THE ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, 100:125-131, 1995 September

       AN OUT-OF-PLANE CO (J = 2-1) SURVEY OF THE MILKY WAY. I. THE DATA

       Seiichi Sakamoto,[1,2] Tetsuo Hasegawa,[1] Masahiko Hayashi,[2,3]
                   Toshihiro Handa,[1] and Tomoharu Oka[1,2]


                                   ABSTRACT

        We present extensive CO (J = 2-1) survey data of the first quadrant
     of the Galaxy taken with the same angular resolution as the Columbia
     CO (J = 1-0) survey.  The CO (J = 2-1) data were compared with the CO
     (J = 1-0) data of Cohen, Dame, & Thaddeus [1986, ApJS, 60, 695].  The
     distribution of CO (J = 2-1) emission mimics that of CO (J = 1-0)
     emission with the CO (J = 2-1)/CO (J = 1-0) intensity ratio (defined
     as R_(2-1/1-0)) of 0.66 averaged over the observed area.  This value
     is typical of nearby giant molecular clouds and of gas disks of spiral
     galaxies and is consistent with the CO emission arising from
     subthermally excited, optically thick gas.  Molecular gas in the inner
     part of the Galaxy tends to exhibit a higher value of R_(2-1/1-0) than
     in the solar neighborhood.

     Subject headings: Galaxy: structure -- ISM: molecules -- surveys

[1] Postal address: Institute of Astronomy, University of Tokyo, Mitaka,
    Tokyo 181, Japan.
[2] Department of Astronomy, University of Tokyo, Bunkyo-ku, Tokyo 113, Japan.
[3] Present address: National Astronomical Observatory, Mitaka, Tokyo 181,
    Japan.