Search

Physical properties of galaxies at z>7 are of interest for understanding both the early phases of star formation and the process of cosmic reionization. Chemical abundance measurements offer valuable information on the integrated star formation history, and hence ionizing photon production, as well as the rapid gas accretion expected at such high redshifts. We use reported measurements of [O III] 88$��$m emission and star formation rate to estimate gas-phase oxygen abundances in five galaxies at z=7.1-9.1 using the direct T_e method. We find typical abundances 12+log(O/H) = 7.9 ($\sim$0.2 times the solar value) and an evolution of 0.9$\pm$0.5 dex in oxygen abundance at fixed stellar mass from z$\simeq$8 to 0. These results are compatible with theoretical predictions, albeit with large (conservative) uncertainties in both mass and metallicity. We assess both statistical and systematic uncertainties to identify promising means of improvement with the Atacama Large Millimeter Array (ALMA) and the James Webb Space Telescope (JWST). In particular we highlight [O III] 52$��$m as a valuable feature for robust metallicity measurements. Precision of 0.1-0.2 dex in T_e-based O/H abundance can be reasonably achieved for galaxies at z$\approx$5-8 by combining [O III] 52$��$m with rest-frame optical strong lines. It will also be possible to probe gas mixing and mergers via resolved T_e-based abundances on kpc scales. With ALMA and JWST, direct metallicity measurements will thus be remarkably accessible in the reionization epoch., 12 pages, 3 figures, 4 tables. Accepted for publication in ApJ

Quasar proximity zones at z > 5.5 correspond to overdense and overionized environments. Galaxies found inside proximity zones can therefore display features that would otherwise be masked by absorption in the intergalactic medium. We demonstrate the utility of this quasar-galaxy synergy by reporting the discovery of the first three “proximate Lyα emitters” (LAEs) within the proximity zone of quasar J0836+0054 at z = 5.795 (Aerith A, B, and C). Aerith A, located behind the quasar with an impact parameter D^{\perp} = 278 \pm 8 pkpc, provides the first detection of an Lyα transverse proximity effect. We model the transmission and show that it constrains the onset of J0836ʼs quasar phase to 0.2Myr < 28Myr < t in the past. The second object, Aerith B at a distance D < 912 pkpc from the quasar, displays a bright and broad double-peaked Lyα emission line. The peak separation implies a low ionizing f_{esc} \leqslant 1%. We fit the Lyα line with an outflowing shell model, finding a typical central density log N_{HI}/cm^{-2} = 19.3_{-0.2}^{+0.8}, outflow velocity v_{out} = 16_{-11}^{+4}km s^{-1}, and gas temperature log T/K = 3.8_{-0.7}^{+0.8} compared to 2 < z < 3 analog LAEs. We detect object Aerith C via an Lyα emission line at z = 5.726. This corresponds with the edge of the quasar’s proximity zone (Dz < 0.02), suggesting that the proximity zone is truncated by a density fluctuation. Via the analyses conducted here, we illustrate how proximate LAEs offer unique insight into the ionizing properties of both quasars and galaxies during hydrogen reionization.

International audience; We report on the detailed analysis of a gravitationally lensed Y-band dropout, A2744_YD4, selected from deep Hubble Space Telescope imaging in the Frontier Field cluster Abell 2744. Band 7 observations with the Atacama Large Millimeter/submillimeter Array (ALMA) indicate the proximate detection of a significant 1 mm continuum flux suggesting the presence of dust for a star-forming galaxy with a photometric redshift of $z\simeq 8$. Deep X-SHOOTER spectra confirms the high-redshift identity of A2744_YD4 via the detection of Lyα emission at a redshift z = 8.38. The association with the ALMA detection is confirmed by the presence of [O iii] 88 μm emission at the same redshift. Although both emission features are only significant at the 4σ level, we argue their joint detection and the positional coincidence with a high-redshift dropout in the Hubble Space Telescope images confirms the physical association. Analysis of the available photometric data and the modest gravitational magnification ($\mu \simeq 2$) indicates A2744_YD4 has a stellar mass of ∼2 × 10(9) ${M}_{\odot }$, a star formation rate of ∼20 ${M}_{\odot }$ yr(−)(1) and a dust mass of ∼6 × 10(6) ${M}_{\odot }$. We discuss the implications of the formation of such a dust mass only $\simeq 200\,\mathrm{Myr}$ after the onset of cosmic reionization.

arXiv:1510.07084v1.-- Infante, Leopoldo et al., We searched for z ≲ 7 Lyman-break galaxies in the optical-to-mid-infrared Hubble Frontier Field and associated parallel field observations of the strong-lensing cluster MACS J0416-2403. We discovered 22 candidates, of which 6 lie at z ≲ 9 and 1 lies at z ≲ 10. Based on the Hubble and Spitzer photometry, all have secure photometric redshifts and a negligible probability of being at lower redshifts according to their peak-probability ratios, . This substantial increase in the number of known high-redshift galaxies allows a solid determination of the luminosity function (LF) at z ≲ 8. The number of high-z candidates in the parallel field is considerably higher than that in the Abell 2744 parallel field. Our candidates have median stellar masses of M, star formation rates (SFRs) of M yr, and SFR-weighted ages of . Finally, we are able to put strong constraints on the z = 7, 8, 9, and 10 LFs. One of the objects in the cluster field is a z ≃ 10 candidate, with a magnification of μ ∼ 20 ± 13. This object is likely the faintest z ∼ 10 object known to date, allowing a first look into the extreme faint end (L ∼ 0.04 L∗) of the z ∼ 10 LF (It is named >Tayna> in the Aymara language)., We acknowledge support from Basal-CATA PFB-06/2007 (LI, FEB, NL, SK, PT), FP7-SPACE-2012-ASTRODEEP-312725 (XS), NSFC grants 11103017 and 11233002 (XS), NASA through Hubble Fellowship grant HST-HF2-51334.01-A awarded by STScI (AZ), CONICYT-Chile grants FONDECYT 1141218 (FEB), gemini-conicyt 32120003 (FEB, NL), and “EMBIGGEN” Anillo ACT1101 (FEB), the Ministry of Economy, Development, and Tourism’s Millennium Science Initiative through grant IC120009, awarded to The Millennium Institute of Astrophysics, MAS (FEB), Spanish consolider project CAD2010-00064 and AYA2012-39475-C02-01 (JMD), the Brazilian funding agency-FAPESP pos-doc fellowship - process number 2014/11806-9 (AM) and CONICYT-Chile grant FONDECYT 3140542 (PT).

The Hubble Frontier Fields (HFF) program combines the capabilities of the Hubble Space Telescope (HST) with the gravitational lensing of massive galaxy clusters to probe the distant Universe to an unprecedented depth. Here, we present the results of the first combined HST and Spitzer observations of the cluster Abell 2744. We combine the full near-infrared data with ancillary optical images to search for gravitationally lensed high-redshift (z > 6) galaxies. We report the detection of 15 I814-dropout candidates at z ~ 6-7 and one Y105-dropout at z ~ 8 in a total survey area of 1.43 arcmin^2 in the source plane. The predictions of our lens model allow us to also identify five multiply-imaged systems lying at redshifts between z ~ 6 and z ~ 8. Thanks to constraints from the mass distribution in the cluster, we were able to estimate the effective survey volume corrected for completeness and magnification effects. This was in turn used to estimate the rest-frame ultraviolet luminosity function (LF) at z ~ 6-8. Our LF results are generally in agreement with the most recent blank field estimates, confirming the feasibility of surveys through lensing clusters. Although based on a shallower observations than what will be achieved in the final dataset including the full ACS observations, the LF presented here extends down to Muv ~ -18.5 at z ~ 7 with one identified object at Muv ~ -15 thanks to the highly-magnified survey areas. This early study forecasts the power of using massive galaxy clusters as cosmic telescopes and its complementarity to blank fields., Comment: 9 pages, 7 figures, 3 tables. accepted for publication in ApJ