| Abstract | Results are presented for a study of the optical emission-line spectrum of the active E3 galaxy NGC 1052, 21-cm observations of the galaxy's neutral hydrogen content, and broad- as well as narrow-band Schmidt photography. These observations are examined together with published radio-continuum measurements, and an attempt is made to elucidate the relationship among the optical emission lines, the nuclear radio source, and the observed high neutral hydrogen content. For an elliptical galaxy with normal optical morphology and color, NGC 1052 is found to have some remarkable properties, including a high H I mass fraction corresponding to an H II mass/blue luminosity ratio of 0.05, a compact (diameter, 0.14 pc) variable radio- (and possibly IR-) emitting core, a region 3 kpc in diameter which emits optical emission lines and a nonthermal radio continuum, and velocity structure in the emission lines along the minor axis of the galaxy. The existence of an ionization mechanism that may operate to a greater or lesser extent in the nuclei of all active galaxies is demonstrated, and it is suggested that the energy spectrum of the relativistic particles assumed to originate in the ultracompact nuclear source is one fundamental parameter determining the appearance of an active nucleus. |
