[en] Looking for bright galaxies born in the early universe is fundamental to investigating the Epoch of Reionization, the era when the first stars and galaxies ionized the intergalactic medium. We utilize Hubble Space Telescope pure-parallel imaging to select galaxy candidates at a time 500–650 million years after the Big Bang, which corresponds to redshifts z ∼ 8–10. These data come from the Brightest of Reionizing Galaxies Survey (BoRG) Cycle 22 data set, which consists of pure-parallel imaging in ∼90 different lines of sight that sum up to an area of ∼420 arcmin². This survey uses five filters and has the advantage (compared to the Cycle 21 BoRG program) of including imaging in the JH ₁₄₀ band, covering continuous wavelengths from the visible to near-infrared (λ = 0.35–1.7 μm). This allows us to perform a reliable selection of galaxies at z ≥ 8 using the photometric-redshift technique. We use these galaxy candidates to constrain the bright end of the rest-frame ultraviolet luminosity function in this epoch. These candidates are excellent targets for follow-up observations, particularly with the James Webb Space Telescope.

[en] We present the analysis of Herschel Spectral and Photometric Imaging Receiver far-infrared (FIR) observations of the z = 2.515 lensed galaxy SMM J163554.2+661225. Combining new 250, 350, and 500 μm observations with existing data, we make an improved fit to the FIR spectral energy distribution of this galaxy. We find a total infrared (IR) luminosity of L(8-1000 μm) = 6.9 ± 0.6 × 10¹¹ L_☉, a factor of three more precise over previous L_IR estimates for this galaxy, and one of the most accurate measurements for any galaxy at these redshifts. This FIR luminosity implies an unlensed star formation rate (SFR) for this galaxy of 119 ± 10 M_☉ yr^–1, which is a factor of 1.9 ± 0.35 lower than the SFR derived from the nebular Paα emission line (a 2.5σ discrepancy). Both SFR indicators assume an identical Salpeter initial mass function (IMF) with slope Γ = 2.35 over a mass range of 0.1-100 M_☉; thus this discrepancy suggests that more ionizing photons may be necessary to account for the higher Paα-derived SFR. We examine a number of scenarios and find that the observations can be explained with a varying star formation history (SFH) due to an increasing SFR, paired with a slight flattening of the IMF. If the SFR is constant in time, then larger changes need to be made to the IMF by either increasing the upper mass cutoff to ∼200 M_☉, or a flattening of the IMF slope to 1.9 ± 0.15, or a combination of the two. These scenarios result in up to double the number of stars with masses above 20 M_☉, which produce the requisite increase in ionizing photons over a Salpeter IMF with a constant SFH.

[en] We measure the rest-frame colors (dust-corrected), infrared luminosities, star formation rates, and stellar masses of 92 galaxies in a Spitzer-selected cluster at z = 1.62. By fitting spectral energy distributions (SEDs) to 10-band photometry (0.4 μm<λ_obs < 8 μm) and measuring 24 μm fluxes for the 12 spectroscopically confirmed and 80 photometrically selected members, we discover an exceptionally high level of star formation in the cluster core of ∼1700 M_sun yr^-1 Mpc^-2. The cluster galaxies define a strong blue sequence in (U-V) color and span a range in color. We identify 17 members with L_IR>10¹¹ L_sun, and these IR luminous members follow the same trend of increasing star formation with stellar mass that is observed in the field at z ∼ 2. Using rates derived from both the 24 μm imaging and SED fitting, we find that the relative fraction of star-forming members triples from the lowest to highest galaxy density regions; e.g., the IR luminous fraction increases from ∼8% at Σ ∼ 10 gal Mpc^-2 to ∼25% at Σ ∼> 100 gal Mpc^-2. The observed increase is a reversal of the well-documented trend at z < 1 and signals that we have reached the epoch when massive cluster galaxies are still forming a substantial fraction of their stars.

[en] We present the discovery and detailed multi-wavelength study of a strongly lensed luminous infrared galaxy at z = 0.816. Unlike most known lensed galaxies discovered at optical or near-infrared wavelengths, this lensed source is red, (r – K_s ) _AB = 3.9, which the data presented here demonstrate is due to ongoing dusty star formation. The overall lensing magnification (a factor of 17) facilitates observations from the blue optical through to 500 μm, fully capturing both the stellar photospheric emission and the re-processed thermal dust emission. We also present optical and near-IR spectroscopy. These extensive data show that this lensed galaxy is in many ways typical of IR-detected sources at z ∼ 1, with both a total luminosity and size in accordance with other (albeit much less detailed) measurements for samples of galaxies observed in deep fields with the Spitzer telescope. Its far-infrared spectral energy distribution is well fit by local templates that are an order of magnitude less luminous than the lensed galaxy; local templates of comparable luminosity are too hot to fit. Its size (D ∼ 7 kpc) is much larger than local luminous infrared galaxies, but in line with sizes observed for such galaxies at z ∼ 1. The star formation appears uniform across this spatial scale. In this source, the luminosity of which is typical of sources that dominate the cosmic infrared background, we find that star formation is spatially extended and well organized, quite unlike the compact merger-driven starbursts that are typical for sources of this luminosity at z ∼ 0.

[en] We present the results from a stellar population modeling analysis of a sample of 162 z = 4.5 and 14 z = 5.7 Lyα emitting galaxies (LAEs) in the Boötes field, using deep Spitzer/IRAC data at 3.6 and 4.5 μm from the Spitzer Lyα Survey, along with Hubble Space Telescope NICMOS and WFC3 imaging at 1.1 and 1.6 μm for a subset of the LAEs. This represents one of the largest samples of high-redshift LAEs imaged with Spitzer IRAC. We find that 30/162 (19%) of the z = 4.5 LAEs and 9/14 (64%) of the z = 5.7 LAEs are detected at ≥3σ in at least one IRAC band. Individual z = 4.5 IRAC-detected LAEs have a large range of stellar mass, from 5 × 10⁸–10¹¹ $M_{\odot <!--\; ???\; -->}$. One-third of the IRAC-detected LAEs have older stellar population ages of 100 Myr–1 Gyr, while the remainder have ages <100 Myr. A stacking analysis of IRAC-undetected LAEs shows this population to be primarily low mass (8–20 × 10⁸ $M_{\odot <!--\; ???\; -->}$) and young (64–570 Myr). We find a correlation between stellar mass and the dust-corrected ultraviolet-based star formation rate (SFR) similar to that at lower redshifts, in that higher mass galaxies exhibit higher SFRs. However, the z = 4.5 LAE correlation is elevated 4–5 times in SFR compared to continuum-selected galaxies at similar redshifts. The exception is the most massive LAEs which have SFRs similar to galaxies at lower redshifts suggesting that they may represent a different population of galaxies than the traditional lower-mass LAEs, perhaps with a different mechanism promoting Lyα photon escape.

[en] We present the highest redshift detections of resolved Lyα emission, using Hubble Space Telescope (HST)/Advanced Camera for Surveys F658N narrowband-imaging data taken in parallel with the Wide Field Camera 3 Early Release Science program in the GOODS Chandra Deep Field-South. We detect Lyα emission from three spectroscopically confirmed z = 4.4 Lyα emitting galaxies (LAEs), more than doubling the sample of LAEs with resolved Lyα emission. Comparing the light distribution between the rest-frame ultraviolet continuum and narrowband images, we investigate the escape of Lyα photons at high redshift. While our data do not support a positional offset between the Lyα and rest-frame ultraviolet (UV) continuum emission, the half-light radius in one out of the three galaxies is significantly (>1σ) larger in Lyα than in the rest-frame UV continuum. Stacking the three LAEs in both the narrowband and UV continuum images, we find that the Lyα light appears larger than the rest-frame UV at 4.2σ significance. This Lyα flux detected with HST is a factor of 4-10 less than observed in similar filters from the ground. These results together imply that the Lyα emission is not strictly confined to its indigenous star-forming regions. Rather, for at least one object the Lyα emission is more extended, with the missing HST flux possibly existing in a diffuse outer halo. This suggests that the radiative transfer of Lyα photons in high-redshift LAEs is complicated, with the interstellar-medium geometry and/or outflows playing a significant role in galaxies at these redshifts.