Dissecting the disk and the jet of a massive (proto)star. An ALMA view of IRAS20126+4104

TL;DR

This study uses ALMA observations to analyze the structure, kinematics, and physical conditions of the disk and jet around the massive protostar IRAS20126+4104, confirming a Keplerian disk and detailed jet properties.

Contribution

First detailed ALMA analysis of IRAS20126+4104's disk and jet, revealing a stable Keplerian disk with complex kinematics and jet structure around a ~12 solar mass protostar.

Findings

Confirmed Keplerian disk around IRAS20126+4104

Derived temperature and density profiles of disk and jet

Estimated accretion rate of ~0.001 solar masses per year

Abstract

We investigate one of the best examples of disk+jet systems around an early B-type (proto)star, IRAS20126+4104. This object is an ideal target for resolution of its disk and the determination of its physical and kinematical structure. Despite its high declination, it has been possible to perform successful observations with the Atacama Large Millimeter and submillimeter Array at 1.4 mm in the continuum emission and a number of molecular tracers. The new data allow us to improve on previous similar observations and confirm the existence of a Keplerian accretion disk around a ~12 Msun (proto)star. From methyl cyanide, we derived the rotation temperature and column density as a function of disk radius. We also obtained a map of the same quantities for the jet using the ratio between two lines of formaldehyde. We use two simple models of the jet and the disk to estimate the basic geometrical and kinematical parameters of the two. We conclude that the disk is stable at all radii. We also estimate an accretion rate of ~0.001 Msun/yr. Our analysis confirms that the jet from IRAS20126+4104 is highly collimated, lies close to the plane of the sky, and expands with velocity increasing with distance. As expected, the gas temperature and column density peak in the bow shock. The disk is undergoing Keplerian rotation but a non-negligible radial velocity component is also present that is equal to ~40% of the rotational component. The disk is slightly inclined with respect to the line of sight and has a dusty envelope that absorbs the emission from the disk surface. This causes a slight distortion of the disk structure observed in high-density tracers. We also reveal a significant deviation from axial symmetry in the SW part of the disk, which might be caused by either tidal interaction with a nearby, lower-mass companion or interaction with the outflowing gas of the jet.