The ALMA-PILS survey: The sulphur connection between protostars and
  comets: IRAS 16293-2422 B and 67P/Churyumov-Gerasimenko
  The evolutionary past of our Solar System can be pieced together by comparing
analogous low-mass protostars with remnants of our Protosolar Nebula - comets.
Sulphur-bearing molecules may be unique tracers of the joint evolution of the
volatile and refractory components. ALMA Band 7 data from the large unbiased
Protostellar Interferometric Line Survey (PILS) are used to search for
S-bearing molecules in the outer disc-like structure, 60 au from IRAS
16293-2422 B, and are compared with data on 67P/C-G stemming from the ROSINA
instrument aboard Rosetta. Species such as SO$_{2}$, SO, OCS, CS, H$_{2}$CS,
H$_{2}$S and CH$_{3}$SH are detected via at least one of their isotopologues
towards IRAS 16293-2422 B. The search reveals a first-time detection of
OC$^{33}$S towards this source and a tentative first-time detection of
C$^{36}$S towards a low-mass protostar. The data show that IRAS 16293-2422 B
contains much more OCS than H$_{2}$S in comparison to 67P/C-G; meanwhile, the
SO/SO$_{2}$ ratio is in close agreement between the two targets. IRAS
16293-2422 B has a CH$_{3}$SH/H$_{2}$CS ratio in range of that of our Solar
System (differences by a factor of 0.7-5.3). It is suggested that the levels of
UV radiation during the initial collapse of the systems may have varied and
have potentially been higher for IRAS 16293-2422 B due to its binary nature;
thereby, converting more H$_{2}$S into OCS. It remains to be conclusively
tested if this also promotes the formation of S-bearing complex organics.
Elevated UV levels of IRAS 16293-2422 B and a warmer birth cloud of our Solar
System may jointly explain the variations between the two low-mass systems.
