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Register a new userThe Most Metal-Rich Intervening Quasar Absorber Known
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The metallicity in portions of high-redshift galaxies has been successfully measured thanks to the gas observed in absorption in the spectra of quasars, in the Damped Lyman-alpha systems (DLAs). Surprisingly, the global mean metallicity derived from DLAs is about 1/10th solar at 0<z<4 leading to the so-called ``missing-metals problem. In this paper, we present high-resolution observations of a sub-DLA system at z_abs=0.716 with super-solar metallicity toward SDSS J1323-0021. This is the highest metallicity intervening quasar absorber currently known, and is only the second super-solar absorber known to date. We provide a detailed study of this unique object from VLT/UVES spectroscopy. We derive [Zn/H]=+0.61, [Fe/H]=-0.51, [Cr/H]=<-0.53, [Mn/H] = -0.37, and [Ti/H] = -0.61. Observations and photoionisation models using the CLOUDY software confirm that the gas in this sub-DLA is predominantly neutral and that the abundance pattern is probably significantly different from a Solar pattern. Fe/Zn and Ti/Zn vary among the main velocity components by factors of ~ 3 and ~ 35, respectively, indicating non-uniform dust depletion. Mn/Fe is super-solar in almost all components, and varies by a factor of ~ 3 among the dominant components. It would be interesting to observe more sub-DLA systems and determine whether they might contribute significantly toward the cosmic budget of metals.
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We present spectroscopic observations of the nearby dwarf galaxy AGC 198691. This object is part of the Survey of HI in Extremely Low-Mass Dwarfs (SHIELD) project, which is a multi-wavelength study of galaxies with HI masses in the range of 10$^{6}$-10$^{7.2}$~M$_{odot}$ discovered by the ALFALFA survey. We have obtained spectra of the lone HII region in AGC 198691 with the new high-throughput KPNO Ohio State Multi-Object Spectrograph (KOSMOS) on the Mayall 4-m as well as with the Blue Channel spectrograph on the MMT 6.5-m telescope. These observations enable the measurement of the temperature-sensitive [OIII]$lambda$4363 line and hence the determination of a direct oxygen abundance for AGC 198691. We find this system to be an extremely metal-deficient (XMD) system with an oxygen abundance of 12+log(O/H) = 7.02 $pm$ 0.03, making AGC 198691 the lowest-abundance star-forming galaxy known in the local universe. Two of the five lowest-abundance galaxies known have been discovered by the ALFALFA blind HI survey; this high yield of XMD galaxies represents a paradigm shift in the search for extremely metal-poor galaxies.
We report the discovery of the most metal-poor dwarf star-forming galaxy (SFG) known to date, J0811+4730. This galaxy, at a redshift z=0.04444, has a Sloan Digital Sky Survey (SDSS) g-band absolute magnitude M_g = -15.41 mag. It was selected by inspecting the spectroscopic data base in the Data Release 13 (DR13) of the SDSS. LBT/MODS spectroscopic observations reveal its oxygen abundance to be 12 + log O/H = 6.98 +/- 0.02, the lowest ever observed for a SFG. J0811+4730 strongly deviates from the main-sequence defined by SFGs in the emission-line diagnostic diagrams and the metallicity - luminosity diagram. These differences are caused mainly by the extremely low oxygen abundance in J0811$+$4730, which is ~10 times lower than that in main-sequence SFGs with similar luminosities. By fitting the spectral energy distributions of the SDSS and LBT spectra, we derive a stellar mass of M* = 10^6.24 - 10^6.29 Msun (statistical uncertainties only), and we find that a considerable fraction of the galaxy stellar mass was formed during the most recent burst of star formation.
Context: The highest redshift quasars at z>~6 receive considerable attention since they provide strong constraints on the growth of the earliest supermassive black holes. They also probe the epoch of reionisation and serve as lighthouses to illuminate the space between them and the observer. The source J1427+3312 (z=6.12) has recently been identified as the first and so far the only known radio-loud quasar at z>6. Aims: We investigated the compact radio structure of J1427+3312 on milli-arcsecond (mas) angular scales, to compare it with that of the second most distant radio-loud quasar J0836+0054 (z=5.77) and with lower-redshift radio quasars in general. Methods: We observed J1427+3312 in phase-reference mode with ten antennas of the European Very Long Baseline Interferometry (VLBI) Network (EVN) at 1.6 GHz on 11 March 2007 and at 5 GHz on 3 March 2007. Results: The source was clearly detected at both frequencies. At 1.6 GHz, it shows a prominent double structure. The two components are separated by 8.3 mas, corresponding to a projected linear distance of ~160 pc. Both components with sub-mJy flux densities appear resolved. In the position of the brightest component at 1.6 GHz, we detected mas-scale radio emission at 5 GHz as well. The radio spectrum of this feature is steep. The double structure and the separation of the components of J1427+3312 are similar to those of the young (<~10^4 yr) compact symmetric objects (CSOs).
From near-infrared spectroscopic measurements of the MgII emission line doublet, we estimate the black hole (BH) mass of the quasar, SMSS J215728.21-360215.1, as being (3.4 +/- 0.6) x 10^10 M_sun and refine the redshift of the quasar to be z=4.692. SMSS J2157 is the most luminous known quasar, with a 3000A luminosity of (4.7 +/- 0.5) x 10^47 erg/s and an estimated bolometric luminosity of 1.6 x 10^48 erg/s, yet its Eddington ratio is only ~0.4. Thus, the high luminosity of this quasar is a consequence of its extremely large BH -- one of the most massive BHs at z > 4.
We present a detailed analysis of a red quasar at z=2.32 with an intervening damped Lyman-alpha absorber (DLA) at z=2.13. Using high quality data from the X-shooter spectrograph at ESO Very Large Telescope we find that the absorber has a metallicity consistent with Solar. We observe strong C I and H$_2$ absorption indicating a cold, dense absorbing medium. Partial coverage effects are observed in the C I lines, from which we infer a covering fraction of $27 pm 6$ % and a physical diameter of the cloud of 0.1 pc. From the covering fraction and size, we estimate the size of the background quasars broad line region. We search for emission from the DLA counterpart in optical and near-infrared imaging. No emission is observed in the optical data. However, we see tentative evidence for a counterpart in the H and K band images. The DLA shows high depletion (as probed by [Fe/Zn]=-1.22) indicating that significant amounts of dust must be present in the DLA. By fitting the spectrum with various dust reddened quasar templates we find a best-fitting amount of dust in the DLA of $A(V)_{rm DLA}=0.28 pm 0.01|_{rm stat} pm 0.07|_{rm sys}$. We conclude that dust in the DLA is causing the colours of this intrinsically very luminous background quasar to appear much redder than average quasars, thereby not fulfilling the criteria for quasar identification in the Sloan Digital Sky Survey. Such chemically enriched and dusty absorbers are thus underrepresented in current samples of DLAs.
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