ATOMS: ALMA three-millimeter observations of massive star-forming regions – XIII. Ongoing triggered star formation within clump-fed scenario found in the massive (∼1500 M⨀) clump

Abstract

ABSTRACT Whether ionization feedback triggers the formation of massive stars is highly debated. Using ALMA 3-mm observations with a spatial resolution of ∼0.05 pc and a mass sensitivity of 1.1 $\rm M_\odot$ per beam at 20 K, we investigate the star formation and gas flow structures within the ionizing feedback-driven structure, a clump-scale massive (≳ 1500 $\rm M_\odot$) bright-rimmed cloud (BRC) associated with IRAS 18290–0924. This BRC is bound only if external compression from ionized gas is considered. A small-scale (≲ 1 pc) age sequence along the direction of ionizing radiation is revealed for the embedded cores and protostars, which suggests triggered star formation via radiation-driven implosion (RDI). Furthermore, filamentary gas structures converge towards the cores located in the BRC’s centre, indicating that these filaments are fueling mass towards cores. The local core-scale mass infall rate derived from H13CO+ J = 1 − 0 blue profile is of the same order of magnitude as the filamentary mass inflow rate, approximately 1 $\rm M_\odot$ kyr−1. A photodissociation region (PDR) covering the irradiated clump surface is detected in several molecules, such as CCH, HCO+, and CS whereas the spatial distribution stratification of these molecules is indistinct. CCH spectra of the PDR possibly indicate a photoevaporation flow leaving the clump surface with a projected velocity of ∼2 km s−1. Our new observations show that RDI accompanied by a clump-fed process is operating in this massive BRC. Whether this combined process works in other massive BRCs is worth exploring with dedicated surveys.