Shocks in the surroundings of the NGC 1333 IRAS 4 system

Abstract

The IRAS 4A system is part of the southern filament of the Perseus NGC 1333 molecular cloud. As most of the star forming regions, NGC 1333 is known to be heavily shaped by external triggers, such as shock fronts around OB stars or supernovae remnants, cloud-cloud collisions, and instabilities. Recently, it has been hypothesized that the entire southwest region of NGC 1333, encompassing the filament where IRAS 4A lie, is due to a colliding “turbulent” cell, a clash that triggered the birth of the protostars on the filaments. However, no specific signatures of a clash have been reported so far, leaving unanswered how and where the energy of this clash, if real, is dispersed. To answer this question, we analyzed new high spatial resolution (~600 au) observations of CH3OH and SiO, known shock tracers, obtained in the context of the Large Program IRAM/NOEMA SOLIS searching for specific signature of the clash event. We detected three parallel elongated structures, called fingers, with narrow line profiles (~1.5 km s−1), peaked at the systemic velocity of the cloud, tracing gas with high density (5-20×105 cm−3) and high temperature (80-160 K). They are chemically different with the northern finger traced by both SiO and CH3OH and the other two only by SiO. Among various possibilities, a train of three consecutive shocks, due to an expanding bubble coming behind NGC 1333 and from the southwest, can reproduce the observations. Finally, we propose a solution for the two-decades long debate on the nature and the origin of the widespread narrow SiO emission observed in the south part of NGC 1333, namely unresolved trains of shocks.