Mon R2: a hub-filament system with an infrared bubble at the hub center

Abstract

A multi-wavelength, multi-scale study of the Mon R2 hub-filament system (HFS) reveals a spiral structure, with the central hub containing more mass than its filaments. ALMA C18O(1-0) emission reveals several accreting filaments connected to a molecular ring (size ∼0.18 pc × 0.26 pc). The molecular ring surrounds the infrared (IR) ring (size ∼0.12 pc × 0.16 pc), which is not usually observed. The IR ring encircles IR dark regions and a population of embedded near-IR sources, including the massive stars IRS 1 and IRS 2. ALMA HNC(3-2) line data reveal a mirrored B-shaped feature (extent ∼19000 AU × 39000 AU) toward the eastern part of the molecular ring, suggesting expansion at ∼2.25 km s−1. Distinct HNC sub-structures in both redshifted and blueshifted velocity components are investigated toward the B-shaped feature. The presence of these braid-like substructures in each velocity component strongly suggests instability in photon-dominated regions. A dusty shell-like feature (extent ∼0.04 pc × 0.07 pc; mass ∼7 M⊙) hosting IRS 1 is identified in the ALMA 1.14 mm continuum map, centered toward the base of the B-shaped feature. The IR and dense molecular rings are likely shaped by feedback from massive stars, driven by high pressure values between 10−8-10−10 dynes cm−2, observed within a 1 pc range of the B0 ZAMS star powering the ultracompact HII region. Overall, these outcomes support that the Mon R2 HFS transitioned from IR-quiet to IR-bright, driven by the interaction between gas accretion and feedback from massive stars.