Dust reddening in z3 DLAs

1
Dust reddening in z3 DLAs
(observed)
Michael Murphy
Collaborators Joe Liske, ESO (Garching)
Jason Prochaska (UCO/Lick)
and thanks to Vivienne Wild, ESO (IoA)
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Evidence for dust reddening?
Pei, Fall, Bechtold (1991) Detection of
reddening at 99.999 confidence level. Mean
reddening Da -0.38 0.13 _at_ ltzabsgt 2.3
Red
Blue
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DLAs and as from SDSS spectra

• R2000, high enough to detect DLAs and fit for
  N(HI). dlog10N(HI)/cm-2 0.2.
• 3 fibres ? Accurate spectrophotometry, da0.01
  per spectrum.
• DR3 DLA database of Prochaska et al. (2005,
  accepted)
• gt400 useful DLAs (more than 20 times PFB91).
• Starting DLA search redshift, zi, defined by SNR
  criterion.
• Ending redshift, zf, is 3000 kms-1 below Lya.

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DLAs from SDSS spectra
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Example SDSS spectrum with DLA
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QSOs are not power-laws
Vanden Berk et al. (2001)
Selected fitting regions
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zem bootstrapping
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Composites in QSO rest-frame
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a-distribution
Blue
Red
Da -0.053 0.014
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Composites in DLA rest-frame
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colour distribution
Blue
Red
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Some numbers

• Da -0.053 0.014 is the measured quantity,
  significant at 3.5s.
• E(B-V) (5.11.5)10-3 for SMC-like dust or
  E(B-V) (1.00.3)10-2 for LMC-like dust ? AV
  0.015 mag.
• D(r-z) 0.027 0.008 mag.
• Using k 10Zn/H(1-10Fe/Zn)
• k 0.03 for Zn/H -1.5, Fe/Zn -0.3?
  E(B-V) 510-3 for SMC-like dust.
• k 0.07 for Zn/H -1.0, Fe/Zn -0.5?
  E(B-V) 1210-3 for SMC-like dust.

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E(B-V) vs. log10N(HI)
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Summary

• 3.5s detection of dust reddeningDa -0.053
  0.014 (1s)E(B-V) (5.11.5)10-3 (1s) for
  SMC-like dustAV 0.015 mag, i.e. extinction of
  4.
• Broadly consistent with expectation from
  depletion measurements
• Dust-to-gas ratio is only 0.03 times ISM values
• Milky Way-like dust disfavoured

? more to come
? more to come
? more to come

• Warning Detailed evaluation of SDSS completeness
  vs. a required at this precision?

• Warning I would bet that lensing is gt0.01 mag.