A large-scale jet and FR I radio source in a spiral galaxy: The host properties and external environment

We have identified a large (approximate to 200 h(75)(-1) kpc), powerful dou ble radio source whose host galaxy is clearly a disk and most likely a spir al. This FR I-like radio galaxy is located very near the center of the rich ness class 0 cluster A428. The existence of such an object violates a funda mental paradigm for radio-loud active galactic nuclei (AGNs). In our first paper, we showed that this object was most consistent with a spiral host cl assification with optical emission-line ratios and colors suggestive of an active nucleus. However, we were not able to confirm actual radio jet emiss ion based on the maps available at that time. In this paper, we present new , higher resolution radio imaging, a radio/millimeter continuum spectrum fo r the nucleus, a detection of H I absorption against the bright radio core, an upper limit to CO emission and the gas mass, and 70 (68 new) optical re dshifts measured in the direction of A428. We confirm the existence of a ra dio jet at 20 cm, extending 42 h(75)(-1) into the southern lobe. At 3.6 cm, we also detect a nuclear jet similar in length to that in M87, although 10 times weaker. We believe that this is the first detection of a radio jet o n these scales in a disk/spiral host galaxy. The nuclear radio spectrum is similar to many blazar- or quasar-like objects, suggesting that the galaxy harbors an imbedded and obscured AGN. We model a turnover in the spectrum a t low frequencies as a result of free-free absorption. We detect very stron g and narrow H I absorption, with nearly the entire 20 cm continuum flux of the core being absorbed, implying an unusually large optical depth (tau ap proximate to 1). The most consistent model is that we are viewing the nucle us through a disklike distribution of gas in the interstellar medium, possi bly through a spiral arm or a warp to account for the above-average column density. From the radial velocity distribution, we find that A428 is in fac t made up of at least two clumps of galaxies separated by similar to 3300 k m s(-1), which themselves appear to be imbedded in a nearly continuous dist ribution of galaxies over 13,000 km s(-1) in velocity space. Thus, the envi ronment around this unusual radio source is more like that of a poor galaxy group imbedded in a filament-like structure viewed end-on.