Multicolour surface photometry of NGC 4486 (M87) and its jet ⋆

Abstract

High-resolution UBVRI surface photometry of the nearby elliptical NGC 4486 (M87) is presented. The subtraction of the contributions of the unresolved nuclear component and the jet structure allows an accurate study also of the inner galaxy regions. The major axis of the core isophotes is found to be aligned with the jet axis, while in the region >3 arcsec the isophotes are, on the contrary, nearly perpendicular to it. On the basis of photometry performed on the isolated jet structure, a change of the spectral index at the position of knot A onwards is found to be significant at the 3σ level. In addition, the radio-optical spectral index in the eastern radio lobe is shown to steepen in the surroundings of the hotspot. The available kinematic data are found to have insufficient resolution to be constrained by the photometric results to verify the presence of a supermassive black hole