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