Nonthermal continuum radiation in three elliptical galaxies

Optical, infrared, and radio observations are presented for three elliptical galaxies (NGC 6454, B2 1652+39, and B2 1101+38) which have flat high-frequency radio spectra. Two of these galaxies emit optical nonthermal continuum radiation, as evidenced by linear polarization of the ultraviolet radiation of the nuclei. No emission lines were detected in the optical spectra of the galaxies, and in that respect they may be related to the BL Lacertae class. The redshifts were obtained from the Ca II H- and K-lines and the G-band in absorption. These galaxies appear to form a sequence by order of increasing contribution of a nonthermal source to the luminosity of the nuclear regions, and their optical properties appear to be intermediate between those of ordinary ellipticals and those of objects like BL Lacertae.