Clustered Star Formation in the center of NGC 253 Contributes to Driving the Ionized Nuclear Wind

TL;DR

This study uses high-resolution ALMA observations to analyze ionized gas in NGC 253's nucleus, revealing embedded star clusters that contribute to the galaxy's large-scale wind and refining understanding of star formation in starburst regions.

Contribution

First detailed ALMA study of ionized gas in NGC 253's nucleus, linking embedded clusters to wind launching and star formation properties.

Findings

Embedded clusters are primary sources of recombination line emission.

Clusters contribute at least 50% to the total starburst activity.

Broad-linewidth emission suggests dynamic processes in clusters.

Abstract

We present new 3 mm observations of the ionized gas toward the nuclear starburst in the nearby (D ~ 3.5 Mpc) galaxy NGC 253. With ALMA, we detect emission from the H40-alpha and He40-alpha lines in the central 200 pc of this galaxy on spatial scales of ~4 pc. The recombination line emission primarily originates from a population of approximately a dozen embedded super star clusters in the early stages of formation. We find that emission from these clusters is characterized by electron temperatures ranging from 7000-10000 K and measure an average singly-ionized helium abundance <Y+> = 0.25 +/- 0.06, both of which are consistent with values measured for HII regions in the center of the Milky Way. We also report the discovery of unusually broad-linewidth recombination line emission originating from seven of the embedded clusters. We suggest that these clusters contribute to the launching of the large-scale hot wind observed to emanate from the central starburst. Finally, we use the measured recombination line fluxes to improve the characterization of overall embedded cluster properties, including the distribution of cluster masses and the fractional contribution of the clustered star formation to the total starburst, which we estimate is at least 50%.