We describe the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) Early Release Science (ERS) observations in the Great Observatories Origins Deep Survey (GOODS) South field. The new WFC3 ERS data provide calibrated, drizzled mosaics in the UV filters F225W, F275W, and F336W, as well as in the near-IR filters F098M (Y s ), F125W (J), and F160W (H) with 1-2 HST orbits per filter. Together with the existing HST Advanced Camera for Surveys (ACS) GOODS-South mosaics in the BViz filters, these panchromatic 10-band ERS data cover 40-50 arcmin 2 at 0.2-1.7 μm in wavelength at 0. 07-0. 15 FWHM resolution and 0. 090 Multidrizzled pixels to depths of AB 26.0-27.0 mag (5σ ) for point sources, and AB 25.5-26.5 mag for compact galaxies. In this paper, we describe (1) the scientific rationale, and the data taking plus reduction procedures of the panchromatic 10-band ERS mosaics, (2) the procedure of generating object catalogs across the 10 different ERS filters, and the specific star-galaxy separation techniques used, and (3) the reliability and completeness of the object catalogs from the WFC3 ERS mosaics. The excellent 0. 07-0. 15 FWHM resolution of HST/WFC3 and ACS makes star-galaxy separation straightforward over a factor of 10 in wavelength to AB 25-26 mag from the UV to the near-IR, respectively. Our main results are: (1) proper motion of faint ERS stars is detected over 6 years at 3.06 ± 0.66 mas year −1 (4.6σ ), consistent with Galactic structure models; (2) both the Galactic star counts and the galaxy counts show mild but significant trends of decreasing count slopes from the mid-UV to the near-IR over a factor of 10 in wavelength; (3) combining the 10-band ERS counts with the panchromatic Galaxy and Mass Assembly survey counts at the bright end (10 mag AB 20 mag) and the Hubble Ultra Deep Field counts in the BV izY s J H filters at the faint end (24 mag AB 30 mag) yields galaxy counts that are well measured over the entire flux range 10 mag AB 30 mag for 0.2-2 μm in wavelength; (4) simple luminosity+density evolution models can fit the galaxy counts over this entire flux range. However, no single model can explain the counts over this entire flux range in all 10 filters simultaneously. More sophisticated models of galaxy assembly are needed to reproduce the overall constraints provided by the current panchromatic galaxy counts for 10 mag AB 30 mag over a factor of 10 in wavelength.

The most frequently proposed model for the origin of quasars holds that the high accretion rates seen in luminous active galactic nuclei (AGN) are primarily triggered during major mergers between gas-rich galaxies. While plausible for decades, this model has only begun to be tested with statistical rigor in the past few years. Here, we report on a Hubble Space Telescope study to test this hypothesis for z=2 quasars with high supermassive black hole masses ( =  M M 10 10 BH 9 1 0 -), which dominate cosmic black hole growth at this redshift. We compare Wide Field Camera 3 F W 160 (rest-frame V-band) imaging of 19 point source-subtracted quasar hosts to a matched sample of 84 inactive galaxies, testing whether the quasar hosts have greater evidence for strong gravitational interactions. Using an expert ranking procedure, we find that the quasar hosts are uniformly distributed within the merger sequence of inactive galaxies, with no preference for quasars in high-distortion hosts. Using a merger/nonmerger cutoff approach, we recover distortion fractions of for inactive galaxies (distribution modes, 68% confidence intervals), with both measurements subjected to the same observational conditions and limitations. The slight enhancement in distorted fraction for quasar hosts over inactive galaxies is not significant, with a probability that the quasar fraction is higherin line with results for lower mass and lower z AGN. We find no evidence that major mergers are the primary triggering mechanism for the massive quasars that dominate accretion at the peak of cosmic quasar activity.

We present a detailed structural and morphological study of a large sample of spectroscopicallyconfirmed galaxies at z ≥ 6, using deep HST near-IR broad-band images and Subaru optical narrowband images. The galaxy sample consists of 51 Lyα emitters (LAEs) at z ≃ 5.7, 6.5, and 7.0, and 16 Lyman-break galaxies (LBGs) at 5.9 ≤ z ≤ 6.5. These galaxies exhibit a wide range of restframe UV continuum morphology in the HST images, from compact features to multiple component systems. The fraction of merging/interacting galaxies reaches 40% ∼ 50% at the brightest end of M 1500 ≤ −20.5 mag. The intrinsic half-light radii r hl,in , after correction for PSF broadening, are roughly between r hl,in ≃ 0. ′′ 05 (0.3 kpc) and 0. ′′ 3 (1.7 kpc) at M 1500 ≤ −19.5 mag. The median r hl,in value is 0. ′′ 16 (∼0.9 kpc). This is consistent with the sizes of bright LAEs and LBGs at z ≥ 6 in previous studies. In addition, more luminous galaxies tend to have larger sizes, exhibiting a weak size-luminosity relation r hl,in ∝ L 0.14 at M 1500 ≤ −19.5 mag. The slope of 0.14 is significantly flatter than those in fainter LBG samples. We discuss the morphology of z ≥ 6 galaxies with nonparametric methods, including the CAS system and the Gini and M 20 parameters, and demonstrate their validity through simulations. We search for extended Lyα emission halos around LAEs at z ≃ 5.7 and 6.5, by stacking a number of narrow-band images. We do not find evidence of extended halos predicted by cosmological simulations. Such Lyα halos, if they exist, could be weaker than predicted. Finally, we investigate any positional misalignment between UV continuum and Lyα emission in LAEs. While the two positions are generally consistent, several merging galaxies show significant positional differences. This is likely caused by a disturbed ISM distribution due to merging activity.

Recent near-infrared power-spectra and panchromatic Extragalactic Background Light (EBL) measurements provide upper limits on the integrated near-infrared surface brightness (SB > ∼ 31mag arcsec −2 at 2µm) that may come from Population III (Pop III) stars and possible accretion disks around resulting stellar-mass black holes (BHs) in the epoch of First Light, broadly taken from z 7-17. Physical parameters for zero metallicity Pop III stars at z > ∼ 7 can be estimated from MESA stellar evolution models through helium-depletion, and for BH accretion disks from quasar microlensing results and multicolor accretion models. Second-generation non-zero metallicity stars can form at higher multiplicity, so that BH accretion disks may be fed by Roche-lobe overflow from lower-mass companions in their AGB stage. The near-infrared SB constraints can be used to calculate the number of caustic transits behind lensing clusters that the James Webb Space Telescope (JWST) and the next generation 25-39 m ground-based telescopes may detect for both Pop III stars and stellar mass BH accretion disks. Because Pop III stars and stellar mass BH accretion disks have sizes of a few×10 −11 arcsec at z > ∼ 7, typical caustic magnifications can be µ 10 4 -10 5 , with rise times of hours and decline times of < ∼ 1 year for cluster transverse velocities of v T < ∼ 1000 km s −1 . Microlensing by intracluster medium objects can modify transit magnifications, and lengthen visibility times. Depending on BH masses, accretion-disk radii and feeding efficiencies, stellar-mass BH accretion-disk caustic transits could outnumber those from Pop III stars. To observe Pop III caustic transits directly may require monitoring 3-30 lensing clusters to AB < ∼ 29 mag over a decade or more. Such a program must be started with JWST at the start of Cycle 1, and -depending on the role of microlensing in the Intra Cluster Light (ICL) -should be continued for decades with the next generation 25-39 m ground-based telescopes, where both JWST and the ground-based facilities each will play a unique and strongly complementary role.