SiO emission in the filamentary Infrared Dark Cloud G035.39-00.33: An ALMA view

TL;DR

This study uses ALMA observations of SiO and other molecules to explore shock activity, star formation, and cloud formation mechanisms in the filamentary IRDC G035.39-00.33, revealing shock-induced structures and potential external triggers from nearby supernova remnants.

Contribution

First detailed ALMA imaging of SiO in this IRDC, linking shock activity, filament morphology, and external influences from supernova remnants and HII regions.

Findings

Broad SiO emission indicates active outflows and star formation.

Narrow SiO emission forms arc-like structures at cloud edges.

IRDC likely shaped by large-scale shocks from SNR and HII region interactions.

Abstract

Filamentary infrared dark clouds (IRDCs) are believed to represent the initial conditions for massive star and cluster formation. We investigate the IRDC G035.39-00.33 using SiO, H13CO+, CH3OH, and CS emission observed with ALMA at 3.5\arcsec\ resolution (0.05 pc). The SiO emission traces shock activity within the cloud, providing insights into current star formation and cloud formation mechanisms. We identify several regions with broad SiO emission clearly associated with outflows, pinpointing the locations of ongoing star formation across the cloud. The ALMA images also reveal a series of spatially extended SiO emission spots with narrow line profiles, aligned along an arc-like path that is also seen in CS and CH3OH emission. While the broad SiO emission is mainly associated with the main cloud filament, as seen in visual extinction, the narrow SiO arch is located at the edge of the cloud, far from the identified sites of star formation activity. The presence of these arc-like morphologies suggests that large-scale shocks may have compressed the gas in the surroundings of the G035.39-00.33 cloud, shaping its filamentary structure. By inspecting the large-scale radio continuum emission around G035.39-00.33, we find that this IRDC is part of a larger star-forming complex where the densest and coolest material appears at the interacting regions between a Supernova Remnant (SNR) and an expanding HII region. In particular, we hypothesize that this IRDC may be spatially coincident with the ionized expanding gas associated with the previously identified SNR G35.6-0.4. We suggest that collisions between giant molecular clouds and expanding gas flows from interacting SNRs and HII regions may be responsible for the observed arc-like structures. Such shock compressions could play an important role in the formation of IRDCs and in the potential triggering of star formation.