A Galactic survey of radio jets from massive protostars

Abstract

In conjunction with a previous southern-hemisphere work, we present the largest radio survey of jets from massive protostars to date with high-resolution, ($\sim 0{_{.}^{\prime\prime}}04$) Jansky Very Large Array (VLA) observations towards two subsamples of massive star-forming regions of different evolutionary statuses: 48 infrared-bright, massive, young, stellar objects (MYSOs) and 8 infrared dark clouds (IRDCs) containing 16 luminous (${\, L_{\rm {bol}}}>10^3{{\rm \, L_{\odot }}}$) cores. For $94{{\ \rm per\ cent}}$ of the MYSO sample we detect thermal radio (α ≥ −0.1 whereby Sν∝να) sources coincident with the protostar, of which $84{{\ \rm per\ cent}}$ (13 jets and 25 candidates) are jet-like. Radio luminosity is found to scale with ${\, L_{\rm {bol}}}$ similarly to the low-mass case supporting a common mechanism for jet production across all masses. Associated radio lobes tracing shocks are seen towards $52{{\ \rm per\ cent}}$ of jet-like objects and are preferentially detected towards jets of higher radio and bolometric luminosities, resulting from our sensitivity limitations. We find jet mass loss rate scales with bolometric luminosity as ${\dot{m}_{\rm jet}}\propto {\, L_{\rm {bol}}}^{0.9\pm 0.2}$, thereby discarding radiative, line-driving mechanisms as the dominant jet-launching process. Calculated momenta show that the majority of jets are mechanically capable of driving the massive, molecular outflow phenomena since pjet > poutflow. Finally, from their physical extent we show that the radio emission can not originate from small, optically-thick Hii regions. Towards the IRDC cores, we observe increasing incidence rates/radio fluxes with age using the proxy of increasing luminosity-to-mass (L/M) and decreasing infrared flux ratios (S70 μm/S24 μm). Cores with $L/M\, <\, 40\, L_\odot \, M_\odot ^{-1}$ are not detected above (5.8 GHz) radio luminosities of ∼1 mJy kpc2.

Zooming into the Collimation Zone in a Massive Protostellar Jet

“…A second possibility is that, in order to achieve a high degree of collimation, jets from high-mass protostars might require restrictive physical conditions in the ambient medium, which will promote external collimation at large distances from the protostar. Recent works support a shock-ionization mechanism for jets from massive protostars, similar to what is observed in low-mass protostellar jets (e.g., Rosero et al 2019, Fedriani et al 2019, Purser et al 2021. This result discards radiatively driven winds from massive protostars and supports an universal launching mechanism for stars of all masses (e.g., Purser et al 2021).…”

“…Recent works support a shock-ionization mechanism for jets from massive protostars, similar to what is observed in low-mass protostellar jets (e.g., Rosero et al 2019, Fedriani et al 2019, Purser et al 2021. This result discards radiatively driven winds from massive protostars and supports an universal launching mechanism for stars of all masses (e.g., Purser et al 2021). However, massive protostars are known to accrete at large rates from very massive and most probably unstable disks (e.g., Sanna et al 2019b, Johnston et al 2020.…”

“…However, bipolar outflows observed in high-mass star-forming regions tend to be less collimated than those observed in low-mass regions (e.g., Arce et al 2007). Recent radio observations have established that very young massive protostars are also commonly associated with compact freefree emission, being the signpost of mass ejected near the protostar (e.g., Moscadelli et al 2016;Purser et al 2016Purser et al , 2021Rosero et al 2016Rosero et al , 2019Sanna et al 2018;Obonyo et al 2019). However, it is not yet clear whether this emission traces the bases of jets as well collimated as those observed in low-mass starforming regions.…”

A Highly Collimated Flow from the High-mass Protostar ISOSS J23053+5953 SMM2

“…As described in Section 3.1, the cm data show a rising spectrum as one would expect from an ionized jet, and the 6 cm radio luminosity S ν d 2 of 1.3 (±0.4) mJy kpc 2 is typical for a high-mass object. Furthermore, the S ν d 2 vs. L bol data for this source falls very near the expected relation for ionized jets (Anglada et al 2018;Rosero et al 2019;Purser et al 2021). Also, based on the extensive Gould Belt survey of cm emission from low mass YSOs (e.g., Dzib et al 2013), at the sensitivity level of our observations, no low-mass YSO should be detected at the distance of ISOSS J23053+5953 SMM2 (see Rosero et al 2019).…”

The first interferometric survey of massive YSOs in the K-band

“…Exceptionally disc instabilities that allow accretion to proceed will allow the formation of a very compact gaseous disc which can be shock-ionised close to the star (G345.4938, Guzmán et al 2020). Jets were recently traced via radio thermal emission and found to be abundant in high-mass star formation (up to 84%, Purser et al 2021). In our sample of MYSOs we find that Brγ emission originates from a smaller area, but co-planar to that of the continuum, therefore if a jet is the underlying mechanism, we most likely trace the base of the jet.…”