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NGC6946 is a high star formation rate face-on spiral galaxy that has hostedten supernovae since 1917. Not surprisingly, a large number of supernovaremnants and candidates have been identified either as optical nebulae withhigh [S II]:H$\alpha$ line ratios (147) or as compact non-thermal radio sources(35). However, there are only seven overlaps between these two samples. Here,we apply [Fe II] 1.644 $\mu$m emission as a new diagnostic to search forsupernova remnants in an attempt to resolve this discrepancy. [Fe II] isexpected to be relatively strong in the radiative shocks of supernova remnantsand almost absent in HII regions. It is less susceptible to the effects ofabsorption along the line of sight than the optical lines normally used toidentify remnants. Using data from the WFC3 camera on HST}, we identify 132 [FeII] emission nebulae in NGC6946 as likely supernova remnants. Of these, 54align with previously known optical supernova remnants. The remaining 78objects are new; of these 44 are visible in new HST imagery in H$\alpha$ and [SII]. This brings the total number of supernova remnant candidates (from opticaland/or IR data) in NGC6946 to 225. A total of 14 coincidences with radiosupernova remnant candidates (out of 30 in our search area) are found in thisexpanded list. The identification of so many new remnant candidates validatesthe use of [Fe II] imagery for finding remnants, and suggests that previousremnant searches in other galaxies may be far from complete.

The Supernova Remnant Population of NGC6946 as Observed in [Fe II] 1.644 $\mu$m with HST