We present submillimeter spectra of the ( proto- ) super star cluster ( SSC ) candidates in the starbursting center of the nearby galaxy NGC 253 identified by \citet 2018ApJ…869..126L .
The 2.5 pc 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 , \sim 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 \sim 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 .