Brice M

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On the nature and size of MgII absorbers
Brice Ménard
INSTITUTE for ADVANCED STUDY Princeton
Stefano Zibetti (MPE, Garching) Daniel Nestor
(Univ. of Florida) David Turnshek (Univ. of
Pittsburgh) and the SDSS Collaboration
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Outline
0. The connection between MgII absorbers and
galaxies
New constraints on MgII systems from the SDSS

1. reddening curves
2. Luminosity
3. Size distribution

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The absorber-galaxy connection

• In 1969 Bahcall Spitzer suggested that
  strong metal lines are related to intervening
  galaxies.
• Late 80s (Bergeron et al.) first galaxy
  identifications
• mid 90s (Steidel et al.) a sample of 58
  absorbing galaxies

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The Sloan Digital Sky Survey

• Low resolution, very short exposures,
  ground-based observations, but 100,000 quasar
  spectra available!
• Great potential for statistical studies

• MgII absorber catalogs
• Nestor and Turnshek 3500 quasar spectra, 1500
  MgII absorbers
• The SDSS absorber database (York et al.) 50,000
  quasar spectra

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SDSS spectra
SDSS spectra fake MgII in random quasars
LINE FINDER Quasars with MgII / Quasars without
Method

• DEFINE REFERENCE QSOs
• ? Redshift ? Reddening biases
• ? Absorption line detectability

QSO with abs Reference QSOs (x N)
STATISTICAL ANALYSIS
Signal
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Real absorber sample / fake samples
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The reddening properties of MgII absorbers
Reddening curves
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Reddening curve in the absorber rest frame
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Imaging MgII absorbing galaxies with the SDSS
40 150 kpc at z 0.5 - 1
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Image centered on a quasar at z1.4
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QSO with strong MgII
Nearby stars
Diffuse light around QSOs
QSO without
Diffuse light around QSOs
Nearby stars
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QSOs with strong MgII, 0.5 lt z_abs lt 0.7
Reference QSOs
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QSOs with strong MgII, 0.7 lt z_abs lt 1.2
Reference QSOs
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QSOs with strong MgII, 1.2 lt z_abs lt 2.0
Reference QSOs
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QSOs with strong MgII, lt z gt 0.6
QSOs with strong MgII, lt z gt 1.0
QSOs with strong MgII, lt z gt 1.6
R h-1 kpc
R h-1 kpc
R h-1 kpc
R h-1 kpc
R h-1 kpc
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Reference QSOs
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Interpreting the signal
Let us write the probability of having a galaxy
with a magnitude m, giving rise to a MgII
absorption line gtW0 , as
Pm gtW0 (r) / r - a
m(r) h mg . Pobs (r) . d2r / ( 2p r dr )
i
m(r) / h mg Pm gtW0 (r) i
m(r, l, z) / h mg (l, z) Pm gtW0 (r, l,
z) i
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Galaxy model spiral
QSOs with strong MgII, lt z gt 0.6
QSOs with strong MgII, lt z gt 1.0
QSOs with strong MgII, lt z gt 1.6
R h-1 kpc
R h-1 kpc
R h-1 kpc
R h-1 kpc
R h-1 kpc
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Galaxy model elliptical
QSOs with strong MgII, lt z gt 0.6
QSOs with strong MgII, lt z gt 1.0
QSOs with strong MgII, lt z gt 1.6
R h-1 kpc
R h-1 kpc
R h-1 kpc
R h-1 kpc
R h-1 kpc
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Results

• We find that
• h Pm gtW0 (r, l, z) i / r - 1.5
• the mean MgII absorbing galaxy has the colors of
  a spiral at z 0.6-1
• The signal behaves as expected as a function of
• scale
• redshift
• wavelength
• These results are based on EDR data only!

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Summary

• SDSS now provides us with a very large number of
  MgII systems
• Testing for systematics is crucial for
  statistical studies.
• What we have learnt
• The mean MgII galaxy has an SMC-like extinction
  curve.
• Correlation W0(MgII) / extinction
• The distribution of impact parameters follows
  P(r) / r -1.5
• It is measured out to 200 h-1 kpc. It is less
  concentrated at higher redshift
• The mean MgII absorbing galaxies has the colors
  of a spiral
• Luminosity between 0.1 and 10 L star
• More quantitative results in the paper. Analysis
  of DR3 in progress

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Yorks data
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Results
lt D m gt lt mabs gt - lt mref gt
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Results
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Results magnitude shifts
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Identification of the absorbing galaxies
gt Gas cross section appears to be driven more
by galaxy mass than by specific star formation
rate.
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Properties of MgII absorbers
Idealized model for the distribution of several
absorbers (Lya, MgII, CIV) Suggested by Steidel.
Correlation between impact parameter (b) and rest
equivalent width (W0)
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Reddening curves from composite spectra

• can be measured up to very high redshifts
• Add more recent spectral data

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• We expect an excess of light around quasars with
  strong MgII absorbers
• We stack images of quasars with absorbers and
  reference quasars
• Same redshift distribution and absorber
  detectability