A search for the damped Ly alpha absorber at z=1.86 toward QSO 1244+3443 with NICMOS

We have carried out a high-resolution imaging search for the galaxy associa ted with the damped Ly alpha absorber (DLA) at z = 1.859 toward the z(em) = quasar QSO 1244+3443, using the Hubble Space Telescope (HST) and the near- infrared camera and multiobject spectrometer (NICMOS). Images were obtained in the broad filter F160W and the narrow filter F187N with camera 2 on NIC MOS with the goal of detecting the rest-frame optical continuum and the H a lpha line emission from the DLA. After point-spread function (PSF) subtract ion, two weak features are seen at projected separations of from 0."16-0.". 24 the quasar. Parts of these features may be associated with the DLA, alth ough we cannot completely rule out that they could be artifacts of the PSF. If associated with the DLA, the objects would be approximate to1-2 h(70)(- 1) kpc in size with integrated flux densities of 2.5 and 3.3 mu Jy in the F 160W filter, implying luminosities at lambda (central) = 5600 Angstrom in t he DLA rest frame of 4.4-5.9 x 10(9) h(70)(-2) L. at z = 1.86, for q(0) = 0 .5. However, no significant H alpha line emission is seen from these object s, suggesting low star formation rates (SFRs). Our 3 sigma upper limit on t he SFR in the DLA is 1.3 h(70)(-2) M. yr(-1) for q(0) = 0.5 (2.4 h(70)(-2) M. yr(-1) for q(0) = 0.1). This together with our earlier result for LBQS 1 210+1731 mark a significant improvement over previous constraints on the st ar formation rates of DLAs. Dust within the DLA could extinguish Ha emissio n, but this would require the dust content in the DLA to be much higher tha n that inferred from previous DLA observations. A combination of low star f ormation rate and some dust extinction is likely to be responsible for the lack of H alpha emission. Alternatively, the objects, if real, may be assoc iated with the host galaxy of the quasar rather than with the DLA. In any c ase, our observations suggest that the DLA is not a large bright protodisk, but a compact object or a low surface brightness galaxy. If the two featur es are PSF artifacts or associated with the quasar host, then the constrain ts on the size and luminosity of the DLA are even more severe.