2020ApJ...896...37F

We present observations of SO and SO₂ lines toward the shocked regions along the L1157 chemically rich outflow, taken in the context of the Seeds of Life in Space IRAM Northern Extended Millimeter Array Large Program, and supported by data from the Submillimeter Array and IRAM-30 m telescope at 1.1-3.6 mm wavelengths. We simultaneously analyze, for the first time, all of the brightest shocks in the blueshifted lobe, namely, B0, B1, and B2. We found the following. (1) SO and SO₂ may trace different gas, given that the large(-scale) velocity gradient analysis indicates for SO₂ a volume density (10⁵–10⁶cm^–3) denser than that of the gas emitting in SO by a factor up to an order of magnitude. (2) Investigating the 0.1 pc scale field of view, we note a tentative gradient along the path of the precessing jet. More specifically, χ(SO/SO₂) decreases from the B0-B1 shocks to the older B2. (3) At a linear resolution of 500-1400 au, a tentative spatial displacement between the two emitting molecules is detected, with the SO peak closer (with respect to SO₂) to the position where the recent jet is impinging on the B1 cavity wall. Our astrochemical modeling shows that the SO and SO₂ abundances evolve on timescales less than about 1000 years. Furthermore, the modeling requires high abundances (2 x 10^–6) of both H₂S/H and S/H injected in the gas phase due to the shock occurrence, so prefrozen OCS only is not enough to reproduce our new observations.