The nature of optical features in the inner region of the 3C 48 host galaxy

The well-known quasar 3C 48 is the most powerful compact steep-spectrum radio-loud QSO at low redshifts. It also has two unusual optical features within the radius of the radio jet (similar to 1): (1) an anomalous, high-velocity narrow-line component, and (2) a bright continuum peak (3C 48A) similar to 1 northeast of the quasar. Both of these optical features have been conjectured to be related to the radio jet. We have obtained Gemini North GMOS integral field unit (IFU) spectroscopy of the central region around 3C 48. We use the unique features of the IFU data to remove unresolved emission at the position of the quasar. The resolved emission at the wavelength of the high-velocity component is peaked <= 0.25 north of the quasar, at the same position angle as the base of the radio jet. These observations appear to confirm that this high-velocity gas is connected with the radio jet. However, most of the emission comes from a region where the jet is still well collimated, rather than from the regions where the radio maps indicate strong disruption. We also present the results of HST STIS spectroscopy of 3C 48A. We show that 3C 48A is dominated by stars with a luminosity-weighted age of similar to 1: 4; 10(8) yr, substantially older than any reasonable estimate for the age of the radio source. Thus, 3C 48A almost certainly cannot be attributed to jet-induced star formation. The host galaxy of 3C 48 is clearly the result of a merger, and 3C 48A seems much more likely to be the distorted nucleus of the merging partner in which star formation was induced during the previous close passage.