An extensive spectrophotometric survey of galaxies with star-burst nuclei was conducted to investigate their basic astrophysical properties and to discover their relationship to other extragalactic objects. Observations of 102 star -burst nuclei were obtained with the 1.6-m telescope of the Penn State Black Moshannon Observatory using a SIT vidicon detector. These objects, which were primarily selected from the Markarian lists, have spectra characterized by strong, narrow, low-ionization emission lines. Their UBV colors, emission-line properties, and radio continua can be consistently explained by the presence of a young, hot star population. The star-burst nuclei are distinguishable from Seyfert nuclei at every wavelength. With the H(PROPORTIONAL) line luminosities ranging from 10('40) to 6 x 10('42) erg s('-1), the total mass of ionizing stars was estimated as 10('7) M(,(CIRCLE)) for the weakest sources to 10('9) M(,(CIRCLE)) for the strongest. The narrow emission-line widths (FWHM < 250 km s('-1)) indicate that the activity is confined to a small central region on the order of a few hundred parsecs in diameter. However, it appears that the gas and the associated young star population are not in dynamic equilibrium with the original nuclear contents; i.e., the median velocity dispersion for the emission lines is about two times smaller than the median value for spectral absorption features of spiral galactic nuclei. Infrared J, H, and K magnitudes are now available for 50 star-burst nuclei. There is no correlation between the infrared and emission-line radiation from these objects. The near-infrared data, therefore, refer primarily to the old, cool star population. The space densities of this star-burst nuclei sample were tabulated as a function of H(PROPORTIONAL) luminosity. Between the reddening correlated ((DELTA)L(H(PROPORTIONAL)) = 3.6) luminosity range of 10('40) erg s('-1) < L(H(PROPORTIONAL)) < 6 x 10('42) erg s('-1), the total space density was found to be 0.0011 Mpc('-3). These galaxies account for 30-50% of the Markarian samples with M(,p) from -17.5 to -22.5 and 3% of the field galaxies in this absolute magnitude range. If all field galaxies can develop nuclear star bursts, then 4.5 x 10('8) years of every galaxy's life is spent with this nuclear activity present. This is equivalent to approximately 40 generations of host stars being created within the nucleus of every field galaxy having a M(,p) in the specified range. Explaining the source of the large gas supply needed for this kind of activity and predicting the possible future of these galaxies with intense nuclear star formation are problems which remain to be investigated in more detail.
- Pub Date:
- March 1982
- Physics: Astronomy and Astrophysics;
- Galactic Nuclei;
- Stellar Radiation;