Blue Channel spectroscopy ofquasar 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, 862005 ApJ 618, 68

2006 In press, astro-ph/0604617NOAO 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 Spectrograph832 l/mm 2nd order

Solar

1/10 Solar

1/100 solar

Lookback 7.7 10.3 11.5 12.1 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