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Register a new userThe HDUV Survey: Six Lyman Continuum Emitter Candidates at z~2 Revealed by HST UV Imaging
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We present six galaxies at z~2 that show evidence of Lyman continuum (LyC) emission based on the newly acquired UV imaging of the Hubble Deep UV legacy survey (HDUV) conducted with the WFC3/UVIS camera on the Hubble Space Telescope (HST). At the redshift of these sources, the HDUV F275W images partially probe the ionizing continuum. By exploiting the HST multi-wavelength data available in the HDUV/GOODS fields, models of the UV spectral energy distributions, and detailed Monte Carlo simulations of the intergalactic medium absorption, we estimate the absolute ionizing photon escape fractions of these galaxies to be very high -- typically >60% (>13% for all sources at 90% likelihood). Our findings are in broad agreement with previous studies that found only a small fraction of galaxies to show high escape fraction. These six galaxies comprise the largest sample yet of LyC leaking candidates at z~2 whose inferred LyC flux has been cleanly observed at HST resolution. While three of our six candidates show evidence of hosting an active galactic nucleus (AGN), two of these are heavily obscured and their LyC emission appears to originate from star-forming regions rather than the central nucleus. This suggests an AGN-aided pathway for LyC escape from these sources. Extensive multi-wavelength data in the GOODS fields, especially the near-IR grism spectra from the 3D-HST survey, enable us to study the candidates in detail and tentatively test some recently proposed indirect methods to probe LyC leakage -- namely, the [OIII]/[OII] line ratio and the H$beta-$UV slope diagram. High-resolution spectroscopic followup of our candidates will help constrain such indirect methods which are our only hope of studying $f_{esc}$ at z~5-9 in the fast-approaching era of the James Webb Space Telescope.
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We present the Hubble Deep UV Legacy Survey (HDUV), a 132 orbit imaging program with the WFC3/UVIS camera onboard the Hubble Space Telescope (HST). The HDUV extends and builds on the few previous UV imaging surveys in the two GOODS/CANDELS-Deep fields to provide deep images over a total area of ~100 arcmin2 in the two filters F275W and F336W. Our release also includes all the F275W imaging data taken by the CANDELS survey, which were aligned using a novel approach and combined with the HDUV survey data. By reaching depths of 27.5-28.0 mag (5sigma, in 0.4 apertures), these are the deepest high-resolution UV data over such a large area taken to date. Such unique UV imaging enables a wide range of science by the community. Among the main goals of the HDUV survey are: (1) provide a complete sample of faint star-forming galaxies at z~1-3, (2) constrain the ionizing photon escape fraction from galaxies at z~2-3, and (3) track the build-up of bulges and the disappearance of clumpy disk galaxies through reliable internal stellar population properties at sub-kpc resolution out to z~3. The addition of the HDUV data further enhances the legacy value of the two GOODS/CANDELS-Deep fields, which now include deep 11-band HST imaging as well as very deep ancillary data from X-ray to radio, enabling unique multi-wavelength studies. Here, we provide an overview of the survey design, describe the data reduction, and highlight a few basic analyses on the images which are released to the community as high level science products via the Mikulski Archive for Space Telescopes (MAST).
We present results from a survey for z~2.85 Lyman-Continuum (LyC) emission in the HS1549+1933 field and place constraints on the amount of ionizing radiation escaping from star-forming galaxies. Using a custom narrowband filter (NB3420) tuned to wavelengths just below the Lyman limit at z>=2.82, we probe the LyC spectral region of 49 Lyman break galaxies (LBGs) and 91 Lya-emitters (LAEs) spectroscopically confirmed at z>=2.82. Four LBGs and seven LAEs are detected in NB3420. Using V-band data probing the rest-frame non-ionizing UV, we observe that many NB3420-detected galaxies exhibit spatial offsets between their LyC and non-ionizing UV emission and are characterized by extremely blue NB3420-V colors, corresponding to low ratios of non-ionizing to ionizing radiation (F_UV/F_LyC) that are in tension with current stellar population synthesis models. We measure average values of F_UV/F_LyC for our LBG and LAE samples, correcting for foreground galaxy contamination and HI absorption in the IGM. We find (F_UV/F_LyC)_corr^LBG=82 +/- 45 and (F_UV/F_LyC)_corr^LAE=7.4 +/- 3.6. These flux-density ratios correspond respectively to relative LyC escape fractions of f_esc,rel^LBG=5-8% and f_esc,rel^LAE=18-49%, absolute LyC escape fractions of f_esc^LBG=1-2% and f_esc^LAE=5-15%, and a comoving LyC emissivity from star-forming galaxies of 8.8-15.0 x 10^24 ergs/s/Hz/Mpc^3. In order to study the differential properties of galaxies with and without LyC detections, we analyze narrowband Lya imaging and rest-frame near-infrared imaging, finding that while LAEs with LyC detections have lower Lya equivalent widths on average, there is no substantial difference in the rest-frame near-infrared colors of LBGs or LAEs with and without LyC detections. These preliminary results are consistent with an orientation-dependent model where LyC emission escapes through cleared paths in a patchy ISM.
We study six luminous Lyman-alpha emitters (LAEs) with very blue rest-frame UV continua at $5.7le z le 6.6$. These LAEs have previous HST and Spitzer IRAC observations. Combining our newly acquired HST images, we find that their UV-continuum slopes $beta$ are in a range of $-3.4le beta le -2.6$. Unlike previous, tentative detections of $beta simeq -3$ in photometrically selected, low-luminosity galaxies, our LAEs are spectroscopically confirmed and luminous ($M_{rm UV}<-20$ mag). We model their broadband spectral energy distributions (SEDs), and find that two $betasimeq-2.6pm0.2$ galaxies can be well fitted with young and dust-free stellar populations. However, it becomes increasingly difficult to fit bluer galaxies. We explore further interpretations by including non-zero LyC escape fraction $f_{rm esc}$, very low metallicities, and/or AGN contributions. Assuming $f_{rm esc}simeq0.2$, we achieve the bluest slopes $betasimeq-2.7$ when nebular emission is considered. This can nearly explain the SEDs of two galaxies with $betasimeq-2.8$ and --2.9 ($sigma_{beta}=0.15$). Larger $f_{rm esc}$ values and very low metallicities are not favored by the strong nebular line emission (evidenced by the IRAC flux) or the observed (IRAC 1 - IRAC 2) color. Finally, we find that the $betasimeq-2.9$ galaxy can potentially be well explained by the combination of a very young population with a high $f_{rm esc}$ ($ge0.5$) and an old, dusty population. We are not able to produce two $beta simeq -3.4 pm0.4$ galaxies. Future deep spectroscopic observations are needed to fully understand these galaxies.
(Abridged) We investigate the Lyman $alpha$ emitter luminosity function (LAE LF) within the redshift range $2.9 leq z leq 6$ from the first instalment of the blind integral field spectroscopic survey MUSE-Wide. This initial part of the survey probes a region of 22.2 arcmin$^2$ in the CANDELS/GOODS-S field. The dataset provided us with 237 LAEs from which we construct the LAE LF in the luminosity range $42.2 leq log L_mathrm{Lyalpha} [mathrm{erg,s}^{-1}]leq 43.5$ within a volume of $2.3times10^5$ Mpc$^3$. For the LF construction we utilise three different non-parametric estimators: The classical $1/V_mathrm{max}$ method, the $C^{-}$ method, and an improved binned estimator for the differential LF. All three methods deliver consistent results, with the cumulative LAE LF being $Phi(log L_mathrm{Lyalpha} [mathrm{erg,s}^{-1}] = 43.5) simeq 3times 10^{-6}$ Mpc$^{-3}$ and $Phi(log L_mathrm{Lyalpha} [mathrm{erg,s}^{-1}] = 42.2) simeq 2 times 10^{-3}$ Mpc$^{-3}$ towards the bright- and faint-end of our survey, respectively. By employing a non-parametric statistical test, as well as by comparing the full sample to sub-samples in redshift bins, we find no supporting evidence for an evolving LAE LF over the probed redshift and luminosity range. We determine the best-fitting Schechter function parameters $alpha = -1.84^{+0.42}_{-0.41}$ and $log L^* [mathrm{erg,s}^{-1}] = 42.2^{+0.22}_{-0.16}$ with the corresponding normalisation $log phi^* [mathrm{Mpc}^{-3}] = -2.71$. When correcting for completeness in the LAE LF determinations, we take into account that LAEs exhibit diffuse extended low surface-brightness haloes. We compare the resulting LF to one obtained where we apply a correction assuming compact point-like emission. We find that the standard correction underestimates the LAE LF at the faint end of our survey by a factor of 2.5.
We report the discovery of J0121+0025, an extremely luminous and young star-forming galaxy (M_UV = -24.11, log[L_Lya / erg s^-1] = 43.8) at z = 3.244 showing copious Lyman continuum (LyC) leakage (f_esc,abs ~ 40%). High signal-to-noise ratio rest-frame UV spectroscopy with the Gran Telescopio Canarias reveals a high significance (7.9 sigma) emission below the Lyman limit (< 912A), with a flux density level f_900A = 0.78 +/- 0.10 uJy, and strong P-Cygni in wind lines of OVI 1033A, NV 1240A and CIV 1550A that are indicative of a young age of the starburst (<10 Myr). The spectrum is rich in stellar photospheric features, for which a significant contribution of an AGN at these wavelengths is ruled out. Low-ionization ISM absorption lines are also detected, but are weak (EW0 ~ 1A) and show large residual intensities, suggesting a clumpy geometry of the gas with a non-unity covering fraction or a highly ionized ISM. The contribution of a foreground and AGN contamination to the LyC signal is unlikely. Deep optical to Spitzer/IRAC 4.5um imaging show that the spectral energy distribution of J0121+0025 is dominated by the emission of the young starburst, with log(M*/Msun) = 9.9 +/- 0.1 and SFR = 981 +/- 232 Msun yr^-1. J0121+0025 is the most powerful LyC emitter known among the star-forming galaxy population. The discovery of such luminous and young starburst leaking LyC radiation suggests that a significant fraction of LyC photons can escape in sources with a wide range of UV luminosities and are not restricted to the faintest ones as previously thought. These findings might shed further light on the role of luminous starbursts to the cosmic reionization.
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