Star Formation in the Radio Galaxy NGC 4410A

The NGC4410 group of galaxies provides us a rare opportunity to study anearby (97 h75^-1 Mpc) example of a radio galaxy (NGC4410A) embedded in anextended X-ray source, with evidence for star formation that can be readilyspatially distinguished from regions dominated by the AGN and shocks. Wepresent broadband and narrowband optical images along with optical and IUEultraviolet spectroscopy for the radio galaxy NGC 4410A and its companion NGC4410B. Our H-alpha+[NII] images reveal six luminous HII regions (L_H-alpha ~1e40 erg/s distributed in an arc near NGC 4410A. Partially completing the ringis a prominent stellar loop containing diffuse ionized gas. This filamentarygas, in contrast to the H II regions, shows spectroscopic signatures of shockionization. The star formation in this system may have been triggered by acollision or interaction between the two galaxies, perhaps by an expandingdensity wave, as in classical models of ring galaxies. Alternatively, the starformation may have been induced by the impact of a radio jet on theinterstellar matter. Extended Ly-alpha is detected in the ultraviolet IUEspectrum. The ultraviolet continuum, which is presumably radiated by thenucleus of NGC4410A, is not extended. NGC4410A appears to be interacting withits neighbors in the NGC4410 group, and could be an example of a spiral galaxytransforming into an elliptical.Comment: 33 pages, 9 figures. Accepted for publication in April, 2002 A