AAS 195th Meeting, January 2000
Session 52. Absorption in the Intergalactic Medium
Display, Thursday, January 13, 2000, 9:20am-6:30pm, Grand Hall

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[52.03] The Taxonomy of MgII Absorbers: A Multivariate Analysis

R. Mellon, C. Churchill, J. Charlton (Penn State), B. Jannuzi (NOAO), S. Kirhakos (IAS), C. Steidel (Caltech), D. Schneider (Penn State)

In order to better understand the range of physical conditions present in the interstellar and halo gas associated with intermediate redshift galaxies, we examined a sample of 45 MgII absorption--selected systems over the redshift range 0.4 to 1.4. MgII and FeII absorption profiles were observed at a resolution of 6 km/s with HIRES/Keck. Lya and CIV were measured in FOS spectra obtained from the Hubble Space Telescope archive (resolution 230 km/s). We performed a multivariate analysis using rest--frame equivalent widths (W) of MgII, FeII, CIV, and Lya and the MgII kinematic spread. Based upon these properties, we find that intermediate redshift absorbers can be organized into five categories: ``Classic'', ``CIV--deficient'', ``Single/Weak'', ``Double'', and ``DLA/HI--Rich''. These categories arise, in part, because there is a strong connection between low--ionization kinematics and the location of an absorber on the W(CIV)--W(MgII) plane. We compare the locations of our intermediate redshift absorbers on the W(CIV)--W(MgII) plane with those of lower and higher redshift data taken from the literature and find evidence for evolution that is connected with the MgII kinematics seen in HIRES/Keck profiles at z > 1.4. We discuss the potential of using the above categories of absorbers to understand galactic evolution from the perspective of the underlying physical processes giving rise to and governing galactic gas and its ionization phases and kinematics.

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

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