The Varied Conditions of Low Redshift Weak MgII Absorbers
Abstract
Quasar absorption lines allow us to study parts of the universe that are otherwise not visible to us. Weak MgII absorbers, defined to be those with rest frame equivalent widths Wr(2796) < 0.30 Å, trace the processes that link galaxies and the intergalactic medium. These absorbers usually have metallicities at solar or super solar values, despite being relatively far (>50kpc) from the luminous galaxies that are normally associated with such high metallicities. Further study of these absorbers will give insight to the origin of this high metallicity material. A previous survey of weak MgII absorbers at redshifts 0 < z < 0.3 (Narayanan et. al 2005), searched 20 quasar lines of sight using data from the Space Telescope Imaging Spectrograph (STIS). The survey used SiII(1260) and CII(1335) as analogs for MgII absorption. Narayanan et. al found 6 weak MgII absorber analogs over a redshift path length of ~5.4. At low redshift, the weak MgII absorbers are a varied population, with some arising from single phase kpc-scale structures, and others from two-phase structure with a small high-density MgII cloud surrounded by a larger ( order of kpc) lower-density region responsible for the CIV absorption. We conducted a survey of ~ 400 quasars observed with the Cosmic Origins Spectrograph on board the Hubble Space Telescope, again using SiII(1260) and CII(1335) as tracers of MgII absorption for z<0.3. We find 35 analogs to weak MgII absorbers in our sample, giving a redshift path density consistent with Narayanan et. al. Our larger sample allows us to build statistics and isolate three classes of absorbers: 1) Weak low ionization absorbers with detected CIV that require two phases; 2) Weak low ionization absorbers with detected CIV that are consistent with a single phase; 3) Weak low ionization absorbers with no detected CIV. The latter tend to be the weakest, and consistently have solar or super solar metallicities. Also notable are those absorbers with no detected OVI,which could then arise in a single higher density phase.
- Publication:
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American Astronomical Society Meeting Abstracts #223
- Pub Date:
- January 2014
- Bibcode:
- 2014AAS...22345806F