A Search for Neutral Gas at Redshift z 0.55
Abstract
We present a sample of approximately 30 high-probability damped Lyman-alpha (DLA) absorption-line systems in the redshift range 0.42<z<0.70. DLA systems track the bulk of the neutral hydrogen gas in the Universe, and they are classically defined to have neutral hydrogen column densities of N(HI)<= 2 x 1020 atoms cm-2. Studies of DLAs, therefore, provide insight into the evolution of gas and galaxies over the age of the Universe. DLAs with z<1.65, for which the redshifted Lyman-alpha line remains in the UV, trace the neutral gas over approximately 70% of the most recent history of the Universe. However, since they can only be confirmed and studied through space-based UV spectroscopy, the number of confirmed DLAs remains relatively low in small redshift intervals at z<1.65. For example, in the 0.42<z<0.70 redshift interval studied here, only 9 DLAs have been confirmed in previous efficient and well-defined MgII-selected surveys. Therefore, in order to significantly improve the statistics in a narrow redshift interval, we have performed a MgII-selected DLA survey at 0.42<z<0.70 using Sloan Digital Sky Survey (SDSS) quasars. Since STIS was unavailable in Cycle 14 of the Hubble Space Telescope (HST) program, we used the ACS-HRC-PR200L prism to obtain spectroscopy of Lyman-alpha. From our initial Cycle 14 sample we have detected and measured approximately 30 high-probability DLA absorption line systems at 0.42<z<0.70. Owing to the poor resolution of the ACS-HRC-PR200L prism, these candidates should be observed at higher resolution near Lyman-alpha to obtain improved N(HI) column densities. This would enable us to infer the DLA incidence and the neutral gas cosmological mass density at 0.42<z<0.70 with improved statistical accuracy.
- Publication:
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American Astronomical Society Meeting Abstracts #215
- Pub Date:
- January 2010
- Bibcode:
- 2010AAS...21546006M