Momentum-driven outflow emission from an O-type YSO

Abstract

Aims. We want to study the physical properties of the ionized jet emission in the vicinity of an O-type young stellar object (YSO), and estimate how efficient is the transfer of energy and momentum from small-to large-scale outflows. Methods. We conducted Karl G. Jansky Very Large Array (VLA) observations, at both 22 and 45 GHz, of the compact and faint radio continuum emission in the high-mass star-forming region G023.01−00.41, with an angular resolution between 0 . 3 and 0 . 1, and a thermal rms of the order of 10 µJy beam −1 . Results. We discovered a collimated thermal (bremsstrahlung) jet emission, with a radio luminosity (L rad ) of 24 mJy kpc 2 at 45 GHz, in the inner 1000 AU from an O-type YSO. The radio thermal jet has an opening angle of 44• and brings a momentum rate of 8×10 −3 M yr −1 km s −1 . By combining the new data with previous observations of the molecular outflow and water maser shocks, we can trace the outflow emission from its driving source through the molecular clump, across more than two order of magnitude in length (500 AU-0.2 pc). We find that the momentum-transfer efficiency, between the inner jet emission and the extended outflow of entrained ambient gas, is near unity. This result suggests that the large-scale flow is swept-up by the mechanical force of the radio jet emission, which originates in the inner 1000 AU from the high-mass YSO.

Discovery of a sub-Keplerian disk with jet around a 20 M⊙ young star

“…3 and 5), and has coordinates of R.A. (J2000) = 18 h 34 m 40. s 283 and Dec. (J2000) = -9 • 00 38 .310 (± 30 mas per coordinate). This position also coincides with the peak position of the radio continuum emission observed with the Very Large Array at the same resolution as the ALMA beam (Sanna et al 2016). The same geometry and symbols will be used in all maps for comparison.…”

“…1. The radio continuum emission imaged with the Karl G. Jansky Very Large Array, at a similar resolution as the ALMA observations, traces a radio thermal jet (from Sanna et al 2016). The lower three contours of the 22 GHz emission start at 5 σ by 1 σ steps of 8 µJy beam −1 , and then increase at steps of 10 σ.…”

“…We therefore want to analyze the spatial morphology and kinematics of dense gas which lies at the center of the bipolar outflow, and, specifically, along a position angle of −33 • on the sky plane (measured east of north). This direction traces the projection of the equatorial plane, hereafter the "disk plane", perpendicular to the molecular outflow and the radio jet orientation (or, simply, the outflow), which is inclined by less than 30 • with respect to the sky plane (Sanna et al 2014(Sanna et al , 2016.…”

“…For clarity, we have rotated this map in order to align the outflow axis, which lies at a position angle of +57 • on the sky plane (Sanna et al 2016), with the vertical axis of the plot. The blueshifted (approaching) lobe of the outflow points now to the north.…”

Radio outburst from a massive (proto)star

“…Indeed, comparison with other studies strongly suggests that a low degree of ionization could be a common feature of all radio jets. For example, Guzmán et al (2010), Purser et al (2016), andSanna et al (2016) find ionized mass loss rates ranging from 2 × 10 −7 to 8 × 10 −6 M ⊙ yr −1 , values even lower than that estimated by us for S255 NIRS 3. In conclusion, our results demonstrate that the ionized component of the jet is dynamically negligible.…”