Molecular jets from low-mass young protostellar objects

Abstract

Molecular jets are seen coming from the youngest protostars in the early phase of low-mass star formation. They are detected in CO, SiO, and SO at (sub)millimeter wavelengths down to the innermost regions, where their associated protostars and accretion disks are deeply embedded and where they are launched and collimated. They are not only the fossil records of accretion history of the protostars but also are expected to play an important role in facilitating the accretion process. Studying their physical properties (e.g., mass-loss rate, velocity, rotation, radius, wiggle, molecular content, shock formation, periodical variation, magnetic field, etc) allows us to probe not only the jet launching and collimation, but also the disk accretion and evolution, and potentially binary formation and planetary formation in the disks. Here, the recent exciting results obtained with high-spatial and high-velocity resolution observations of molecular jets in comparison to those obtained in the optical jets in the later phase of star formation are reviewed. Future observations of molecular jets with a large sample at high spatial and velocity resolution with ALMA are expected to lead to a breakthrough in our understanding of jets from young stars.

An ALMA study of outflow parameters of protoclusters: outflow feedback to maintain the turbulence

“…These typically low accretion rates of 10 −5 M ⊙ yr −1 imply that the majority of the outflows in our studied regions are associated with low-mass star formation (see e.g., Machida & Hosokawa 2013;Frank et al 2014;Lee 2020). In the case of low-mass star formation, it is observed that the accretion rate falls off with time at an approximate −1 law (Caratti o Garatti et al 2012).…”

Detection of a dense SiO jet in the evolved protostellar phase

“…The Class 0 sources are embedded within dense envelopes and have sufficient surrounding material to exhibit typically very high accretion rates onto the protostar. During this phase, protostars usually show outflows with very high mass-loss rates ∼ 10 −6 -10 −7 M yr −1 , which could produce high density jets (5-10 × 10 6 cm −3 ) (Ellerbroek et al 2013;Lee 2020). Due to its high critical density, the SiO (5-4) molecular transition is the most commonly observed tracer of such high density material (Gibb et al 2004;Podio et al 2015Podio et al , 2021.…”

“…The jets in the younger sources, such as those in the Class 0 phase, are predominantly detected via molecular gas tracers, e.g., CO, SiO, and SO in the (sub)millimeter and H 2 at infrared wavelengths. Conversely, in the older Class I, and II populations, the jets are mainly traced by the atomic and ionized gas, e.g., O, Hα, and S II (Bally 2016;Lee 2020).…”

ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP) II. Survey overview: a first look at 1.3 mm continuum maps and molecular outflows

“…Low-velocity bipolar outflows are nearly ubiquitous in accreting, rotating, and magnetized protostellar systems (Snell et al 1980;Cabrit & Bertout 1992;Bontemps et al 1996;Dunham et al 2014;Yıldız et al 2015;Kim et al 2019). The lower transitions of CO are the most useful tracers of molecular outflows since their low energy levels are easily populated by collisions with H 2 and He molecules at the typical densities and temperatures of molecular clouds (Bally 2016;Lee 2020). The outflows appear as bipolar from the polar regions along the axis of rotation at the early collapsing phase, driven by the first core (Larson 1969), and remain active throughout the journey of protostellar accretion from the outer pseudodisk region (Bate 1998;Masunaga & Inutsuka 2000;Tomisaka 2002;Machida et al 2014;Lee 2020).…”

“…The lower transitions of CO are the most useful tracers of molecular outflows since their low energy levels are easily populated by collisions with H 2 and He molecules at the typical densities and temperatures of molecular clouds (Bally 2016;Lee 2020). The outflows appear as bipolar from the polar regions along the axis of rotation at the early collapsing phase, driven by the first core (Larson 1969), and remain active throughout the journey of protostellar accretion from the outer pseudodisk region (Bate 1998;Masunaga & Inutsuka 2000;Tomisaka 2002;Machida et al 2014;Lee 2020). As protostars evolve, the physical properties of outflow components diversify significantly based on the natal environment.…”