The structure and kinematics of dense gas in NGC 2068

Johnstone

et al. 2021

ApJ

We present the four-year survey results of monthly submillimeter monitoring of eight nearby (<500 pc) starforming regions by the JCMT Transient Survey. We apply the Lomb-Scargle Periodogram technique to search for and characterize variability on 295 submillimeter peaks brighter than 0.14 Jy beam −1 , including 22 disk sources (Class II), 83 protostars (Class 0/I), and 190 starless sources. We uncover 18 secular variables, all of them protostars. No single-epoch burst or drop events and no inherently stochastic sources are observed. We classify the secular variables by their timescales into three groups: Periodic, Curved, and Linear. For the Curved and Periodic cases, the detectable fractional amplitude, with respect to mean peak brightness, is ∼4% for sources brighter than ∼0.5 Jy beam −1 . Limiting our sample to only these bright sources, the observed variable fraction is 37% (16 out of 43). Considering source evolution, we find a similar fraction of bright variables for both Class 0 and Class I. Using an empirically motivated conversion from submillimeter variability to variation in mass accretion rate, six sources (7% of our full sample) are predicted to have years-long accretion events during which the excess mass accreted reaches more than 40% above the total quiescently accreted mass: two previously known eruptive Class I sources, V1647 Ori and EC 53 (V371 Ser), and four Class 0 sources, HOPS 356, HOPS 373, HOPS 383, and West 40. Considering the full protostellar ensemble, the importance of episodic accretion on few years timescale is

Section: B2 Serpens Main Ec 53 (V371 Serp): Periodic Groupmentioning

confidence: 57%

Section: B10 Orion Ngc 2068 Hops 373: Curved Groupmentioning

confidence: 73%

The JCMT Transient Survey: Four-year Summary of Monitoring the Submillimeter Variability of Protostars

Johnstone

et al. 2021

ApJ

“…These processes have been studied from an observational point of view at different spatial scales. At large-scales (~ 1 pc) or clump scales, gravoturbulent fragmentation (or thermal Jeans fragmentation) seems to describe well the observations (e. g., Román-Zúñiga et al 2009,Takahashi et al 2013; Walker-Smith et al 2013; Samal et al 2015; Kainulainen et al 2016; Sharma et al 2016; Hacar et al 2017b), although there are cases where the effects of feedback (Busquet et al 2016), or large-scale collapse (Csengeri et al 2017) seem to be important as well. The term of ‘gravoturbulent fragmentation’ refers to the fragmentation that takes place in a turbulent and self-gravitating cloud.…”

Section: Introductionmentioning

confidence: 67%

Thermal Jeans Fragmentation within ∼1000 au in OMC-1S

Palau

Zapata

Román-Zúñiga

et al. 2018

ApJ

We present subarcsecond 1.3 mm continuum ALMA observations towards the Orion Molecular Cloud 1 South (OMC-1S) region, down to a spatial resolution of 74 AU, which reveal a total of 31 continuum sources. We also present subarcsecond 7 mm continuum VLA observations of the same region, which allow to further study fragmentation down to a spatial resolution of 40 AU. By applying a Mean Surface Density of Companions method we find a characteristic spatial scale at ~ 560 AU, and we use this spatial scale to define the boundary of 19 'cores' in OMC-1S as groupings of millimeter sources. We find an additional characteristic spatial scale at ~ 2900 AU, which is the typical scale of the filaments in OMC-1S, suggesting a two-level fragmentation process. We measured the fragmentation level within each core and find a higher fragmentation towards the southern filament. In addition, the cores of the southern filament are also the densest (within 1100 AU) cores in OMC-1S. This is fully consistent with previous studies of fragmentation at spatial scales one order of magnitude larger, and suggests that fragmentation down to 40 AU seems to be governed by thermal Jeans processes in OMC-1S.

“…In simulations with turbulent driving, prestellar cores displayed a higher core-to-core velocity dispersion than protostellar cores, and the reverse was true in simulations with decaying turbulence. Observational evidence for both scenarios exists: while Perseus (Kirk et al 2007) agrees with driven turbulence, Ophiuchus (André et al 2007) and NGC 2068(Walker-Smith et al 2013) agree better with the decaying turbulence scenario.…”

Section: Core Motionsmentioning

confidence: 82%

Fragmentation and kinematics of dense molecular cores in the filamentary infrared-dark cloud G011.11–0.12

Ragan¹,

Henning²,

Beuther³

et al. 2015

A&A

We present new Plateau de Bure Interferometer observations of a region in the filamentary infrared-dark cloud (IRDC) G011.11-0.12 containing young, star-forming cores. In addition to the 3.2 mm continuum emission from cold dust, we map this region in the N 2 H + (1−0) line to trace the core kinematics with an angular resolution of 2 and velocity resolution of 0.2 km s −1 . These data are presented in concert with recent Herschel results, single-dish N 2 H + (1−0) data, SABOCA 350 µm continuum data, and maps of the C 18 O (2−1) transition obtained with the IRAM 30 m telescope. We recover the star-forming cores at 3.2 mm continuum, while in N 2 H + they appear at the peaks of extended structures. The mean projected spacing between N 2 H + emission peaks is 0.18 pc, consistent with simple isothermal Jeans fragmentation. The 0.1 pc-sized cores have low virial parameters on the criticality borderline, while on the scale of the whole region, we infer that it is undergoing large-scale collapse. The N 2 H + linewidth increases with evolutionary stage, while CO isotopologues show no linewidth variation with core evolution. Centroid velocities of all tracers are in excellent agreement, except in the starless region where two N 2 H + velocity components are detected, one of which has no counterpart in C 18 O. We suggest that gas along this line of sight may be falling into the quiescent core, giving rise to the second velocity component, possibly connected to the global collapse of the region.