Rotational Structure and Outflow in the Infrared Dark Cloud 18223-3

TL;DR

This study uses high-resolution observations to investigate the rotation, outflow, and infall processes in a massive star-forming infrared dark cloud, revealing a large rotating structure with signs of a Keplerian disk and a young outflow system.

Contribution

It provides detailed observational evidence of a massive star-forming core with a large rotating structure and outflow, and models the velocity gradient as rotationally infalling gas, advancing understanding of early massive star formation stages.

Findings

Detection of a large (28,000 AU) rotating structure with a velocity gradient.

Confirmation of outflow orientation and properties consistent with high-mass star formation.

Evidence for a Keplerian disk within a larger infalling rotating envelope.

Abstract

We examine an Infrared Dark Cloud (IRDC) at high spatial resolution as a means to study rotation, outflow, and infall at the onset of massive star formation. Submillimeter Array observations combined with IRAM 30 meter data in 12CO(2--1) reveal the outflow orientation in the IRDC 18223-3 region, and PdBI 3 mm observations confirm this orientation in other molecular species. The implication of the outflow's presence is that an accretion disk is feeding it, so using high density tracers such as C18O, N2H+, and CH3OH, we looked for indications of a velocity gradient perpendicular to the outflow direction. Surprisingly, this gradient turns out to be most apparent in CH3OH. The large size (28,000 AU) of the flattened rotating object detected indicates that this velocity gradient cannot be due solely to a disk, but rather from inward spiraling gas within which a Keplerian disk likely exists. From the outflow parameters, we derive properties of the source such as an outflow dynamical age of ~37,000 years, outflow mass of ~13 M_sun, and outflow energy of ~1.7 x 10^46 erg. While the outflow mass and energy are clearly consistent with a high-mass star forming region, the outflow dynamical age indicates a slightly more evolved evolutionary stage than previous spectral energy distribution (SED) modeling indicates. The calculated outflow properties reveal that this is truly a massive star in the making. We also present a model of the observed methanol velocity gradient. The rotational signatures can be modeled via rotationally infalling gas. These data present evidence for one of the youngest known outflow/infall/disk systems in massive star formation. A tentative evolutionary picture for massive disks is discussed.