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.

We present a systematic investigation of the circumgalactic medium (CGM) within projected distances d < 160 kpc of luminous red galaxies (LRGs). The sample comprises 16 intermediatered-shift (z = 0.21-0.55) LRGs of stellar mass M-star > 10(11 )M(circle dot). Combining far-ultraviolet Cosmic Origin Spectrograph spectra from the Hubble Space Telescope and optical echelle spectra from the ground enables a detailed ionization analysis based on resolved component structures of a suite of absorption transitions, including the full H I Lyman series and various ionic metal transitions. By comparing the relative abundances of different ions in individually matched components, we show that cool gas (T similar to 10(4) K) density and metallicity can vary by more than a factor of 10 in an LRG halo. Specifically, metal-poor absorbing components with <1/10 solar metallicity are seen in 50 percent of the LRG haloes, while gas with solar and super-solar metallicity is also common. These results indicate a complex multiphase structure and poor chemical mixing in these quiescent haloes. We calculate the total surface mass density of cool gas, Sigma(cool) by applying the estimated ionization fraction corrections to the observed H column densities. The radial profile of Sigma(cool) is best described by a projected Einasto profile of slope alpha = 1 and scale radius r(s) = 48 kpc. We find that typical LRGs at z similar to 0.4 contain cool gas mass of Sigma(cool) = (1 - 2) x 10(10)M(circle dot) at d < 160 kpc (or as much as Sigma(cool) approximate to 4 x 10(10) M-circle dot at d < 500 kpc), comparable to the cool CGM mass of star-forming galaxies. Furthermore, we show that high-ionization O VI and low-ionization absorption species exhibit distinct velocity profiles, highlighting their different physical origins. We discuss the implications of our findings for the origin and fate of cool gas in LRG haloes.

We report the results from a search for z > 6.5 quasars using the Dark Energy Survey (DES) Year 3 data set combined with the VISTA Hemisphere Survey (VHS) and WISE All-Sky Survey. Our photometric selection method is shown to be highly efficient in identifying clean samples of high-redshift quasars, leading to spectroscopic confirmation of three new quasars -VDES J0244-5008 (z = 6,724), VDES J0020-3653 (z = 6.834), and VDES J0246-5219 (z = 6.90) - which were selected as the highest priority candidates in the survey data without any need for additional follow-up observations. We have obtained spectroscopic observations in the near-infrared for VDES J0244-5008 and VDES J0020-3653 as well as our previously identified quasar, VDES J0224-471 1 at z = 6.50 from Reed et al, We use the near-infrared spectra to derive virial black hole masses from the full width at half-maximum of the Mg II line. These black hole masses are similar or equal to 1-2 x 10(9) M-circle dot. Combined with the bolometric luminosities of these quasars of L-bot similar or equal to 1-3 x 10(47), these imply that the Eddington ratios are high, similar or equal to 0.6-1.1. We consider the C iv emission line properties of the sample and demonstrate that our highredshift quasars do not have unusual C iv line properties when compared to carefully matched low-redshift samples. Our new DES + VHS z > 6.5 quasars now add to the growing census of luminous, rapidly accreting supermassive black holes seen well into the epoch of reionization.

Observing the signature of accretion from the intergalactic medium (IGM) on to galaxies at z similar to 3 requires the detection of faint (L << L*) galaxies embedded in a filamentary matrix of low-density (rho < 100 <(rho)over bar>), metal-poor gas (Z similar to 10(-2.5) Z(circle dot)) coherent over hundreds of kpc. We study the gaseous environment of three Ly alpha emitters (LAEs) at z = 2.7 - 2.8, found to be aligned in projection with a background QSO over similar to 250 kpc along the slit of a long-slit spectrum. The lack of detection of the LAEs in deep continuum images and the low inferred Ly alpha luminosities show the LAEs to be intrinsically faint, low-mass galaxies (L less than or similar to 0.1L*, M-star less than or similar to 0.1M*). An echelle spectrum of the QSO reveals strong Ly alpha absorption within +/- 200 km s(-1) from the LAEs. Our absorption line analysis leads to HI column densities in the range of logN(H I)/cm(-2) = 16-18. Associated absorption from ionic metal species CIV and Si IV constrains the gas metallicities to similar to 0.01 solar if the gas is optically thin, and possibly as low as similar to 0.001 solar if the gas is optically thick, assuming photoionization equilibrium. While the inferred metallicities are at least a factor of 10 lower than expected metallicities in the interstellar medium (ISM) of these LAEs, they are consistent with the observed chemical enrichment level in the IGM at the same epoch. Total metal abundances and kinematic arguments suggest that these faint galaxies have not been able to affect the properties of their surrounding gas. The projected spatial alignment of the LAEs, together with the kinematic quiescence and correspondence between the LAEs and absorbing gas in velocity space, suggests that these observations probe a possible filamentary structure. Taken together with the blue-dominant Ly alpha emission line profile of one of the objects, the evidence suggests that the absorbing gas is part of an accretion stream of low-metallicity gas in the IGM.

We identify a strong Ly? damping wing profile in the spectrum of the quasar P183+05 at z=6.4386. Given the detection of several narrow metal absorption lines at z=6.40392, the most likely explanation for the absorption profile is that it is due to a damped Ly? system. However, in order to match the data a contribution of an intergalactic medium 5%?38% neutral or additional weaker absorbers near the quasar is also required. The absorption system presented here is the most distant damped Ly? system currently known. We estimate an H i column density of 10(20.680.25) cm(?2), metallicity [O/H] = ?2.92 0.32, and relative chemical abundances of a system consistent with a low-mass galaxy during the first Gyr of the universe. This object is among the most metal-poor damped Ly? systems known and, even though it is observed only ?850 Myr after the big bang, its relative abundances do not show signatures of chemical enrichment by Population III stars.

We report the Subaru Hyper Suprime-Cam (HSC) discovery of two Ly alpha blobs (LABs), dubbed z70-1 and z49-1 at z = 6.965 and z = 4.888, respectively, that are Ly alpha emitters with a bright (log Lly alpha/[crg s(-1)] > 43.4 and and spatially extended Ly alpha emission, and present the photometric and spectroscopic properties of a total of seven LABs: the two new LABs and five previously known LABs at z = 5.7-6.6. The z70-1 LAB shows extended Ly alpha emission with a scale length of 1.4 +/- 0.2 kpc, about three times larger than the UV continuum emission, making z70-1 the most distant LAB identified to date. All of the seven LABs, except z49-1, exhibit no active galactic nucleus (AGN) signatures such as X-ray emission, N v lambda 1240 emission, or Ly alpha line broadening, while z49-1 has a strong C iv lambda 1548 emission line indicating an AGN on the basis of the UV-line ratio diagnostics. We carefully model the point-spread functions of the HSC images and conduct two-component exponential profile fitting to the extended Ly alpha emission of the LABs. The Ly alpha scale lengths of the core (star-forming region) and halo components are r(c) = 0.6-1.2 kpc and r(h) = 2.0-13.8 kpc, respectively. The relations between the scale lengths and galaxy properties (Ly alpha luminosity L-Ly alpha, Ly alpha rest-frame equivalent width EW0, and UV continuum magnitude M-UV) of our LABs are similar to those of Ly alpha halos (LAHs) identified around star-forming galaxies found previously by the Very Large Telescope/MUSE at similar redshifts, suggesting that our LABs are likely the bright version of high-z LAHs.

We report the first detection of multiphase gas within a quiescent galaxy beyond z approximate to 0. The observations use the brighter image of doubly lensed QSO HE 0047-1756 to probe the interstellar medium (ISM) of the massive (M-star approximate to 10(11) M-circle dot) elliptical lens galaxy at z(gal) = 0.408. Using Hubble Space Telescope's Cosmic Origins Spectrograph (COS), we obtain a medium-resolution FUV spectrum of the lensed QSO and identify numerous absorption features from H-2 in the lens ISM at projected distance d = 4.6 kpc. The H-2 column density is log N(H-2)/cm(-2) 17.8(-0.3)(+0.1) with a molecular gas fraction of f(H2) = 2%-5% , roughly consistent with some local quiescent galaxies. The new COS spectrum also reveals kinematically complex absorption features from highly ionized species O VI and N V with column densities log N(O VI) cm(-2) = 15.2 +/- 0.1 and log N(N V) cm(-2) = 14.6 +/- 0.1, among the highest known in external galaxies. Assuming the high-ionization absorption features originate in a transient warm (T similar to 105 K) phase undergoing radiative cooling from a hot halo surrounding the galaxy, we infer a mass accretion rate of similar to 0.5-1.5 M-circle dot yr(-1). The lack of star formation in the lens suggests that the bulk of this flow is returned to the hot halo, implying a heating rate of similar to 1048 erg yr(-1). Continuous heating from evolved stellar populations (primarily SNe Ia but also winds from AGB stars) may suffice to prevent a large accumulation of cold gas in the ISM, even in the absence of strong feedback from an active nucleus.