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, ($\sim 0.04^{\prime\prime}$) VLA observations towards two subsamples of massive star-forming regions of different evolutionary statuses: 48 infrared-bright, massive YSOs and 8 IRDCs containing 16 luminous (${\rm L_{bol}}>10^3\,{\rm L_\odot}$) cores. For $94\%$ of the MYSO sample we detect thermal radio ($\alpha \geq -0.1$ whereby $S_\nu \propto \nu^\alpha$) sources coincident with the protostar, of which $84\%$ (13 jets and 25 candidates) are jet-like. Radio luminosity is found to scale with ${\rm L_{bol}}$ similarly to the low-mass case supporting a common mechanism for jet production across all masses. Associated radio lobes tracing shocks are seen towards $52\%$ 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 $\dot{m}_{\rm jet} \propto {\rm L_{bol}}^{0.9\pm0.2}$, 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 $p_{\rm jet}>p_{\rm outflow}$. Finally, from their physical extent we show that the radio emission can not originate from small, optically-thick \textsc{Hii} regions. Towards the IRDC cores, we observe increasing incidence rates/radio fluxes with age using the proxy of increasing luminosity-to-mass $\left( \frac{L}{M} \right)$ and decreasing infrared flux ratios $\left(\frac{S_{70 \rm \mu m}}{S_{24 \rm \mu m}}\right)$. Cores with $\frac{L}{M}<40\,{\rm L_{sol}}{\rm M_{sol}}^{-1}$ are not detected above ($5.8{\rm GHz}$) radio luminosities of $\sim1{\rm mJy\,kpc}^2$.