ABSTRACT

The infrared luminous galaxy MK 231 appears to exhibit characteristics similar to those of active galactic nuclei — it has been classified as a Seyfert 1 system. However, it has been shown to contain 3 ×x 1010 M⊙ of gas via CO observations. If the CO is confined to the region shielded by dust as in galactic molecular clouds, the molecular gas occupies a much smaller volume than previously thought. The ultimate questions are which characteristic is primarily responsible for most of the luminosity and whether AGN and starbursts are interdependent or coincidental.

THE SUPERGIANT MOLECULAR CLOUD

Scoville et al. (1989) and Radford et al. (1991) have discussed the physical conditions implied by the molecular observations of MK 231. It is inferred from CO observations, that 3 × 1010 M⊙ of molecular gas (H2) resides within a volume of radius RCo < 3 kpc. However, recent infrared observations reveal that the emission from dust at λ ≃ 10 μm arises within a volume of size RIR < 400 pc (Keto et al. 1992). This is an important complementary result to the CO observations because studies within our galaxy show clearly that the molecular gas is largely confined to the region shielded by dust extinction (Young et al. 1982).