SPECTRAL EVIDENCE FOR SHOCK-IONIZED GAS ALONG THE JETS OF NGC-4258

We use Fabry-Perot and long-slit spectra with radio, molecular, and X- ray data sets to study the twisted, multistrand jets in the nearby act ive galaxy NGC 4258 (M106). Their several arcminute extent and the ext ensive wavelength coverage of their interaction with the ISM make thes e jets an important laboratory for studying the processes likely to do minate the appearance of high-z radio galaxies. A VLA A-array image at 20 cm traces the jet down to 2 '' (70 pc) radius and shows that it is perpendicular to the subparsec nuclear disk that is delineated by H2O masers. Our long-slit spectra span the jet and range over 3640-8560 A ngstrom at 4.5 Angstrom resolution. We measure a central stellar veloc ity dispersion of 171 km s(-1). This is smaller than the line widths o f the ionized gas and is too low to explain the observed oscillations in the centroids of the emission-line profiles by virial motion within the bulge potential. Mean stellar velocities agree with those of the gas along the jet axis and are consistent with bar-forced motions in t he large-scale disk of the galaxy. From the emission-line flux ratios, we find LINER-like gaseous excitation along the jets and constrain th e gas temperatures. For the N+ and O+ emitting gas, we found that T < 10(4) K, and for the S+ gas T < 19,000 K. The O++ temperature is weakl y constrained to be less than 30,000 K. Flux ratios remain constant al ong the SE jet, with ionization parameter log U approximate to -3.5, O ur models show that these ratios can be generated by approximate to 35 0 km s(-1) shocks velocities consistent with the amplitude of kinemati c oscillations in the emission-line profiles and with the observed the rmal X-ray spectrum of the jet of temperature 0.3 keV. A modest ambien t gas density of 0.2 cm(-3) can produce both the jet's X-ray flux and enough ionizing photons to account for the jet's H alpha flux. In cont rast, the present ionizing flux from the AGN is approximate to 10(3) t imes too low to directly photoionize the jets. Therefore, molecular ga s that is known to lie along the jets may be shocked and photoionized locally as it is entrained. We constrain the star formation induced by the SE jet. The jets do not emit a continuum within the interval lamb da lambda = 0.38-0.88 mu m down to a surface brightness of 3 x 10(-17) ergs cm(-2) s(-1) Angstrom(-1) arcsec(-2).