A SEARCH FOR MOLECULAR CLOUDS AT HIGH GALACTIC LATITUDE

Abstract

We carried out CO survey toward IR-excess clouds using SRAO 6-m telescope in search of molecular <TEX>$H_2$</TEX>. These clouds, which show far-infrared excess over what is expected from HI column density, are considered to be candidates of molecular clouds. In order to find new high Galactic latitude clouds, we made mapping observations for 14 IR-excess clouds selected from Reach et al.(1998) in <TEX>$^{12}CO$</TEX> J = 1 - 0 line, supplementing the similar survey in southern hemisphere (Onishi et al. 2001). <TEX>$^{12}CO$</TEX> emission is detected from three IR-excess clouds among 14 objects. Three newly detected clouds exhibit somewhat clumpy morphology and column densities amount to <TEX>${\sim}10^{21}\;cm^{-2}$</TEX>. One of three clouds, DIR120-28, show discrepancy between IR-excess center and CO emission center. It seems that IR-excess may not be an effective tracer of molecular gas. Instead, optical depth<TEX>$(\tau)$</TEX> excess, i.e., IR-excess corrected for temperature dependence, may be more effective tracer of molecular clouds, since, by combining statistics from both hemispheres, we found that the detection rate is higher for IR-excess clouds with lower dust temperature.