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J.A. Graham (Carnegie-DTM), C.I. Fassett (Williams College)
Blue stars are identified in the region of the inner gaseous filaments (Blanco et al. ApJ 198, L63, 1975) and the X-ray jet (Kraft et al. ApJ 531, L9, 2000) NE of the main body of the radio galaxy NGC5128 (Cen A). Comparison between the X-ray contours and optical images shows that the X-ray jet passes through the diffuse region DF5 and just N of DF6 as identified in Dufour & van den Bergh (ApJ 226, L73, 1978). From the scale on the web image (http://chandra.harvard.edu), the X-ray jet extends there almost to the inner filaments themselves. In an 8\arcmin .8 \times 8 \arcmin .8 field centered on the inner filaments, UBV photometry has been obtained for stars brighter than V = 24m.5. The measurements were made on CCD images obtained with the 2.5m du Pont telescope at Las Campanas Observatory. The photometry has been used to identify faint blue stars which most likely formed from the interaction of the jet with local concentrations of dust and gas. The region DF6 is resolved into a cluster containing luminous blue stars which are evidently very young. Other loose groups are observed but compared with the aggregates seen further out (Graham ApJ 502, 245 1998), these inner stars are spread much more widely over the 9\arcmin field. However, the brightest and presumably the youngest blue stars lie close to the X-ray jet. We suggest that, in this case, the raw material for star formation is to be found in the many small dust patches or globules, seen silhouetted against the galaxy and that star formation is again triggered by shocks initiated by the jet. The brightest blue object, which is measurably diffuse and may be a very young globular cluster, is located at the southern edge of optical knot A (Graham & Price ApJ 247, 813, 1981). Our preliminary photometry is V = 20m.11, B-V = +0m.32, U-B = -1m.09. There are no velocity data for the blue stars but we suspect that they are dispersing into the NGC5128 halo even more rapidly than their counterparts in the outlying field (Fassett & Graham ApJ (in press), 2000).
The author(s) of this abstract have provided an email address for comments about the abstract: graham@jag.ciw.edu