Search

We present UV and optical observations from the Cosmic Origins Spectrograph on the Hubble Space Telescope and Keck of a z = 0.27395 Lyman limit system (LLS) seen in absorption against the QSO PG1630+377. We detect H I absorption with log N(H I) = 17.06 ± 0.05 as well as Mg II, C III, Si III, and O VI in this system. The column densities are readily explained if this is a multi-phase system, with the intermediate and low ions arising in a very low metallicity ([Mg/H] = -1.71 ± 0.06) photoionized gas. We identify via Keck spectroscopy and Large Binocular Telescope imaging a 0.3 L* star-forming galaxy projected 37 kpc from the QSO at nearly identical redshift (z = 0.27406 and Δv = -26 km s-1) with near solar metallicity ([O/H] = -0.20 ± 0.15). The presence of very low metallicity gas in the proximity of a near-solar metallicity, sub-L* galaxy strongly suggests that the LLS probes gas infalling onto the galaxy. A search of the literature reveals that such low-metallicity LLSs are not uncommon. We found that 50% (4/8) of the well-studied z ≲ 1 LLSs have metallicities similar to the present system and show sub-L* galaxies with ρ < 100 kpc in those fields where redshifts have been surveyed. We argue that the properties of these primitive LLSs and their host galaxies are consistent with those of cold mode accretion streams seen in galaxy simulations. [ABSTRACT FROM AUTHOR]

We present an analysis of the Ly forest towards 3C 273 from the Space Telescope Imaging Spectrograph at 7 km s resolution, along with reprocessed data from the Far Ultraviolet Spectroscopic Explorer. The high ultraviolet flux of 3C 273 allows us to probe the weak, low- absorbers. The main sample consists of 21 H i absorbers that we could discriminate to a sensitivity of . The redshift density for absorbers with is below the mean for other lines of sight; for , it is consistent with numerical model predictions. The Doppler parameter distribution is consistent with other low- samples. We find no evidence for a break in the column density power-law distribution to . A broad Ly absorber is within km s and 1.3 local-frame Mpc of two galaxies, with an O vi absorber 700 km s away, similarly close to three galaxies and indicating overdense environments. We detect clustering on the km s scale at significance for , consistent with the level predicted from hydrodynamical simulations, and indication for a Ly forest void at . We find at least two components for the Virgo absorber, but the total column is not significantly changed. [ABSTRACT FROM AUTHOR]

QSO absorption lines are sensitive to very low density gas, and consequently, QSO spectroscopy provides a powerful tool for measuring the distribution, physical conditions, and metal enrichment of baryons in the intergalactic medium and in “dark galaxies”. However, ultraviolet spectroscopy is required to study QSO absorbers in the nearby universe where the connections between the absorbing gas and galaxies/environment can be probed. This talk reviewed several recent studies of low-z QSO absorbers in order to demonstrate the value of combining high-resolution ultraviolet spectroscopy with complementary information on the absorber environment, e.g., mapping of 21 cm emission in the vicinity of the absorbers; some notes on these examples are presented in this paper. The absorbers probed range from high-N(H I) damped Lyman α absorbers down to very low-column Lyα forest clouds with log N(H I) < 13.5. The high-N(H I) systems are candidate “dark galaxies” – these systems are more metal enriched than the high-z IGM, possibly due to in-situ star formation, and some of the absorbers are highly metal enriched. However, we have obtained follow-up 21cm emission mapping with the VLA and deep optical imaging, and while we do find H I clouds associated with the absorbers in 21cm emission, we often do not find any evidence of in-situ stars. At this juncture, it seems more likely that these low-z absorbers were enriched with metals within galaxies and were subsequently transported out into the IGM, e.g., by tidal stripping or galactic winds. This contribution also summarizes some recent results on the search for lost baryons in the “warm-hot” (shock-heated) low-redshift IGM. [ABSTRACT FROM PUBLISHER]

We present high-resolution ultraviolet spectra of absorption-line systems towards the low- z quasi-stellar object (QSO) . Coupled with ground-based imaging and spectroscopic galaxy redshifts, we find evidence that many of these absorbers do not arise in galaxy haloes but rather are truly intergalactic gas clouds distributed within large-scale structures, and moreover, the gas is cool and has relatively high metallicity . Hubble Space Telescope ( HST) Space Telescope Imaging Spectrograph (STIS) data reveal a dramatic cluster of 13 H i Lyman α (Lyα) lines within a 1000 km s−1 interval at . We find 10 galaxies at this redshift with impact parameters ranging from to . The velocities and velocity spread of the Lyα lines in this complex are unlikely to arise in the individual haloes of the nearby galaxies; instead, we attribute the absorption to intragroup medium gas, possibly from a large-scale filament viewed along its long axis. Contrary to theoretical expectations, this gas is not the shock-heated warm-hot intergalactic medium (WHIM); the width of the Lyα lines all indicate a gas temperature , and metal lines detected in the Lyα complex also favour photoionized, cool gas. No O vi absorption lines are evident, which is consistent with photoionization models. Remarkably, the metallicity is near-solar, (2σ uncertainty), yet the nearest galaxy which might pollute the intergalactic medium is at least away. Tidal stripping from nearby galaxies appears to be the most likely origin of this highly enriched, cool gas. More than six Abell galaxy clusters are found within 4° of the sight line suggesting that the QSO line of sight passes near a node in the cosmic web. At , we find absorption systems as well as galaxies at the redshift of the nearby clusters Abell 564 and Abell 559. We conclude that the sight line pierces a filament of gas and galaxies feeding into these clusters. The absorber at associated with Abell 564/559 also has a high metallicity with , but again the closest galaxy is relatively far from the sight line . The Doppler parameters and H i column densities of the Lyα lines observed along the entire sight line are consistent with those measured towards other low- z QSOs, including a number of broad lines. [ABSTRACT FROM AUTHOR]

A correction to the article "High-metallicity, photoionized gas in intergalactic large-scale filaments," by Bastien Aracil, published in volume 367, pages139-155 (2006) is presented.