Blue Channel spectroscopy of quasar absorption lines: Metal abundances and dust in DLYAs

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Blue Channel spectroscopy ofquasar absorption
linesMetal 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, 86
• 2005 ApJ 618, 68
• 2006 In press, astro-ph/0604617
• NOAO public access UA allocations

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Background for non-astronomers
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For zlt1.6 (corresponding to 70 age of the
Universe) Lyman alpha observed with HST
interesting lines of metals in blue
from ground
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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
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Complication Atoms of abundant elements freeze
out onto dust grains
Iron Variable depletion depending on when
the last supernova blast passed through
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Solution Look for ZINC Doesnt
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 Zgt1.6
hundred DLYAs measured Before SDSS QSO
Absorption line Key Project had ONE zlt1.6 DLYA

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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
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MMT Blue Spectrograph832 l/mm 2nd order
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Solar
1/10 Solar
1/100 solar
Lookback 7.7
10.3 11.5
12.1 time (billion years)
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• 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

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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