Dense Cores, Filaments, and Outflows in the S255IR Region of High-mass Star Formation

Abstract

We investigate at a high angular resolution the spatial and kinematic structure of the S255IR high mass star-forming region, which demonstrated recently the first disk-mediated accretion burst in the massive young stellar object. The observations were performed with ALMA in Band 7 at an angular resolution ∼ 0. 1, which corresponds to ∼ 180 AU. The 0.9 mm continuum, C 34 S(7-6) and CCH N = 4 − 3 data show a presence of very narrow (∼ 1000 AU), very dense (n ∼ 10 7 cm −3 ) and warm filamentary structures in this area. At least some of them represent apparently dense walls around the high velocity molecular outflow with a wide opening angle from the S255IR-SMA1 core, which is associated with the NIRS3 YSO. This wide-angle outflow surrounds a narrow jet. At the ends of the molecular outflow there are shocks, traced in the SiO(8-7) emission. The SiO abundance there is enhanced by at least 3 orders of magnitude. The CO(3-2) and SiO(8-7) data show a collimated and extended high velocity outflow from another dense core in this area, SMA2. The outflow is bent and consists of a chain of knots, which may indicate periodic ejections possibly arising from a binary system consisting of low or intermediate mass protostars. The C 34 S emission shows evidence of rotation of the parent core. Finally, we detected two new low mass compact cores in this area (designated as SMM1 and SMM2), which may represent prestellar objects.

The disk-outflow system around the rare young O-type protostar W42-MME

“…The peak flux density (Rayleigh-Jeans temperature or radiation temperature) of A, B, C, D, and E is found to be 4.36 mJy beam −1 (6.5 K), 0.94 mJy beam −1 (1.4 K), 0.39 mJy beam −1 (0.58 K), 0.15 mJy beam −1 (0.23 K), and 0.14 mJy beam −1 (0.21 K), respectively. Here, a conversion factor between flux density and radiation temperature for the ALMA beam is ∼150 K Jy −1 (see also Zinchenko et al 2020). The ALMA continuum source "A" hosts the powering source of the H 2 outflow and the proposed infrared jet.…”

“…All these findings suggest the impact of the outflow/jet to the ambient gas around W42-MME, which is an IRc of the 6.7 GHz MME. Recently, flaring methanol masers have been found to trace episodic accretion events in young protostars (e.g., Bertout 1989;Hirota et al 2018;Hunter et al 2018;MacLeod et al 2018;Chen et al 2020;Liu et al 2020;Zinchenko et al 2020;Stecklum et al 2021). Hence, our findings appear to show the episodic ejection from W42-MME.…”

“…Hence, our findings appear to show the episodic ejection from W42-MME. Such episodic ejection is presumably driven by accretion events, which are known to occur in such objects (see Hirota et al 2018;Zinchenko et al 2020;Liu et al 2020, and references therein). Together, W42-MME would be a good candidate for monitoring of the methanol (and water) masers in case of a flare.…”

“…The position-velocity diagram enables us to examine the kinematics of the source "A", and hints the presence of a Keplerian-like rotation of the core "A". However, the resolution of these data is not sufficient for a reliable conclusion (see also Zinchenko et al 2020;Liu et al 2020). Using the rotation velocity information (i.e., M sin 2 i), we compute the dynamical central mass of the core to be ∼9-12 M .…”

ALMA discovery of a dual dense probably rotating outflow from a massive young stellar object G18.88MME

“…These are considered as two flavours of the same mass-ejection process in protostars. However, the study of connection between these two forms in MYSOs is still lacking (e.g., Arce et al 2007;Frank et al 2014) and very few observations of the simultaneous presence of a highly collimated jet and a wide-angle outflow in MYSOs exist (e.g., Torrelles et al 2011;Zinchenko et al 2020). No models predict the simultaneous existence of a jet and a wide-angle outflow as well as rotation of both the components together in MYSOs (e.g., Torrelles et al 2011).…”