ON THE NEBULOSITY SURROUNDING THE BL LACERTAE OBJECT PKS 2155-304

High-resolution imaging of the bright BL Lacertae object PKS 2155-304 reveals a symmetric nebulosity extending up to 15" from the nucleus and confirms the presence of a faint galaxy located approximately 4" away from the nucleus. We show that the redshift of z = 0.117, previously attributed to the BL Lac object, pertains in fact to the companion galaxy. The radial brightness profile of the surrounding nebulosity is consistent with that of an elliptical galaxy of effective radius of 4".5 which, assuming an absolute magnitude typical of luminous ellipticals, puts the object at z approximately 0.1. The field of PKS 2155-304 appears to be rich in galaxies, one of which is at z = 0.116. A scenario in which the BL Lac object is hosted by a giant elliptical (M(v) approximately -22.5), which is the brightest member of a group of galaxies, is suggested by our observations.