Jet-induced emission-line nebulosity and star formation in the high-redshift radio galaxy 4C 41.17

The high-redshift radio galaxy 4C 41.17 has been shown in earlier work to c onsist of a powerful radio source in which there is strong evidence for jet -induced star formation along the radio axis. We argue that nuclear photoio nization is not responsible for the excitation of the emission line clouds, and we construct a jet-cloud interaction model to explain the major featur es revealed by the detailed radio, optical,: and spectroscopic data of 4C 4 1.17. The interaction of a high-powered (similar to 10(46) ergs s(-1)) jet with a dense:cloud in the halo of 4C 41.17 produces shock-excited emission- line nebulosity through similar to 1000 km: s(-1) shocks and induces star f ormation. The C rv luminosity emanating from the shock implies that the; pr eshock density in the line-emitting cloud is high enough (hydrogen density similar to 1-10 cm(-3)) that shock-initiated star formation could proceed o n a timescale (similar to a few x 10(6) yr) well within the estimated dynam ical age (similar to 3 x 10(7) yr) of the radio source. Broad (FWHM approxi mate to 1100-1400 km s(-1)) emission lines are attributed to the disturbanc e of the gas cloud by a partial bow shock, and narrow emission lines (FWHM approximate to 500-650 km s(-1); in particular, C rv lambda lambda 1548, 15 50) arise in precursor emission in relatively low-metallicity gas or in sho cked line emission in the lateral regions of the bow shock. The implied baryonic mass similar to 8 x 10(10) M-circle dot of the cloud i s high and implies that Milky Way size condensations existed in the environ ments of forming radio galaxies at a redshift of 3.8. Our interpretation of the data provides a physical basis for the alignment of the radio, emissio n-line, and UV continuum images in some of the highest redshift radio galax ies, and the analysis presented here may form a basis for the calculation o f densities and cloud masses in other high-redshift radio galaxies.