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 high-mass 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 ({θ<SUB>maj</SUB>, θ<SUB>min</SUB>} = {1.4 arcsec, 0.8 arcsec} ∼ {0.02 pc, 0.01 pc}) and high-sensitivity (0.2 mJy beam<SUP>-1</SUP>; ∼0.2 M<SUB>☉</SUB>) 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<SUB>☉</SUB> < M<SUB>c</SUB> < 10.4 M<SUB>☉</SUB>. 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.