NGC1275: a BL Lacertae object?

Abstract

NGC1275 APPEARS in Seyfert's list1 of galaxies which have many high excitation emission lines in the nuclei. Seyfert remarks that all the emission lines in these galaxies are unusually broad. Khachikian and Weedman2 separated the Seyfert galaxies into two classes In class 1, the Balmer lines are broader than the forbidden lines; in class 2, the forbidden lines and Balmer lines are the same width. The lines in class 2 galaxies have full widths at half maximum intensity typically between 500 and 1,000 km s−1. These widths are generally greater than those of the forbidden lines in class 1 objects, but the Balmer lines in class 1 objects are usually several thousands of km s−1 wide. Class 2 Seyferts are also characterised by an extremely high [O(III)] : Hβ ratio. There are also significant differences in the UBV colour amongst Seyfert of class 1 and 2, the class 1 Seyfert's having larger UV excess. NGC1275 was called a Seyfert 2 galaxy by Khachikian and Weedman2, as it showed no indication of the broad, intense Balmer lines that characterised class 1 Seyferts, the forbidden lines widths and its [O(III)] : Hβ ratio were similar to those in class 2 Seyferts: however, the emission lines were very weak relative to the continum. Moreover, there was an extended system of Hα filaments having about the recession velocity of the galaxy3. It is not known how much of the emission lines seen in the nucleus comes from these filaments projected on it. I suggest here, on the basis of its weak emission line spectrum, its lack of the characteristic broad hydrogen lines and the variability and polarisation of its nucleus, that NGC1275 should be called a BL Lactertae object rather than a Seyfert galaxy.