Progress in Understanding the Nature of Weak MgII Absorbers

Details Progress in Understanding the Nature of Weak MgII Absorbers Progress in Understanding the Nature of Weak MgII Absorbers

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005aas...20720306c&link_type=abstract

American Astronomical Society Meeting 207, #203.06; Bulletin of the American Astronomical Society, Vol. 37, p.1502

Astronomy and Astrophysics

Astronomy

Scientific paper

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(HI) ˜ 15-16 [cm-2] Lyman-alpha forest clouds. This talk will summarize our recent (Narayanan et al. 2005; Lynch et al. 2005; Milutinović 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 ˜1; 2) Typical single cloud weak MgII absorbers at z ˜1 have two phases of gas with n ˜ 0.1 and n ˜ 0.001 [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.

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