Star Formation Associated with the X‐Ray Jet in Centaurus A

Abstract

Blue stars are identified in the region of the inner gaseous filaments in the radio lobe northeast of the main body of the radio galaxy Centaurus A (NGC 5128). Comparison between the X-ray images recently acquired with the Chandra Observatory and optical images shows that the X-ray jet passes just north of the diffuse region DF 6 identified by Dufour & van den Bergh (1978). In an 88 × 88 field centered on the inner filaments, UBV photometry has been obtained for stars brighter than V = 24.5 mag. The photometry has been used to identify 31 blue stars with V brighter than 23.0 mag. Positions, photometry, and finding charts are given. We believe that most of these stars formed from the interaction of the jet with local concentrations of dust and gas. DF 6 itself is resolved into a tight association of blue stars that are evidently young. Other loose groups are observed and compared with the loose aggregates seen farther out. The brightest blue stars are presumably the youngest stars and tend to lie close to the X-ray jet. We suggest that the raw material for star formation is found in dust patches of small angular size in the area and that star formation is triggered by shocks initiated by the jet. The brightest blue object, with V = 18.85 mag, is most likely a peculiar foreground star and a point X-ray source. The second brightest blue object, with V = 20.11 mag, is slightly diffuse and thus probably an unresolved cluster at the distance of NGC 5128.