Aperture synthesis of CO emission in extremely luminous infrared galaxies

Abstract

The Owens Valley millimeter-wave interferometer has been used for high-resolution (4"-7") apertuare synthesis mapping of the CO(J + 1-0) emission in the extremely luminous IRAS galaxies, VV 114, NGC 16114, VII Zw 31, and Mrk 231. The bolometric luminoisities of these galaxies are between 4 x 10^11^ and 3 x 10^12^ L_sun_. In the latter three, the interferometeric observations reveal the existence of compact emission sources centered on the optical/infrared nulcei; in VV 114 two concentrations of emission, extending over an area approximately 4 kpc in extent are seen. The derived masses of molecular hydrogen gas in these concentrations are in the range 0.6-5.6 x 10^9^ M_sun_. In Mrk 231, the entire single-dish CO flux is detected in a compact source <7" in size, correspongind to 3 kpc radius. In VV 114, NGC 1614, and VII Zw 31, the compact emission regions account for approximately 30% - 58% of the total single-dish CO flux. The mean molecular gas surface densities averaged over each of the compact regions read 3000 M_sun_ pc^-2^, a factor of 30 higher than obtained for corresponding regions in the nculeus of the Galaxy. We suggest that the concentration of large masses of molecular gas in galactic nuclei initiates energetic activity in these galaxies via a nuclear starburst and possible resutls in the formation of an AGN.