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.

Highlights

  • The existence of filaments has been known for a long time (Schneider & Elmegreen 1979; Ungerechts & Thaddeus 1987), the tight relation between filaments and star formation has only been clearly revealed by Herschel observations, which introduce a new paradigm for Galactic star formation (André et al 2014; Molinari et al 2014)

  • With the aim of characterizing the properties of dense photodissociation region (PDR) around H I shell and ionized (H II) regions and their relation with the star formation observed at their edges, we present the results of dust continuum mapping observations of the RCW 120 region with the ArTéMiS bolometer camera on the Atacama Pathfinder Experiment (APEX) 12 m telescope

  • Combination of ArTéMiS and Herschel data The ArTéMiS raw data are affected by a high level of sky noise, which is strongly correlated over the detectors of the focal plane

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Summary

Introduction

The existence of filaments has been known for a long time (Schneider & Elmegreen 1979; Ungerechts & Thaddeus 1987), the tight relation between filaments and star formation has only been clearly revealed by Herschel observations, which introduce a new paradigm for Galactic star formation (André et al 2014; Molinari et al 2014). The Galactic interstellar medium (ISM) and their properties have been extensively studied and discussed (Arzoumanian et al 2011; Palmeirim et al 2013; Schisano et al 2014, 2020; Cox et al 2016; Li et al 2016). One of their most striking properties is their typical inner width of 0.1 pc that seems to be quasiuniversal (André et al 2016; Arzoumanian et al 2019) and which could result from their formation process (Federrath 2016; André 2017). Understanding filaments as a whole (formation, evolution) has become a new quest of star formation studies (e.g., Zhang et al 2019)

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