| Abstract | The Parkes 64-m radio telescope has been used to make H I and H2CO observations of the lenticular galaxy NGC 5128 with improved resolution and to detect OH absorption in the same galaxy. The H I profile (4 km/s resolution) is shown to be generally typical of any edge-on galaxy with well-defined rotation. The H I mass is estimated to be about 1 billion solar masses, and a total mass of 400 billion solar masses is derived on the assumption that the galaxy is viewed edge-on. Five H I absorption components are identified, with the strongest at 551 km/s centered on the optical nucleus. The 1667-MHz OH observations (0.8 km/s resolution) yield absorption features at 551 km/s and possibly at 546 km/s. The 4830-MHz H2CO spectrum, obtained with a resolution of 0.5 km/s, shows three well-defined absorption features together with a fainter feature at 547.9 km/s. Additional H2CO absorption was detected southeast of the nucleus. Noting that all the absorption velocities are higher than the systematic velocity of 535 km/s, it is concluded that if the absorption is against the nucleus, such velocities can only be explained by infalling gas clouds probably associated with the dust lane. |
