A Survey for High-Latitude Molecular Clouds toward Infrared-Excess Clouds with NANTEN

Abstract

Abstract A survey for high Galactic latitude molecular clouds was carried out toward the far-infrared-excess clouds of Reach et al. (1998, AAA 070.131.207) using the NANTEN telescope. All 68 infrared-excess clouds that are observable from NANTEN were mapped in the $J = 1 \hbox{--} 0$ line of 12CO. CO emission was detected from 32 infrared excess clouds, corresponding to a CO detection rate of 47%. Most of these CO clouds were identified and mapped as high-latitude clouds for the first time. The CO detection rate for the cold ($T_\mathrm{dust} \lt 17 \,\mathrm{K}$) infrared excess clouds is 72%, which is more than a factor of two higher than that of warmer ones, 33%. This indicates that the cold clouds are well shielded from external UV radiation, resulting in a high CO abundance and a low temperature of the clouds. The infrared-excess clouds with no CO emission are most likely to be molecular hydrogen clouds because the temperature is similar to, or lower than, that of the surrounding H i gas. The molecular gas without CO emission seems to occupy more than 90% of the area of the infrared-excess clouds.