The Molecular ISM in the Super Star Clusters of the Starburst NGC 253
  We present submillimeter spectra of the (proto-)super star cluster (SSC)
candidates in the starbursting center of the nearby galaxy NGC 253 identified
by Leroy et al. (2018). The 2.5pc resolution of our ALMA cycle 3 observations
approach the size of the SSCs and allows the study of physical and chemical
properties of the molecular gas in these sources. In the 14 SSC sources and in
the frequency ranges 342.0-345.8 GHz and 353.9-357.7 GHz we detect 55 lines
belonging to 19 different chemical species. The SSCs differ significantly in
chemical complexity, with the richest clusters showing 19 species and the least
complex showing 4 species. We detect HCN isotopologues and isomers (H$^{13}$CN,
HC$^{15}$N, H$^{15}$NC), abundant HC$_3$N, SO and S$^{18}$O, SO$_2$, and
H$_2$CS. The gas ratios CO/HCN, CO/HCO$^+$ are low, ~1-10, implying high dense
gas fractions in the SSCs. Line ratio analyses suggests chemistry consistent
with photon-dominated regions and mechanical heating. None of the SSCs near the
galaxy center show line ratios that imply an X-ray dominated region, suggesting
that heating by any (still unknown) AGN does not play a major role. The gas
temperatures are high in most sources, with an average rotational temperature
of ~130 K in SO$_2$. The widespread existence of vibrationally excited HCN and
HC$_3$N transitions implies strong IR radiation fields, potentially trapped by
a greenhouse effect due to high continuum opacities.
