Rest Frame Optical Spectra of Lyman Break Galaxies: Other Lensing Arcs around MS1512-cB58

We have obtained near-infrared spectra of two images of the galaxy at z=2.72 which is gravitationally lensed by the foreground cluster MS1512+36. The brighter arc, cB58, is an image of only the nucleus and the southern half of the background galaxy, while the fainter image, A2, encompasses the entire background galaxy. Thus the gravitational lensing provides spatial resolution on a smaller scale than is routinely available by other methods. Our observations indicate no evidence for any systematic rotational velocity gradient across the face of this galaxy. The nucleus and outer regions of the galaxy do not differ in their gas reddening or excitation level, based on the identical Hα/5007 ratios. cB58 (which is more dominated by the nucleus) has relatively stronger continuum emission, perhaps because of a higher ratio of old to young stars, compared to the outer parts of the galaxy. A second emission line source, denoted as K1, at a slightly lower redshift was serendipitously detected in the slit. It appears to be the gravitationally lensed image of another background galaxy in the same group as cB58

A CANDELS WFC3 Grism Study of Emission-Line Galaxies at z ~ 2: A Mix of Nuclear Activity and Low-Metallicity Star Formation

We present Hubble Space Telescope Wide Field Camera 3 (WFC3) slitless grism spectroscopy of 28 emission-line galaxies at z ~ 2, in the GOODS-S region of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey. The high sensitivity of these grism observations, with >1σ detections of emission lines to f > 2.5 × 10^(–18) erg s^(–1) cm^(–2), means that the galaxies in the sample are typically ~7 times less massive (median M_* = 10^(9.5) M_☉) than previously studied z ~ 2 emission-line galaxies. Despite their lower mass, the galaxies have [O III]/Hβ ratios which are very similar to previously studied z ~ 2 galaxies and much higher than the typical emission-line ratios of local galaxies. The WFC3 grism allows for unique studies of spatial gradients in emission lines, and we stack the two-dimensional spectra of the galaxies for this purpose. In the stacked data the [O III] emission line is more spatially concentrated than the Hβ emission line with 98.1% confidence. We additionally stack the X-ray data (all sources are individually undetected), and find that the average L_([O III])/L_(0.5-10keV) ratio is intermediate between typical z ~ 0 obscured active galaxies and star-forming galaxies. Together the compactness of the stacked [O III] spatial profile and the stacked X-ray data suggest that at least some of these low-mass, low-metallicity galaxies harbor weak active galactic nuclei

Near-Infrared Observations of the Environments of Radio Quiet QSOs at z >~ 1

We present the results of an infrared survey of QSO fields at z=0.95, 0.995 and 1.5. Each z<1 field was imaged to typical continuum limits of J=20.5, Kprime=19 (5 sigma), and line fluxes of 1.3E10{-16}ergs/cm^2/s (1 sigma)in a 1% interference filter. 16 fields were chosen with z~0.95 targets, 14 with z~0.995 and 6 with z~1.5. A total area of 0.05 square degrees was surveyed, and two emission-line objects were found. We present the infrared and optical photometry of these objects. Optical spectroscopy has confirmed the redshift of one object (at z=0.989) and is consistent with the other object having a similar redshift. We discuss the density of such objects across a range of redshifts from this survey and others in the literature. We also present number-magnitude counts for galaxies in the fields of radio quiet QSOs, supporting the interpretation that they exist in lower density environments than their radio loud counterparts. The J-band number counts are among the first to be published in the J=16--20.Comment: 34 pages, including 12 figures; accepted for publication in the Ap

The Distribution of Lya-Emitting Galaxies at z=2.3

We present the detection of 34 Ly-alpha emission-line galaxy candidates in a 80x80x60 co-moving Mpc region surrounding the known z=2.38 galaxy cluster J2143-4423. The space density of Ly-alpha emitters is comparable to that found by Steidel et al. when targeting a cluster at redshift 3.09, but is a factor of 5.8 +/- 2.5 greater than that found by field samples at similar redshifts. The distribution of these galaxy candidates contains several 5-10 Mpc scale voids. We compare our observations with mock catalogs derived from the VIRGO consortium Lambda-CDM n-body simulations. Fewer than 1% of the mock catalogues contain voids as large as we observe. Our observations thus tentatively suggest that the galaxy distribution at redshift 2.38 contains larger voids than predicted by current models. Three of the candidate galaxies and one previously discovered galaxy have the large luminosities and extended morphologies of "Ly-alpha blobs".Comment: 10 pages, 8 figures, emulateapj5, Accepted for publication in Ap

Ultraviolet-Bright, High-Redshift ULIRGS

We present Spitzer Space Telescope observations of the z=2.38 lya-emitter over-density associated with galaxy cluster J2143-4423, the largest known structure (110 Mpc) above z=2. We imaged 22 of the 37 known lya-emitters within the filament-like structure, using the MIPS 24um band. We detected 6 of the lya-emitters, including 3 of the 4 clouds of extended (>50 kpc) lyman alpha emission, also known as Lya Blobs. Conversion from rest-wavelength 7um to total far-infrared luminosity using locally derived correlations suggests all the detected sources are in the class of ULIRGs, with some reaching Hyper-LIRG energies. Lya blobs frequently show evidence for interaction, either in HST imaging, or the proximity of multiple MIPS sources within the Lya cloud. This connection suggests that interaction or even mergers may be related to the production of Lya blobs. A connection to mergers does not in itself help explain the origin of the Lya blobs, as most of the suggested mechanisms for creating Lya blobs (starbursts, AGN, cooling flows) could also be associated with galaxy interactions.Comment: 12 pages, 3 figures, accepted by ApJ Letter

Polycyclic Aromatic Hydrocarbon Emission within Lyα Blobs

We present Spitzer observations of Lyα blobs (LABs) at z = 2.38-3.09. The mid-infrared ratios (4.5 μm/8 μm and 8 μm/24 μm) indicate that ~60% of LAB infrared counterparts are cool, consistent with their infrared output being dominated by star formation and not active galactic nuclei (AGNs). The rest have a substantial hot dust component that one would expect from an AGN or an extreme starburst. Comparing the mid-infrared to submillimeter fluxes (~850 μm or rest-frame far-infrared) also indicates that a large percentage (~2/3) of the LAB counterparts have total bolometric energy output dominated by star formation, although the number of sources with submillimeter detections or meaningful upper limits remains small (~10). We obtained Infrared Spectrograph (IRS) spectra of six infrared-bright sources associated with LABs. Four of these sources have measurable polycyclic aromatic hydrocarbon (PAH) emission features, indicative of significant star formation, while the remaining two show a featureless continuum, indicative of infrared energy output completely dominated by an AGN. Two of the counterparts with PAHs are mixed sources, with PAH line-to-continuum ratios and PAH equivalent widths indicative of large energy contributions from both star formation and AGN. Most of the LAB infrared counterparts have large stellar masses, around 10^(11) M_⊙. There is a weak trend of mass upper limit with the Lyα luminosity of the host blob, particularly after the most likely AGN contaminants are removed. The range in likely energy sources for the LABs found in this and previous studies suggests that there is no single source of power that is producing all the known LABs

Far-Ultraviolet Number Counts on Field Galaxies

The far-ultraviolet (FUV) number counts of galaxies constrain the evolution of the star formation rate density of the universe. We report the FUV number counts computed from FUV imaging of several fields including the Hubble Ultra Deep Field, the Hubble Deep Field North, and small areas within the GOODS-North and South fields. These data were obtained with the Hubble Space Telescope (HST) Solar Blind Channel of the Advance Camera for Surveys. The number counts sample an FUV AB magnitude range from 21 to 29 and cover a total area of 15.9 arcmin^2, ~4 times larger than the most recent HST FUV study. Our FUV counts intersect bright FUV Galaxy Evolution Explorer counts at 22.5 mag and they show good agreement with recent semi-analytic models based on dark matter "merger trees" by R. S. Somerville et al. We show that the number counts are ~35% lower than in previous HST studies that use smaller areas. The differences between these studies are likely the result of cosmic variance; our new data cover more lines of sight and more area than previous HST FUV studies. The integrated light from field galaxies is found to contribute between 65.9^(+8)_(–8) and 82.6^(+12)_(–)12 photons s^(–1) cm^(–2) sr^(–1) Å^(–1) to the FUV extragalactic background. These measurements set a lower limit for the total FUV background light

CANDELS: The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey

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 point-source 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

PAH Emission Within Lyman Alpha Blobs

We present Spitzer observations of Lya Blobs (LAB) at z=2.38-3.09. The mid-infrared ratios (4.5/8um and 8/24um) indicate that ~60% of LAB infrared counterparts are cool, consistent with their infrared output being dominated by star formation and not active galactic nuclei (AGN). The rest have a substantial hot dust component that one would expect from an AGN or an extreme starburst. Comparing the mid-infrared to submillimeter fluxes (~850um or rest frame far infrared) also indicates a large percentage (~2/3) of the LAB counterparts have total bolometric energy output dominated by star formation, although the number of sources with sub-mm detections or meaningful upper limits remains small (~10). We obtained Infrared Spectrograph (IRS) spectra of 6 infrared-bright sources associated with LABs. Four of these sources have measurable polycyclic aromatic hydrocarbon (PAH) emission features, indicative of significant star formation, while the remaining two show a featureless continuum, indicative of infrared energy output completely dominated by an AGN. Two of the counterparts with PAHs are mixed sources, with PAH line-to-continuum ratios and PAH equivalent widths indicative of large energy contributions from both star formation and AGN. Most of the LAB infrared counterparts have large stellar masses, around 10^11 Mo. There is a weak trend of mass upper limit with the Lya luminosity of the host blob, particularly after the most likely AGN contaminants are removed. The range in likely energy sources for the LABs found in this and previous studies suggests that there is no single source of power that is producing all the known LABs.Comment: 34 pages, 5 figures, accepted by Ap

Spitzer Infrared Properties of Lyman α Emitters

We present results on the infrared properties of Lyman α emitters. At z=0.3 we demonstrate that our sample of 50 GALEX-identified emitters possess the same extinction properties as similarly ultraviolet-bright galaxies at the same redshift. The AGN fraction for these z=0.3 sources is low, 10-20%, and they show no correlation between Lyα flux and total infrared luminosity. At z=2.4-3.1 we discuss a sample of Lyman α blobs. Roughly two thirds of these blobs have infrared counterparts with infrared and sub-mm colors indicating they are dominated by star formation. Of the six IRS spectra taken of blob counterparts, four show PAH features. Their equivalent widths indicate two are strongly star formation dominated, while the other two are mixed sources with a significant contribution from an AGN