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Session 5 - High Luminosity AGN.
Display session, Monday, June 10
Tripp Commons,

[5.12] The Metallicity of the Three Damped Ly\alpha Absorbers Toward the QSO 2206-199N

K. C. Roth (IfA, U. of Hawaii)

We have obtained high-resolution (\Delta v=6 km s^-1) spectra of the QSO 2206-199N using the KECK HIRES spectrograph. The spectral region covered includes 4020--6400 Å\ with small wavelength gaps redward of 5100 ÅThe total integration time is 60 minutes with a resulting signal-to-noise ratio of 15--20 longward of the Ly\alpha forest. This QSO in interesting in that there are two high-redshift damped Ly\alpha absorbers (z_abs=1.921; 2.076) along the line of sight. We have detected several weak metal lines associated with the first system, including Zn II, Cr II and Ni II. Our measured (log + 12) abundances are Zn/H = 4.27, Cr/H = 4.80, and Ni/H = 5.14, well below the solar values of 4.65, 5.68, and 6.25, respectively. If one assumes the Zn abundance accurately reflects the system metallicity and that Cr and Ni are processed into dust grains, we find a metallicity of 42% solar, with 69% of the Cr II and 81% of Ni II depleted from the gas phase. We have also detected weak metal lines of Ti II arising from a low redshift (z_abs=0.752) system which is also most likely a damped system, bringing the total number of such absorbers along the line of sight to three. This is the first time the Ti II \lambda 3385 and \lambda 3243 absorption lines have been detected at z>0, having previously been seen only in the Milky Way and the Magellanic Clouds. We do not detect the corresponding Mn II lines, with a resulting (log) abundance ratio of Ti/Mn \geq -0.02, which is greater than the solar value of -0.6. This discrepancy cannot be explained by dust since Ti depletes more easily onto grains than Mn; therefore, another mechanism must be producing this anomalous abundance ratio. Nucleosynthesis enrichment of young galactic material can produce such an effect, based on observations of metal-poor stars in the Milky Way bulge and halo. At a metallicity of [Fe/H] = -1.5 dex, [Mn/Fe] is deficient with respect to solar (-0.3) while Ti is overabundant ([Ti/Fe] = 0.3). These values are consistent with our observations and suggest that the z_abs=0.752 absorber is metal poor, with a system metallicity \leq 3% solar.

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