The role of Galactic H II regions in the formation of filaments

Abstract

Context. Massive stars and their associated ionized (H II) regions could play a key role in the formation and evolution of filaments that host star formation. However, the properties of filaments that interact with H II regions are still poorly known. Aims. To investigate the impact of H II regions on the formation of filaments, we imaged the Galactic H II region RCW 120 and its surroundings where active star formation takes place and where the role of ionization feedback on the star formation process has already been studied. Methods. We used the large-format bolometer camera ArTéMiS on the APEX telescope and combined the high-resolution ArTéMiS data at 350 and 450 μm with Herschel-SPIRE/HOBYS data at 350 and 500 μm to ensure good sensitivity to a broad range of spatial scales. This allowed us to study the dense gas distribution around RCW 120 with a resolution of 8′′ or 0.05 pc at a distance of 1.34 kpc. Results. Our study allows us to trace the median radial intensity profile of the dense shell of RCW 120. This profile is asymmetric, indicating a clear compression from the H II region on the inner part of the shell. The profile is observed to be similarly asymmetric on both lateral sides of the shell, indicating a homogeneous compression over the surface. On the contrary, the profile analysis of a radial filament associated with the shell, but located outside of it, reveals a symmetric profile, suggesting that the compression from the ionized region is limited to the dense shell. The mean intensity profile of the internal part of the shell is well fitted by a Plummer-like profile with a deconvolved Gaussian full width at half maximum of 0.09 pc, as observed for filaments in low-mass star-forming regions. Conclusions. Using ArTéMiS data combined with Herschel-SPIRE data, we found evidence for compression from the inner part of the RCW 120 ionized region on the surrounding dense shell. This compression is accompanied with a significant (factor 5) increase of the local column density. This study suggests that compression exerted by H II regions may play a key role in the formation of filaments and may further act on their hosted star formation. ArTéMiS data also suggest that RCW 120 might be a 3D ring, rather than a spherical structure.

Dust polarized emission observations of NGC 6334

“…The crests traced by DisPerSE may correspond to "filament-crests" or to "shellcrests" associated with shell-like structures around H II regions (such as those around sources II and IV). We mention briefly possible differences between "filament-crests" and "shell-crests" below (see also Zavagno et al 2020, who present a study of the properties of shell-crests and filament-crests in the RCW 120 H II region).…”

APEX CO observations towards the photodissociation region of RCW 120

“…Therefore, conclusions from this model, even if it supports the idea of triggered star formation, must be taken with caution. Detailed analysis of the interplay between the H II region and the PDR (Tremblin et al 2014;Figueira et al 2018;Zavagno et al 2020) might be a better indicator but are also not exempt from some uncertainties (Dale et al 2015) regarding induced star formation.…”

“…RCW 120 is a well-studied Galactic H II region because of its ovoid shape and its relatively close distance (1.34 kpc, Russeil 2003;Zavagno et al 2007). Thanks to these advantages, this region has received a lot of attention from observers and simulations, and has been studied in several papers (Zavagno et al 2007(Zavagno et al , 2010(Zavagno et al , 2020Deharveng et al 2009;Anderson et al 2012Anderson et al , 2015Tremblin et al 2014;Kirsanova et al 2014Kirsanova et al , 2019Torii et al 2015;Walch et al 2015;Mackey et al 2016;Figueira et al 2017Figueira et al , 2018Marsh & Whitworth 2019). Figueira et al (2017) showed that two clumps observed at millimeter wavelength host different kinds of sources with respect to their evolutionary stage.…”

HII regions and high-mass starless clump candidates II. Fragmentation and induced star formation at ~0.025 pc scale: An ALMA continuum study

“…At this stage, it is not clear whether this turbulence increment could change a fragmentation from thermal-dominated to turbulentdominated. The fragmentation at 0.01 pc scale in the most massive star-forming clump (M ∼ 4) impacted by the H ii region RCW 120 (Kirsanova et al 2019;Zavagno et al 2020) is investigated by Figueira et al (2018) and they suggested that turbulent fragmentation is dominant due to the H ii region feedback. Even for the cases where the fragmentation at around 0.02 pc scale in the clumps is still thermal-dominated under the vigorous feedback of H ii regions, the fragments could be more massive or less numerous (Liu et al 2017).…”