A kinematic search for supernova remnants in giant extragalactic H II regions

We have obtained velocity fields of the Giant H II complexes NGC 5471 in M101, NGC 2363 in NGC 2366, and the largest H II region in NGC 2403 from Ha observations using the TAURUS imaging Fabry-Perot interferometer. We have detected five Ha sources with velocity profiles which are broad when compared with the surrounding H II region. Region B in NGC 5471 has been previously determined to contain a supernova remnant by the presence of nonthermal radio continuum radiation and enhanced [O I] and [S II] emission (Skillman 1985) and broad Hα emission (Chu & Kennicutt 1986). Two broad Ha sources in NGC 2363 coincide with regions where strong splitting has been found in the [O III] line (Roy et al. 1991). Two more broad Ha sources have been identified in the largest H II region in NGC 2403. VLA radio continuum observations with a resolution of 2″ at λ6 and λ20 cm of all 3 H II complexes are presented. In addition, high resolution (subarcsecond) VLA images of NGC 5471 were made at λ2 and λ6 cm. The presence of a nonthermal source in region NGC 5471 B was confirmed while region NGC 5471 A appears to be dominated by thermal emission. The nonthermal spectral index in NGC 2363 A indicates the existence of one or more supernova remnants at the position of a large velocity width source detected in Hα emission. No similar nonthermal sources were detected in NGC 2403 # 1. Supernovae explosions and stellar winds are considered as causes for these large velocity width sources (LVWS). If the emission from the LVWSs is attributed to single supernova remnants, they are unusually luminous in both nonthermal radio continuum and Hα emission. The very large Hα luminosities could be a result of high velocity gas being ionized by the neighboring stellar cluster.