[en] We present an analysis of the stellar populations of 102 visually selected early-type galaxies (ETGs) with spectroscopic redshifts (0.35 ≲ z ≲ 1.5) from observations in the Early Release Science program with the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST). We fit one- and two-component synthetic stellar models to the ETGs UV-optical-near-IR spectral energy distributions and find that a large fraction (∼40%) are likely to have experienced a minor (f_YC ≲ 10% of stellar mass) burst of recent (t_YC ≲ 1 Gyr) star formation. The measured age and mass fraction of the young stellar populations do not strongly trend with measurements of galaxy morphology. We note that massive (M > 10^10.5 M _☉) recent star-forming ETGs appear to have larger sizes. Furthermore, high-mass, quiescent ETGs identified with likely companions populate a distinct region in the size-mass parameter space, in comparison with the distribution of massive ETGs with evidence of recent star formation (RSF). We conclude that both mechanisms of quenching star formation in disk-like ETGs and (gas-rich, minor) merger activity contribute to the formation of young stars and the size-mass evolution of intermediate redshift ETGs. The number of ETGs for which we have both HST WFC3 panchromatic (especially UV) imaging and spectroscopically confirmed redshifts is relatively small, therefore, a conclusion about the relative roles of both of these mechanisms remains an open question.

[en] We present a Monte Carlo simulation designed to predict the vertical velocity dispersion of brown dwarfs in the Milky Way. We show that since these stars are constantly cooling, the velocity dispersion has a noticeable trend with the spectral type. With realistic assumptions for the initial mass function, star formation history, and the cooling models, we show that the velocity dispersion is roughly consistent with what is observed for M dwarfs, decreases to cooler spectral types, and increases again for the coolest types in our study (∼T9). We predict a minimum in the velocity dispersions for L/T transition objects, however, the detailed properties of the minimum predominately depend on the star formation history. Since this trend is due to brown dwarf cooling, we expect that the velocity dispersion as a function of spectral type should deviate from the constancy around the hydrogen-burning limit. We convert from velocity dispersion to vertical scale height using standard disk models and present similar trends in disk thickness as a function of spectral type. We suggest that future, wide-field photometric and/or spectroscopic missions may collect sizable samples of distant ($\sim <!--\; ???\; -->1$ kpc) dwarfs that span the hydrogen-burning limit. As such, we speculate that such observations may provide a unique way of constraining the average spectral type of hydrogen burning.

[en] We report the detection of Lyα emission at ∼9538 Å in the Keck/DEIMOS and Hubble Space Telescope WFC3 G102 grism data from a triply imaged galaxy at $z=6.846\pm <!--\; ??\; -->0.001$ behind galaxy cluster MACS J2129.4−0741. Combining the emission line wavelength with broadband photometry, line ratio upper limits, and lens modeling, we rule out the scenario that this emission line is [O ii] at z = 1.57. After accounting for magnification, we calculate the weighted average of the intrinsic Lyα luminosity to be $\sim <!--\; ???\; -->1.3\times <!--\; ??\; -->{10}^{42}\mathrm{e}\mathrm{r}\mathrm{g}{\mathrm{s}}^{-<!--\; ???\; -->1}$ and Lyα equivalent width to be 74 ± 15 Å. Its intrinsic UV absolute magnitude at 1600 Å is −18.6 ± 0.2 mag and stellar mass $(1.5\pm <!--\; ??\; -->0.3)\times <!--\; ??\; -->{10}^7{M}_{\odot <!--\; ???\; -->}$, making it one of the faintest (intrinsic $L_{\mathrm{U}\mathrm{V}}\sim <!--\; ???\; -->0.14L_{\mathrm{U}\mathrm{V}}^{\ast <!--\; ???\; -->}$) galaxies with Lyα detection at $z\sim <!--\; ???\; -->7$ to date. Its stellar mass is in the typical range for the galaxies thought to dominate the reionization photon budget at $z\gtrsim <!--\; ???\; -->7;$ the inferred Lyα escape fraction is high ($\gtrsim <!--\; ???\; -->10$%), which could be common for sub-L* $z\gtrsim <!--\; ???\; -->7$ galaxies with Lyα emission. This galaxy offers a glimpse of the galaxy population that is thought to drive reionization, and it shows that gravitational lensing is an important avenue for probing the sub-L* galaxy population.

[en] We present our analysis of the Lyman continuum (LyC) emission and escape fraction of 111 spectroscopically verified galaxies with and without active galactic nuclei (AGN) from 2.26 < z < 4.3. We extended our ERS sample from Smith et al. with 64 galaxies in the GOODS North and South fields using WFC3/UVIS F225W, F275W, and F336W mosaics we independently drizzled using the HDUV, CANDELS, and UVUDF data. Among the 17 AGN from the 111 galaxies, one provided a LyC detection in F275W at $m_{\mathrm{A}\mathrm{B}}$ = 23.19 mag (signal-to-noise ratio, S/N, ≃ 133) and GALEX NUV at $m_{\mathrm{A}\mathrm{B}}$ = 23.77 mag (S/N ≃ 13). We simultaneously fit SDSS and Chandra spectra of this AGN to an accretion disk and Comptonization model, and find $f_{\mathrm{e}\mathrm{s}\mathrm{c}}$ values of $f_{\mathrm{e}\mathrm{s}\mathrm{c}}^{\mathrm{F}275\mathrm{W}}\simeq <!--\; ???\; -->{28}_{-<!--\; ???\; -->4}^{+20}\mathrm{\%<!--\; \%\; -->}$ and $f_{\mathrm{e}\mathrm{s}\mathrm{c}}^{\mathrm{N}\mathrm{U}\mathrm{V}}\simeq <!--\; ???\; -->{30}_{-<!--\; ???\; -->5}^{+22}\mathrm{\%<!--\; \%\; -->}$. For the remaining 110 galaxies, we stack image cutouts that capture their LyC emission using the F225W, F275W, and F336W data of the GOODS and ERS samples, and both combined, as well as subsamples of galaxies with and without AGN, and all galaxies. We find the stack of 17 AGN dominate the LyC production from $⟨<!--\; ???\; -->z⟩<!--\; ???\; -->$ ≃ 2.3–4.3 by a factor of ∼10 compared to all 94 galaxies without AGN. While the IGM of the early universe may have been reionized mostly by massive stars, there is evidence that a significant portion of the ionizing energy came from AGN.

[en] We perform the first spatially resolved stellar population study of galaxies in the early universe ( z = 3.5–6.5), utilizing the Hubble Space Telescope Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey imaging data set over the GOODS-S field. We select a sample of 418 bright and extended galaxies at z  = 3.5–6.5 from a parent sample of ∼8000 photometric-redshift-selected galaxies from Finkelstein et al. We first examine galaxies at 3.5 ≲ z ≲ 4.0 using additional deep K -band survey data from the HAWK-I UDS and GOODS Survey which covers the 4000 Å break at these redshifts. We measure the stellar mass, star formation rate, and dust extinction for galaxy inner and outer regions via spatially resolved spectral energy distribution fitting based on a Markov Chain Monte Carlo algorithm. By comparing specific star formation rates (sSFRs) between inner and outer parts of the galaxies we find that the majority of galaxies with high central mass densities show evidence for a preferentially lower sSFR in their centers than in their outer regions, indicative of reduced sSFRs in their central regions. We also study galaxies at z ∼ 5 and 6 (here limited to high spatial resolution in the rest-frame ultraviolet only), finding that they show sSFRs which are generally independent of radial distance from the center of the galaxies. This indicates that stars are formed uniformly at all radii in massive galaxies at z  ∼ 5–6, contrary to massive galaxies at z ≲ 4.

[en] We present a robust measurement and analysis of the rest-frame ultraviolet (UV) luminosity functions at z = 4–8. We use deep Hubble Space Telescope imaging over the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey/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 × 10⁶ Mpc³ over this epoch, allowing us to perform a robust search for faint $(M_{\mathrm{U}\mathrm{V}}=-<!--\; ???\; -->$18) and bright (M${}_{\mathrm{U}\mathrm{V}}<<!--\; <\; -->-<!--\; ???\; -->$21) high-redshift 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 $z\approx <!--\; ???\; -->$ 6–8. We measure both a stepwise luminosity function for candidate galaxies in our redshift samples, and 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 $M_{\mathrm{U}\mathrm{V}}^{\ast <!--\; ???\; -->}$ is consistent with −21 at $z⩾<!--\; ???\; -->$ 5, which is different than that inferred based on previous trends at lower redshift, and brighter at ∼2σ significance than previous measures at z = 6 and 7. At z = 8, a single power law 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 $M_{\mathrm{U}\mathrm{V}}^{\ast <!--\; ???\; -->}$ is consistent with models where the impact of dust attenuation on the bright end of the luminosity function decreases at higher redshift, although 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 $M_{\mathrm{U}\mathrm{V}}=-<!--\; ???\; -->17$, correcting for dust attenuation, and find that the SFR density declines proportionally to (1 $+z$)${}^{-<!--\; ???\; -->4.3\pm <!--\; ??\; -->0.5}$ at $z><!--\; >\; -->$ 4, which is consistent with observations at $z⩾<!--\; ???\; -->$ 9. Our observed luminosity functions are consistent with a reionization history that starts at $z\gtrsim <!--\; ???\; -->$ 10, completes at $z><!--\; >\; -->$ 6, and reaches a midpoint (x${}_{\mathrm{H}\mathrm{I}\mathrm{I}}=$ 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, although consistent with recent estimates of bright $z\sim <!--\; ???\; -->$ 10 galaxies.

[en] 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 arcmin² 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 BVizY_sJH 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.

[en] We used near-infrared data obtained with the Wide Field Camera 3 on the Hubble Space Telescope to identify objects having the colors of brown dwarfs (BDs) in the field of the massive galactic cluster NGC 3603. These are identified through a combination of narrow- and medium-band filters which span the J and H bands and are particularly sensitive to the presence of the 1.3-1.5 μm H₂O molecular band unique to BDs. We provide a calibration of the relationship between effective temperature and color for both field stars and BDs. This photometric method provides effective temperatures for BDs to an accuracy of ±350 K relative to spectroscopic techniques. This accuracy is shown to be not significantly affected by either stellar surface gravity or uncertainties in the interstellar extinction. We identify nine objects having effective temperatures between 1700 and 2200 K, typical of BDs, observed J-band magnitudes in the range 19.5-21.5, and that are strongly clustered toward the luminous core of NGC 3603. However, if these are located at the distance of the cluster, they are far too luminous to be normal BDs. We argue that it is unlikely that these objects are either artifacts of our data set, normal field BDs/M-type giants, or extragalactic contaminants and, therefore, might represent a new class of stars having the effective temperatures of BDs but with luminosities of more massive stars. We explore the interesting scenario in which these objects would be normal stars that have recently tidally ingested a hot Jupiter, the remnants of which are providing a short-lived extended photosphere to the central star. In this case, we would expect them to show the signature of fast rotation.