CIRPASS Near-Infrared Integral Field Spectroscopy of Damped Lyman-α Systems

We assess the feasibility of detecting star formation in damped Lyman-α systems (DLAs) at z>1 through near-infrared spectroscopy using the Cambridge Infrared Panoramic Survey Spectrograph (CIRPASS) integral field unit on the 8-m Gemini telescopes. Although their relation to galaxies is not well established, high-z DLAs contain most of the neutral gas in the Universe, and this reservoir is depleted with time --- presumably through star formation. Line emission should be an indicator of star formation activity, but searches based on Lyman-α are unreliable because of the selective extinction of this resonant UV line. Using the more robust lines Hα /Hβ /[Oriptsize III] forces a move to the near-infrared at z>1. For line emission searches, spectroscopy is more sensitive than imaging, but previous long-slit spectroscopic searches have been hampered by the likelihood that any star forming region in the DLA galaxy disk would fall outside the narrow slit (see Bunker et al. 1999 MNRAS 309, 875). The integral field unit of CIRPASS will cover sufficient solid angle (13''x 4'') to intercept these, even in the extreme case of large galactic disks at high redshift. On an 8-m class telescope, star formation rates of 1 M_sun yr^-1 will be reached at z≈ 1.4 with Hα in H-band (10 σ , 3 hours for for compact regions of star formation and H₀=70 km s^{-1 Mpc{-1}}, Ω _M=1). Such star formation rates are below L^* for the high-z Lyman-break population, and are comparable locally to the luminous giant Hriptsize II complexes in M101. It appears that CIRPASS on Gemini will have both the sensitivity and the survey area to measure star formation rates in z>1 damped Lyman-α systems. Hence, CIRPASS observations will potentially probe the nature of damped Lyman-α systems and address their relation to galaxies.