HUBBLE SPACE TELESCOPE OBSERVATIONS OF SUB-DAMPED Ly α ABSORBERS AT z < 0.5, AND IMPLICATIONS FOR GALAXY CHEMICAL EVOLUTION

• Published in: The Astrophysical journal 2015-06, Vol.806 (1), p.1-22
• Main Authors: Som, Debopam, Kulkarni, Varsha P, Meiring, Joseph, York, Donald G, Peroux, Celine, Lauroesch, James T, Aller, Monique C, Khare, Pushpa
• Format: Article
• Language: English
• Subjects: ABSORPTION; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; Chemical evolution; COMPUTERIZED SIMULATION; COSMIC DUST; Delay; DETECTION; ELECTRON DENSITY; ELEMENT ABUNDANCE; EMISSION; GALACTIC EVOLUTION; GALAXIES; Hubble Space Telescope; IONIZATION; LYMAN LINES; Manganese; METALLICITY; QUASARS; RED SHIFT; SPACE; TELESCOPES
• ISSN: 1538-4357; 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/806/1/25

We report observations of four sub-damped Ly alpha (sub-DLA) quasar absorbers at z < 0.5 obtained with the Hubble Space Telescope Cosmic Origins Spectrograph. We measure the available neutrals or ions of C, N, O, Si, P, S, Ar, Mn, Fe, and/or Ni. Our data have doubled the sub-DLA metallicity samples at z < 0.5 and improved constraints on sub-DLA chemical evolution. All four of our sub-DLAs are consistent with near-solar or super-solar metallicities and relatively modest ionization corrections; observations of more lines and detailed modeling will help to verify this. Combining our data with measurements from the literature, we confirm previous suggestions that the N(H sub(I))-weighted mean metallicity of sub-DLAs exceeds that of DLAs at all redshifts studied, even after making ionization corrections for sub-DLAs. The absorber toward PHL 1598 shows significant dust depletion. The absorbers toward PHL 1226 and PKS 0439-433 show the S/P ratio consistent with solar, i.e., they lack a profound odd-even effect. The absorber toward Q0439-433 shows super-solar Mn/Fe. For several sub-DLAs at z < 0.5, [N/S] is below the level expected for secondary N production, suggesting a delay in the release of the secondary N or a tertiary N production mechanism. We constrain the electron density using Si sub(II)* and C sub(II)* absorption. We also report different metallicity versus Delta V sub(90) relations for sub-DLAs and DLAs. For two sub-DLAs with detections of emission lines from the underlying galaxies, our measurements of the absorption-line metallicities are consistent with the emission-line metallicities, suggesting that metallicity gradients are not significant in these galaxies.