The active elliptical galaxy NGC 1052

A radio and optical study is presented of the active elliptical galaxy NGC 1052. Spectrophotometry scans and spatially resolved optical spectra of the nuclear regions have been obtained. The emission-line intensities are closely matched by a shock-heating model with a shock velocity of 130km/s and a pre-shock particle number density of 3/cm³. The diameter of the emission-line region is measured to be 20 arcsec which is the same as the diameter of the radio halo observed with short-baseline interferometers. Consideration is given to the origin of the shocks and it is shown that the thermal pressure in the shocked gas is comparable with the relativistic gas pressure provided by the electrons which are responsible for the synchrotron emission from the radio halo. Furthermore the total luminosity of the compact nuclear radio source, known from VLBI measurements to have a diameter of O.14 pc, is ample to drive both the radio halo and the optical emission lines. The mass of ionized gas in the galaxy is shown lo be about 5 × 10⁵M_⊙ and the volume filling factor to be 4 × 10⁻⁶. New 21-cm observations of the galaxy show the presence of an emission line with a width of 470±50km/s and an intensity corresponding to a neutral hydrogen mass of $$(2.2^{+0.6}_{-1.3})\times 10^9 M_\odot$$. The hydrogen mass to blue luminosity ratio is 0.05 in solar units. It is shown that if the neutral hydrogen is distributed in space like the stars, then it provides the ambient interstellar density necessary to explain the conditions in the shock waves. The optical emission lines and possibly also the 21-cm line show velocity structure along the minor axis of the galaxy. Schmidt photographs in the light of Hα and a broader red band do show the 20 arcsec nuclear-emission line region but do not give any evidence for a more extended distribution of recombining gas.