2006ApJ...642..307Y

We have performed large-scale CO observations with the millimeter/submillimeter telescope NANTEN toward a FIR looplike structure whose angular extent is ∼20°x20° around (l,b)~(109°,-45°) in Pegasus. Its diameter corresponds to ∼25 pc at a distance of 100 pc, adopted from that of the star HD 886 (B2 IV) near the center of the loop. We covered the looplike structure in the ¹²CO (J=1-0) emission at 4'-8' grid spacing and in the ¹³CO (J=1-0) emission at 2' grid spacing for the ¹²CO-emitting regions. The ¹²CO distribution is found to consist of 78 small clumpy clouds of mass 0.04-11 M_☉, of which ∼83% have very small masses <1.0 M_☉. ¹³CO observations revealed significant ¹³CO emission in 18 of the 78 ^ 12^CO clouds. ¹³CO emission was detected in the region where the column density of H₂derived from ¹²CO is >5x10²⁰/cm2, corresponding to A_V∼1 mag, which takes into account that of H I. We find no indication of star formation in these clouds in the IRAS and 2MASS point source catalogs. The very low mass clouds, M≤1 M_☉, identified are unusual in that they have a very weak ^ 12^CO peak temperature of 0.5-2.7 K and that they aggregate in a region of a few parsecs with no main massive clouds; in contrast, similar low-mass clouds <1 M_☉in other regions previously observed including those at high Galactic latitude are all associated with more massive main clouds of ∼100 M_☉. Comparison with a theoretical work on molecular cloud formation suggests that the very low mass clouds may have been formed in the shocked layer through thermal instability. HD 886 may be the source of the mechanical luminosity via stellar winds to create shocks, forming the looplike structure where the very low mass clouds are embedded.