Unveiling the early-stage anatomy of a protocluster hub with ALMA

Abstract

High-mass stars shape the interstellar medium in galaxies, and yet, largely because the initial conditions are poorly constrained, we do not know how they form. One possibility is that highmass stars and star clusters form at the junction of filamentary networks, referred to as 'hubs'. In this Letter we present the complex anatomy of a protocluster hub within an Infrared Dark Cloud (IRDC), G035.39-00.33, believed to be in an early phase of its evolution. We use high-angular resolution ({θmaj, θmin} = {1.4 arcsec, 0.8 arcsec} ~ {0.02 pc, 0.01 pc}) and high-sensitivity (0.2 mJy beam-1; ~0.2M⊙) 1.07 mm dust continuum observations from the Atacama Large Millimeter Array (ALMA) to identify a network of narrow, 0.028 ± 0.005 pc wide, filamentary structures. These are a factor of ≥3 narrower than the proposed 'quasi-universal' ~0.1 pc width of interstellar filaments. Additionally, 28 compact objects are reported, spanning a mass range 0.3 M⊙< Mc < 10.4 M⊙. This indicates that at least some low-mass objects are forming coevally with more massive counterparts. Comparing to the popular 'bead-on-a-string' analogy, the protocluster hub is poorly represented by a monolithic clump embedded within a single filament. Instead, it comprises multiple intra-hub filaments, each of which retains its integrity as an independent structure and possesses its own embedded core population.