The H I and Ionized Gas Disk of the Seyfert Galaxy NGC 1144 = Arp 118: A Violently Interacting Galaxy with Peculiar Kinematics

摘要

We present observations of the distribution and kinematics of neutral and ionized gas in NGC 1144, a galaxy that forms part of the Arp 118 system. Ionized gas is present over a huge spread in velocity (1100 km s-1) in the disk of NGC 1144, but H I emission is detected over only one-third of this velocity range, in an area that corresponds to the NW half of the disk. In the nuclear region of NGC 1144, a jump in velocity in the ionized gas component of 600 km s-1 is observed. Faint, narrow H I absorption lines are also detected against radio sources in the SE part of the disk of NGC 1144, which includes regions of massive star formation and a Seyfert nucleus. The peculiar H I distribution, which is concentrated in the NW disk, seems to be the inverse of the molecular distribution that is concentrated in the SE disk. Although this may partly be the result of the destruction of H I clouds in the SE disk, there is circumstantial evidence that the entire H I emission spectrum of NGC 1144 is affected by a deep nuclear absorption line covering a range of 600 km s-1 and is likely blueshifted with respect to the nucleus. In this picture, a high column density H I stream is associated with the nuclear ionized gas velocity discontinuity, and the absorption effectively masks any H I emission that would be present in the SE disk of NGC 1144.