The Chemical Composition of Damped Lymanalpha Galaxies

1
The Chemical Composition of
Damped Lyman-alpha Galaxies
Varsha P.
Kulkarni University
of South Carolina
Collaborators
Donald G. York (Univ. of
Chicago) Celine Peroux (European
Southern Observatory) Joseph
Meiring, Soheila Gharanfoli (Univ. of South
Carolina) Pushpa
Khare (Utkal Univ.) Giovanni
Vladilo (Triesete)
James T. Lauroesch (Northwestern Univ. )
S. Michael Fall (Space Telescope
Science Inst.)
Bruce E. Woodgate (NASA/GSFC) Mark
Chun Marianne Takamiya (Univ. of Hawaii)

ACKNOWLEDGMENTS U.S.
National Science Foundation, NASA/STScI
2
Evolution of Metallicity

• Damped Ly-alpha absorbers (DLAs) and sub-DLAs
  contribute a large fraction of H I in galaxies,
  and are best existing probes of element
  abundances in distant galaxies over 90 of
  cosmic history.
• Most cosmic chemical evolution models predict
  rise in global mean interstellar metallicity of
  galaxies with time, from low values at high z to
  near-solar values at z0 (e.g. Pei Fall 1995
  Malaney Chaboyer 1996 Pei, Fall, Hauser
  1999 Somerville et al. 2001).
• Do DLA data show rise of global metallicity
  with time progressing to solar value at z0?

3
What made the DLA Z(z) relation uncertain?
So does the DLA global metallicity evolve?
Considerable debate existed over whether or not
the global (NHI-weighted mean) metallicity of
DLAs shows evolution (e.g., Pettini et al. 1999
Prochaska Wolfe 1999 Prochaska et al. 2001,
2003 Savaglio 2001 Kulkarni Fall 2002)
Main Problem Metallicity-redshift relation
very sensitive to the low-z end But very few
measurements at low z (none existed at z
lt 0.4) --Zn II ?? 2026, 2062 lines lie in
UV for z lt 0.6, and in blue for 0.6 lt z
lt 1.5 --DLA Ly-alpha lines lie in UV for z
lt 1.6 So need access to UV/ blue-efficient
spectrographs
4
Why is Z(z) at z lt 1.5 important?
?? z lt 1.5 is 70 of the age of the Universe!
?? Cosmic star formation rate was much higher
at 1 lt z lt 1.5 than at z0 ? ? So metallicity
at low z should be higher Most cosmic
chemical evolution models predict such a
rise. ----gt Low-z end important to clarify
shape of Z(z) relation ? Can also clarify the
relation of DLAs to present-day galaxies.
5
Low-z End of Metallicity-Redshift Relation
(Kulkarni et al. 2005, ApJ, 618, 68)
?????Data from?HST SpaceTelescope Imaging
Spectrograph ? 4 DLAs at 0.09 lt z lt 0.52
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Abundances at Intermediate Redshifts
(Khare, Kulkarni, Lauroesch, York, Crotts,
Nakamura 2004, ApJ, 616, 86, Meiring,
Kulkarni, Khare, et al. 2006a, MNRAS, 370, 43)
MMT/VLT/Magellan spectra for DLAsat 0.6 lt
z lt 1.5 discovered with HST or SDSS Spectral
resolution 75 km/s, but high S/N enables
detection of Zn, Cr, Fe, Mn, Ni, Si, etc.
Together with HST data, doubled the z lt 1.5
DLA Zn sample, tripled the z lt 1 sample.
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The role of Sub-DLAs in Cosmic Metal
Budget(Kulkarni, Khare et al. 2006, ApJ,
submitted Khare, Kulkarni, et al. 2006, AA,
submitted)

• We have now discovered a few more such metal-rich
  sub-DLAs at 0.7 lt z lt 1.5 with Magellan MIKE
  (Meiring et al. 2006b, MNRAS, submitted)
• Fraction of Metal-rich Sub-DLAs seems larger than
  fraction of Metal-rich DLAs
• If a significant population of metal-rich
  sub-DLAs is found, sub-DLAs could help to reduce
  the Missing Metals Problem.

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Metallcity Evolution of Sub-DLAs
30 Sub-DLAs, 119 DLAs Sub-DLA global metallicity
seems higher than that of DLAs. Sub-DLAs may
contribute several times than DLAs to the
metal-budget at z lt 1
9
Are Sub-DLAs more metal-rich due to Selection
Effects?
No indication that the observed trends are due to
sample selection, or use of Zn , or use of
N(HI)-weighting. But larger samples are needed!
10
Star Formation Rates of Quasar
Absorbers(Kulkarni, Woodgate, York, Meiring,
Thatte, Palunas, Wassell 2006, ApJ, 636, 30)
Our Goal To increase the sample of star
formation rate (SFR) measurements in
heavy-element quasar absorbers. Our Technique
Ly-? search with narrow-band Fabry-Perot (FP)
imaging. Tuning the FP to different wavelengths
allows sampling of various redshifts. Sample
Selection Targets with well-detected systems at
2.3 lt zabs lt zem-0.6 from York et al. (1991)
quasar absorber catalog, with mixed ionization
(Si II, Al II, or O I with CIV and/or Si IV)
11
Observations

• NASA/GSFC Fabry Perot Imager at APO 3.5 m
  telescope.
• Blue and Vis-broad etalons with various
  blocking filters
• to cover 4000-4350 A. FWHM 6-15 A.
  Automatic temperature control program kept
  wavelength settings fixed. Calibrated with
  emission lines from Ar/Kr lamps.
• Nine observing runs during 10/2000-5/2004.
• Total NB integrations of 24,000-43,200 s per
  field.
• (Among deepest existing NB images of quasar
  absorbers.)
• Broad-band B images to sample rest-frame UV
  continuum emission near Ly-?.
• Field of view 3.5 diameter around the quasar
  (2.3 Mpc2 at z2.4 for H0 70, ?m0.27, ??0.73)

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Some Example Images
Q0216 B
Q0216 NB
Q2233 B
Q2233 NB
3 s Ly-a flux limits of 1.9x10-17 to 5.4x10-17
erg s-1 cm-2 --------gt 3 s SFR limits of
0.8-2.4 Msolar yr-1
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One notable example 3c196 zabs0.437(Gharanfoli,
Kulkarni, Chun, Takamiya, AJ, in press)
Keck LRIS spectra of galaxy 4 (1.5
away) Subtracted quasar contribution to obtain
galaxy spectrum H-a, H-b, O II, O III emission
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Star Formation History of Quasar Absorbers
SFR estimates from emission-line searches for
absorbers from our study and literature. LD5,
LD0 Expected mean SFR for DLAs in large-disk
scenario for closed-box model (Bunker et al.
1999) for q00.5, q00 H5, H0 Expected mean SFR
for DLAs in hierarchical scenario (Bunker et al.
1999) for q00.5, q00
Our limits are among the tightest existing limits
for quasar absorbers. SFRs of most heavy-element
absorbers lie below the large-disk prediction
many lie even below the hierarchical prediction.
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Why Image Quasar Absorbers?

• Quasar absorbers thought to be progenitors of
  present-day galaxies
• DLAs and sub-DLAs contain a large fraction of H I
  in galaxies at high z, possibly enough to form
  all stars at the present epoch
• But connection of DLAs/sub-DLAs with galaxies is
  not clear. Are they proto-spirals? dwarf
  galaxies?
• low surface brightness (LSB) galaxies?
  
• merging sub-galactic fragments?
• Why is it Difficult to Image them?
• Absorber galaxies are
• --much fainter than background quasars.
• --often at small angular separations from the
  quasars
• Most previous studies lacked flux sensitivity to
  rule out LSBs and angular resolution to rule out
  dwarf galaxies

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Gemini Adaptive Optics Observations (Chun,
Gharanfoli, Kulkarni, Takamiya 2006, AJ, 131,
686)

• 4 DLAs and 1 sub-DLA at 0.1 lt z lt 0.5
• Hokupaa 36-element natural guide star adaptive
  optics system on Gemini-North
• 1024x1024 HgCdTe QUIRC near-IR camera
• plate scale 0.02/pixel FWHM of 0.19-0.50
  with AO
• H or K images obtained with dithering

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Some Example Images
Before PSF subtraction
After PSF subtraction (zoomed)
Q0235164 H Band
Q1127-145 H Band
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CONCLUSIONS

• Most DLAs at z lt 1.5 appear to be metal-poor
  (10-20 solar). Global mean metallicity of DLAs
  appears to evolve slowly at best, in contrast
  with predictions based on cosmic chemical
  evolution models and global star formation
  history from galaxy imaging surveys.
• SFRs in a large fraction of heavy-element
  quasar absorbers may be far below the global SFR
  inferred from emission-based galaxy surveys!
• But some sub-DLAs seem to be very metal-rich. We
  have discovered several solar/supersolar
  absorbers at 0.7 lt z lt 1.5!
• If a large population of such metal-rich
  objects is found, sub-DLAs may help to reduce the
  Missing Metals Problem.

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FUTURE WORK

• POTENTIAL SELECTION EFFECTS
• ---Small number statistics?
• Need abundances of many more z lt 1.5
  absorbers.
• ---Or is dust selection bias important?
• Need IR imaging to reduce potential dust
  attenuation effects in Ly-alpha searches.
• ---Or are star-forming regions compact (and lost
  in quasar PSF)?
• Need high-resolution imaging