Sara L. Ellison

The host of GRB 030323 at z=3.372: A very high column density DLA system with a low metallicity

We present photometry and spectroscopy of the afterglow of GRB 030323. VLT spectra of the afterglow show damped Lyα (DLA) absorption and low- and high-ionization lines at a redshift z = 3.3718 ± 0.0005. The inferred neutral hy- drogen column density, log N(Hi) = 21.90 ± 0.07, is larger than any (GRB- or QSO-) DLA H uf769 column density inferred directly from Lyα in absorption. From the afterglow photometry, we derive a conservative upper limit to the host-galaxy extinction: AV < 0.5 mag. The iron abundance is (Fe/H) = −1.47 ± 0.11, while the metallicity of the gas as measured from sulphur is (S/H) = −1.26 ± 0.20. We derive an upper limit on the H2 molecular fraction of 2N(H2)/(2N(H2) + N(Hi)) < 10 −6 .I n the Lyα trough, a Lyα emission line is detected, which corresponds to a star-formation rate (not corrected for dust extinction) of roughly 1 Myr −1 . All these results are consistent with the host galaxy of GRB 030323 consisting of a low metallicity gas with a low dust content. We detect fine-structure lines of silicon, Si uf769uf769*, which have never been clearly detected in QSO-DLAs; this suggests that these lines are produced in the vicinity of the GRB explosion site. Under the assumption that these fine-structure levels are populated by particle collisions, we estimate the H uf769 volume density to be nHi = 10 2 −10 4 cm −3 .H ST/ACS imaging 4 months after the burst shows an extended AB(F606W) = 28.0 ± 0.3 mag object at a distance of 0.

The c IV mass density of the universe at redshift 5

In order to search for metals in the Lyα forest at redshifts zabs > 4, we have obtained spectra of high signal-to-noise ratio and moderately high resolution of three QSOs at zem > 5.4 discovered by the Sloan Digital Sky Survey. These data allow us to probe to metal enrichment of the intergalactic medium at early times with higher sensitivity than previous studies. We find 16 C IV absorption systems with column densities log N(C ) = 12.50-13.98 over a total redshift path ΔX = 3.29. In the redshift interval z = 4.5-5.0, where our statistics are most reliable, we deduce a comoving mass density of C3+ ions Ω = (4.3 ± 2.5) × 10-8 (90% confidence limits) for absorption systems with log N(C ) ≥ 13.0 (for an Einstein-de Sitter cosmology with h = 0.65). This value of Ω is entirely consistent with those measured at z < 4; we confirm the earlier finding by Songaila that neither the column density distribution of C IV absorbers nor its integral show significant redshift evolution over a period of time that stretches from ~1.25 to ~4.5 Gyr after the big bang. This somewhat surprising conclusion may be an indication that the intergalactic medium was enriched in metals at z 5, perhaps by the sources responsible for its reionization. Alternatively, the C IV systems we see may be associated with outflows from massive star-forming galaxies at later times, while the truly intergalactic metals may reside in regions of the Lyα forest of lower density than those probed up to now.

Distinct abundance patterns in multiple damped Lyα galaxies: Evidence for truncated star formation?

Following our previous work on metal abundances of a double damped Ly system with a line-of-sight separation 2000 km s 1 (Ellison & Lopez 2001), we present VLT UVES abundances of 3 new systems spanning a total of6000 km s 1 at z 2:5 toward the southern QSO CTQ247. These abundances are supplemented with echelle observations of another double damped Ly system in the literature. We propose a definition in terms of velocity shift of the sub-class multiple damped Ly system, which is motivated by its possible connection with large-scale structure. We find that the abundance ratio (S/Fe) is systematically low in multiple systems compared with single systems, and with a small scatter. The same behavior is found in 2 more single DLA systems taken from the literature that show evidence of belonging to a galaxy group. Although (Si/Fe) ratios are also generally lower in multiple DLAs than in single DLAs, the eect is less striking since the scatter is larger and there are a number of low (Si/Fe) DLAs in the literature. We suggest that this can be explained with a combination of detection bias and, to a lesser extent, the scatter in ionization corrections for dierent absorbers. We investigate whether consistently low/Fe ratios could be due to dust depletion or ionization corrections and find that the former eect would emphasize the observed trend of low/Fe in multiple systems even further. Ionization may have a minor eect in some cases, but at a level that would not change our conclusions. We thus conclude that the low/Fe ratios in multiple DLAs have a nucleosynthetic origin and suggest that they could be explained by reduced star formation in multiple damped Ly systems, possibly due to environmental eects. There seems to be independent evidence for this scenario from the mild odd-even eect and from the relatively high N/ ratios we observe in these multiple systems.

The Absorption and Emission Kinematics in the z = 0.7450 Mg II Absorber toward Q1331+17*

We present a comparative analysis of the galaxy emission and quasar (QSO) absorption kinematics of a zabs ~ 0.7450 Mg II system and its candidate absorbing galaxy (G5) located 386 (28.3 h kpc) from the QSO. We have obtained a spectrum of the galaxy candidate, previously identified as a luminous edge-on disk, and detect the [O II] λ3727 doublet at a systemic redshift of zsys = 0.7450. From slit spectroscopy of this galaxy, we find vrot 210 km s-1, possibly as large as 350 km s-1. Plotted on the same velocity scale, the systemic redshift of the galaxy coincides with the center of the absorption system, although the absorption components span more than 100 km s-1 in either direction. However, once the sense of the rotation is taken into account, there is no absorbing gas at the projected velocity of the disk rotation curve. This implies incompatibility with a simple disk scenario. Moreover, a reanalysis of archival Hubble Space Telescope (HST) data reveals that the galaxy is only 0.3L*, considerably less luminous than previously reported in the literature. This is incompatible with the established Tully-Fisher relation at this redshift, unless approximately 2 mag of total extinction is invoked. Careful inspection of the archival HST data reveals that G5 may well be composed of two galaxies, although the quality of the data does not permit a detailed investigation of this. This possibility is further supported by the identification of a second faint emission line at λobs = 5674 A, whose distinct spatial and velocity profiles indicate that it arises in a different galaxy at a different redshift. Analysis of the absorption lines shows evidence for superbubbles in the interstellar medium of the absorbing galaxy, based on the striking symmetry between components and large Mg I/Mg II and Mg I/Fe II ratios, indicative of large densities. The large velocity separations between line pairings, Δv ~ 150 km s-1, indicate that these bubbles may be powered by OB associations comparable to the largest observed at z = 0 and that the gas is probably enriched to at least 1/10 solar metallicity. This is consistent with observations at low redshift that extended Mg II halos are often seen in galaxies that contain disturbed gas. Superbubbles may also explain why the absorber has a relatively large Mg II equivalent width relative to the luminosity of the associated galaxy (or galaxies).