On the radio and NIR jet of PKS 2155-304 and its close environment

TL;DR

This study uses high-resolution near-IR and radio imaging to explore the environment and jet structures of the bright BL Lac object PKS 2155-304, revealing a faint galaxy group and extended radio jets without NIR or X-ray counterparts.

Contribution

First high-resolution adaptive optics near-IR imaging of PKS 2155-304's environment combined with archival radio data to analyze its faint galaxy group and jet structures.

Findings

Detected an old radio jet ~20 kpc from the nucleus.

Identified a ~2 kpc jet-like structure in radio images.

No counterparts of jets in NIR or X-ray observations.

Abstract

PKS 2155-304 is one of the brightest BL Lac object in the sky and a very well studied target from radio to TeV bands. We report on high-resolution (~ 0.12 arcsec) direct imaging of the field of PKS 2155-304 using adaptive optics near-IR observations in J and Ks bands obtained with the ESO multi-conjugate adaptive optic demonstrator (MAD) at the Very Large Telescope. These data are complemented with archival VLA images at various frequencies to investigate the properties of the close environment of the source. We characterized the faint galaxies that form the poor group associated to the target. No radio emission is present for these galaxies, while an old radio jet at ~ 20 kpc from the nucleus of PKS 2155-304 and a jet-like structure of ~ 2 kpc (~ 1 arcsec) in the eastern direction are revealed. No counterparts of these radio jets are found in the NIR or in archival Chandra observations.