The Zwicky Transient Facility (ZTF) is a new optical time-domain survey that uses the Palomar 48 inch Schmidt telescope. A custom-built wide-field camera provides a 47 deg 2 field of view and 8 s readout time, yielding more than an order of magnitude improvement in survey speed relative to its predecessor survey, the Palomar Transient Factory. We describe the design and implementation of the camera and observing system. The ZTF data system at the Infrared Processing and Analysis Center provides near-real-time reduction to identify moving and varying objects. We outline the analysis pipelines, data products, and associated archive. Finally, we present on-sky performance analysis and first scientific results from commissioning and the early survey. ZTF's public alert stream will serve as a useful precursor for that of the Large Synoptic Survey Telescope.

We present spectra taken with the Infrared Spectrograph 8 on Spitzer covering the 5 − 38µm region of the ten Ultraluminous Infrared Galaxies (ULIRGs) found in the IRAS Bright Galaxy Sample. Among the BGS ULIRGs, we find a factor of 50 spread in the rest-frame 5.5 − 60µm spectral slope. The 9.7µm silicate optical depths range from at least τ 9.7 ≤ 0.4 to τ 9.7 ≥ 4.2, implying line of sight extinctions of A V ∼ 8 mag to nearly A V ≥ 78 mag. There is evidence for water ice and hydrocarbon absorption and C 2 H 2 and HCN absorption features in four and possibly six of the 10 BGS ULIRGs, indicating shielded molecular clouds and a warm, dense ISM. We have detected [NeV] emission in three of the ten BGS ULIRGs, at flux levels of 5 − 18 × 10 −14 erg cm −2 sec −1 and [NeV] 14.3/[NeII] 12.8 line flux ratios of 0.12 − 0.85. The remaining BGS ULIRGs have limits on their [NeV]/[NeII] line flux ratios which range from ≤ 0.15 to ≤ 0.01. Among the BGS ULIRGs, the AGN fractions implied by either the [NeV]/[NeII] or [OIV]/[NeII] line flux ratios (or their upper limits) are significantly lower than implied by

The Zwicky Transient Facility (ZTF) is a new robotic time-domain survey currently in progress using the Palomar 48-inch Schmidt Telescope. ZTF uses a 47 square degree field with a 600 megapixel camera to scan the entire northern visible sky at rates of ∼3760 square degrees/hour to median depths of g∼20.8 and r∼20.6 mag (AB, 5σ in 30 sec). We describe the Science Data System that is housed at IPAC, Caltech. This comprises the data-processing pipelines, alert production system, data archive, and user interfaces for accessing and analyzing the products. The real-time pipeline employs a novel image-differencing algorithm, optimized for the detection of point-source transient events. These events are vetted for reliability using a machine-learned classifier and combined with contextual information to generate data-rich alert packets. The packets become available for distribution typically within 13 minutes (95th percentile) of observation. Detected events are also linked to generate candidate moving-object tracks using a novel algorithm. Objects that move fast enough to streak in the individual exposures are also extracted and vetted. We present some preliminary results of the calibration performance delivered by the real-time pipeline. The reconstructed astrometric accuracy per science image with respect to Gaia DR1 is typically 45 to 85 milliarcsec. This is the RMS per-axis on the sky for sources extracted with photometric S/N10 and hence corresponds to the typical astrometric uncertainty down to this limit. The derived photometric precision (repeatability) at bright unsaturated fluxes varies between 8 and 25 millimag. The high end of these ranges corresponds to an airmass approaching ∼2-the limit of the public survey. Photometric calibration accuracy with respect to Pan-STARRS1 is generally better than 2%. The products support a broad range of scientific applications: fast and young supernovae; rare flux transients; variable stars; eclipsing binaries; variability from active galactic nuclei;

The Spitzer Space Telescope has revealed a significant population of high-redshift (z $ 2) dust-obscured galaxies with large mid-infrared to ultraviolet luminosity ratios. Due to their optical faintness, these galaxies have been previously missed in traditional optical studies of the distant universe. We present a simple method for selecting this high-redshift population based solely on the ratio of the observed mid-infrared 24 m to optical R-band flux density. We apply this method to observations of the %8.6 deg 2 NOAO Deep Wide-Field Survey Boötes field, and uncover %2600 dust-obscured galaxy candidates [i.e., 0.089 arcmin À2 ) with 24 m flux densities F 24 m ! 0:3 mJy and (R À ½24) ! 14 (i.e., F (24 m)/F (R) k1000]. These galaxies have no counterparts in the local universe. They represent 7% AE 0:6% of the 24 m source population at F 24 m ! 1 mJy but increase to %13% AE 1% of the population at %0.3 mJy. These galaxies exhibit evidence of both star formation and AGN activity, with the brighter 24 m sources being more AGN-dominated. We have measured spectroscopic redshifts for 86 of these galaxies, and find a broad redshift distribution centered atz % 1:99 AE 0:05. The space density of this population is AE DOG (F 24m ! 0:3 mJy) ¼ (2:82 AE 0:05) ; 10 À5 h 3 70 Mpc À3 , similar to that of bright submillimeter-selected galaxies at comparable redshifts. These redshifts imply large luminosities, with median L (8 m) % 4 ; 10 11 L . The infrared luminosity density contributed by this relatively rare dust-obscured galaxy population is log (IRLD) % 8:23 þ0:18 À0:30 . This is %60 þ40 À15 % of that contributed by z $ 2 ultraluminous infrared galaxies (ULIRGs, with L IR > 10 12 L ); our simple selection thus identifies a significant fraction of z $ 2 ULIRGs. This IRLD is %26% AE 14% of the total contributed by all z $ 2 galaxies. We suggest that these dust-obscured galaxies are the progenitors of luminous ($4L Ã ) present-day galaxies, seen undergoing an extremely luminous, short-lived phase of both bulge and black hole growth. They may represent a brief evolutionary phase between submillimeter-selected galaxies and less obscured quasars or galaxies.

28 pages, 19 figures, ApJ in pressInternational audienceWe study how the proportion of star-forming galaxies evolves between z=0.8 and 0 as a function of galaxy environment, using the O II line in emission as a signature of ongoing star formation. Our high-z data set comprises 16 clusters, 10 groups, and another 250 galaxies in poorer groups and the field at z=0.4-0.8 from the ESO Distant Cluster Survey, plus another 9 massive clusters at similar redshifts. As a local comparison, we use galaxy systems selected from the Sloan Digital Sky Survey (SDSS) at 0.04=550 km s-1, where the fraction of galaxies with O II emission does not vary systematically with velocity dispersion. We quantify the evolution of the proportion of star-forming galaxies as a function of the system velocity dispersion and find that it is strongest in intermediate-mass systems (?~500-600 km s-1 at z=0). To understand the origin of the observed trends, we use the Press-Schechter formalism and the Millennium Simulation and show that galaxy star formation histories may be closely related to the growth history of clusters and groups. If the scenario we propose is roughly correct, the link between galaxy properties and environment is extremely simple to predict purely from a knowledge of the growth of dark matter structures. Based on observations obtained at the ESO Very Large Telescope (VLT) as part of the Large program 166.A-0162 (the ESO Distant Cluster Survey). Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with proposal 9476

We present R $ 600, 10Y37 m spectra of 53 ultraluminous infrared galaxies (ULIRGs), taken using the Infrared Spectrograph on board Spitzer. The spectra show fine-structure emission lines of neon, oxygen, sulfur, silicon, argon, chlorine, iron, and phosphorous; molecular hydrogen lines, and C 2 H 2 , HCN, and OH À absorption features. We employ diagnostics based on the fine-structure lines, the polycyclic aromatic hydrocarbon (PAH) features and the 9.7 m silicate absorption feature, to show that the infrared emission from most ULIRGs is powered mostly by star formation, with only $20% of ULIRGs hosting an AGN with a greater IR luminosity than the starburst. The detection of [Ne v] k14.32 in just under half the sample, however, implies that an AGN contributes significantly to the mid-IR flux in $42% of ULIRGs. The starbursts and AGNs in ULIRGs appear more extincted, and for the starbursts more compact than those in lower luminosity systems. The excitations and electron densities in the narrow-line regions of ULIRGs appear comparable to those of starbursts with LP10 11.5 L , although the NLR gas in ULIRGs may be more dense. We show that the [Ne ii] k12.81 + [Ne iii] k15.56 luminosity correlates with both infrared luminosity and the luminosity of the 6.2 and 11.2 m PAH features, and derive a calibration between PAH luminosity and star formation rate. Finally, we show that ULIRGs with silicate absorption strengths S sil of 0:8 P S sil P 2:4 are likely to be powered mainly by star formation, but that ULIRGs with S sil P 0:8, and possibly those with S sil k 2:4, contain an IR-luminous AGN.

The Zwicky Transient Facility (ZTF), a public–private enterprise, is a new time-domain survey employing a dedicated camera on the Palomar 48-inch Schmidt telescope with a 47 deg2 field of view and an 8 second readout time. It is well positioned in the development of time-domain astronomy, offering operations at 10% of the scale and style of the Large Synoptic Survey Telescope (LSST) with a single 1-m class survey telescope. The public surveys will cover the observable northern sky every three nights in g and r filters and the visible Galactic plane every night in g and r. Alerts generated by these surveys are sent in real time to brokers. A consortium of universities that provided funding (“partnership”) are undertaking several boutique surveys. The combination of these surveys producing one million alerts per night allows for exploration of transient and variable astrophysical phenomena brighter than r ∼ 20.5 on timescales of minutes to years. We describe the primary science objectives driving ZTF, including the physics of supernovae and relativistic explosions, multi-messenger astrophysics, supernova cosmology, active galactic nuclei, and tidal disruption events, stellar variability, and solar system objects.

We describe Hubble Space Telescope (HST ) imaging of 10 of the 20 ESO Distant Cluster Survey (EDisCS) fields. Each $40 arcmin 2 field was imaged in the F814W filter with the Advanced Camera for Surveys Wide Field Camera. Based on these data, we present visual morphological classifications for the $920 sources per field that are brighter than I auto ¼ 23 mag. We use these classifications to quantify the morphological content of 10 intermediate-redshift (0:5 < z < 0:8) galaxy clusters within the HST survey region. The EDisCS results, combined with previously published data from seven higher redshift clusters, show no statistically significant evidence for evolution in the mean fractions of elliptical, S0, and late-type (Sp+Irr) galaxies in clusters over the redshift range 0:5 < z < 1:2. In contrast, existing studies of lower redshift clusters have revealed a factor of $2 increase in the typical S0 fraction between z ¼ 0:4 and 0, accompanied by a commensurate decrease in the Sp+Irr fraction and no evolution in the elliptical fraction. The EDisCS clusters demonstrate that cluster morphological fractions plateau beyond z % 0:4. They also exhibit a mild correlation between morphological content and cluster velocity dispersion, highlighting the importance of careful sample selection in evaluating evolution. We discuss these findings in the context of a recently proposed scenario in which the fractions of passive (E, S0) and star-forming (Sp, Irr) galaxies are determined primarily by the growth history of clusters.