@phdthesis{oai:nagoya.repo.nii.ac.jp:00009418,
 author = {山本, 宏昭 and Yamamoto, Hiroaki},
 month = {Sep},
 note = {We have carried out the high Galactic molecular clouds observations with the NANTEN telescope in order to reveal the distribution and physical properties of molecular clouds at high Galactic latitude. The three types of an observation have been executed at high Galactic region.Firstly, a Survey for high Galactic latitude molecular clouds was carried out toward the 68 of far-infrared-excess clouds of Reach et al. (1998) by using  12CO(J=1-0) line.  CO emission was detected from 32 infrared excess clouds, corresponding to the detection rate of 47%.  The CO detection rates for the cold and warm infrared excess cloud whose dust temperature are lower and higher than 17K is 72% and 33%, respectively.  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 HI gas.  The molecular gas without CO emission seems to occupy more than 90% of the area of the infrared-excess clouds. Next, we carried out a CO survey of high Galactic latitude molecular clouds toward an HI filament including MBM 53, 54, and  55.  We covered the whole area of the HI filament in 12CO  (J=1-0) with a 4′grid spacing.  The filament consists of many clumpy molecular clouds.  110 12CO clouds are identified and total mass is estimated to be ～1200M⊙ .13CO (J=1-0) observations were carried out toward the region of high 12CO intensities in order to  measure the optical depth of molecular gas.There is no detection in C^18O (J=1-0) line in the observed region.  This indicates that there are no clouds dense enough to lead star-formation in the near future.These observations spatially resolved the entire gas distribution of MBM 53,54, and 55 for the first time, and we have found a massive cloud, HLCG 92-35 whose mass is ～330M⊙, corresponding to 1/4 of the total mass.  This CO cloud occupies the Galactic western half of a circular HI cloud toward (l, b) ～ (92°,-35°) , and the HI to CO mass ratio is estimated to be the largest in the observed region.  Far-infrared-excess clouds toward HLCG 92-35 are the largest in the observed region.  The ratio of the luminosity of the infrared excess to CO mass is also significantly larger than those of the other clouds, by a factor of ～5.  These facts indicate that HLCG 92-35 is a CO-forming molecular cloud, which is younger than the MBM clouds in terms of molecular cloud formation.  Some past explosive event has been suggested by Gir et al. (1994) toward the HI filament. Toward HLCG 92-35, the molecular gas distributed along the western edge of the HI cloud, which implies that the molecular gas may be formed by a compression of expanding HI shell. Finally, we carried out large scale CO observations toward a loop-like structure in far infrared whose angular extent is about 20x20 degree around (l, b) ~(109°, -45°) in Pegasus whose diameter corresponds to ～26 pc at a distance of 100 pc, the same as that of a star HD886 (B2IV) at the center of the loop.  We covered the loop-like 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 12 CO emitting regions.  The 12CO distribution is found to consist of 78 small clumpy clouds whose mass ranges from 0.04 M⊙ to 11 M⊙ . Interestingly, about 83% of the 12CO clouds have very small masses less than 1.0 M⊙.13CO observations revealed that 19 of the 78 12CO clouds show significant 13CO emission.  13CO emission was detected the region where the molecular column density of 12CO clouds is greater than 5x20^20 cm^{-2},  corresponding to Av of ～1 mag.  We find no indication of star formation in these clouds in IRAS Point Source Catalog and 2MASS Point Source Catalog.  The very low mass clouds identified are unusual in the sense that they have very weak 12CO Tpeak of 0.5 K-2.7 K and that they aggregate in a region of a few pc with no main massive clouds; contrarily to  this, similar low mass clouds less than 1 M⊙ are seen in the other regions previously observed including high Galactic latitude are all associated with more massive main clouds of ～100 M⊙.  A comparison with a theoretical work on molecular cloud formation (Koyama & Inutsuka 2002) suggests that the very small clouds may have been formed in the shocked layer through the thermal instability.  The star HD886 (B21V) may be the source of the mechanical luminosity via stellar winds to create shocks, forming the loop-like structure where the very small clouds are embedded., 名古屋大学博士学位論文 学位の種類:博士(理学) (課程) 学位授与年月日:平成17年9月30日},
 school = {名古屋大学, Nagoya University},
 title = {An Observational Study of Molecular Clouds at High Galactic Latitude},
 year = {2005}
}