AAS 203rd Meeting, January 2004
Session 113 Molecules and Atoms at High Z and Low Z
Poster, Thursday, January 8, 2004, 9:20am-4:00pm, Grand Hall

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[113.06] Housing Weak Mg II Absorbers In The Cosmic Web

N. Milutinovic, J.C. Charlton, J. Ding, J.R. Masiero, C. Palma (Penn State), J.R. Rigby (U. of Arizona)

We present an investigation of the geometry and morphology of weak MgII systems (Wr(2796)<0.3 Å). These absorbers trace abundant, metal-enriched regions (close to solar metallicity) that may lie in faint dwarf galaxies or in intergalactic space. Generally, models show that they have a ~10pc region of higher density gas and a ~1kpc region that represents a lower density phase of higher ionization absorption.

We based our work on a search of 35 quasar spectra from the archive of high resolution, ultra-violet HST/STIS data. When possible, we supplemented these spectra with Keck/HIRES and HST/FOS data that cover more transitions over a larger range of wavelengths. When MgII is not covered we used other low ionization transitions, CII and SiII, to trace the MgII phase.

In a comparison between absorption systems detected in low and/or high ionization gas (traced by CIV absorption), we found the following:

1. Almost all of weak MgII analog systems have an associated high ionization phase. In some cases the CIV has only a single component, kinematically centered on the low ionization absorption, and in other cases there are additional CIV components offset in velocity. There is one system in quasar 3c 273 without a high ionization cloud.

2. There are twice as many CIV-only systems as systems with both CIV and weak MgII analog absorption detected.

3. The CIV absorption in weak MgII systems is on average stronger than that in the CIV-only systems.

4. The CIV absorption in weak MgII systems has similar kinematic structure as that in the CIV-only systems.

Based on these results and on physical properties of the different phases of the absorbers we consider possible geometries. We suggest that sheetlike geometries are favored, due to the relatively small cross-section of CIV-only systems.

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