Discovery of a very red nucleus in the radio elliptical IC5063 (PKS2048 – 57)

Abstract

We report here the discovery of an extremely red IR source in the nucleus of the elliptical galaxy IC5063 (PKS2048 – 57). The observed (2.2–3.8) µm colour index within a 5 arc s aperture is 2.1 mag while the colours at shorter wavelengths and in the 5–10 arc s annulus around the nucleus are close to those of normal elliptical galaxies. The IR excess could arise from a BL LAC type nucleus with a steep non-thermal spectrum (α ∼ −4.5 defined by F α vα), similar to the recently identified ‘red QSOs’ typified by 1413 + 135 (refs 1, 2).