1-4 micron spectrophotometry of dust in the Taurus dark cloud: Water ice distribution in Heiles Cloud 2

We have conducted near infrared spectroscopy of 61 background stars toward Heiles Cloud 2 in the Taurus molecular cloud complex. We used a low-dispers ion spectrometer, PASP2, which can simultaneously obtain the spectrum with a wavelength coverage between 1.3 and 4.2 mu m. For 56 of 61 objects, the v isual extinction (A(V)) and the optical depth of water ice at lambda = 3.1 mu m (tau(ICE)) have been estimated: for 50 of 56 objects, these were syste matically estimated from our data only. In order to investigate the water i ce distribution in Heiles Cloud 2, we have constructed a "water ice map" in which tau(ICE), is plotted at the position of each object. The water ice m ap is then compared with the (CO)-O-18 (J = 1-0) Map obtained by millimeter observations performed by Sunada & Kitamura. We find that the distribution of water ice is closely correlated with that of (CO)-O-18. Strong water ic e absorption is seen only toward the dense (CO)-O-18 clumps, while less wat er ice absorption is detected toward the outer region of the cloud. There i s an A(V) threshold for the positive ice detection (A(V0)), as suggested by previous observations, but with a significant scatter; A(V0) = 2-5 mag. Th e scatter might be caused by the different contribution of the inner water- containing portion of the cloud along the line of sight. The value of tau(I CE) increases with increasing of A(V) and the slope of Delta tau(ICE)/Delta A(V) is 0.067, consistent with the previously observed values for the Taur us molecular cloud.