Massive 70 μm quiet clumps - II. Non-thermal motions driven by gravity in massive star formation?
Abstract
The dynamic activity in massive star-forming regions prior to the formation of bright protostars is still not fully investigated. In this work, we present observations of HCO+ J = 1-0 and N2H+ J = 1-0 made with the IRAM 30 m telescope towards a sample of 16 Herschel-identified massive 70 μm quiet clumps associated with infrared dark clouds. The clumps span a mass range from 300 to 2000 M⊙. The N2H+ data show that the regions have significant non-thermal motions with velocity dispersion between 0.28 and 1.5 km s-1, corresponding to Mach numbers between 2.6 and 11.5. The majority of the 70 μm quiet clumps have asymmetric HCO+ line profiles, indicative of significant dynamical activity. We show that there is a correlation between the degree of line asymmetry and the surface density Σ of the clumps, with clumps of Σ ≳ 0.1 g cm-2 having more asymmetric line profiles, and so are more dynamically active, than clumps with lower Σ. We explore the relationship between velocity dispersion, radius and Σ and show how it can be interpreted as a relationship between an acceleration generated by the gravitational field, aG, and the measured kinetic acceleration, ak, consistent with the majority of the non-thermal motions originating from self-gravity. Finally, we consider the role of external pressure and magnetic fields in the interplay of forces.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- February 2018
- DOI:
- 10.1093/mnras/stx2672
- arXiv:
- arXiv:1710.04904
- Bibcode:
- 2018MNRAS.473.4975T
- Keywords:
-
- turbulence;
- stars: evolution;
- stars: formation;
- stars: kinematics and dynamics;
- stars: massive;
- radio lines: stars;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Accepted for publication in MNRAS. 12 pages, 10 figures. arXiv admin note: substantial text overlap with arXiv:1511.03670