Blue Channel spectroscopy of quasar absorption lines: Metal abundances and dust in DLYAs Jill Bechtold, Jun Cui (Steward Observatory) Varsha Kulkarni, Joe Meiring, Pushpa Khare (Univ. S. Carolina) Don York (Chicago) James Lauroesch (Northwestern) And others 2004 ApJ 616, ApJ 618, In press, astro-ph/ NOAO public access & UA allocations

Background for non-astronomers

For z<1.6 (corresponding to 70% age of the Universe) Lyman alpha observed with HST; interesting lines of metals in blue from ground

Use DLYAs to observe relative abundances of the elements in the interstellar gas clouds of distant galaxies as a function of cosmic time each generation of stars  supernovae, planetary nebula winds  more “heavy elements”

Complication: Atoms of abundant elements freeze out onto dust grains Iron: Variable “depletion” depending on when the last supernova blast passed through

Solution: Look for ZINC Doesn’t freeze out onto dust grains Zinc and Iron have similar nucleosynthetic histories In same spectra region: typically see lines from Chromium Chromium is heavily depleted, so strength tells you about dust Zn/H versus z (or equivalently look-back time)  evolution of metallicity Ground-based: Z>1.6 ~ hundred DLYAs measured Before SDSS: QSO Absorption line Key Project had ONE z<1.6 DLYA

Experiment: Use SDSS quasar spectra to find very strong Mg II absorbers, with strong Mg I Follow-up with HST to look for characteristic damped Lyman alpha line (Rao+, Becker+, Kulkarni+, Bechtold+ HST programs) Measure Zinc, chromium, iron absorption lines with MMT Spectra

MMT Blue Spectrograph 832 l/mm 2 nd order

Solar 1/10 Solar 1/100 solar Lookback time (billion years)

Expect low redshift damped Ly alpha absorbers to be more metal rich Probably due to selection effect: high Zn/H systems missing more metals  more dust, background quasar dimmed

New Sample for follow-up studies Chandra X-ray Spectroscopy of absorption: Soft X-ray absorption due to oxygen Zn/H  iron peak elements Pop II Stars: (old stars in Milky Way) have enhanced oxygen WRT iron peak, due to massive star supernovae early on MAESTRO spectroscopy detect Zn, Cr, other trace elements history of nucleosynthesis