Search

We present high-resolution echelle spectra of seven proximate damped Lyman α (PDLA) systems. The relative velocity separation of each PDLA from the background quasar is . Combining our sample with a further nine PDLAs from the literature we compare the chemical properties of the proximate systems with a control sample of intervening DLAs. The PDLAs are usually excluded from statistical studies of absorption-selected galaxies and this sample constitutes the first systematic study of their chemical and ionization properties. Taken at face value, the sample of 16 PDLAs exhibits a wide range of metallicities, ranging from to , including the DLA with the lowest N(Si ii)/ N(H i) yet reported in the literature. However, some of these abundances may require ionization corrections. We find several pieces of evidence that indicate enhanced ionization and the presence of a hard ionizing spectrum in PDLAs which lead to properties that contrast with the intervening DLAs, particularly when the N(H i) is low. The abundances of Zn, Si and S in PDLAs with log N(H i) > 21, where ionization corrections are minimized, are systematically higher than the intervening population by a factor of around 3. We also find possible evidence for a higher fraction of N v absorbers amongst the PDLAs, although the statistics are still modest. 6/7 of our echelle sample show high ionization species (Si iv, C iv, O vi or N v) offset by >100 km s−1 from the main low ion absorption. We analyse fine-structure transitions of C ii★ and Si ii★ to constrain the PDLA distance from the quasi-stellar object (QSO). Lower limits range from tens of kpc to >160 kpc for the most stringent limit. We conclude that (at least some) PDLAs do exhibit different characteristics relative to the intervening population out to 3000 km s−1 (and possibly beyond). None the less, the PDLAs appear distinct from lower column density associated systems, and the inferred QSO–absorber separations mean they are unlikely to be associated with the QSO host. No trends with are found, although this requires a larger sample with better emission redshifts to confirm. We speculate that the PDLAs preferentially sample more massive galaxies in more highly clustered regions of the high-redshift Universe. [ABSTRACT FROM AUTHOR]

We present equivalent width measurements and limits of six diffuse interstellar bands (DIBs, λ 4428, λ 5705, λ 5780, λ 5797, λ 6284, and λ 6613) in seven damped Lyα absorbers (DLAs) over the redshift range 0.091 ≤ z ≤ 0.524, sampling 20.3 ≤ log N(Hi) ≤ 21.7. Based upon the Galactic DIB–N(H i) relation, the λ 6284 DIB equivalent width upper limits in four of the seven DLAs are a factor of 4–10 times below the λ 6284 DIB equivalent widths observed in the Galaxy, but are not inconsistent with those present in the Magellanic Clouds. Assuming the Galactic DIB–E(B − V) relation, we determine reddening upper limits for the DLAs in our sample. Based upon the E(B − V) limits, the gas-to-dust ratios, N(H i)/E(B − V), of the four aforementioned DLAs are at least ~5 times higher than that of the Galactic ISM and are more consistent with the Large Magellanic Cloud. The ratios of two other DLAs are at least a factor of a few times higher. The best constraints on reddening derive from the upper limits for the λ 5780 and λ 6284 DIBs, which yield E(B − V) ≤ 0.08 mag for four of the seven DLAs and are more consistent with the Magellanic Clouds rather than the Galaxy. Our results suggest that, in DLAs, quantities related to dust, such as reddening and metallicity, appear to have a greater impact on DIB strengths than does H i gas abundance. The molecules responsible for the DIBs in DLA selected sightlines are underabundant relative to sightlines in the Galaxy of similarly high N(H i). Using DIBs to study the ISM of DLAs provide evidence that at least some population of DLAs are more Magellanic-like than Galactic-like. [ABSTRACT FROM PUBLISHER]

We present a sample of 33 damped Lyman α systems (DLAs) discovered in the Sloan Digital Sky Survey (SDSS) whose absorption redshifts ( zabs) are within 6000 km s−1 of the quasi-stellar object's (QSO) systemic redshift ( zsys). Our sample is based on non-broad absorption line (non-BAL) QSOs from Data Release 3 (DR3) of the SDSS. We estimate that our search is ≈100 per cent complete for absorbers with N(H i) . The derived number density of DLAs per unit redshift, n( z), within is higher (3.5σ significance) by almost a factor of 2 than that of intervening absorbers observed in the SDSS DR3, i.e. there is evidence for an overdensity of galaxies near the QSOs. This provides a physical motivation for excluding DLAs at small velocity separations in surveys of intervening ‘field’ DLAs. In addition, we find that the overdensity of proximate DLAs is independent of the radio-loudness of the QSO, consistent with the environments of radio-loud and radio-quiet QSOs being similar. [ABSTRACT FROM AUTHOR]

We present the discovery of a red supergiant star that exploded as supernova 2003gd in the nearby spiral galaxy M74. The Nubble Space Telescope (HST) and the Gemini Telescope imaged this galaxy 6 to 9 months before the supernova explosion, and subsequent HST images confirm the positional coincidence of the supernova with a single resolved star that is a red supergiant of 8[sup+4,sub-2] solar masses. This confirms both stellar evolution models and supernova theories predicting that cool red supergiants are the immediate progenitor stars of type II — plateau supernovae. [ABSTRACT FROM AUTHOR]