The Non-Damped Nature of Twelve Low-Redshift Damped Lyman Alpha Candidate Systems

Abstract

Hubble Space Telescope (HST) UV spectroscopy of 12 candidate low-redshift damped Lyman alpha (DLA) systems in 11 QSOs (z=0.103 in Q0054+144, z=0.969 and z=0.987 in Q0302-223, z=0.478 in Q0454-220, z=1.476 in Q1047+550, z=1.070 in Q1206+459, z=1.228 in Q1247+267, z=0.399 in Q1318+290B, z=0.519 in Q1329+412, z=0.276 in Q1451-375, z=0.204 in Q2112+059, z=0.263 in Q2251+113) are presented; the observations demonstrate that they are not DLAs with $N(HI)\ge2\times10^{20}$ atoms cm$^{-2}$. In all cases except two the systems either do not exist or are well below the DLA threshold column density; the exceptions are a z=0.474 system in Q0454-220 which has $N(HI)=3\times10^{19}$ atoms cm$^{-2}$ and a z=1.223 system in Q1247+267 which has $N(HI)=8\times10^{19}$ atoms cm$^{-2}$. Despite the availability of data in the HST archives demonstrating that these are not suitable targets, many have unfortunately been approved for observation with Chandra, Gemini, and/or HST with the intent of doing followup work on low-redshift DLAs. Furthermore, these results indicate that the low-redshift DLA statistics derived from IUE spectra and presented by Lanzetta, Wolfe, & Turnshek (1995) and Wolfe et al. (1995) are invalid.