CO-Line Emission from the Clumpy Irregular Galaxy Markarian 297

Abstract 12CO (J = 1–0)-line emission has been detected in the direction of the clumpy irregular galaxy Mrk 297 (Arp 209, NGC 6052). The CO emission region is compact, associated with the brightest optical knots and slightly extended toward the east. The estimated molecular mass is ~ 5 × 109 M⊙, comparable to the HI mass. The FIR-to-CO luminosity ratio suggests that this galaxy is a typical star burster. The kinematics of the CO and H I gases are discussed based on a radial-penetration encounter model of two galaxies on the line of sight. A mildly disturbed component, which is seen nearly face-on, contains both H I and molecular gas, and the tidal disturbance may have caused the active star formation in dense molecular clouds. On the other hand, the more disturbed edge-on component contains much H I, but little molecular gas, which may have become dissociated during a tidal encounter.