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(Abridged) We explore the chemistry of the most abundant C, O, S, and N bearing species in molecular clouds, in the context of the IRAM 30 m Large Programme Gas phase Elemental abundances in Molecular Clouds (GEMS). In this work, we aim to assess the limitations introduced in the observational works when a uniform density is assumed along the line of sight for fitting the observations, developing a very simple numerical model of a turbulent box. We perform a MHD simulation in order to reproduce the turbulent steady-state of a turbulent box with properties typical of a molecular filament before collapse. We post-process the results of the MHD simulation with a chemical code to predict molecular abundances, and then post-process this cube with a radiative transfer code to create synthetic emission maps for a series of rotational transitions observed during the GEMS project. From the chemical point of view, we find that turbulence produces variations on the predicted abundances, but they are more or less critical depending on the chosen transition and the chemical age. When compared to real observations, the results from the turbulent simulation provides a better fit than when assuming a uniform gas distribution along the line of sight. In the view of our results, we conclude that taking into account turbulence when fitting observations might significantly improve the agreement with model predictions. This is especially important for sulfur bearing species that are very sensitive to the variations of density produced by turbulence at early times (0.1 Myr). The abundance of CO is also quite sensitive to turbulence when considering the evolution beyond a few 0.1 Myr., Comment: Published in Astronomy and Astrophysics

Recent observations suggest that planets formation starts early, in protostellar disks of $\le10^5$ yrs, which are characterized by strong interactions with the environment, e.g., through accretion streamers and molecular outflows. To investigate the impact of such phenomena on disk physical and chemical properties it is key to understand what chemistry planets inherit from their natal environment. In the context of the ALMA Large Program Fifty AU STudy of the chemistry in the disk/envelope system of Solar-like protostars (FAUST), we present observations on scales from ~1500 au to ~60 au of H$_2$CO, HDCO, and D$_2$CO towards the young planet-forming disk IRS~63. H$_2$CO probes the gas in the disk as well as in a large scale streamer (~1500 au) impacting onto the South-East (SE) disk side. We detect for the first time deuterated formaldehyde, HDCO and D$_2$CO, in a planet-forming disk, and HDCO in the streamer that is feeding it. This allows us to estimate the deuterium fractionation of H$_2$CO in the disk: [HDCO]/[H$_2$CO]$\sim0.1-0.3$ and [D$_2$CO]/[H$_2$CO]$\sim0.1$. Interestingly, while HDCO follows the H$_2$CO distribution in the disk and in the streamer, the distribution of D$_2$CO is highly asymmetric, with a peak of the emission (and [D]/[H] ratio) in the SE disk side, where the streamer crashes onto the disk. In addition, D$_2$CO is detected in two spots along the blue- and red-shifted outflow. This suggests that: (i) in the disk, HDCO formation is dominated by gas-phase reactions similarly to H$_2$CO, while (ii) D$_2$CO was mainly formed on the grain mantles during the prestellar phase and/or in the disk itself, and is at present released in the gas-phase in the shocks driven by the streamer and the outflow. These findings testify on the key role of streamers in the build-up of the disk both concerning the final mass available for planet formation and its chemical composition., Comment: 12 pages, 10 figures, accepted for publication on A&A

Over the past few years, chemical studies have revealed multiple structures in the vicinity of young stellar objects (YSOs). It has become evident that specific physical conditions are associated with the emission of particular molecular lines, allowing us to use molecular probes of the YSO physics. Consequently, chemical surveys are now necessary to fully constrain the origin of the observed structures. Several surveys have been conducted to explore the chemistry of YSOs, focusing on Class 0 and Class II objects. However, our knowledge of intermediate objects, that are Class I objects, remains limited. To bridge the gap and establish the relationship between observed structures and molecular line emission at the Class I evolutionary stage, we investigate the spatial distribution of key molecular gas species in the low-mass Class I protostar L1489 IRS (IRAS 04016+2610), a source part of the ChemYSO survey. We performed a 3mm line survey at high spatial and high spectral resolution using the NOEMA interferometer and the IRAM-30m telescope. We present here the ten brightest lines of our survey, in which we identified a new ~ 3 000 au long streamer in HC3N, C2H, and c-C3H2 emission, likely associated with more localized accretion shocks probed in SO. In addition, two ~ 10 000 au bubbles are seen with the dense molecular tracers HCO+, CS, and HCN around the YSO. Additionally, potential indicators of a second outflow appear in CS and HCN emission, but its nature remains to be confirmed. The late infall identified at large scales may originate from the nearby prestellar core L1489 and is likely responsible for the formation of an external warped disk in this system. The detection of a potential second outflow could be the direct evidence of a binary system. Finally, we hypothesize that the bubbles may result from the magnetic pressure as observed in numerical simulations., Comment: 16 pages, 12 figures, accepted for publication in Astronomy & Astrophysics

The origin of the chemical diversity observed around low-mass protostars probably resides in the earliest history of these systems. We aim to investigate the impact of protostellar feedback on the chemistry and grain growth in the circumstellar medium of multiple stellar systems. In the context of the ALMA Large Program FAUST, we present high-resolution (50 au) observations of CH$_3$OH, H$_2$CO, and SiO and continuum emission at 1.3 mm and 3 mm towards the Corona Australis star cluster. Methanol emission reveals an arc-like structure at $\sim$1800 au from the protostellar system IRS7B along the direction perpendicular to the major axis of the disc. The arc is located at the edge of two elongated continuum structures that define a cone emerging from IRS7B. The region inside the cone is probed by H$_2$CO, while the eastern wall of the arc shows bright emission in SiO, a typical shock tracer. Taking into account the association with a previously detected radio jet imaged with JVLA at 6 cm, the molecular arc reveals for the first time a bow shock driven by IRS7B and a two-sided dust cavity opened by the mass-loss process. For each cavity wall, we derive an average H$_2$ column density of $\sim$7$\times$10$^{21}$ cm$^{-2}$, a mass of $\sim$9$\times$10$^{-3}$ M$_\odot$, and a lower limit on the dust spectral index of $1.4$. These observations provide the first evidence of a shock and a conical dust cavity opened by the jet driven by IRS7B, with important implications for the chemical enrichment and grain growth in the envelope of Solar System analogues., Comment: 12 pages, 8 figures, 3 tables. Accepted Letter in Astronomy & Astrophysics

The first hydrostatic core (FHSC) phase is a brief stage in the protostellar evolution that is difficult to detect. Our goal is to characterize the chemical evolution of gas and dust during the formation of the FHSC. Moreover, we are interested in analyzing, for the first time with 3D magnetohydrodynamic (MHD) simulations, the role of grain growth in its chemistry. We postprocessed $2\times10^{5}$ tracer particles from a $\texttt{RAMSES}$ non-ideal MHD simulation using the codes $\texttt{NAUTILUS}$ and $\texttt{SHARK}$ to follow the chemistry and grain growth throughout the simulation. A great chemical inheritance is seen, as gas-phase abundances of most of the C, O, N, and S reservoirs in the hot corino at the end of the simulation match the ice-phase abundances from the prestellar phase. Additionally, interstellar complex organic molecules (iCOMs) such as methyl formate, acetaldehyde, and formamide are formed during the warm-up process. The typical grain size in the hot corino $(n_{\rm H}>10^{11}\ {\rm cm^{-3}})$ increases forty-fold during the last 30 kyr, with negligible effects on its chemical composition. At moderate densities $(10^{10}

Methanol is a ubiquitous species commonly found in the molecular interstellar medium. It is also a crucial seed species for the building-up of the chemical complexity in star forming regions. Thus, understanding how its abundance evolves during the star formation process and whether it enriches the emerging planetary system is of paramount importance. We used new data from the ALMA Large Program FAUST (Fifty AU STudy of the chemistry in the disk/envelope system of Solar-like protostars) to study the methanol line emission towards the [BHB2007] 11 protobinary system (sources A and B), where a complex structure of filaments connecting the two sources with a larger circumbinary disk has been previously detected. Twelve methanol lines have been detected with upper energies in the range [45-537] K along with one 13CH3OH transition. The methanol emission is compact and encompasses both protostars, separated by only 28 au and presents three velocity components, not spatially resolved by our observations, associated with three different spatial regions, with two of them close to 11B and the third one associated with 11A. A non-LTE radiative transfer analysis of the methanol lines concludes that the gas is hot and dense and highly enriched in methanol with an abundance as high as 1e-5. Using previous continuum data, we show that dust opacity can potentially completely absorb the methanol line emission from the two binary objects. Although we cannot firmly exclude other possibilities, we suggest that the detected hot methanol is resulting from the shocked gas from the incoming filaments streaming towards [BHB2007] 11 A and B, respectively. Higher spatial resolution observations are necessary to confirm this hypothesis., Comment: 17 pages, accepted in A&A

We present $10$ main-sequence ALPINE galaxies (log($M/M_{\odot}$) = 9.2-11.1 and ${\rm SFR}=23-190\,{\rm M_{\odot}\,yr^{-1}}$) at $z\sim4.5$ with optical [OII] measurements from Keck/MOSFIRE spectroscopy and Subaru/MOIRCS narrow-band imaging. This is the largest such multi-wavelength sample at these redshifts, combining various measurements in the ultra-violet, optical, and far-infrared including [CII]$_{158{\rm \mu m}}$ line emission and dust continuum from ALMA and H$\alpha$ emission from Spitzer photometry. For the first time, this unique sample allows us to analyze the relation between [OII] and total star-formation rate (SFR) and the interstellar medium (ISM) properties via [OII]/[CII] and [OII]/\halpha luminosity ratios at $z\sim4.5$. The [OII]$-$SFR relation at $z\sim4.5$ cannot be described using standard local descriptions, but is consistent with a metal-dependent relation assuming metallicities around $50\%$ solar. To explain the measured dust-corrected luminosity ratios of $L[OII]/L[CII] \sim 0.98^{+0.21}_{-0.22}$ and $L[OII]/LHa \sim -0.22^{+0.13}_{-0.15}$ for our sample, ionization parameters $\log(U)< -2$ and electron densities $\log(\rm n_e / {\rm [cm^{-3}]}) \sim 2.5-3$ are required. The former is consistent with galaxies at $z\sim2-3$, however lower than at $z>6$. The latter may be slightly higher than expected given the galaxies' specific SFR. The analysis of this pilot sample suggests that typical log($ M/M_{\odot})$ > 9 galaxies at $z\sim4.5$ to have broadly similar ISM properties as their descendants at $z\sim2$ and suggest a strong evolution of ISM properties since the Epoch of Reionization at $z>6$., Comment: 14 pages, 8 figures, Accepted for publication to MNRAS

Context. Studying gas chemistry in protoplanetary disks is key to understanding the process of planet formation. Sulfur chemistry in particular is poorly understood in interstellar environments, and the location of the main reservoirs remains unknown. Protoplanetary disks in Taurus are ideal targets for studying the evolution of the composition of planet forming systems. Aims. We aim to elucidate the chemical origin of sulfur-bearing molecular emission in protoplanetary disks, with a special focus on H$_2$S emission, and to identify candidate species that could become the main molecular sulfur reservoirs in protoplanetary systems. Methods. We used IRAM 30m observations of nine gas-rich young stellar objects (YSOs) in Taurus to perform a survey of sulfur-bearing and oxygen-bearing molecular species. In this paper we present our results for the CS 3-2 ($\nu_0$ = 146.969 GHz), H$_2$CO 2$_{11}$-1$_{10}$ ($\nu_0$ = 150.498 GHz), and H$_2$S 1$_{10}$-1$_{01}$ ($\nu_0$ = 168,763 GHz) emission lines. Results. We detected H$_2$S emission in four sources out of the nine observed, significantly increasing the number of detections toward YSOs. We also detected H$_2$CO and CS in six out of the nine. We identify a tentative correlation between H$_2$S 1$_{10}$-1$_{01}$ and H$_2$CO 2$_{11}$-1$_{10}$ as well as a tentative correlation between H$_2$S 1$_{10}$-1$_{01}$ and H$_2$O 8$_{18}$-7$_{07}$. By assuming local thermodynamical equilibrium, we computed column densities for the sources in the sample, with N(o-H$_2$S) values ranging between $2.6\times10^{12}$ cm$^{-2}$ and $1.5\times10^{13}$ cm$^{-2}$., Comment: 13 pages, 6 figures, 6 tables

Aims: Interstellar molecules form early in the evolutionary sequence of interstellar material that eventually forms stars and planets. To understand this evolutionary sequence, it is important to characterize the chemical composition of its first steps. Methods: In this paper, we present the result of a 2 and 3 mm survey of five cold clumps identified by the Planck mission. We carried out a radiative transfer analysis on the detected lines in order to put some constraints on the physical conditions within the cores and on the molecular column densities. We also performed chemical models to reproduce the observed abundances in each source using the gas-grain model Nautilus. Results: Twelve molecules were detected: H2CO, CS, SO, NO, HNO, HCO+, HCN, HNC, CN, CCH, CH3OH, and CO. Here, CCH is the only carbon chain we detected in two sources. Radiative transfer analyses of HCN, SO, CS, and CO were performed to constrain the physical conditions of each cloud with limited success. The sources have a density larger than $10^4$ cm$^{-3}$ and a temperature lower than 15 K. The derived species column densities are not very sensitive to the uncertainties in the physical conditions, within a factor of 2. The different sources seem to present significant chemical differences with species abundances spreading over one order of magnitude. The chemical composition of these clumps is poorer than the one of Taurus Molecular Cloud 1 Cyanopolyyne Peak (TMC-1 CP) cold core. Our chemical model reproduces the observational abundances and upper limits for 79 to 83\% of the species in our sources. The "best" times for our sources seem to be smaller than those of TMC-1, indicating that our sources may be less evolved and explaining the smaller abundances and the numerous non-detections. Also, CS and HCN are always overestimated by our models., Comment: Accepted for publication in A&A

Gas phase Elemental abundances in Molecular CloudS (GEMS) is an IRAM 30m Large Program designed to estimate the S, C, N, and O depletions and gas ionization degree, X(e-), in a set of star-forming filaments of Taurus, Perseus and Orion. Our immediate goal is to build up a complete database of molecular abundances that can serve as an observational basis for estimating X(e-) and the C, O, N, and S depletions through chemical modeling. We observed and derived the abundances of 14 species (13CO, C18O, HCO+, H13CO+, HC18O+, HCN, H13CN, HNC, HCS+, CS, SO, 34SO, H2S, and OCS) in 244 positions, covering the AV 3 to 100 mag, n(H2) a few 10$^{3}$ to 10$^6$ cm$^{-3}$, and Tk 10 to 30 K ranges in these clouds, avoiding protostars, HII regions, and outflows. A statistical analysis is carried out to identify general trends between different species and with physical parameters. Relations between molecules reveal strong linear correlations which define three different families: (1) 13CO and C18O; (2) H13CO+, HC18O+, H13CN, and HNC; and (3) the S-bearing molecules. The abundances of the CO isotopologs increase with the gas kinetic temperature until TK 15 K. For higher temperatures, the abundance remains constant with a scatter of a factor of 3. The abundances of H13CO+, HC18O+, H13CN, and HNC are well correlated with each other, and all of them decrease with molecular hydrogen density, following the law n(H2)$^{-0.8\pm0.2}$. The abundances of S-bearing species also decrease with n(H2) at a rate of (S-bearing/H)gas n(H2)$^{-0.6\pm0.1}$. The abundances of molecules belonging to groups 2 and 3 do not present any clear trend with gas temperature. At scales of molecular clouds, the C18O abundance is the quantity that better correlates with the cloud mass. We discuss the utility of the 13CO/C18O, HCO+/H13CO+, and H13CO+/H13CN abundance ratios as chemical diagnostics of star formation in external galaxies., Comment: 28 pages, 22 figures. Accepted for publication in A&A

We present a new mass function of galaxy clusters and groups using optical/near-infrared wavelength spectroscopic and photometric data from the Observations of Redshift Evolution in Large-Scale Environments (ORELSE) survey. At $z\sim1$, cluster mass function studies are rare regardless of wavelength and have never been attempted from an optical/near-infrared perspective. This work serves as a proof of concept that $z\sim1$ cluster mass functions are achievable without supplemental X-ray or Sunyaev-Zel'dovich (SZ) data. Measurements of the cluster mass function provide important contraints on cosmological parameters and are complementary to other probes. With ORELSE, a new cluster finding technique based on Voronoi tessellation Monte-Carlo (VMC) mapping, and rigorous purity and completeness testing, we have obtained $\sim$240 galaxy overdensity candidates in the redshift range $0.55

CS is among the most abundant gas-phase S-bearing molecules in cold dark molecular clouds. It is easily observable with several transitions in the millimeter wavelength range, and has been widely used as a tracer of the gas density in the interstellar medium in our Galaxy and external galaxies. Chemical models fail to account for the observed CS abundances when assuming the cosmic value for the elemental abundance of sulfur. The CS+O -> CO + S reaction has been proposed as a relevant CS destruction mechanism at low temperatures, and could explain the discrepancy between models and observations. Its reaction rate has been experimentally measured at temperatures of 150-400 K, but the extrapolation to lower temperatures is doubtful. Here we calculate the CS+O reaction rate at temperatures <150 K which are prevailing in the interstellar medium. We performed ab initio calculations to obtain the three lowest PES of the CS+O system. These PESs are used to study the reaction dynamics, using several methods to eventually calculate the CS+O thermal reaction rates. We compare the results of our theoretical calculations for 150-400 K with those obtained in the laboratory. Our detailed theoretical study on the CS+O reaction, which is in agreement with the experimental data obtained at 150-400 K, demonstrates the reliability of our approach. After a careful analysis at lower temperatures, we find that the rate constant at 10 K is negligible, which is consistent with the extrapolation of experimental data using the Arrhenius expression. We use the updated chemical network to model the sulfur chemistry in TMC1 based on molecular abundances determined from GEMS project observations. In our model, we take into account the expected decrease of the cosmic ray ionization rate along the cloud. The abundance of CS is still overestimated when assuming the cosmic value for the sulfur abundance., Comment: 11 pages, 10 figures, accepted in Astronomy & Astrophysics

Utilizing spectroscopic observations taken for the VIMOS Ultra-Deep Survey (VUDS), new observations from Keck/DEIMOS, and publicly available observations of large samples of star-forming galaxies, we report here on the relationship between the star formation rate (SFR) and the local environment ($\delta_{gal}$) of galaxies in the early universe ($2

A large effort has been made to detect warm gas in the planet formation zone of circumstellar discs using space and ground-based near infrared facilities. GV Tau N, the most obscured component of the GV Tau system, is an outstanding source, being one of the first targets detected in HCN and the only one detected in CH$_4$ so far. Although near infrared observations have shed light on its chemical content, the physical structure and kinematics of the circumstellar matter remained unknown. We use interferometric images of the HCN 3-2 and $^{13}$CO 3-2 lines, and far-IR observations of $^{13}$CO, HCN, CN and H$_2$O transitions to discern the morphology, kinematics, and chemistry of the dense gas close to the star. These observations constitute the first detection of H$_2$O towards GV Tau N. Moreover, ALMA high spatial resolution (~ 7 au) images of the continuum at 1.1 mm and the HCN 3-2 line resolve different gas components towards GV Tau N, a gaseous disc with R~25 au, an ionized jet, and one (or two) molecular outflows. The asymmetric morphology of the gaseous disc shows that it has been eroded by the jet. All observations can be explained if GV Tau N is binary, and the primary component has a highly inclined individual disc relative to the circumbinary disc. We discuss the origin of the water and the other molecules emission according to this scenario. In particular, we propose that the water emission would come from the disrupted gaseous disc and the molecular outflows., Comment: 12 pages, 8 figures. Accepted for publication in MNRAS

We present ALMA observations of a merging system at z ~ 4.57, observed as a part of the ALMA Large Program to INvestigate [CII] at Early times (ALPINE) survey. Combining ALMA [CII] 158 micron and far-infrared continuum data with multi-wavelength ancillary data we find that the system is composed of two massive (Mstar >~ 10^10 Msun) star-forming galaxies experiencing a major merger (stellar mass ratio r_mass ~ 0.9) at close spatial (~13 kpc; projected) and velocity (delta_v < 300 km/s) separations, and two additional faint narrow [CII]-emitting satellites. The overall system belongs to a larger-scale protocluster environment and is coincident to one of its overdensity peaks. ALMA reveals also the presence of [CII] emission arising from a circumgalactic gas structure, extending up to a diameter-scale of ~30 kpc. Our morpho-spectral decomposition analysis shows that about 50% of the total flux resides between the individual galaxy components, in a metal-enriched gaseous envelope characterized by a disturbed morphology and complex kinematics. Similarly to observations of shock-excited [CII] emitted from tidal tails in local groups, our results can be interpreted as a possible signature of interstellar gas stripped by strong gravitational interactions, with a possible contribution from material ejected by galactic outflows and emission triggered by star formation in small faint satellites. Our findings suggest that mergers could be an efficient mechanism of gas mixing in the circumgalactic medium around high-z galaxies, and thus play a key role in the galaxy baryon cycle at early epochs., Comment: 12 pages, 7 figures. Accepted for publication in A&A

Sulphur is one of the most abundant elements in the Universe. Surprisingly, sulphuretted molecules are not as abundant as expected in the interstellar medium, and the identity of the main sulphur reservoir is still an open question. Our goal is to investigate the H$_{2}$S chemistry in dark clouds, as this stable molecule is a potential sulphur reservoir. Using millimeter observations of CS, SO, H$_{2}$S, and their isotopologues, we determine the physical conditions and H$_{2}$S abundances along the cores TMC 1-C, TMC 1-CP, and Barnard 1b. The gas-grain model Nautilus is then used to model the sulphur chemistry and explore the impact of photo-desorption and chemical desorption on the H$_2$S abundance. Our model shows that chemical desorption is the main source of gas-phase H$_2$S in dark cores. The measured H$_{2}$S abundance can only be fitted if we assume that the chemical desorption rate decreases by more than a factor of 10 when $n_{\rm H}>2\times10^{4}$. This change in the desorption rate is consistent with the formation of thick H$_2$O and CO ice mantles on grain surfaces. The observed SO and H$_2$S abundances are in good agreement with our predictions adopting an undepleted value of the sulphur abundance. However, the CS abundance is overestimated by a factor of $5-10$. Along the three cores, atomic S is predicted to be the main sulphur reservoir. We conclude that the gaseous H$_2$S abundance is well reproduced, assuming undepleted sulphur abundance and chemical desorption as the main source of H$_2$S. The behavior of the observed H$_{2}$S abundance suggests a changing desorption efficiency, which would probe the snowline in these cores. Our model, however, overestimates the observed gas-phase CS abundance. Given the uncertainty in the sulphur chemistry, our data are consistent with a cosmic elemental S abundance with an uncertainty of a factor of 10., Comment: 23 pages, 16 figures

Here we present new red sequence overdensity measurements for 77 fields in the high-$z$ Clusters Occupied by Bent Radio AGN (COBRA) survey, based on $r$- and $i$-band imaging taken with Lowell Observatory's Discovery Channel Telescope. We observe 38 COBRA fields in $r$-band and 90 COBRA fields in $i$-band. By combining the $r$- and $i$-band photometry with our 3.6$\mu$m and 4.5$\mu$m $Spitzer$ IRAC observations, we identify 39 red sequence cluster candidates that host a strong overdensity of galaxies when measuring the excess of red sequence galaxies relative to a background field. We initially treat the radio host as the cluster center and then determine a new cluster center based on the surface density of red sequence sources. Using our color selection, we identify which COBRA cluster candidates have strong red sequence populations. By removing foreground and background contaminants, we more securely determine which fields include cluster candidates with a higher significance than our single-band observations. Additionally, of the 77 fields we analyze with a redshift estimate, 26 include newly estimated photometric redshifts., Comment: 53 pages, 25 figures, 9 tables. Accepted to ApJ on 10/23/19

We use observations of chlorine-bearing species in molecular absorbers at intermediate redshifts to investigate chemical properties and $^{35}$Cl/$^{37}$Cl isotopic ratios in the absorbing sightlines. Chloronium (H$_2$Cl$^+$) is detected along three independent lines of sight in the z=0.89 and z=0.68 molecular absorbers located in front of the lensed quasars PKS 1830-211 and B 0218+357, respectively. Hydrogen chloride (HCl) was observed only toward PKS 1830-211, and is found to behave differently from H$_2$Cl$^+$. It is detected in one line of sight with an abundance ratio [H$_2$Cl$^+$]/[HCl] $\sim 1$, but remains undetected in the other, more diffuse, line of sight, with a ratio [H$_2$Cl$^+$]/[HCl]~$>17$. The absorption profiles of these two chlorine-bearing species are compared to other species and discussed in terms of the physical properties of the absorbing gas. Our findings are consistent with the picture emerging from chemical models where different species trace gas with different molecular hydrogen fraction. The $^{35}$Cl/$^{37}$Cl isotopic ratios are measured in the different lines of sight and are discussed in terms of stellar nucleosynthesis., Comment: Accepted for publication in Astronomy & Astrophysics 10 pages, 2 figures

Aims. Our goal is to complete the inventory of S-bearing molecules and their abundances in the prototypical photodissociation region (PDR) the Horsehead nebula to gain insight into sulphur chemistry in UV irradiated regions. Based on the WHISPER millimeter (mm) line survey, our goal is to provide an improved and more accurate description of sulphur species and their abundances towards the core and PDR positions in the Horsehead. Methods. The Monte Carlo Markov chain (MCMC) methodology and the molecular excitation and radiative transfer code RADEX were used to explore the parameter space and determine physical conditions and beam-averaged molecular abundances. Results. A total of 13 S-bearing species (CS, SO, SO2, OCS, H2CS - both ortho and para - HDCS, C2S, HCS+, SO+, H2S, S2H, NS and NS+) have been detected in the two targeted positions. This is the first detection of SO+ in the Horsehead and the first detection of NS+ in any PDR. We find a differentiated chemical behaviour between C-S and O-S bearing species within the nebula. The C-S bearing species C2S and o-H2CS present fractional abundances a factor grater than two higher in the core than in the PDR. In contrast, the O-S bearing molecules SO, SO2, and OCS present similar abundances towards both positions. A few molecules, SO+, NS, and NS+, are more abundant towards the PDR than towards the core, and could be considered as PDR tracers. Conclusions. This is the first complete study of S-bearing species towards a PDR. Our study shows that CS, SO, and H2S are the most abundant S-bearing molecules in the PDR with abundances of a few 1E-9. We recall that SH, SH+, S, and S+ are not observable at the wavelengths covered by the WHISPER survey. At the spatial scale of our observations, the total abundance of S atoms locked in the detected species is < 1E-8, only ~0.1% of the cosmic sulphur abundance., Comment: 15 pages, 7 figures, 6 tables

The Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey is an ongoing imaging and spectroscopic campaign initially designed to study the effects of environment on galaxy evolution in high-redshift ($z\sim1$) large-scale structures. We use its rich data in combination with a powerful new technique, Voronoi tessellation Monte-Carlo (VMC) mapping, to search for serendipitous galaxy overdensities at $0.55 < z < 1.37$ within 15 ORELSE fields, a combined spectroscopic footprint of $\sim$1.4 square degrees. Through extensive tests with both observational data and our own mock galaxy catalogs, we optimize the method's many free parameters to maximize its efficacy for general overdensity searches. Our overdensity search yielded 402 new overdensity candidates with precisely measured redshifts and an unprecedented sensitivity down to low total overdensity masses ($\mathcal{M}_{tot} \gtrsim 5\times 10^{13} M_{\odot}$). Using the mock catalogs, we estimated the purity and completeness of our overdensity catalog as a function of redshift, total mass, and spectroscopic redshift fraction, finding impressive levels of both 0.92/0.83 and 0.60/0.49 for purity/completeness at $z=0.8$ and $z=1.2$, respectively, for all overdensity masses at spectroscopic fractions of $\sim$20%. With VMC mapping, we are able to measure precise systemic redshifts, provide an estimate of the total gravitating mass, and maintain high levels of purity and completeness at $z\sim1$ even with only moderate levels of spectroscopy. Other methods (e.g., red-sequence overdensities and hot medium reliant detections) begin to fail at similar redshifts, which attests to VMC mapping's potential to be a powerful tool for current and future wide-field galaxy evolution surveys at $z\sim1$ and beyond., Comment: 39 pages, 18 figures, 6 tables, accepted by MNRAS

Ortho-to-para (o/p) ratios of species like water, ammonia and formaldehyde (H2CO) are believed to encode information about the formation history of the molecule. Measurements of o/p ratios in protoplanetary disks could thus be used to constrain their physical and chemical histories. We present the first measurement of the H2CO o/p ratio in a protoplanetary disk, using three ortho and two para lines observed with the Sub-millimeter Array (SMA) combined with one highly resolved measurement of a single H2CO line with ALMA toward the disk around Herbig Ae star HD 163296. We find a disk-averaged H2CO o/p ratio of 1.8-2.8 (depending on the assumed disk structure), corresponding to a spin temperature of 11-22 K. We also derive a rotational temperature of 24 K from the flux ratio of the three ortho lines. The observed spatial distribution, as seen by ALMA, as well as the rotational temperature and the o/p ratio, at the large scales the SMA is most sensitive to, are consistent with a low-temperature formation pathway, most likely grain surface chemistry, of H2CO in this disk., Comment: 9 pages, 7 figures, 4 tables; Accepted for publication in ApJ

We evaluated the effectiveness of different indicators of cluster virialization using 12 large-scale structures in the ORELSE survey spanning from $0.7

We studied AGN activity in twelve LSSs in the ORELSE survey, at 0.65

We have used the Herschel-HIFI instrument to observe both nuclear spin symmetries of amidogen (NH2) towards the high-mass star-forming regions W31C (G10.6-0.4), W49N (G43.2-0.1), W51 (G49.5-0.4) and G34.3+0.1. The aim is to investigate the ratio of nuclear spin types, the ortho-to-para ratio (OPR), of NH2. The excited NH2 transitions are used to construct radiative transfer models of the hot cores and surrounding envelopes in order to investigate the excitation and possible emission of the ground state rotational transitions of ortho-NH2 N_(K_a,K_c} J=1_(1,1) 3/2 - 0_(0,0) 1/2 and para-NH2 2_(1,2) 5/2 - 1_(0,1) 3/2$ used in the OPR calculations. Our best estimate of the average OPR in the envelopes lie above the high temperature limit of three for W49N, specifically 3.5 with formal errors of \pm0.1, but for W31C, W51, and G34.3+0.1 we find lower values of 2.5\pm0.1, 2.7\pm0.1, and 2.3\pm0.1, respectively. Such low values are strictly forbidden in thermodynamical equilibrium since the OPR is expected to increase above three at low temperatures. In the translucent interstellar gas towards W31C, where the excitation effects are low, we find similar values between 2.2\pm0.2 and 2.9\pm0.2. In contrast, we find an OPR of 3.4\pm0.1 in the dense and cold filament connected to W51, and also two lower limits of >4.2 and >5.0 in two other translucent gas components towards W31C and W49N. At low temperatures (T \lesssim 50 K) the OPR of H2 is <10^-1, far lower than the terrestrial laboratory normal value of three. In such a "para-enriched H2" gas, our astrochemical models can reproduce the variations of the observed OPR, both below and above the thermodynamical equilibrium value, by considering nuclear-spin gas-phase chemistry. The models suggest that values below three arise in regions with temperatures >20-25 K, depending on time, and values above three at lower temperatures., Comment: 21 pages, 23 figures. Accepted by Astronomy and Astrophysics 30 Nov 2015

Using new spectroscopic observations obtained as part of the VIMOS Ultra-Deep Survey (VUDS), we perform a systematic search for overdense environments in the early universe ($z>2$) and report here on the discovery of Cl J0227-0421, a massive protocluster at $z=3.29$. This protocluster is characterized by both the large overdensity of spectroscopically confirmed members, $\delta_{gal}=10.5\pm2.8$, and a significant overdensity in photometric redshift members. The halo mass of this protocluster is estimated, by a variety of methods, to be roughly $3\times10^{14}$ $\mathcal{M}_{\odot}$ at $z\sim3.3$, which, evolved to $z=0$ results in a halo mass rivaling or exceeding that of the Coma cluster. The properties of 19 spectroscopically confirmed member galaxies are compared with a large sample of VUDS/VVDS galaxies in lower density field environments at similar redshifts. We find tentative evidence for an excess of redder, brighter, and more massive galaxies within the confines of the protocluster relative to the field population, which suggests that we may be observing the beginning of environmentally-induced quenching. The properties of these galaxies are investigated, including a discussion of the brightest protocluster galaxy which appears to be undergoing vigorous coeval nuclear and starburst activity. The remaining member galaxies appear to have characteristics which are largely similar to the field population. Though we find weaker evidence of the suppression of the median star formation rates amongst and differences in stacked spectra of member galaxies with respect to the field, we defer any conclusions of these trends to future work with the ensemble of protostructures that are found in the full VUDS sample., Comment: 23 pages, 15 figures, 3 tables, accepted for publication in A&A after minor changes, v3/v4 contains an additional online table and minor topical changes

We present the Spitzer Extragalactic Representative Volume Survey (SERVS), an 18 square degrees medium-deep survey at 3.6 and 4.5 microns with the post-cryogenic Spitzer Space Telescope to ~2 microJy (AB=23.1) depth of five highly observed astronomical fields (ELAIS-N1, ELAIS-S1, Lockman Hole, Chandra Deep Field South and XMM-LSS). SERVS is designed to enable the study of galaxy evolution as a function of environment from z~5 to the present day, and is the first extragalactic survey both large enough and deep enough to put rare objects such as luminous quasars and galaxy clusters at z>1 into their cosmological context. SERVS is designed to overlap with several key surveys at optical, near- through far-infrared, submillimeter and radio wavelengths to provide an unprecedented view of the formation and evolution of massive galaxies. In this paper, we discuss the SERVS survey design, the data processing flow from image reduction and mosaicing to catalogs, as well as coverage of ancillary data from other surveys in the SERVS fields. We also highlight a variety of early science results from the survey., Comment: 21 pages, 23 figures, published in PASP. This version differs slightly from PASP, mainly due to formatting issues. Figure 2 was also corrected from the previous version

We present a submillimetre survey of seven high-z galaxy clusters (0.64

We present robust statistical estimates of the accuracy of early-type galaxy stellar masses derived from spectral energy distribution (SED) fitting as functions of various empirical and theoretical assumptions. Using large samples consisting of 40,000 galaxies from the Sloan Digital Sky Survey, of which 5,000 are also in the UKIRT Infrared Deep Sky Survey, with spectroscopic redshifts in the range 0.05 \leq z \leq 0.095, we test the reliability of some commonly used stellar population models and extinction laws for computing stellar masses. Spectroscopic ages (t), metallicities (Z), and extinctions (A) are also computed from fits to SDSS spectra using various population models. These constraints are used in additional tests to estimate the systematic errors in the stellar masses derived from SED fitting, where t, Z, and A are typically left as free parameters. We find reasonable agreement in mass estimates among stellar population models, with variation of the IMF and extinction law yielding systematic biases on the mass of nearly a factor of 2, in agreement with other studies. Removing the near-infrared bands changes the statistical bias in mass by only 0.06 dex, adding uncertainties of 0.1 dex at the 95% CL. In contrast, we find that removing an ultraviolet band is more critical, introducing 2{\sigma} uncertainties of 0.15 dex. Finally, we find that stellar masses are less affected by absence of metallicity and/or dust extinction knowledge. However, there is a definite systematic offset in the mass estimate when the stellar population age is unknown, up to a factor of 2.5 for very old (12 Gyr) stellar populations. We present the stellar masses for our sample, corrected for the measured systematic biases due to photometrically determined ages, finding that age errors produce lower stellar masses by 0.15 dex, with errors of 0.02 dex at the 95% CL for the median stellar age subsample., Comment: Accepted for Publication in the Astronomical Journal

We present the analysis of the luminosity function of a large sample of galaxy clusters from the Northern Sky Optical Cluster Survey, using latest data from the Sloan Digital Sky Survey. Our global luminosity function (down to M_r<= -16) does not show the presence of an upturn at faint magnitudes, while we do observe a strong dependence of its shape on both richness and cluster-centric radius, with a brightening of M^* and an increase of the dwarf to giant ratio with richness, indicating that more massive systems are more efficient in creating/retaining a population of dwarf satellites. This is observed both within physical (0.5 R_200) and fixed (0.5 Mpc) apertures, suggesting that the trend is either due to a global effect, operating at all scales, or to a local one but operating on even smaller scales. We further observe a decrease of the relative number of dwarf galaxies towards the cluster center; this is most probably due to tidal collisions or collisional disruption of the dwarfs since merging processes are inhibited by the high velocity dispersions in cluster cores and, furthermore, we do not observe a strong dependence of the bright end on the environment. We find indication that the dwarf to giant ratio decreases with increasing redshift, within 0.07

We study the star/galaxy classification efficiency of 13 different decision tree algorithms applied to photometric objects in the Sloan Digital Sky Survey Data Release Seven (SDSS DR7). Each algorithm is defined by a set of parameters which, when varied, produce different final classification trees. We extensively explore the parameter space of each algorithm, using the set of $884,126$ SDSS objects with spectroscopic data as the training set. The efficiency of star-galaxy separation is measured using the completeness function. We find that the Functional Tree algorithm (FT) yields the best results as measured by the mean completeness in two magnitude intervals: $14\le r\le21$ ($85.2%$) and $r\ge19$ ($82.1%$). We compare the performance of the tree generated with the optimal FT configuration to the classifications provided by the SDSS parametric classifier, 2DPHOT and Ball et al. (2006). We find that our FT classifier is comparable or better in completeness over the full magnitude range $15\le r\le21$, with much lower contamination than all but the Ball et al. classifier. At the faintest magnitudes ($r>19$), our classifier is the only one able to maintain high completeness ($>$80%) while still achieving low contamination ($\sim2.5%$). Finally, we apply our FT classifier to separate stars from galaxies in the full set of $69,545,326$ SDSS photometric objects in the magnitude range $14\le r\le21$., Comment: Submitted to AJ

We present an analysis of stellar population gradients in 4,546 Early-Type Galaxies with photometry in $grizYHJK$ along with optical spectroscopy. A new approach is described which utilizes color information to constrain age and metallicity gradients. Defining an effective color gradient, $\nabla_{\star}$, which incorporates all of the available color indices, we investigate how $\nabla_{\star}$ varies with galaxy mass proxies, i.e. velocity dispersion, stellar (M_star) and dynamical (M_dyn) masses, as well as age, metallicity, and alpha/Fe. ETGs with M_dyn larger than 8.5 x 10^10, M_odot have increasing age gradients and decreasing metallicity gradients wrt mass, metallicity, and enhancement. We find that velocity dispersion and alpha/Fe are the main drivers of these correlations. ETGs with 2.5 x 10^10 M_odot =< M_dyn =< 8.5 x 10^10 M_odot, show no correlation of age, metallicity, and color gradients wrt mass, although color gradients still correlate with stellar population parameters, and these correlations are independent of each other. In both mass regimes, the striking anti-correlation between color gradient and alpha-enhancement is significant at \sim 4sigma, and results from the fact that metallicity gradient decreases with alpha/Fe. This anti-correlation may reflect the fact that star formation and metallicity enrichment are regulated by the interplay between the energy input from supernovae, and the temperature and pressure of the hot X-ray gas in ETGs. For all mass ranges, positive age gradients are associated with old galaxies (>5-7 Gyr). For galaxies younger than \sim 5 Gyr, mostly at low-mass, the age gradient tends to be anti-correlated with the Age parameter, with more positive gradients at younger ages., Comment: Accepted for Publication in the Astronomical Journal

We present a new sample of 25 fossil groups (FGs) at z < 0.1, along with a control sample of seventeen bright ellipticals located in non-fossil systems. Both the global properties of FGs (e.g. X-ray luminosity) as well as the photometric properties (i.e. isophotal shape parameter, a4) and spectroscopic parameters (e.g. the alpha-enhancement) of their first-ranked ellipticals are consistent with those of the control sample. This result favors a scenario where FGs are not a distinct class of systems, but rather a common phase in the life of galaxy groups. We also find no evidence for an evolutionary sequence explaining the formation of galaxies in fossil systems through the merging of galaxies in compact groups., Comment: 4 pages, 3 figures, to appear in the ASP Conference Series Proceedings of "Galaxies in Isolation: Exloring Nature vs. Nurture", Granada, 2009

We present the complete galaxy cluster catalog from the Northern Sky Optical Cluster Survey, a new, objectively defined catalog of candidate galaxy clusters at z<0.25 drawn from the Digitized Second Palomar Observatory Sky Survey (DPOSS). The data presented here cover the Southern Galactic Cap, as well as the less-well calibrated regions of the Northern Galactic Cap. In addition, due to improvements in our cluster finder and measurement methods, we provide an updated catalog for the well-calibrated Northern Galactic Cap region previously published in Paper II. The complete survey covers 11,411 square degrees, with over 15,000 candidate clusters. We discuss improved photometric redshifts, richnesses and optical luminosities which are provided for each cluster. A variety of substructure measures are computed for a subset of over 11,000 clusters. We also discuss the derivation of dynamical radii r_200 and its relation to cluster richness. A number of consistency checks between the three areas of the survey are also presented, demonstrating the homogeneity of the catalog over disjoint sky areas. We perform extensive comparisons to existing optically and X-ray selected cluster catalogs, and derive new X-ray luminosities and temperatures for a subset of our clusters. We find that the optical and X-ray luminosities are well correlated, even using relatively shallow ROSAT All Sky Survey and DPOSS data. This survey provides a good comparison sample to the MaxBCG catalog based on Sloan Digital Sky Survey Data, and complements that survey at low redshifts 0.07

We use SDSS-DR4 photometric and spectroscopic data out to redshift z~0.1 combined with ROSAT All Sky Survey X-ray data to produce a sample of twenty-five fossil groups (FGs), defined as bound systems dominated by a single, luminous elliptical galaxy with extended X-ray emission. We examine possible biases introduced by varying the parameters used to define the sample and the main pitfalls are discussed. The spatial density of FGs, estimated via the V/V_ MAX} test, is 2.83 x 10^{-6} h_{75}^3 Mpc^{-3} for L_x > 0.89 x 10^42 h_{75}^-2 erg/s consistent with Vikhlinin et al. (1999), who examined an X-ray overluminous elliptical galaxy sample (OLEG). We compare the general properties of FGs identified here with a sample of bright field ellipticals generated from the same dataset. These two samples show no differences in the distribution of neighboring faint galaxy density excess, distance from the red sequence in the color-magnitude diagram, and structural parameters such as a$_{4}$ and internal color gradients. Furthermore, examination of stellar populations shows that our twenty-five FGs have similar ages, metallicities, and $\alpha$-enhancement as the bright field ellipticals, undermining the idea that these systems represent fossils of a physical mechanism that occurred at high redshift. Our study reveals no difference between FGs and field ellipticals, suggesting that FGs might not be a distinct family of true fossils, but rather the final stage of mass assembly in the Universe., Comment: 18 pages, Accepted to AJ

We present the Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey, a systematic search for structure on scales greater than 10 Mpc around 20 well-known clusters at 0.6 < z < 1.3. We describe the survey design, the cluster sample, and our extensive observational data covering at least 25' around each target cluster. We use adaptively-smoothed red galaxy density maps from our wide-field optical imaging to identify candidate groups/clusters and intermediate-density large scale filaments/walls in each cluster field. Because photometric techniques can be highly uncertain, the crucial component of this survey is the unprecedented amount of spectroscopic coverage. We are using the wide-field, multi-object spectroscopic capabilities of the DEep Multi-Object Imaging Spectrograph to obtain 100-200+ confirmed cluster members in each field. Our survey has already discovered the Cl 1604 supercluster at z = 0.9. Here, we present the results on two additional clusters, Cl 0023+0423 at z = 0.84 and RX J1821.6+6827 at z = 0.82. The optically-selected Cl 0023+0423 is a four-way group-group merger with constituent groups having velocity dispersions between 206-479 km/s. The galaxy population is dominated by blue, star-forming galaxies, with a substantial contribution from recent starbursts. In contrast, the X-ray-selected RX J1821.6+6827 is a largely-isolated, massive cluster with a measured velocity dispersion of 926 +/- 77 km/s. The cluster exhibits a well defined red sequence with a large quiescent galaxy population. The results from these two targets, along with preliminary findings on other ORELSE clusters, suggest that optical selection may be more effective than X-ray surveys at detecting less-evolved, dynamically-active systems at these redshifts. [Abridged], Comment: 47 pages, 12 figures, revised version accepted to AJ

We describe 2DPHOT, a general purpose analysis environment for source detection and analysis in deep wide-field images. 2DPHOT is an automated tool to obtain both integrated and surface photometry of galaxies in an image, to perform reliable star-galaxy separation with accurate estimates of contamination at faint flux levels, and to estimate completeness of the image catalog. We describe the analysis strategy on which 2DPHOT is based, and provide a detailed description of the different algorithms implemented in the package. This new environment is intended as a dedicated tool to process the wealth of data from wide-field imaging surveys. To this end, the package is complemented by 2DGUI, an environment that allows multiple processing of data using a range of computing architectures., Comment: Accepted to PASP

The Cl1604 supercluster at z=0.9 is one of a small handful of such structures discovered in the high redshift universe, and is the first target observed as part of the Observations of Redshift Evolution in Large Scale Environments (ORELSE) Survey. To date, Cl1604 is the largest structure mapped at z~1, with the most constituent clusters and the largest number of spectroscopically confirmed member galaxies. In this paper we present the results of a spectroscopic campaign to create a three-dimensional map of Cl1604 and to understand the contamination by fore- and background large scale structures. Combining new Deep Imaging Multi-object Spectrograph observations with previous data yields redshifts for 1,383 extragalactic objects in a ~ 0.08 sq. deg region, 449 of which are supercluster members. We examine the complex three dimensional structure of Cl1604, providing velocity dispersions for eight of the member clusters and groups. Our extensive spectroscopic dataset is used to examine potential biases in cluster velocity dispersion measurements in the presence of overlapping structures and filaments. We also discuss other structures found along the line-of-sight, including a filament at z=0.6 and two serendipitously discovered clusters/groups at z~1.2., Comment: Final version, appearing in ApJ

We present a comparison of optical and X-ray properties of galaxy clusters in the northern sky. We determine the recovery rate of X-ray detected clusters in the optical as a function of richness, redshift and X-ray luminosity, showing that the missed clusters are typically low contrast systems when observed optically. We employ four different statistical tests to test for the presence of substructure using optical two-dimensional data, finding that approximately 35% of the clusters show strong signs of substructure. However, the results are test-dependent, with variations also due to the magnitude range and radius utilized.We have also performed a comparison of X-ray luminosity and temperature with optical galaxy counts (richness). We find that the slope and scatter of the relations between richness and the X-ray properties are heavily dependent on the density contrast of the clusters. The selection of substructure-free systems does not improve the correlation between X-ray luminosity and richness, but this comparison also shows much larger scatter than one obtained using the X-ray temperature. In the latter case, the sample is significantly reduced because temperature measurements are available only for the most massive (and thus high contrast) systems. However, the comparison between temperature and richness is very sensitive to the exclusion of clusters showing signs of substructure. The correlation of X-ray luminosity and richness is based on the largest sample to date ($\sim$ 750 clusters), while tests involving temperature use a similar number of objects as previous works ($\lsim$100). The results presented here are in good agreement with existing literature., Comment: 32 pages, 18 figures, ApJ in press, including minor changes following the ApJ's edition

We report the discovery of four groups of galaxies along the line of sight to the B1608+656 gravitational lens system. One group is at the redshift of the primary lensing galaxy (z = 0.631) and appears to have a low mass, with eight spectroscopically-confirmed members and an estimated velocity dispersion of 150+/-60 km/s. The three other groups are in the foreground of the lens. These groups contain ~10 confirmed members each, and are located at redshifts of 0.265, 0.426, and 0.520. Two of the three additional groups are centered roughly on the lens system, while the third is centered ~1 arcminute south of the lens. We find that each group provides an external convergence (kappa_ext) of ~0.005--0.060, depending on the assumptions made in calculating the convergence. For lens systems where no additional observables that can break the mass-sheet degeneracy exist, the determination of H_0 will be biased high by a factor of (1-kappa_ext)^{-1} if the external convergence is not properly included in the model. For the B1608+656 system, the stellar velocity dispersion of the lensing galaxy has been measured, thus breaking the mass-sheet degeneracy due to the group that is physically associated with the lens. The effect of the other groups along the line of sight can be folded into the overall uncertainties due to large-scale structure (LSS) along the line of sight. Because the B1608+656 system appears to lie along an overdense line of sight, the LSS will cause the measurement of H_0 to be biased high for this system. The systematic bias introduced by LSS could be 5% or greater. (Abridged), Comment: Accepted for publication in ApJ. Minor changes to match accepted version. 10 pages, 7 figures

The localization of the short-duration, hard-spectrum GRB 050509b was a watershed event. 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. 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 that is ~4" to the west of the XRT position reported previously. Close to this position is a bright elliptical galaxy with redshift z=0.2248, about 1' from the center of a rich cluster of galaxies. Based on positional coincidences, the GRB and the bright elliptical are likely to be physically related. We thus have discovered evidence that at least some short-duration, hard-spectra GRBs arise at cosmological distances. However, while GRB 050509b was underluminous compared to long-duration GRBs, we demonstrate that the ratio of the blast-wave energy to the gamma-ray energy is consistent with that of long-duration 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. We limit the properties of a Li-Paczynski ''mini-supernova.'' Other progenitor models are still viable, and additional rapidly localized bursts from the Swift mission will undoubtedly help to further clarify the progenitor picture. (abridged), Comment: ApJ, in press. 35 pages, 9 figures

Color gradients in early-type galaxies contain valuable clues about their formation and evolutionary histories and mechanisms. We examine color gradients in 1,700 early-type galaxies in 159 galaxy clusters spanning a redshift range of 0.05 to 0.2. We find that color gradients strongly depend on the environment where galaxies reside, with steeper color gradients in poor rather than rich clusters. No dependence of color gradients on galaxy luminosity is found in either rich or poor clusters. The difference in color gradients can be explained by a change in the internal metallicity and/or an age gradient in these galaxies. Our results support a reasonable picture whereby young early-type galaxies form in a dissipative collapse process, and then undergo increased (either major or minor) merging activity in richer rather than in poor clusters., Comment: 3 figures, 2 tables, accepted for publication on ApJL

In this paper we present an objectively defined catalog of 459 small, high density groups of galaxies out to z~0.2 in a region of 6260 square degrees in the northern sky derived from the Digitized Second Palomar Observatory Sky Survey. Our catalog extends down to r = 19.0 and has a median redshift of z_med = 0.12, making it complementary to Hickson's catalog for the nearby universe (z_med = 0.03). The depth and angular coverage of this catalog makes it valuable for studies of the general characteristics of small groups of galaxies and how galaxies evolve in and around them. We also examine the relationship between compact groups and large scale structure., Comment: accepted to AJ

The morphology of clusters of galaxies may be described with a set of parameters which contain information about the formation and evolutionary history of these systems. In this paper we present a preliminary study of the morphological parameters of a sample of 28 compact Abell clusters extracted from DPOSS data. The morphology of galaxy clusters is parameterized by their apparent ellipticity, position angle of the major axis, centre coordinates, core radius and beta-model power law index. Our procedure provides estimates of these parameters by simultaneously fitting them all, overcoming some of the difficulties induced by sparse data and low number statistics typical of this kind of analysis. The cluster parameters were fitted in a 3 x 3 h^-2 sqMpc region, measuring the background in a 2

The Cl 1604 supercluster at z~0.9 is known to contain at least four distinct member clusters, separated in both projection and redshift. In this paper we present deep, multicolor wide-field imaging of a region spanning ~45' on a side, corresponding to 21 h^{-1}_{70} Mpc (physical) at the supercluster redshift. We select galaxies whose colors correspond to those of spectroscopically confirmed cluster members in the r' vs. (r'-i') color-magnitude diagram. Using an adaptive kernel, we generate a map of the projected red galaxy density and identify numerous new candidate clusters which are likely supercluster members. Assuming that all of the density peaks are associated with the supercluster, its transverse size is ~10 h^{-1}_{70} Mpc, which is still significantly smaller than the nearly 93 h^{-1}_{70} Mpc depth in redshift space., Comment: 5 pages, 5 figures. Accepted for publication in AJ. Figures and text updated with corrections

We analyze longslit spectral observations of fourteen Wolf-Rayet galaxies from the sample of Schaerer, Contini & Pindao (1999). All 14 galaxies show broad Wolf-Rayet emission in the blue region of the spectrum, consisting of a blend of NIII4640, CIII4650, CIV4658, and HeII4686 emission lines, which is a spectral characteristic of WN stars. Broad CIV5808 emission, termed the red bump, is detected in 9 galaxies and CIII5996 is detected in 6 galaxies. These emission features are due to WC stars. We derive the numbers of late WN and early WC stars from the luminosity of the blue and red bumps, respectively. The number of O stars is estimated from the luminosity of the Hbeta emission line, after subtracting the contribution of WR stars. The Schaerer & Vacca 1998 (hereafter SV98) models predict that the number of WR stars relative to O stars, N_WR/N_O, increases with metallicity. For low metallicity galaxies, the results agree with predictions of evolutionary synthesis models for galaxies with a burst of star formation, and indicates an IMF slope -2 < Gamma < -2.35 in the low metallicity regime. For high metallicity galaxies our observations suggest a Salpeter IMF (Gamma = -2.35) and an extended short burst. The main possible sources of error are the adopted luminosities for single WCE and WNL stars. We also report, for the first time, NGC 450 as a galaxy with WR characteristics., Comment: 34 pages. Accepted for publication in MNRAS

We present an optically selected galaxy cluster catalog from ~ 2,700 square degrees of the Digitized Second Palomar Observatory Sky Survey (DPOSS), spanning the redshift range 0.1 < z < 0.5, providing an intermediate redshift supplement to the previous DPOSS cluster survey. This new catalog contains 9,956 cluster candidates and is the largest resource of rich clusters in this redshift range to date. The candidates are detected using the best DPOSS plates based on seeing and limiting magnitude. The search is further restricted to high galactic latitude (|b| > 50), where stellar contamination is modest and nearly uniform. We also present a performance comparison of two different detection methods applied to this data, the Adaptive Kernel and Voronoi Tessellation techniques. In the regime where both catalogs are expected to be complete, we find excellent agreement, as well as with the most recent surveys in the literature. Extensive simulations are performed and applied to the two different methods, indicating a contamination rate of ~ 5%. These simulations are also used to optimize the algorithms and evaluate the selection function for the final cluster catalog. Redshift and richness estimates are also provided, making possible the selection of subsamples for future studies., Comment: 64 pages, 32 figures. Accepted to AJ; appearing in September. Version with full resolution figures is available at http://www.astro.caltech.edu/~paal/paper/NoSOCS_IV.ps.gz