Search for a High-Redshift Damped Lyman-Alpha Absorber with NICMOS

Abstract

We present high-resolution HST NICMOS images of a quasar field known spectroscopically to have a damped Lyman-a absorber (DLA) at z = 1.892. The images were obtained in broad and narrow-band near-IR filters, with the aim of detecting the DLA in rest-frame continuum and Ha emission. The coronagraph was used for some continuum images to decrease the light from the background quasar. The coronagraphic images show a very faint feature containing four continuum emission knots, 0.7′ away from the quasar. The non-coronagraphic broad and narrow-band images show a brighter object ≈ 0.25″ from the quasar. However, the Hα contribution to the narrow-band emission from this object is negligible. Thus, either the DLA has a very low star formation rate 0 ± 2.6(4.8) M⊙ yr^(-1) for q_0 = 0.5(0.1), or dust extinction effects are important, or the object is not the DLA. In any case, our images suggest compact, somewhat clumpy objects at best, rather than large, well-formed proto-galactic disks.