Transcript How dusty are DLAs? (observed) Collaborators:

How dusty are
(observed) DLAs?
Michael Murphy
Collaborators:
Joe Liske, ESO (Garching)
Jason Prochaska, UCO/Lick (Santa Cruz)
Stephane Herbert-Fort, IAP (Paris)
and thanks to:
Vivienne Wild, IoA (Cambridge)
27 May 2016
Michael Murphy, IoA, U. Cambridge
IAU 199, Shanghai
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Evidence for dust reddening?:
Pei, Fall, Bechtold
(1991):
Blue
Red
Detection of
reddening “at
99.999%
confidence level.”
Mean reddening:
Da = -0.38 ± 0.13
@ <zabs> ≈ 2.3
Not that Da!
27 May 2016
Michael Murphy, IoA, U. Cambridge
IAU 199, Shanghai
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DLAs and as from SDSS spectra:
 R~2000, high enough to detect DLAs and fit for
N(HI). dlog10[N(HI)/cm-2] ~ 0.2.
 3” fibres → Accurate spectrophotometry, |da|~0.01
per spectrum.
 DR3 DLA database of Prochaska, Herbert-Fort &
Wolfe (2005, submitted):
• >400 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.
27 May 2016
Michael Murphy, IoA, U. Cambridge
IAU 199, Shanghai
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DLAs from SDSS spectra:
27 May 2016
Michael Murphy, IoA, U. Cambridge
IAU 199, Shanghai
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Example SDSS spectrum with DLA:
27 May 2016
Michael Murphy, IoA, U. Cambridge
IAU 199, Shanghai
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QSOs are not power-laws:
Vanden Berk et al. (2001)
27 May 2016
Michael Murphy, IoA, U. Cambridge
IAU 199, Shanghai
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zem bootstrapping:
27 May 2016
Michael Murphy, IoA, U. Cambridge
IAU 199, Shanghai
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a-distribution:
Blue
Red
27 May 2016
Michael Murphy, IoA, U. Cambridge
IAU 199, Shanghai
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colour distribution:
Blue
27 May 2016
Michael Murphy, IoA, U. Cambridge
Red
IAU 199, Shanghai
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Composite spectra:
27 May 2016
Michael Murphy, IoA, U. Cambridge
IAU 199, Shanghai
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Some numbers:
 Da = -0.053 ± 0.014 is the measured quantity,
significant at ≈3.5s.
 E(B-V) = (5.1±1.5)×10-3 for SMC-like dust [or E(B-V) =
(1.0±0.3)×10-2 for LMC-like dust] → AV ~ 0.015 mag.
 D(r’-z’) = 0.027 ± 0.008 mag.
 Using k = 10[Zn/H](1-10[Fe/Zn]):
• k = 0.03 for [Zn/H] = -1.5, [Fe/Zn] = -0.3
→ E(B-V) ≈ 5×10-3 for SMC-like dust.
• k = 0.07 for [Zn/H] = -1.0, [Fe/Zn] = -0.5
→ E(B-V) ≈ 12×10-3 for SMC-like dust.
27 May 2016
Michael Murphy, IoA, U. Cambridge
IAU 199, Shanghai
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E(B-V) vs. log10N(HI):
27 May 2016
Michael Murphy, IoA, U. Cambridge
IAU 199, Shanghai
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Summary:
 3.5s detection of dust reddening:
Da = -0.053 ± 0.014 (1s)
E(B-V) = (5.1±1.5)×10-3 (1s) for SMC-like dust
 Broadly consistent with expectation from depletion
measurements → more to come
 Dust-to-gas ratio is only ~0.03 times ISM values
→ more to come
 Milky Way-like dust disfavoured → more to come
 Warning: Detailed evaluation of SDSS
completeness vs. a required at this precision?
 Warning: I would bet that lensing is >0.01 mag.
27 May 2016
Michael Murphy, IoA, U. Cambridge
IAU 199, Shanghai
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