2018/09/30 by Hope How-Huan Chen, Jaime E. Pineda, Alyssa A. Goodman +25 · 65 citations
Physics and Astronomy · #Astro and Planetary Science #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Lagrangian coherent structures #Magnetohydrodynamic drive #Mass distribution #Molecular cloud #Ophiuchus #RADIUS #Turbulence #Velocity dispersion #astro-ph.GA
paper · pdf · open access · doi:10.3847/1538-4357/ab1a40
published in The Astrophysical Journal 877(2), 93 (IOP Publishing) · Accepted by ApJ in April, 2019
openalex created_date 2018/10/05 · arxiv created 2019/05/15 · openalex publication_date 2019/05/29 · arxiv updated 2019/08/14 · openalex updated_date 2026/08/05
Abstract We present the observation and analysis of newly discovered coherent structures in the L1688 region of Ophiuchus and the B18 region of Taurus. Using data from the Green Bank Ammonia Survey, we identify regions of high density and near-constant, almost-thermal velocity dispersion. We reveal 18 coherent structures are revealed, 12 in L1688 and 6 in B18, each of which shows a sharp “transition to coherence” in velocity dispersion around its periphery. The identification of these structures provides a chance to statistically study the coherent structures in molecular clouds. The identified coherent structures have a typical radius of 0.04 pc and a typical mass of 0.4 M ☉ , generally smaller than previously known coherent cores identified by Goodman et al., Caselli et al., and Pineda et al. We call these structures “droplets.” We find that, unlike previously known coherent cores, these structures are not virially bound by self-gravity and are instead predominantly confined by ambient pressure. The droplets have density profiles shallower than a critical Bonnor–Ebert sphere, and they have a velocity ( V LSR ) distribution consistent with the dense gas motions traced by NH 3 emission. These results point to a potential formation mechanism through pressure compression and turbulent processes in the dense gas. We present a comparison with a magnetohydrodynamic simulation of a star-forming region, and we speculate on the relationship of droplets with larger, gravitationally bound coherent cores, as well as on the role that droplets and other coherent structures play in the star formation process.