We have discovered 16 Type Ia supernovae (SNe Ia) with the Hubble Space Telescope (HST) and have used them to provide the first conclusive evidence for cosmic deceleration that preceded the current epoch of cosmic acceleration. These objects, discovered during the course of the GOODS ACS Treasury program, include 6 of the 7 highest-redshift SNe Ia known, all at z > 1.25, and populate the Hubble diagram in unexplored territory. The luminosity distances to these objects, and to 170 previously reported SNe Ia, have been determined using empirical relations between light-curve shape and luminosity. A purely kinematic interpretation of the SN Ia sample provides evidence at the > 99% confidence level for a transition from deceleration to acceleration or similarly, strong evidence for a cosmic jerk. Using a simple model of the -2expansion history, the transition between the two epochs is constrained to be at z = 0.46 ± 0.13. The data are consistent with the cosmic concordance model of Ω M ≈ 0.3, Ω Λ ≈ 0.7 (χ 2 dof = 1.06), and are inconsistent with a simple model of evolution or dust as an alternative to dark energy. For a flat Universe with a cosmological constant, we measure Ω M = 0.29± 0.05 0.03 (equivalently, Ω Λ = 0.71). When combined with external flat-Universe constraints including the cosmic microwave background and large-scale structure, we find w = −1.02± 0.13 0.19 (and w < −0.76 at the 95% confidence level) for an assumed static equation of state of dark energy, P = wρc 2 . Joint constraints on both the recent equation of state of dark energy, w 0 , and its time evolution, dw/dz, are a factor of ∼ 8 more precise than its first estimate and twice as precise as those without the SNe Ia discovered with HST. Our constraints are consistent with the static nature of and value of w expected for a cosmological constant (i.e., w 0 = −1.0, dw/dz = 0), and are inconsistent with very rapid evolution of dark energy. We address consequences of evolving dark energy for the fate of the Universe.

We present accurate photometric redshifts in the 2-deg 2 COSMOS field. The redshifts are computed with 30 broad, intermediate, and narrow bands covering the UV (GALEX), Visible-NIR (Subaru, CFHT, UKIRT and NOAO) and mid-IR (Spitzer/IRAC). A χ 2 template-fitting method (Le Phare) was used and calibrated with large spectroscopic samples from VLT-VIMOS and Keck-DEIMOS. We develop and implement a new method which accounts for the contributions from emission lines ([O II], Hβ, Hα and Lyα) to the spectral energy distributions (SEDs). The treatment of emission lines improves the photo-z accuracy by a factor of 2.5. Comparison of the derived photo-z with 4148 spectroscopic redshifts (i.e. ∆z = z s − z p ) indicates a dispersion of σ ∆z/(1+zs) = 0.007 at i + AB < 22.5, a factor of 2 − 6 times more accurate than earlier photo-z in the COSMOS, CFHTLS and COMBO-17 survey fields. At fainter magnitudes i + AB < 24 and z < 1.25, the accuracy is σ ∆z/(1+zs) = 0.012. The deep NIR and IRAC coverage enables the photo-z to be extended to z ∼ 2 albeit with a lower accuracy (σ ∆z/(1+zs) = 0.06 at i + AB ∼ 24). The redshift distribution of large magnitude-selected samples is derived and the median redshift is found to range from z m = 0.66 at 22 < i + AB < 22.5 to z m = 1.06 at 24.5 < i + AB < 25. At i + AB < 26.0, the multi-wavelength COSMOS catalog includes approximately 607,617 objects. The COSMOS-30 photo-z enable the full exploitation of this survey for studies of galaxy and large scale structure evolution at high redshift.

The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) is designed to document the first third of galactic evolution, over the approximate redshift (z) range 8-1.5. It will image >250,000 distant galaxies using three separate cameras on the Hubble Space Telescope, from the mid-ultraviolet to the near-infrared, and will find and measure Type Ia supernovae at z > 1.5 to test their accuracy as standardizable candles for cosmology. Five premier multi-wavelength sky regions are selected, each with extensive ancillary data. The use of five widely separated fields mitigates cosmic variance and yields statistically robust and complete samples of galaxies down to a stellar mass of 10 9 M to z ≈ 2, reaching the knee of the ultraviolet luminosity function of galaxies to z ≈ 8. The survey covers approximately 800 arcmin 2 and is divided into two parts. The CANDELS/Deep survey (5σ point-source limit H = 27.7 mag) covers ∼125 arcmin 2 within Great Observatories Origins Deep Survey (GOODS)-N and GOODS-S. The CANDELS/Wide survey includes GOODS and three additional fields (Extended Groth Strip, COSMOS, and Ultra-deep Survey) and covers the full area to a 5σ pointsource limit of H 27.0 mag. Together with the Hubble Ultra Deep Fields, the strategy creates a three-tiered "wedding-cake" approach that has proven efficient for extragalactic surveys. Data from the survey are nonproprietary and are useful for a wide variety of science investigations. In this paper, we describe the basic motivations for the survey, the CANDELS team science goals and the resulting observational requirements, the field selection and geometry, and the observing design. The Hubble data processing and products are described in a companion paper.

We have discovered 21 new Type Ia supernovae (SNe Ia) with the Hubble Space Telescope (HST) and have used them to trace the history of cosmic expansion over the last 10 billion yr. These objects, which include 13 spectroscopically confirmed SNe Ia at z ! 1, were discovered during 14 epochs of reimaging of the GOODS fields North and South over 2 yr with the Advanced Camera for Surveys on HST. Together with a recalibration of our previous HSTdiscovered SNe Ia, the full sample of 23 SNe Ia at z ! 1 provides the highest redshift sample known. Combining these data with previous SN Ia data sets, we measured H z ð Þ at discrete, uncorrelated epochs, reducing the uncertainty of H z > 1 ð Þfrom 50% to under 20%, strengthening the evidence for a cosmic jerk-the transition from deceleration in the past to acceleration in the present. The unique leverage of the HST high-redshift SNe Ia provides the first meaningful constraint on the dark energy equation-of-state parameter at z ! 1. The result remains consistent with a cosmological constant [w z ð Þ ¼ À1] and rules out rapidly evolving dark energy (dw/dz 3 1). The defining property of dark energy, its negative pressure, appears to be present at z > 1, in the epoch preceding acceleration, with $98% confidence in our primary fit. Moreover, the z > 1 sample-averaged spectral energy distribution is consistent with that of the typical SN Ia over the last 10 Gyr, indicating that any spectral evolution of the properties of SNe Ia with redshift is still below our detection threshold.

This paper describes the Hubble Space Telescope imaging data products and data reduction procedures for the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS). This survey is designed to document the evolution of galaxies and black holes at z ∼ 1.5 − 8, and to study Type Ia SNe beyond z > 1.5. Five premier multi-wavelength sky regions are selected, each with extensive multiwavelength observations. The primary CANDELS data consist of imaging obtained in the Wide Field Camera 3 / infrared channel (WFC3/IR) and UVIS channel, along with the Advanced Camera for Surveys (ACS). The CANDELS/Deep survey covers ∼ 125 square arcminutes within GOODS-N and GOODS-S, while the remainder consists of the CANDELS/Wide survey, achieving a total of ∼ 800 square arcminutes across GOODS and three additional fields (EGS, COSMOS, and UDS). We summarize the observational aspects of the survey as motivated by the scientific goals and present a detailed description of the data reduction procedures and products from the survey. Our data reduction methods utilize the most up to date calibration files and image combination procedures. We have paid special attention to correcting a range of instrumental effects, including CTE degradation for ACS, removal of electronic bias-striping present in ACS data after SM4, and persistence effects and other artifacts in WFC3/IR. For each field, we release mosaics for individual epochs and eventual mosaics containing data from all epochs combined, to facilitate photometric variability studies and the deepest possible photometry. A more detailed overview of the science goals and observational design of the survey are presented in a companion paper.

The Cosmic Evolution Survey (COSMOS) is designed to probe the correlated evolution of galaxies, star formation, active galactic nuclei (AGNs), and dark matter (DM) with large-scale structure (LSS) over the redshift range z > 0:5Y 6. The survey includes multiwavelength imaging and spectroscopy from X-rayYtoYradio wavelengths covering a 2 deg 2 area, including HST imaging. Given the very high sensitivity and resolution of these data sets, COSMOS also provides unprecedented samples of objects at high redshift with greatly reduced cosmic variance, compared to earlier surveys. Here we provide a brief overview of the survey strategy, the characteristics of the major COSMOS data sets, and a summary the science goals.

We follow the galaxy stellar mass assembly by morphological and spectral type in the COSMOS 2 deg 2 field. We derive the stellar mass functions and stellar mass densities from z = 2 to z = 0.2 using 196,000 galaxies selected at F 3.6 μm > 1 μJy with accurate photometric redshifts (σ (z phot −z spec )/(1+z spec ) = 0.008 at i + < 22.5). Using a spectral classification, we find that z ∼ 1 is an epoch of transition in the stellar mass assembly of quiescent galaxies. Their stellar mass density increases by 1.1 dex between z = 1.5-2 and z = 0.8-1 (Δt ∼ 2.5 Gyr), but only by 0.3 dex between z = 0.8-1 and z ∼ 0.1 (Δt ∼ 6 Gyr). Then, we add the morphological information and find that 80%-90% of the massive quiescent galaxies (log M ∼ 11) have an elliptical morphology at z < 0.8. Therefore, a dominant mechanism links the shutdown of star formation and the acquisition of an elliptical morphology in massive galaxies. Still, a significant fraction of quiescent galaxies present a Spi/Irr morphology at low mass (40%-60% at log M ∼ 9.5), but this fraction is smaller than predicted by semi-analytical models using a "halo quenching" recipe. We also analyze the evolution of star-forming galaxies and split them into "intermediate activity" and "high activity" galaxies. We find that the most massive "high activity" galaxies end their high star formation rate phase first. Finally, the space density of massive star-forming galaxies becomes lower than the space density of massive elliptical galaxies at z < 1. As a consequence, the rate of "wet mergers" involved in the formation of the most massive ellipticals must decline very rapidly at z < 1, which could explain the observed slow down in the assembly of these quiescent and massive sources.

We present a robust measurement and analysis of the rest-frame ultraviolet (UV) luminosity functions at z = 4 to 8. We use deep Hubble Space Telescope imaging over the CANDELS/GOODS fields, the Hubble Ultra Deep Field and the Hubble Frontier Field deep parallel observations near the Abell 2744 and MACS J0416.1-2403 clusters. The combination of these surveys provides an effective volume of 0.6-1.2 ×10 6 Mpc 3 over this epoch, allowing us to perform a robust search for faint (M UV = −18) and bright (M UV < −21) highredshift galaxies. We select candidate galaxies using a well-tested photometric redshift technique with careful screening of contaminants, finding a sample of 7446 candidate galaxies at 3.5 < z < 8.5, with >1000 galaxies at z ≈ 6 -8. We measure both a stepwise luminosity function for candidate galaxies in our redshift samples, as well as a Schechter function, using a Markov Chain Monte Carlo analysis to measure robust uncertainties. At the faint end our UV luminosity functions agree with previous studies, yet we find a higher abundance of UV-bright candidate galaxies at z ≥ 6. Our best-fit value of the characteristic magnitude M * UV is consistent with −21 at z ≥ 5, different than that inferred based on previous trends at lower redshift, and brighter at ∼2σ significance than previous measures at z = 6 and 7 (Bouwens et al. 2007(Bouwens et al. , 2011b. At z = 8, a single powerlaw provides an equally good fit to the UV luminosity function, while at z = 6 and 7, an exponential cutoff at the bright end is moderately preferred. We compare our luminosity functions to semi-analytical models, and find that the lack of evolution in M * UV is consistent with models where the impact of dust attenuation on the bright end of the luminosity function decreases at higher redshift, though a decreasing impact of feedback may also be possible. We measure the evolution of the cosmic star-formation rate (SFR) density by integrating our observed luminosity functions to M UV = −17, correcting for dust attenuation, and find that the SFR density declines proportionally to (1+z) −4.3±0.5 at z > 4, consistent with observations at z ≥ 9. Our observed luminosity functions are consistent with a reionization history that starts at z 10, completes at z > 6, and reaches a midpoint (x HII = 0.5) at 6.7 < z < 9.4. Finally, using a constant cumulative number density selection and an empirically derived rising star-formation history, our observations predict that the abundance of bright z = 9 galaxies is likely higher than previous constraints, though consistent with recent estimates of bright z ∼ 10 galaxies.