Molecular clouds in the Carina arm

From a new survey of the 2.6 mm line of CO in the southern Milky Way, 37 molecular clouds were identified along the Carina arm from l = 282 deg to 336 deg with masses generally greater than 10 to the 5th solar mass. The clouds lie approximately every 700 pc along a spiral segment that is nearly 25 kpc long and has a pitch of about 10 deg. The total mass of these clouds is 40 x 10 to the 6th solar mass, or rougly 1 x 10 to the 6th solar mass each on average. The abrupt tangent point in molecular clouds at l = 280 deg and the characteristic loop structure in the l-v diagram are unmistakable evidence of a CO spiral arm in Carina. This arm apparently connects with the northern hemisphere Sagittarius arm to form a single 10 deg spiral which extends more than two-thirds of the way around the Galaxy.