ALMA Observations toward the S-shaped Outflow and the Envelope around NGC 1333 IRAS 4A2

Abstract

Abstract We have analyzed the ALMA archival data of the SO (J N = 65 − 54 and J N = 76 − 65), CO (J = 2 − 1), and CCH (N = 3 − 2, J = 7/2 − 5/2, F = 4 − 3) lines from the Class 0 protobinary system, NGC 1333 IRAS 4A. The images of SO (J N = 65 − 54) and CO (J = 2 − 1) successfully separate two northern outflow lobes connected to each protostar, IRAS 4A1 and IRAS 4A2. The outflow from IRAS 4A2 shows an S-shaped morphology, consisting of a flattened envelope around IRAS 4A2 with two outflow lobes connected to both edges of the envelope. The flattened envelope surrounding IRAS 4A2 has a velocity gradient opposite to that of the circumbinary envelope. The observed features are reproduced by the magnetohydrodynamic simulation of the collapsing core whose magnetic field direction is misaligned with the rotational axis. Our simulation shows that the intensity of the outflow lobes is enhanced on one side, resulting in the formation of S-shaped morphology. The S-shaped outflow can also be explained by the precessing outflow launched from an unresolved binary with a separation larger than 12 au (0.″04). Additionally, we discovered a previously unknown extremely high-velocity component at ∼45–90 km s−1 near IRAS 4A2 with CO. CCH (J N,F = 7/23,4 − 5/22,3) emission shows two pairs of blobs attached to the bottom of a shell-like feature, and the morphology is significantly different from that of the SO and CO lines. Toward IRAS 4A2, the S-shaped outflow shown in SO is overlapped with the edges of CCH shells, while CCH shells have velocity gradients opposite to those of the flattened structure around IRAS 4A2.