EPoS Contribution

Detection of a Keplerian accretion disk around an extragalactic high-mass YSO Anna F. McLeod CEA, Durham U, Durham, UK
Over the last decade, millimetre observations have revealed Keplerian accretion disks and rotating gaseous structures around massive young stellar objects, providing evidence for disk-mediated accretion up to stellar masses of about 20 M⊙. However, our observational knowledge of high-mass star-forming accretion structures has thus far been limited to the Milky Way, probing only a single metallicity environment in a massive galaxy. I will talk about a rotating gaseous structure around an extragalactic young, massive star in the Large Magellanic Cloud, detected with ALMA. The motions of the molecular gas in this structure show radial flow of material falling from larger scales onto a central disk-like structure, with the latter exhibiting signs of Keplerian rotation, i.e. a rotating toroid feeding an accretion disk and thus the growth of the central star. The system is in almost all aspects (e.g., mass accretion rate, disk stability, disk mass vs stellar mass) comparable to Milky Way high-mass young stellar objects accreting gas via a Keplerian disk. The key difference between this source and its Galactic counterparts is that it is optically revealed, rather than being deeply embedded in its natal material as is expected of such a young massive star. We suggest that this is the consequence of the star having formed in a low-metallicity and low-dust content environment, thus providing important constraints for models of the formation and evolution of massive stars and their circumstellar disks.

Caption: The HH 1177 system - a jet-launching, disk-bearing, extragalactic high-mass YSO. Top figure, left panel, inset: three-colour composite of the star-forming region N180 in the Large Magellanic Cloud (red = [SII]λ6717, green = Hα, blue = [OIII]λ5007), observed with VLT/MUSE. Main left panel: the red- and blue-shifted wings of the Hα emission line highlighting the externally-irradiated HH 1177 jet emerging from the central star. Right panel: same as the main left panel but continuum-subtracted and zoomed in onto the driving star of the HH 1177 system, with the CS velocity map overlaid showing the rotating molecular gas at the location of the central star (scaled up for illustrative purposes). Bottom plots: Kinematics in the inner (R < 6000 AU, left) and outer (R > 6000 AU, right) regions of the rotating gas traced by CS. Shown are the redshifted (orange circles) and blueshifted (dark blue squares) radial velocity profiles of the outer envelope of the rotating gas. Dot-dashed and dotted curved correspond to Keplerian and free fall kinematics for an assumed fixed central source mass of 15 M⊙, while the dashed curve corresponds to the best-fit Keplerian (inner regions) or free fall (outer regions) curves, showing that the inner regions are best described by Keplerian-like motions, while the outer regions are best described by free fall. Masses of the central source derived from the Keplerian and free fall fits are indicated in the legend. The shaded area indicates Keplerian rotation for the mass range 10 M⊙ < M < 40 M⊙.
Collaborators: J. Henshaw, UK M. Reiter, US P. Klaassen, UK R. Kuiper, DE A. Ginsburg, US	Key publication Relevant topic(s): Accretion Extra-Galactic SF High-Mass SF
Relevant Big Question: How do massive stars form?