernovae (SNe Ia) from the HST Cluster Supernova Survey. The SNe Ia were discovered over the redshift interval 0.623 < z < 1.415. Fourteen of these SNe Ia pass our strict selection cuts and are used in combination with the world's sample of SNe Ia to derive the best current constraints on dark energy. Ten of our new SNe Ia are beyond redshift z = 1, thereby nearly doubling the statistical weight of HST-discovered SNe Ia beyond this redshift. Our detailed analysis corrects for the recently identified correlation between SN Ia luminosity and host galaxy mass and corrects the NICMOS zeropoint at the count rates appropriate for very distant SNe Ia. Adding these supernovae improves the best combined constraint on dark energy density, ρ DE (z), at redshifts 1.0 < z < 1.6 by 18% (including systematic errors). For a flat ΛCDM universe, we find Ω Λ = 0.729 +0.014 −0.014 (68% CL including systematic errors). For a flat wCDM model, we measure a constant dark energy equation-of-state parameter w = −1.013 +0.068 −0.073 (68% CL). Curvature is constrained to ∼ 0.7% in the owCDM model and to ∼ 2% in a model in which dark energy is allowed to vary with parameters w 0 and w a . Tightening further the constraints on the time evolution of dark energy will require several improvements, including high-quality multi-passband photometry of a sample of several dozen z > 1 SNe Ia. We describe how such a sample could be efficiently obtained by targeting cluster fields with WFC3 on HST.The updated supernova Union2.1 compilation of 580 SNe is available at http://supernova.lbl.gov/Union ⋆ is less than the mass threshold. We begin by noting that.We can then integrate this probability over all true host masses less than the threshold:⋆ )P (m true ⋆ ) up to a normalization constant found by requiring the integral to be unity when integrating over all possible true masses. P (m true ⋆ ) is estimated from the observed distribution for each type of survey. The SNLS (Sullivan et al. 2010) and SDSS (Lampeitl et al. 2010) host masses were assumed to be representative of untargeted surveys, while the mass distribution in Kelly et al. (2010) was assumed typical of nearby targeted surveys. As these distributions are approximately log-normal, we use this model for P (m true ⋆) using the mean and RMS from the log of the host masses from these surveys (with the average measurement errors subtracted in quadrature), giving log 10 P (m true ⋆ ) = N (µ = 9.88, σ 2 = 0.92 2 ) for untargeted surveys and log 10 P (m true ⋆ ) = N (10.75, 0.66 2 ) for targeted surveys. When host mass measurements are available, P (m obs ⋆ |m true ⋆ ) is also modeled as a log-normal; when no measurement is available, a flat distribution is used.For a supernova from an untargeted survey with no host mass measurement (including supernovae presented in this paper which are not in a cluster), P (m trueis the integral of P (m true ⋆ ) up to the threshold mass: 0.55. Similarly, nearby supernovae from targeted surveys w...

We present an optical/near IR selected catalog of 79 clusters distributed over an area of 5.1 square degrees. The catalog was constructed from images obtained with the 4-Shooter CCD mosaic camera on the Hale 5m telescope operating in \scan" mode. The survey, hereafter known as the Palomar Distant Cluster Survey (PDCS), was conducted in two broad band lters that closely resemble V and I. The 4 limiting magnitudes for our 300 s exposures are 23.8 (V ) and 22.5 (I). A matched lter algorithm was developed and employed to identify the cluster candidates by using positional and photometric data simultaneously. The clusters cover the range 0:2 < z < 1:2, based on the redshift estimates derived in the cluster detection procedure. An accurate selection function is generated from extensive simulations. We nd that the cumulative surface density of clusters with richness class R 1 is about a factor of 5 higher than the extrapolated density of R 1 Abell clusters. The PDCS results are consistent with a constant comoving density of clusters to z < 0:6, albeit at the above high density level. Constraints on cluster abundances at z > 0:6 will be possible with the acquisition of spectroscopic redshifts for a large subset of these cluster candidates. We also present a supplemental catalog of 28 clusters that do not satisfy all our selection criteria but which include some of the most distant systems detected in the survey. Finding charts for all 107 cluster candidates are provided. (Astro-ph readers: due to their large size, the nding charts are not included in this version of the paper).Subject headings: galaxies: clustering; cosmology: observations { 3 { { 5 { associated with CCD readout; one is exposing essentially 100% of the time), 2) Data taken in TDI mode can be extremely well at-elded (see Schneider, Schmidt, & Gunn 1994 and x2.3 of this paper). This property is especially important for these survey images, as the Texas Instruments CCDs have very poor fringing properties at near-infrared wavelengths. 3) The con guration of the 4-Shooter focal plane (Figure 1) is well-suited for two-lter observations in TDI mode.The PDCS data were obtained by moving the telescope north along lines of constant Right Ascension (equinox 1950.0) at a rate of 0 00 : 893 s 1 ; this yields a CCD transit time of 300 seconds. Because of the aforementioned pyramid shadowing in the 4-Shooter, the e ective exposure time is 293 seconds. The data are acquired in two colors, nearly simultaneously, by making use of the fact that the 4-Shooter can be equipped with one set of lters for the leading two cameras (CCDs 1 and 4, see Figure 1) in the scan and another set for the trailing ones (CCDs 2 and 3).A survey eld consists of eight adjacent scans. Each scan requires approximately 80 minutes to complete and overlaps the adjacent scan by 30 00 . The total area imaged in each eld is usually slightly larger than a square degree (see Table 1).Imaging of the ve elds began in October 1986 and required approximately three years to complete. The data were all obtained...

The localization of the short-duration, hard-spectrum gamma-ray burst GRB 050509b by the Swift satellite was a watershed event. Never before had a member of this mysterious subclass of classic GRBs been rapidly and precisely positioned in a sky accessible to the bevy of ground-based follow-up facilities. Thanks to the nearly immediate relay of the GRB position by Swift, we began imaging the GRB field 8 minutes after the burst and continued for the following 8 days. Though the Swift X-ray Telescope (XRT) discovered an X-ray afterglow of GRB 050509b, the first ever of a short-hard burst, no convincing optical/infrared candidate afterglow or supernova was found for the object. We present a re-analysis of the XRT afterglow and find an absolute position of R.A. = 12 h 36 m 13. s 59, Decl. = +28 • 59 ′ 04. ′′ 9 (J2000), with a 1σ uncertainty of 3. ′′ 68 in R.A., 3. ′′ 52 in Decl.; this is about 4 ′′ to the west of the XRT position reported previously. Close to this position is a bright elliptical galaxy with redshift z = 0.2248 ± 0.0002, about 1 ′ from the center of a rich cluster of galaxies. This cluster has detectable diffuse emission, with a temperature of kT = 5.25 +3.36 −1.68 keV. We also find several (∼11) much fainter galaxies consistent with the XRT position from deep Keck imaging and have obtained Gemini spectra of several of these sources. Nevertheless we argue, based on positional coincidences, that the GRB and the bright elliptical are likely to be physically related. We thus have discovered evidence that supports the notion that at least some short-duration, hard-spectra GRBs are at cosmological distances.We also explore the connection of the properties of the burst and the afterglow, finding that GRB 050509b was underluminous in both of these relative to long-duration GRBs. However, we also demonstrate that the ratio of the blast-wave energy to the γ-ray energy is consistent with that of long-duration GRBs. This suggests a comparably high efficiency of γ-ray conversion as in long GRBs as might be expected if the same emission mechanism is at work in short and long GRBs. Based on this analysis, on the location of the GRB (40 ± 13 kpc from a bright galaxy), on the galaxy type (elliptical), and the lack of a coincident supernova, we suggest that there is now observational consistency with the hypothesis that short-hard bursts arise during the merger of a compact binary (two neutron stars, or a neutron star and a black hole). In this context, we limit the properties of a Li-Paczyński "mini-supernova" that is predicted to arise on ∼day timescales. Other progenitor models are still viable, and additional rapidly localized bursts from the Swift mission will undoubtedly help to further clarify the progenitor picture.

How much dark matter is there in the universe and where is it located? These are two of the most fundamental questions in cosmology. We use in this paper optical and X-ray mass determinations of galaxies, groups, and clusters of galaxies to suggest that most of the dark matter may reside in very large halos around galaxies, typically extending to 1200 kpc for bright galaxies. We show that the mass-to-light ratio of galaxy systems does not increase significantly with linear scale beyond the very large halos suggested for individual galaxies. Rather, the total mass of large-scale systems such as groups and rich clusters of galaxies, even superclusters, can on average be accounted for by the total mass of their member galaxies, including their large halos (which may be stripped off in the dense cluster environment but still remain in the clusters) plus the mass of the hot intracluster gas. This conclusion also suggests that we may live in a low-density universe with ⍀ 1 0.2-0.3.

We investigate the properties of the 525 spectroscopically confirmed members of the Cl1604 supercluster at z ∼ 0.9 as part of the Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey. In particular, we focus on the photometric, stellar mass, morphological, and spectral properties of the 305 member galaxies of the eight clusters and groups that comprise the Cl1604 supercluster. Using an extensive Keck LRIS/DEIMOS spectroscopic database in conjunction with ten-band ground-based, Spitzer, and Hubble Space Telescope imaging, we investigate the buildup of the red sequence in groups and clusters at high redshift. Nearly all of the brightest and most massive red-sequence galaxies present in the supercluster environment are found to lie within the bounds of the cluster and group systems, with a surprisingly large number of such galaxies present in low-mass group systems. Despite the prevalence of these red-sequence galaxies, we find that the average cluster galaxy has a spectrum indicative of a star-forming galaxy, with a star formation rate between those of z ∼ 1 field galaxies and moderate redshift cluster galaxies. The average group galaxy is even more active, exhibiting spectral properties indicative of a starburst. The presence of massive, red galaxies and the high fraction of starbursting galaxies present in the group environment suggest that significant processing is occurring in group environments at z ∼ 1 and earlier. There is a deficit of low-luminosity red-sequence galaxies in all Cl1604 clusters and groups, suggesting that such galaxies transition to the red sequence at later times. Extremely massive (∼ 10 12 M ⊙ ) red-sequence galaxies routinely observed in rich clusters at z ∼ 0 are also absent from the Cl1604 clusters and groups. We suggest that such galaxies form at later times through merging processes. There are significant populations of transition galaxies at intermediate stellar masses [log(M * ) = 10.25-10.75] present in the group and cluster environments, suggesting that this range is important for the buildup of the red-sequence mass function at z ∼ 1. Through a comparison of the transitional populations present in the Cl1604 cluster and group systems, we find evidence that massive blue cloud galaxies are quenched earliest in the most dynamically relaxed systems and at progressively later times in dynamically unrelaxed systems.