The Extended Narrow‐Line Region of 3C 299

We present results of HST observations of the radio galaxy 3C 299. Thebroad-band F702W (R) and F555W (V) images (WFPC2/PC) show an elliptical galaxy,with a comet-like structure extending to the NE in the radio jet direction. The[OIII]$\lambda$5007 emission line map, shows a bi-conical structure centered onthe nucleus, that overlaps the structure found in the broad-band filters. Theradio core coincides with the center of the bi-conical structure and the radioaxes are aligned with the direction of the cones. These data show clearevidence of a strong interaction between the radio jet and the NE morphology ofthe galaxy. We show evidence that this NE region is an ENLR; the line-ratiodiagnostics show that models involving gas shocked by the radio-jet plusionization from a precursor HII region, produced itself by the ionizing photonsof the postshocked gas on the preshocked gas provide a good match to theobservations. We investigate the spatial behavior of the ionizing parameter$U$, by determining the [OIII]/[OII] line ratio which is sensitive to thechange of the ionization parameter, and trace its behavior over the ENLR alongthe radio jet direction. We find that [OIII]/[OII] does not follow a simpledilution model, but rather that it is approximately constant over a large rangeof distance from the nucleus thus requiring a local source of ionization whichseems to be compatible with the shock models driven by the radio jet.Comment: 17 pages, 9 Postscript figures, ApJ accepted, uses aaspp.st