High-resolution imaging of forbidden Fe II 1.64 microns, Brackett-gamma, and H2 1-0 S(1) emission in the starburst galaxy NGC 253

Abstract

We present 1" resolution imaging of the nuclear region of the starburst galaxy NGC 253 in the near-infrared lines of [Fe II] 1.64 microns, Brackett-γ, and H_2_ 1-0 S(1), together with the adjacent continuum. The data reveal an emission region extended some 10" northeast of the nucleus, with several embedded compact peaks or hot spots. The continuum and the three spectral lines have the same general distribution but differ in detail. The line emission from H_2_ and Brγ are closely matched in the circumnuclear region. However, the H_2_ emission reveals wispy structures which are more prominent to the northwest of the nucleus. We propose that the Brγ and H_2_ emission lines are excited in star formation regions and that the [Fe II] emission traces the distribution of supernova remnants. The hot spots are compact (<= 12 pc) circumnuclear star formation regions containing a mixture of H II regions, supernova remnants, and supergiants. There is evidence that many of the supernova remnants in NGC 253 may be more luminous than their counterparts in the Galaxy. These observations constrain the stellar populations in the circumnuclear region and indicate that the radio emission is dominated by nonthermal emission processes.