Velocity structure of the 50 pc long NGC 6334 filamentary cloud

Abstract

Context. The interstellar medium is observed to be organized in filamentary structures, and in neutral (H I) and ionized (H II) bubbles. The expanding nature of these bubbles shapes the surrounding medium and possibly plays a role in the formation and evolution of the interstellar filaments. The impact of the expansion of these bubbles on the interstellar medium is not well understood. Aims. Our aim is to describe the kinematics of a filamentary molecular cloud forming high-mass stars and hosting multiple H II regions in order to study the possible environmental impact on the properties of molecular filaments. Methods. We present APEX 13CO and C18O(2–1) mapping observations of the 10 × 50 pc NGC 6334 molecular cloud complex. We investigated the gas velocity structure along and across the 50 pc long cloud and toward velocity-coherent filaments (VCFs). Results. The NGC 6334 complex is observed to have a coherent velocity structure smoothly varying by ~5 km s−1 over its 50 pc elongation parallel to the Galactic plane. We identify a sample of 75 VCFs in the C18O(2–1) position-position-velocity cube and present the properties of 47 VCFs with a length ≳1 pc (five beams). We measure a large number of velocity gradients along the VCFs. The amplitudes of these velocity gradients and the velocity dispersion measured along the crests increase with the column density of the VCFs. We derive the column density and velocity power spectra of the VCFs. These power spectra are well represented with power laws showing similar slopes for the two quantities (with a mean of about −2), although some differ by up to a factor of 2. The position velocity diagrams perpendicular to three VCFs (selected from different physical environments) show the V-shaped velocity pattern corresponding to a bent structure in velocity space with the filament at the tip of the V surrounded by an extended structure connected to it with a velocity gradient. This velocity structure is qualitatively similar to that resulting from numerical simulations of filament formation from large-scale compression from propagating shock fronts. In addition, the radial profiles perpendicular to these VCFs hint to small-scale internal impacts from neighboring H II bubbles on two of them, while the third is mostly unaffected. Conclusions. The observed opposite curvature in velocity space (V- and A-shaped) toward the VCFs points to various origins of large-scale external compressions from propagating H I bubbles. This suggests the plausible importance of multiple H I compressions, separated in space and time, in the formation and evolution of molecular clouds and their star formation history. These atomic compressions due to past and distant star formation events are complemented by the impact of H II bubbles from present time and local star formation activity.

Multi-scale physical properties of NGC 6334 as revealed by local relative orientations between magnetic fields, density gradients, velocity gradients, and gravity

“…The integrated intensity (moment 0) maps of these lines are shown in Appendix A. For the NANTEN2 CO (1-0) and JCMT 13 CO (3-2) observations, we only consider the line emission from -12 to 4 km s −1 since most of the large-scale line emission in the NGC 6334 region is within this velocity range (Arzoumanian et al 2022). A second and fainter velocity component in the NGC 6334 region from -20 to -12 km s −1 has been previously reported (Fukui et al 2018), but is not considered in this work.…”

“…Figure 3(a) shows the velocity centroid map of the NGC 6334 complex traced by NANTEN2 CO (1-0) observations (Fukui et al 2018). The velocity structures of NGC 6334 and its surrounding material are coherent and there is a global velocity gradient of 0.1 km s −1 pc −1 from northeast to southwest along the direction of the galactic plane, but the origin of this global velocity gradient is still unclear (Arzoumanian et al 2022).…”

A potential new phase of massive star formation

“…It could be that the hub velocity field is the result of both rotation and kinematics driven by a strong magnetic fields that provides support against collapse (e.g. Inoue et al 2018;Bonne et al 2020;Arzoumanian et al 2022). However, a simpler explanation would be that gravity is the main driver of the observed velocity field, as suggested by the infall spectral signatures discussed above.…”

The SEDIGISM survey: Molecular cloud morphology

“…The filamentary nature of molecular clouds is ubiquitous in the Galaxy and most of the star-forming clumps are situated in large scale filamentary structures (Schneider & Elmegreen 1979;Arzoumanian et al 2011;Polychroni et al 2013;Hacar et al 2013;Li et al 2016;Olmi et al 2016;Kainulainen et al 2017;Bresnahan et al 2018;Mattern et al 2018;Ballesteros-Paredes et al 2020;Arzoumanian et al 2022). The evolution of filaments is influenced by various mechanisms, e.g., ISM turbulence, shocked flows, supernovae feedback, galactic shear (Chen et al 2020;Colombo et al 2021).…”

“…Relating the cloud morphology to its properties and Galactic environment may provide us a better understanding of molecular clouds and star formation. It could also help us understand the physical processes behind the structure of clouds (Arzoumanian et al 2022).…”