VLA detection of OH absorption from the elliptical galaxy NGC 1052

Abstract

VLA observations of OH absorption towards the elliptical galaxy NGC 1052 are presented. Both OH lines, at 1665 and 1667 MHz, were detected in absorption towards the center of NGC 1052. The hyperfine ratio of the two OH lines ($\tau$$_{1667}$/$\tau$$_{1665}$) is 2.6$\pm$0.8 as compared to 1.8 expected for the excitation under LTE conditions for an optically thin cloud. The column density of OH is estimated to be $2.73(\pm0.26)\times10^{14} cm^{-2}$ assuming $T_{ex} \sim$10 K. The centers of both the OH lines are redshifted from the systemic velocity of the galaxy by $\sim$173 km s$^{-1}$. The velocity of OH line coincides with the velocity corresponding to the strongest HI absorption. We suggest that OH absorption is arising from a molecular cloud falling towards the nucleus. The OH line, though narrower, is found to be within the much broader and smoother H$_2$O megamaser emission. The possible link between OH/HI and $H_2O$ emission is discussed.