Diverse nuclear star-forming activities in the heart of NGC 253 resolved with ten-pc scale ALMA images

TL;DR

This study uses high-resolution ALMA imaging to resolve the nuclear starburst region of NGC 253 into eight distinct star-forming clumps, revealing diverse chemical compositions and physical conditions at a 10-pc scale.

Contribution

First detailed 8 pc resolution imaging of NGC 253's nuclear starburst, uncovering chemically diverse star-forming clumps with varying molecular spectra.

Findings

Resolved 8 star-forming clumps within 200 pc of NGC 253.

Detected significant spectral variation among clumps, with one showing rich molecular lines.

Identified hot, chemically rich environments localized within 10-pc star-forming regions.

Abstract

We present an 8 pc x 5 pc resolution view of the central ~ 200 pc region of the nearby starburst galaxy NGC 253, based on ALMA Band 7 ({\lambda} ~ 0.85 mm or {\nu} ~ 350 GHz) observations covering 11 GHz. We resolve the nuclear starburst of NGC 253 into eight dusty star-forming clumps, 10 pc in scale, for the first time. These clumps, each of which contains (4-10) x 10^4 M_sun of dust (assuming that the dust temperature is 25 K) and up to 6 x 10^2 massive (O5V) stars, appear to be aligned in two parallel ridges, while they have been blended in previous studies. Despite the similarities in sizes and dust masses of these clumps, their line spectra vary drastically from clump to clump although they are separated by only ~ 10 pc. Specifically, one of the clumps, Clump 1, exhibits line confusion-limited spectra with at least 36 emission lines from 19 molecules (including CH3OH, HNCO, H2CO, CH3CCH, H2CS, and H3O+) and a hydrogen recombination line (H26{\alpha}), while much fewer kinds of molecular lines are detected in some other clumps where fragile species, such as complex organic molecules and HNCO, completely disappear from their spectra. We demonstrate the existence of hot molecular gas ($T_rot (SO2) = 90 {\pm} 11 K) in the former clump, which suggests that the hot and chemically rich environments are localized within a 10-pc scale star-forming clump.