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Session 11 - QSOs and Radio Galaxies.
Display session, Monday, June 08
We present new Keck HIRES spectra of 6 QSO absorption systems that show Ca II \lambda\lambda 3934,3968 and/or Na I \lambda\lambda 5890,5896 absorption. The new observations include a number of systems studied previously by others at lower resolution. With these high resolution observations (\sim 7 km s^-1 FWHM), it is possible to accurately measure the Na I and Ca II column densities and to detect weak individual components in QSO absorption systems. High equivalent width Ca II absorption lines typically break up into multiple components which mimics the trend observed in dominant strong lines like Mg II \lambda\lambda2796,2804. The Mg II lines have more detectable components over a larger total velocity range and are useful for measuring low column density components. The Ca II and Na I lines provide a better measure of velocity structure in the high column density components than the Mg II lines because they are not strongly saturated. Multiple narrow absorption components in Ca II and/or Na I are detected in the z_a = 0.0047 absorption system in 3C 232 due to NGC 3067, the z_a = 0.0668 absorption system in the spectrum of PKS 0446-208, and the z_a = 0.524 absorption system in the spectrum of the BL Lac object AO 0235+164. The ratio of Na I/Ca II column densities is a useful indicator of dust depleted gas in our Galaxy because Ca is more readily depleted onto grains than Na. We discuss the column density ratios in the individual components in these absorption systems.
Program listing for Monday