# Unveiling the Early-Stage Anatomy of a Protocluster Hub with ALMA

Henshaw, JD, Jimenez-Serra, I, Longmore, SN, Caselli, P, Pineda, JE, Avison, A, Barnes, AT, Tan, JC and Fontani, F (2016) Unveiling the Early-Stage Anatomy of a Protocluster Hub with ALMA. Monthly Notices of the Royal Astronomical Society Letters. ISSN 1745-3933

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 ($\{\theta_{\rm maj}, \theta_{\rm min}\}=\{1.''4, 0.''8\}\sim\{0.02\,{\rm pc}, 0.01\,{\rm pc}\}$) 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.