Probing the physics of star formation (ProPStar): II. The first systematic search for streamers toward protostars.

Context. The detections of narrow channels of accretion toward protostellar disks, known as streamers, have increased in number in the last few years. However, it is unclear whether streamers are a common feature around protostars that were previously missed, or if they are a rare phenomenon. Aims. Our goals are to obtain the incidence of streamers toward a region of clustered star formation and to trace the origins of their gas to determine whether they originate within the filamentary structure of molecular clouds or from beyond. Methods. We used combined observations of the nearby NGC 1333 star-forming region, carried out with the NOEMA interferometer and the IRAM 30m single dish. Our observations cover the area between the systems IRAS 4 and SVS 13. We traced the chemically fresh gas within NGC 1333 with HC3N molecular gas emission and the structure of the fibers in this region with N2H+ emission. We fit multiple velocity components in both maps and used clustering algorithms to recover velocity-coherent structures. Results. We find streamer candidates toward 7 out of 16 young stellar objects within our field of view. This represents an incidence of approximately 40% of young stellar objects with streamer candidates in a clustered star-forming region. The incidence increases to about 60% when we only considered embedded protostars. All streamers are found in HC3N emission. Conclusions. Given the different velocities between HC3N and N2H+ emission, and because by construction, N2H+ traces the fiber structure, we suggest that the gas that forms the streamers comes from outside the fibers. This implies that streamers can connect cloud material that falls onto the filaments with protostellar disk scales. [ABSTRACT FROM AUTHOR]