2017ApJ...849...81A

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 (λ≃0.85 mm or ν∼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) × 10⁴ M_☉ of dust (assuming that the dust temperature is 25 K) and up to 6×10² 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 (H26α), while far 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±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.