A case study of H2O masers tracing a proto-stellar jet from POETS

In the following, we show a compelling example of the information we have obtained by mapping H2O maser emission at 22.2 GHz in the vicinity of a young star. Usually, at this frequency water masers trace shocks against the ambient medium due to material ejected by the star, but they can also trace internal shocks happening along streamlines of gas that follow magnetic field lines (blue lines below). The latter phenomenology is particularly interesting because it allows us to probe a physical process called, magneto-hydrodynamic disk wind. These winds are thought to regulate stellar growth by expelling material that orbits too fast to become part of the star.

Caption: prototypical example of H2O maser emission tracing a jet in the star-forming region IRAS21078+5211.

The left plot shows a cartoon of the proto-stellar system, where circumstellar material lying on the (equatorial) "Disk" plane, and orbiting around the young stellar object (YSO), is dragged along the (perpendicular) " Jet" direction following the magnetic field lines (blue streamlines). Magnetic fields swirl around as a result of the different forces at work. Water masers (small red/orange spheres) can be produces by shocks along these streamlines where gas is forced to flow out. Therefore, by observing H2O maser emission, one can draw the path of the gas streamlines, whose geometry and velocity tell us many physical properties of the system.
The right plot shows another view of some blobs of gas emitting H2O maser, that flow in opposite directions away from the YSO and run along the magnetic streamlines. The observer's eye to the right measures a number of gas properties by looking at the H2O masers, such as the line-of-sight velocity (VLSR) of gas, via maser line's Doppler shift, and the streamlines' geometry (𝕽, 𝜙).

These observations at 22.2 GHz were obtained by combining together 26 radio telescopes spread around the world, in order to achieve a superlative spectral sensitivity of 1 mJy /0.2 km/s within a small angular resolution of 1 mas only.

More details in, Moscadelli et al. 2022, Nature Astronomy, 6, 1068

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