A&A 424, 107-118 (2004)
The optical-near-infrared colour of the host galaxies of BL Lacertae objectsJ. K. Kotilainen1 and R. Falomo2
1 Tuorla Observatory, University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland
2 INAF - Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
(Received 26 February 2004 / Accepted 24 May 2004 )
We present H-band (1.65 m) imaging of 23 low redshift ( z 0.3) BL Lac objects that were previously investigated by us in the optical R-band. For all the observed objects, the host galaxy is clearly detected and well represented by an elliptical model, with average scale length R(e) = 7.2 3.6 kpc and average absolute magnitude M(H) = -25.9 0.6. BL Lac hosts are therefore luminous (massive) elliptical galaxies indistinguishable from those of low redshift radio galaxies and inactive ellipticals. The best-fit H-band Kormendy relation of = 3.7 log (kpc) + 14.8 mag arcsec -2 is in agreement with that obtained for normal ellipticals and radio galaxies. This structural and dynamical similarity indicates that all massive elliptical galaxies can experience nuclear activity without significant perturbation of their global structure.
Key words: galaxies: BL Lacertae objects: general -- galaxies: active -- galaxies: elliptical and lenticular, cD -- galaxies: nuclei -- galaxies: photometry -- infrared: galaxies
© ESO 2004