Unmasking Damped LyUnmasking Damped Ly Absorbing Absorbing

Galaxies:Galaxies:

Hsiao-Wen Chen(MIT Center for Space Research)

Ken Lanzetta (Stony Brook University)

Rob Kennicutt (Steward Observatory)

Michael Rauch (Carnegie Observatories)

Damped Ly Absorbers (DLAs)N(HI) ≥ 2 x 1020 cm-2

Abell 2218 at z = 0.18 (Zwaan et al. 2002)

High-redshift analog of local HI galaxies

Proximity to a glaring, background QSO --

Proximity to a glaring, background QSO -- challenging to find the DLA galaxy

5”

z ≤ 1 Sample

• 23 known DLAs in available UV spectra of QSOs

• 14 confirmed DLA galaxies

• 4 candidate DLA galaxies; 3 unidentified

Morphology of z < 1 DLA galaxies

5”10”

5”

18”

z = 0.101 z = 0.473 z = 0.613

z = 0.525 z = 0.524

z = 0.221

Spectral properties of z < 1 DLA galaxies

Chen, Kennicutt, & Rauch (2005)

Utility of the DLA galaxy sample

• To study the neutral gaseous extent of intermediate-redshift galaxies

• To understand the nature of DLA galaxies by examining their luminosity distribution function: dwarf dominated vs. a typical field sample

• To investigate the metal content of DLA galaxies: missing metal?

HI extent of intermediate-z galaxies

Chen & Lanzetta (2003)

HI cross section of distant galaxies

Chen & Lanzetta (2003)

Luminosity distribution of z < 1 DLA galaxies

Chen & Lanzetta (2003)

N(z) ∫ (L) (L) dL

< 40% of DLAs at z < 1 arise in galaxiesOf luminosity LB < 0.1 LB*

Chemical enrichment history in HI

Prochaska et al. (2003)

• low metal

• large scatter

Abundance profiles of the z < 1 DLA galaxies

Chen, Kennicutt, & Rauch (2005)

Z () = ( 0.02 +/- 0.20) - ( 0.041 +/- 0.012 ) kpc

Abundance profiles of the z < 1 DLA galaxies

Chen, Kennicutt, & Rauch (2005)

Z () = ( 0.02 +/- 0.20) - ( 0.041 +/- 0.012 ) kpc

Z = 0.7 dex

Summary: Intermediate redshift galaxies possess extended

neutral gas to r = 24 - 30 h-1 kpc.

The luminosity distribution function of the DLA galaxies is consistent with expectations, if they are drawn from the known field galaxy population.

Abundance profiles of DLA galaxies can be characterized by a metallicity gradient of Z/ = -0.041 +/- 0.012 dex/kpc.

The predicted N(HI)-weighted mean metallicity in the DLA population is <Z> = -0.50 +/- 0.07 over 100 random lines of sight.

Conclusions:DLA galaxies at z < 1 have a range of

luminosity, morphology, and spectral properties, representative of the field galaxy population. An especially large contribution from dwarf galaxies is not necessary.

The low metal content and large scatter observed in the DLAs can arise naturally as a combination of gas cross-section selection and metallicity gradients commonly seen in local disk galaxies.

Gamma-ray burst afterglows as probes

36”

HST/NICMOS (+4 d)

w/ J. X. Prochaska & J. S. Bloom

Gamma-ray burst afterglows as probes

36”

HST/NICMOS (+1 yr)

NICMOS/F160W

ACS/F814W

10”

10”

• GRB host-DLA

• Classic DLA

w/ J. X. Prochaska & J. S. Bloom