Context : The majority of stars form in binary or higher order systems .
The evolution of each protostar in a multiple system may start at different times and may progress differently .
The Class 0 protostellar system IRAS 16293 - 2422 contains two protostars , “ A ” and “ B ” , separated by \sim 600 au and embedded in a single , 10 ^ { 4 } au scale envelope .
Their relative evolutionary stages have been debated .

Aims : We aim to study the relation and interplay between the two protostars A and B at spatial scales of 60 au up to \sim 10 ^ { 3 } au .

Methods : We selected molecular gas line transitions of the species CO , H _ { 2 } CO , HCN , CS , SiO , and C _ { 2 } H from the ALMA-PILS spectral imaging survey ( 329–363 GHz ) and used them as tracers of kinematics , density , and temperature in the IRAS 16293 - 2422 system .
The angular resolution of the PILS data set allows us to study these quantities at a resolution of 0.5″ ( 60 au at the distance of the source ) .

Results : Line-of-sight velocity maps of both optically thick and optically thin molecular lines reveal : ( i ) new manifestations of previously known outflows emanating from protostar A ; ( ii ) a kinematically quiescent bridge of dust and gas spanning between the two protostars , with an inferred density between 4 \times 10 ^ { 4 } \mathrm { cm } ^ { -3 } and \sim 3 \times 10 ^ { 7 } \mathrm { cm } ^ { -3 } ; and ( iii ) a separate , straight filament seemingly connected to protostar B seen only in C _ { 2 } H , with a flat kinematic signature .
Signs of various outflows , all emanating from source A , are evidence of high-density and warmer gas ; none of them coincide spatially and kinematically with the bridge .

Conclusions : We hypothesize that the bridge arc is a remnant of filamentary substructure in the protostellar envelope material from which protostellar sources A and B have formed .
One particular morphological structure appears to be due to outflowing gas impacting the quiescent bridge material .
The continuing lack of clear outflow signatures unambiguously associated to protostar B and the vertically extended shape derived for its disk-like structure lead us to conclude that source B may be in an earlier evolutionary stage than source A .