AAS 207th Meeting, 8-12 January 2006
Session 203 The Intergalactic Medium in Absorption and Emission
Oral, Thursday, 2:00-3:30pm, January 12, 2006, Delaware A

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[203.06] Progress in Understanding the Nature of Weak MgII Absorbers

J.C. Charlton, R.S. Lynch, N. Milutinovic, A. Narayanan (Penn State), J.R. Rigby (U. Arizona)

A population of thin structures, with close to the solar metallicity, exists apart from luminous galaxies. These objects cover a fraction of the sky comparable to luminous galaxies. They are surveyed through weak MgII absorption (Wr(2796) < 0.3Å), and correspond to \log N({\rm HI}) ~15-16 [{\rm cm}-2] Lyman-alpha forest clouds. This talk will summarize our recent (Narayanan et al. 2005; Lynch et al. 2005; Milutinovic et al. 2005) and ongoing studies of the physical properties and evolution of weak MgII absorbers from z=2.5 until the present. Key results are: 1) There is a peak epoch of the incidence of structures that produce weak MgII absorption at z~; 2) Typical single cloud weak MgII absorbers at z~ have two phases of gas with n~0.1 and n~0.001 [{\rm cm}-3], which give rise to MgII and CIV absorption, respectively. However, the absorption produced by these phases changes with time, subject to changes in the extragalactic background radiation; 3) The geometry of the weak MgII structures is likely to be sheetlike or filamentary, and although they do not arise in luminous galaxies, many are likely to arise in the surrounding environment, i.e. within 100kpc. Putting together available information, possibilities for the nature of weak MgII absorbers include collapsed metal-rich structures in the cosmic web and supernovae ejecta in invisible satellite galaxies. We acknowledge support from NASA under grant NAG5-6399 NNG04GE73G and by NSF under grant AST 04-07138 and the REU Supplement Program.

The author(s) of this abstract have provided an email address for comments about the abstract: charlton@astro.psu.edu

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