We present the discovery of two z > 6 quasars, selected as i-band dropouts in the Very Large Telescope Survey Telescope ATLAS survey. Our first quasar has redshift, z = 6.31 +/- 0.03, z-band magnitude, z(AB) = 19.63 +/- 0.08 and rest frame 1450 angstrom absolute magnitude, M-1450 = -27.8 +/- 0.2, making it the joint second most luminous quasar known at z > 6. The second quasar has z = 6.02 +/- 0.03, z(AB) = 19.54 +/- 0.08 and M-1450 = -27.0 +/- 0.1. We also recover a z = 5.86 quasar discovered by Venemans et al., in preparation. To select our quasars, we use a new 3D colour space, combining the ATLAS optical colours with mid-infrared data from the Wide-field Infrared Survey Explorer. We use i(AB) - z(AB) colour to exclude main-sequence stars, galaxies and lower redshift quasars, W1 - W2 to exclude L dwarfs and z(AB) - W2 to exclude T dwarfs. A restrictive set of colour cuts returns only our three high redshift quasars and no contaminants, albeit with a sample completeness of similar to 50 per cent. We discuss how our 3D colour space can be used to reject the majority of contaminants from samples of bright 5.7 < z < 6.3 quasars, replacing follow-up near-infrared photometry, whilst retaining high completeness.

We present the results of an Ly alpha profile analysis of 12 Ly alpha emitters (LAEs) at z similar to 2.2 with high-resolution Ly alpha spectra. We find that all 12 objects have an Ly alpha profile with the main peak redward of the systemic redshift defined by nebular lines, and five have a weak, secondary peak blueward of the systemic redshift (blue bump). The average velocity offset of the red main peak (the blue bump, if any) with respect to the systemic redshift is Delta nu(Ly alpha,r) = 174 +/- 19 km s(-1) (Delta nu(Ly alpha,b) = -316 +/- 45 km s(-1)), which is smaller than (comparable to) that of Lyman break galaxies (LBGs). The outflow velocities inferred from metal absorption lines in three individual and one stacked spectra are comparable to those of LBGs. The uniform expanding shell model constructed by Verhamme et al. reproduces not only the Ly alpha profiles but also other observed quantities, including the outflow velocity and the FWHM. of nebular lines for the non-blue-bump objects. On the other hand, the model predicts too high FWHMs of nebular lines for the blue bump objects, although this discrepancy may disappear if we introduce additional Ly alpha photons produced by gravitational cooling. We show that the small D nu(Ly alpha,r) values of our sample can be explained by low neutral. hydrogen column densities of log(N-H (I)) = 18.9 cm(-2) on average. This value is more than one order of magnitude lower than those of LBGs but is consistent with recent findings that LAEs have high ionization parameters and low H (I) gas masses. This result suggests that low N-H (I) values, giving reduced numbers of resonant scattering of Ly alpha photons, are the key to the strong Ly alpha emission of LAEs.

We present the first results of a survey for high-redshift, z >= 6, quasars using izY multicolour photometric observations from the Dark Energy Survey (DES). Here we report the discovery and spectroscopic confirmation of the Z(AB), Y-AB = 20.2, 20.2 (M-1450 = -26.5) quasar DES J0454-4448 with a redshift of z = 6.09 +/- 0.02 based on the onset of the Ly alpha forest and an H I near zone size of 4.1(-1.2)(+1.1) proper Mpc. The quasar was selected as an i-band drop out with i-z = 2.46 and z(AB) < 21.5 from an area of similar to 300 deg(2). It is the brightest of our 43 candidates and was identified for spectroscopic follow-up solely based on the DES i-z and z-Y colours. The quasar is detected by WISE and has W1(AB) = 19.68. The discovery of one spectroscopically confirmed quasar with 5.7 < z < 6.5 and z(AB) <= 20.2 is consistent with recent determinations of the luminosity function at z similar to 6. DES when completed will have imaged -5000 deg2 to Y-AB = 23.0 (5 sigma point source) and we expect to discover 50-100 new quasars with z > 6 including 3-10 with z > 7 dramatically increasing the numbers of quasars currently known that are suitable for detailed studies.

We investigate the origin of extragalactic continuum emission and its relation to the stellar population of a recently discovered peculiar z = 3.344 Ly alpha emitter. Based on an analysis of the broad-band colours and morphology, we find further support for the idea that the underlying galaxy is being fed by a large-scale (L >= 35 kpc) accretion stream. ArchivalHST images show small-scale (similar to 5 kpc) tentacular filaments converging near a hotspot of star formation, possibly fueled by gas falling in along the filaments. The spectral energy distribution of the tentacles is broadly compatible with either (1) non-ionizing rest-frame far-UV continuum emission from stars formed in a 60 million-year-old starburst; (2) nebular two-photon continuum radiation, arising from collisional excitation cooling; or (3) a recombination spectrum emitted by hydrogen fluorescing in response to ionizing radiation escaping from the galaxy. The latter possibility simultaneously accounts for the presence of asymmetric Ly alpha emission from the large-scale gaseous filament, and the nebular continuum in the smaller scale tentacles as caused by the escape of ionizing radiation from the galaxy. Possible astrophysical explanations for the nature of the tentacles include: a galactic wind powered by the starburst; infalling gas during cold accretion, or tails of interstellar medium dragged out of the galaxy by satellite haloes that have plunged through the main halo. The possibility of detecting extragalactic two-photon continuum emission in space-based, broad-band images suggests a tool for studying the gaseous environment of high-redshift galaxies at much greater spatial detail than possible with Lya or other resonance line emission.

We present multisightline absorption spectroscopy of cool gas around three lensing galaxies at z = 0.4-0.7. These lenses have half-light radii r(e) = 2.6-8 kpc and stellar masses of log M-*/M-circle dot = 10.9-11.4, and therefore resemble nearby passive elliptical galaxies. The lensed QSO sightlines presented here occur at projected distances of d = 3-15 kpc (or d approximate to 1-2 r(e)) from the lensing galaxies, providing for the first time an opportunity to probe both interstellar gas at r similar to r(e) and circumgalactic gas at larger radii r >> r(e) of these distant quiescent galaxies. We observe distinct gas absorption properties among different lenses and among sightlines of individual lenses. Specifically, while the quadruple lens for HE 0435-1223 shows no absorption features to very sensitive limits along all four sightlines, strong MgII, Fe II, Mg I, and Ca II absorption transitions are detected along both sightlines near the double lens for HE 0047-1756, and in one of the two sightlines near the double lens for HE 1104-1805. The absorbers are resolved into 8-15 individual components with a line-of-sight velocity spread of Delta v approximate to 300-600 km s(-1). The large ionic column densities, log N greater than or similar to 14, observed in two components suggest that these may be Lyman limit or damped Ly a absorbers with a significant neutral hydrogen fraction. The majority of the absorbing components exhibit a uniform supersolar Fe/Mg ratio with a scatter of < 0.1 dex across the full Delta v range. Given a predominantly old stellar population in these lensing galaxies, we argue that the observed large velocity width and Fe-rich abundance pattern can be explained by SNe Ia enriched gas at radius r similar to r(e). We show that additional spatial constraints in line-of-sight velocity and relative abundance ratios afforded by a multisightline approach provide a powerful tool to resolve the origin of chemically enriched cool gas in massive haloes.

We present physical properties of spectroscopically confirmed Ly alpha emitters (LAEs) with very large rest-frame Ly alpha equivalent widths EW0(Ly alpha). Although the definition of large EW0(Ly alpha) LAEs is usually difficult due to limited statistical and systematic uncertainties, we identify six LAEs selected from similar to 3000 LAEs at z similar to 2 with reliable measurements of EW0 (Ly alpha) similar or equal to 200-400 angstrom given by careful continuum determinations with our deep photometric and spectroscopic data. These large EW0(Ly alpha) LAEs do not have signatures of AGN, but notably small stellar masses of M star = 10(7-8)M(circle dot) and high specific star formation rates (star formation rate per unit galaxy stellar mass) of similar to 100 Gyr(-1). These LAEs are characterized by the median values of L(Ly alpha) = 3.7 x 10(42) erg s(-1) and M-UV = -18.0 as well as the blue UV continuum slope of beta = -2.5 +/- 0.2 and the low dust extinction E(B -V)(star) = 0.02(-0.02)(+0.04), which indicate a high median Lya escape fraction of f(esc)(Ly alpha) = 0.68 +/- 0.30. This large f(esc)(Ly alpha) value is explained by the low H (I) column density in the interstellar medium which is consistent with full width at half-maximum (FWHM) of the Ly alpha line, FWHM(Ly alpha) = 212 +/- 32 km s(-1), significantly narrower than those of small EW0(Ly alpha) LAEs. Based on the stellar evolution models, our observational constraints of the large EW0 (Ly alpha), the small beta, and the rest-frame He (II) EW imply that at least a half of our large EW0(Ly alpha) LAEs would have young stellar ages of less than or similar to 20 Myr and very low metallicities of Z < 0.02 Z(circle dot) regardless of the star formation history.

Gas metallicity is a key quantity used to determine the physical conditions of gaseous clouds in a wide range of astronomical environments, including interstellar and intergalactic space. In particular, considerable effort in circumgalactic medium (CGM) studies focuses on metallicity measurements because gas metallicity serves as a critical discriminator for whether the observed heavy ions in the CGM originate in chemically enriched outflows or in more chemically pristine gas accreted from the intergalactic medium. However, because the gas is ionized, a necessary first step in determining CGM metallicity is to constrain the ionization state of the gas which, in addition to gas density, depends on the ultraviolet background radiation field (UVB). While it is generally acknowledged that both the intensity and spectral slope of the UVB are uncertain, the impact of an uncertain spectral slope has not been properly addressed in the literature. This Letter shows that adopting a different spectral slope can result in an order of magnitude difference in the inferred CGM metallicity. Specifically, a harder UVB spectrum leads to a higher estimated gas metallicity for a given set of observed ionic column densities. Therefore, such systematic uncertainties must be folded into the error budget for metallicity estimates of ionized gas. An initial study shows that empirical diagnostics are available for discriminating between hard and soft ionizing spectra. Applying these diagnostics helps reduce the systematic uncertainties in CGM metallicity estimates.

This paper presents a study of the chemical compositions in cool gas around a sample of 27 intermediate-redshift galaxies. The sample comprises 13 massive quiescent galaxies at z = 0.40-0.73 probed by QSO sightlines at projected distances d = 3-400 kpc, and 14 star-forming galaxies at z = 0.10-1.24 probed by QSO sightlines at d = 8-163 kpc. The main goal of this study is to examine the radial profiles of the gas-phase Fe/alpha ratio in galaxy haloes based on the observed Fe II to MgII column density ratios. Because Mg+ and Fe+ share similar ionization potentials, the relative ionization correction is small in moderately ionized gas and the observed ionic abundance ratio N(Fe II)/N(Mg II) places a lower limit to the underlying (Fe/Mg) elemental abundance ratio. For quiescent galaxies, a median and dispersion of log < N(Fe II)/N(Mg II)>(med) < -0.06 +/- 0.15 is found at d less than or similar to 60 kpc, which declines to log < N(Fe II)/N(Mg II)>(med) < -0.3 at d greater than or similar to 100 kpc. On the other hand, star-forming galaxies exhibit log < N(Fe II)/N(Mg II)> = -0.25 +/- 0.21 at d less than or similar to 60 kpc and log < N(Fe II)/N(Mg II)> = -0.9 +/- 0.4 at larger distances. Including possible differential dust depletion or ionization correction would only increase the inferred (Fe/Mg) ratio. The observed N(Fe II)/N(Mg II) implies supersolar Fe/alpha ratios in the inner halo of quiescent galaxies. An enhanced Fe abundance indicates a substantial contribution by Type Ia supernovae in the chemical enrichment, which is at least comparable to what is observed in the solar neighbourhood or in intracluster media but differs from young star-forming regions. In the outer haloes of quiescent galaxies and in haloes around star-forming galaxy, however, the observed N(Fe II)/N(Mg II) is consistent with an alpha-element enhanced enrichment pattern, suggesting a core-collapse supernovae dominated enrichment history.

We report the first detection of extended neutral hydrogen (H I) gas in the interstellar medium (ISM) of a massive elliptical galaxy beyond z similar to 0. The observations utilize the doubly lensed images of QSO HE 0047-1756 at z(QSO) = 1.676 as absorption-line probes of the ISM in the massive (M-star approximate to 10(11) M-circle dot) elliptical lens at z = 0.408, detecting gas at projected distances of d = 3.3 and 4.6 kpc on opposite sides of the lens. Using the Space Telescope Imaging Spectrograph, we obtain UV absorption spectra of the lensed QSO and identify a prominent flux discontinuity and associated absorption features matching the Lyman series transitions at z = 0.408 in both sightlines. The H I column density is log N(H I)= 19.6-19.7 at both locations across the lens, comparable to what is seen in 21 cm images of nearby ellipticals. The H I gas kinematics are well-matched with the kinematics of the Fe II absorption complex revealed in ground-based echelle data, displaying a large velocity shear of approximate to 360 km s(-1) across the galaxy. We estimate an ISM Fe abundance of 0.3-0.4 solar at both locations. Including likely dust depletions increases the estimated Fe abundances to solar or supersolar, similar to those of the hot ISM and stars of nearby ellipticals. Assuming 100% covering fraction of this Fe-enriched gas, we infer a total Fe mass of M-cool(Fe) similar to (5-8) x 10(4) M-circle dot in the cool ISM of the massive elliptical lens, which is no more than 5% of the total Fe mass observed in the hot ISM.

We present Ly alpha and UV-nebular emission line properties of bright Ly alpha emitters (LAEs) at z = 6-7 with a luminosity of log L-Ly alpha/[erg s(-1)] = 43-44 identified in the 21 deg(2) area of the SILVERRUSH early sample developed with the Subaru Hyper Suprime-Cam survey data. Our optical spectroscopy newly confirms 21 bright LAEs with clear Ly alpha emission, and contributes to making a spectroscopic sample of 96 LAEs at z = 6-7 in SILVERRUSH. From the spectroscopic sample, we select seven remarkable LAEs as bright as Himiko and CR7 objects, and perform deep Keck/MOSFIRE and Subaru/nuMOIRCS near-infrared spectroscopy reaching the 3 sigma flux limit of similar to 2 x 10(-18) erg s(-1) for the UV-nebular emission lines of He II lambda 1640, CIV lambda lambda 1548,1550, and OIII]lambda lambda 1661,1666. Except for one tentative detection of C (IV), we find no strong UV-nebular lines down to the flux limit, placing the upper limits of the rest-frame equivalent widths (EW0) of similar to 2-4 angstrom for C-IV, He-II, and O-III] lines. We also investigate the VLT/X-SHOOTER spectrum of CR7 whose 6 sigma detection of He (II) is claimed by Sobral et al. Although two individuals and the ESO archive service carefully reanalyzed the X-SHOOTER data that are used in the study of Sobral et al., no He II signal of CR7 is detected, supportive of weak UV-nebular lines of the bright LAEs even for CR7. The spectral properties of these bright LAEs are thus clearly different from those of faint dropouts at z similar to 7 that have strong UV-nebular lines shown in the various studies. Comparing these bright LAEs and the faint dropouts, we find anti-correlations between the UV-nebular line EW0 and the UV-continuum luminosity, which are similar to those found at z similar to 2-3.