JWST View of the Supernebula in NGC 5253. I. Overview and Continuum Features

Abstract

We present 5-28$\mu$m imaging spectroscopy of the "supernebula" in the dwarf galaxy NGC 5253 made with the JWST MIRI-MRS integral field spectrometer. NGC 5253 hosts a luminous ($L\sim 10^9{\mathrm{L}}_{\odot }$) HII region, powered by a giant young star cluster, a possible local analogue to super star cluster formation at Cosmic Dawn and Noon. In this paper, the first in a series about the mid-infrared line and continuum emission in the center of NGC 5253, we present an overview and continuum spectra. The mid-infrared images reveal four continuum sources that we identify as hot dust emission from luminous HII regions. The dominant source is the pc-scale supernebula core seen at radio wavelengths. We find that the MIR to radio continuum flux ratio is identical to that of Galactic HII regions. The 9.7$\mu$m silicate feature is present and strongest in absorption toward the supernebula. PAH features at 6.2, 6.8, 7.7, 8.6, and 11.2$\mu$m are detected across the region, although weakly, particularly in the supernebula. Unusual PAH line profiles are seen, including a broad 6$\mu$m feature, likely in part aliphatic, from the extended starburst region and strong 11.0$\mu$m emission from the supernebula. These observations suggest dust processing by intense radiation fields and possible dust production and dispersal by Wolf-Rayet stars within the region.

Accepted, ApJ. Substantially revised