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 (${\theta_{\rm maj}, \theta_{\rm min}}={1.4{\rm arcsec}, 0.8{\rm arcsec}}\sim{0.02{\rm pc}, 0.01{\rm pc}}$) and high-sensitivity ($0.2$mJy beam$^{-1}$; $\sim0.2$M${\odot}$) 1.07 mm dust continuum observations from the Atacama Large Millimeter Array (ALMA) to identify a network of narrow, $0.028\,\pm\,0.005$pc wide, filamentary structures. These are a factor of $\gtrsim3$ narrower than the proposed 'quasi-universal' $\sim0.1$pc width of interstellar filaments. Additionally, 28 compact objects are reported, spanning a mass range $0.3{\rm M{\odot}}<M_{\rm c}<10.4{\rm M_{\odot}}$. 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.