HIGH-RESOLUTION CO OBSERVATIONS OF NGC-7252 - A COUNTERROTATING CENTRAL MOLECULAR GAS DISK

We report 2".4 resolution interferometric observations of the CO emission in the merger galaxy NGC 7252. The molecular gas concentration around the nucleus of this galaxy is well resolved and shows solid body rotation in a direction opposite to the motion of the ionized gas in the outer parts of the galaxy. The CO surface brightness distribution is complex, yet the kinematics of the molecular gas bears striking resemblance to that of the inner ionized gas disk. The CO can be traced farther into the galactic center than the H-alpha emission, but a small central hole (approximately 300 pc radius) apparently free of gas remains. At larger radii, there is a gap between the molecular gas disk and the outlying atomic gas found in H I maps. The molecular gas observations are discussed in light of recent numerical simulations showing the formation of a kinematically decoupled gas concentration at the center of a merger remnant. Details of the gas distribution as a function of radius may have been produced by powerful winds generated in the active star-forming phase of the recent past. Based on these observations, we suggest that NGC 7252 is well on its way to becoming an elliptical with a counterrotating stellar core.