The Carbon Monoxide Distribution in the Inner Galaxy

Abstract

The latitude distribution of the emission from the ¹²CO J=l→0 rotational transition has been surveyed for the region 350° ⩽ 1 ⩽ 25° at b = 0′, “math type po dito”. Most of the ¹²CO emission in the inner Galaxy, the region extending from the galactic center to 4 kpc radius, is produced by three large and massive objects: the nuclear disk/bar, the 3-kpc arm and the “+135 km s⁻¹ feature”. These structures all have observed HI counterparts and each shows extremely large deviations (50–180 km s⁻¹) from circular motion. Observations of ¹³CO in selected directions show that the two structures outside the nuclear disk each span at least 2 kpc in length and that together they imply ⩾ 10⁵⁵ ergs in kinetic energy of expansion away from the galactic nucleus.