N. Bouche et al., H alpha imaging with Hubble Space Telescope-NICMOS of an elusive damped Lyalpha cloud at z=0.6, ASTROPHYS J, 550(2), 2001, pp. 585-592
Despite previous intensive ground-based imaging and spectroscopic campaigns
and wideband Hubble Space Telescope (HST) imaging of the z = 0.927 QSO 3C
336 field, the galaxy that hosts the damped Ly alpha system along this line
of sight has eluded detection. We present a deep narrowband H alpha image
of the field of this z(abs) = 0.656 damped Ly alpha absorber, obtained thro
ugh the F108N filter of NICMOS1 on board the HST. The goal of this project
was to detect any H alpha emission 10 times closer than previous studies to
unveil the damped absorber. We do not detect H alpha emission between 0."0
5 and 6" (0.24 and 30 h(-1) kpc) from the QSO, with a 3 sigma flux limit of
3.70 x 10(-17) h(-2) ergs s(-1) cm(-2) for an unresolved source, correspon
ding to a star formation rate (SFR) of 0.3 h(-2) M. yr(-1). This leads to a
3 sigma upper limit of 0.15 M. yr(-1) kpc(-2) on the SFR density, or a max
imum SFR of 1.87 M. yr(-1) assuming a disk of 4 kpc in diameter. This resul
t adds to the number of low-redshift damped Ly alpha absorbers that are not
associated with the central regions of Milky Way-like disks. Damped Ly alp
ha absorption can arise from high-density concentrations in a variety of ga
lactic environments including some that, despite their high local H I densi
ties, are not conducive to widespread star formation.