ALBERT

Beschreibung: From the Sloan Digital Sky Survey (SDSS) Data Release 12, which covers the full Baryonic Oscillation Spectroscopic Survey (BOSS) footprint, we investigate the possible variation of the fine-structure constant over cosmological time-scales. We analyse the largest quasar sample considered so far in the literature, which contains 13 175 spectra (10 363 from SDSS-III/BOSS DR12 + 2812 from SDSS-II DR7) with redshift z  〈 1. We apply the emission-line method on the [O iii ] doublet ( 4960, 5008 Å) and obtain α/α = (0.9 ± 1.8) x 10 –5 for the relative variation of the fine-structure constant. We also investigate the possible sources of systematics: misidentification of the lines, sky OH lines, H β and broad line contamination, Gaussian and Voigt fitting profiles, optimal wavelength range for the Gaussian fits, chosen polynomial order for the continuum spectrum, signal-to-noise ratio and good quality of the fits. The uncertainty of the measurement is dominated by the sky subtraction. The results presented in this work, being systematics limited, have sufficient statistics to constrain robustly the variation of the fine-structure constant in redshift bins ( z   0.06) over the last 7.9 Gyr. In addition, we study the [Ne iii ] doublet ( 3869, 3968 Å) present in 462 quasar spectra and discuss the systematic effects on using these emission lines to constrain the fine-structure constant variation. Better constraints on α/α (〈 10 –6 ) using the emission-line method would be possible with high-resolution spectroscopy and large galaxy/qso surveys.

Beschreibung: Using VLT/X-shooter, we searched for emission line galaxies associated with four damped Lyman α systems (DLAs) and one sub-DLA at 2.73 ≤ z ≤3.25 towards QSO J2358+0149. We detect [O iii ] emission from a ‘low-cool’ DLA at z abs = 2.9791 (having log N (H i ) = 21.69 ± 0.10, [Zn/H] = –1.83 ± 0.18) at an impact parameter of, ~ 12 kpc. The associated galaxy is compact with a dynamical mass of (1–6) x 10 9 M , very high excitation ([O iii ]/[O ii ] and [O iii ]/[Hβ] both greater than 10), 12+[O/H]≤8.5 and moderate star formation rate (SFR ≤2 M  yr –1 ). Such properties are typically seen in the low- z extreme blue compact dwarf galaxies. The kinematics of the gas is inconsistent with that of an extended disc and the gas is part of either a large scale wind or cold accretion. We detect Lyα emission from the z abs = 3.2477 DLA [having log N (H i ) = 21.12 ± 0.10 and [Zn/H] = –0.97 ± 0.13]. The Lyα emission is redshifted with respect to the metal absorption lines by 320 km s –1 , consistent with the location of the red hump expected in radiative transport models. We derive SFR ~0.2–1.7 M  yr –1 and Lyα escape fraction of ≥10 per cent. No other emission line is detected from this system. Because the DLA has a small velocity separation from the quasar (~500 km s –1 ) and the DLA emission is located within a small projected distance ( 〈 5 kpc), we also explore the possibility that the Lyα emission is being induced by the QSO itself. QSO-induced Lyα fluorescence is possible if the DLA is within a physical separation of 340 kpc to the QSO. Detection of stellar continuum light and/or the oxygen emission lines would disfavour this possibility. We do not detect any emission line from the remaining three systems.

Beschreibung: We present spectroscopic observations of six high redshift ( z em  〉 2) quasars, which have been selected for their Lyman α (Lyα) emission region being only partially covered by a strong proximate ( z abs  ~  z em ) coronagraphic damped Lyα system (DLA). We detected spatially extended Lyα emission envelopes surrounding these six quasars, with projected spatial extent in the range 26 ≤ d Lyα ≤ 51 kpc. No correlation is found between the quasar ionizing luminosity and the Lyα luminosity of their extended envelopes. This could be related to the limited covering factor of the extended gas and/or due to the AGN being obscured in other directions than towards the observer. Indeed, we find a strong correlation between the luminosity of the envelope and its spatial extent, which suggests that the envelopes are probably ionized by the AGN. The metallicity of the coronagraphic DLAs is low and varies in the range –1.75 〈 [Si/H] 〈 –0.63. Highly ionized gas is observed to be associated with most of these DLAs, probably indicating ionization by the central AGN. One of these DLAs has the highest Al iii /Si ii ratio ever reported for any intervening and/or proximate DLA. Most of these DLAs are redshifted with respect to the quasar, implying that they might represent infalling gas probably accreted on to the quasar host galaxies through filaments.

Beschreibung: Energy & Fuels DOI: 10.1021/acs.energyfuels.6b01323

Beschreibung: We present an analysis of the molecular hydrogen absorption system at z abs  = 2.811 in the spectrum of the blazar Q 0528–250. We demonstrate that the molecular cloud does not cover the background source completely. The partial coverage reveals itself as a residual flux at the bottom of the saturated H 2 absorption lines. This amounts to about (2.22 ± 0.54) per cent of the continuum and does not depend on the wavelength. This value is small and it explains why this effect has not been detected in previous studies of this quasar spectrum. However, it is robustly detected and is significantly higher than the zero-flux level at the bottom of the saturated lines of the Lyα forest, (–0.21 ± 0.22) per cent. The presence of the residual flux could be caused by unresolved quasar multicomponents, by light scattered by dust and/or by jet–cloud interaction. The H 2 absorption system is very well described by a two-component model without the inclusion of additional components when we take partial coverage into account. The derived total column densities in the H 2 absorption components A and B are log N (H 2 )(cm –2 ) = 18.10 ± 0.02 and 17.82 ± 0.02, respectively. HD molecules are present only in component B. Given the column density, log N (HD) = 13.33 ± 0.02, we find N (HD)/2 N (H 2 ) = (1.48 ± 0.10) x 10 – 5 , significantly lower than previous estimations. We argue that it is crucial to take into account the partial coverage effects in any analysis of H 2 bearing absorption systems, in particular when studying the physical state of the high-redshift interstellar medium.

Beschreibung: Energy & Fuels DOI: 10.1021/ef502553x

Beschreibung: Recent chemical abundance measurements of damped Ly α absorbers (DLAs) revealed an intrinsic scatter in their metallicity of ~0.5 dex out to z  ~ 5. In order to explore the origin of this scatter, we build a semi-analytic model which traces the chemical evolution of the interstellar matter in small regions of the Universe with different mean density, from over- to underdense regions. We show that the different histories of structure formation in these regions, namely halo abundance, mass and stellar content, are reflected in the chemical properties of the protogalaxies, and in particular of DLAs. We calculate mean metallicity–redshift relations and show that the metallicity dispersion arising from this environmental effect amounts to ~0.25 dex and is an important contributor to the observed overall intrinsic scatter.

Beschreibung: We report long-slit spectroscopic observations of the quasar SDSS J082303.22+052907.6 ( $z_{\rm C\, {\small {IV}}}$  ~ 3.1875), whose broad-line region (BLR) is partly eclipsed by a strong damped Lyman α (DLA; log N (H i ) = 21.7) cloud. This allows us to study the narrow-line region (NLR) of the quasar and the Lyman α emission from the host galaxy. Using cloudy models that explain the presence of strong N v and P v absorption together with the detection of Si ii * and O i ** absorption in the DLA, we show that the density and the distance of the cloud to the quasar are in the ranges 180 〈  n H  〈 710 cm –3 and 580 〉  r 0  〉 230 pc, respectively. Sizes of the neutral (~2–9pc) and highly ionized phases (~3–80pc) are consistent with the partial coverage of the C iv BLR by the C iv absorption from the DLA (covering factor of ~0.85). We show that the residuals are consistent with emission from the NLR with C iv /Lyman α ratios varying from 0 to 0.29 through the profile. Remarkably, we detect extended Lyman α emission up to 25 kpc to the north and west directions and 15 kpc to the south and east. We interpret the emission as the superposition of strong emission in the plane of the galaxy up to 10 kpc with emission in a wind of projected velocity ~500 km s –1 which is seen up to 25 kpc. The low metallicity of the DLA (0.27 solar) argues for at least part of this gas being infalling towards the active galactic nucleus and possibly being located where accretion from cold streams ends up.

Beschreibung: This paper presents a survey of X-ray-selected active galactic nuclei (AGNs) with optical spectroscopic follow-up in a ~ 18 deg 2 area of the equatorial XMM-XXL north field. A sample of 8445 point-like X-ray sources detected by XMM–Newton above a limiting flux of $F_{\rm 0.5{\rm -}10\, keV} 〉 10^{-15} \rm \,erg\, cm^{-2}\, s^{-1}$ was matched to optical (Sloan Digital Sky Survey, SDSS) and infrared (IR; WISE ) counterparts. We followed up 3042 sources brighter than r = 22.5 mag with the SDSS Baryon Oscillation Spectroscopic Survey (BOSS) spectrograph. The spectra yielded a reliable redshift measurement for 2578 AGNs in the redshift range z = 0.02–5.0, with 0.5-2 keV luminosities ranging from 10 39 -10 46 erg s – 1 . This is currently the largest published spectroscopic sample of X-ray-selected AGNs in a contiguous area. The BOSS spectra of AGN candidates show a distribution of optical line widths which is clearly bimodal, allowing an efficient separation between broad- and narrow-emission line AGNs. The former dominate our sample (70 per cent) due to the relatively bright X-ray flux limit and the optical BOSS magnitude limit. We classify the narrow-emission line objects (22 per cent of the full sample) using standard optical emission line diagnostics: the majority have line ratios indicating the dominant source of ionization is the AGN. A small number (8 per cent of the full sample) exhibit the typical narrow line ratios of star-forming galaxies, or only have absorption lines in their spectra. We term the latter two classes ‘elusive’ AGN, which would not be easy to identify correctly without their X-ray emission. We also compare X-ray ( XMM–Newton ), optical colour (SDSS) and and IR ( WISE ) AGN selections in this field. X-ray observations reveal, by far, the largest number of AGN. The overlap between the selections, which is a strong function of the imaging depth in a given band, is also remarkably small. We show using spectral stacking that a large fraction of the X-ray AGNs would not be selectable via optical or IR colours due to host galaxy contamination. A substantial fraction of AGN may therefore be missed by these longer wavelength selection methods.

Beschreibung: We present a tentative detection of the large-scale structure of Ly α emission in the Universe at redshifts z = 2–3.5 by measuring the cross-correlation of Ly α surface brightness with quasars in Sloan Digital Sky Survey/Baryon Oscillation Spectroscopic Survey. We use a million spectra targeting luminous red galaxies at z 〈 0.8, after subtracting a best-fitting model galaxy spectrum from each one, as an estimate of the high-redshift Ly α surface brightness. The quasar–Ly α emission cross-correlation is detected on scales 1 ~ 15 h –1 Mpc, with shape consistent with a CDM model with $\Omega _{\rm m} =0.30^{+0.10}_{-0.07}$ . The predicted amplitude of this cross-correlation is proportional to the product of the mean Ly α surface brightness, 〈μ α 〉, the amplitude of mass fluctuations and the quasar and Ly α emission bias factors. We infer 〈μ α 〉 ( b α /3) = (3.9 ± 0.9) x 10 –21 erg s –1  cm –2 Å –1  arcsec –2 , where b α is the Ly α emission bias. If star-forming galaxies dominate this emission, we find SFR = (0.28 ± 0.07)(3/ b α ) yr –1  Mpc –3 . For b α = 3, this value is ~30 times larger than previous estimates from individually detected Ly α emitters, but consistent with the total SFR derived from dust-corrected, continuum UV galaxy surveys, if most of the Ly α photons from these galaxies avoid dust absorption and are reemitted after diffusing in large gas haloes. Heating of intergalactic gas by He ii photoionization from quasar radiation or jets may alternatively explain the detected correlation, and cooling radiation from gas in galactic haloes may also contribute. We also detect redshift space anisotropy of the quasar–Ly α emission cross-correlation, finding evidence at the 3.0 level that it is radially elongated, which may be explained by radiative-transfer effects. Our measurements represent the first application of the intensity mapping technique to optical observations.