Spatially Resolved Emission of a High-redshift DLA Galaxy with the Keck/OSIRIS IFU

We present the first Keck/OSIRIS infrared IFU observations of a high-redshift damped Lyα (DLA) galaxy detected in the line of sight to a background quasar. By utilizing the Laser Guide Star Adaptive Optics to reduce the quasar point-spread function to FWHM ~ 0.''15, we were able to search for and map the foreground DLA emission free from the quasar contamination. We present maps of the Hα and [O III] λλ5007, 4959 emission of DLA 2222-0946 at a redshift of z ~ 2.35. From the composite spectrum over the Hα emission region, we measure a star formation rate of 9.5 ± 1.0 M _⊙ yr^-1 and a dynamical mass of M _dyn = 6.1 × 10⁹ M _⊙. The average star formation rate surface density is langΣ_SFRrang = 0.55 M _⊙ yr^-1 kpc^-2, with a central peak of 1.7 M _⊙ yr^-1 kpc^-2. Using the standard Kennicutt-Schmidt relation, this corresponds to a gas mass surface density of Σ_gas = 243 M _⊙ pc^-2. Integrating over the size of the galaxy, we find a total gas mass of M _gas = 4.2 × 10⁹ M _⊙. We estimate the gas fraction of DLA 2222-0946 to be f _gas ~ 40%. We detect [N II] λ6583 emission at 3σ significance with a flux corresponding to a metallicity of 75% solar. Comparing this metallicity with that derived from the low-ion absorption gas ~6 kpc away, ~30% solar, indicates possible evidence for a metallicity gradient or enriched in/outflow of gas. Kinematically, both Hα and [O III] emission show relatively constant velocity fields over the central galactic region. While we detect some red and blueshifted clumps of emission, they do not correspond with rotational signatures that support an edge-on disk interpretation.

The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.