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 ($\{\hat{I}{¸}_{\mathrm{maj}},\hat{I}{¸}_{\min }\}=\{1.4\mathrm{arcsec},0.8\mathrm{arcsec}\}\sim \{0.02\mathrm{pc},0.01\mathrm{pc}\}$) and high-sensitivity ($0.2$mJy beam${}^{-1}$; $\sim 0.2$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 $\gtrsim 3$ narrower than the proposed 'quasi-universal' $\sim 0.1$pc width of interstellar filaments. Additionally, 28 compact objects are reported, spanning a mass range $0.3{\mathrm{M}}_{\odot }<M_{\mathrm{c}}<10.4{\mathrm{M}}_{\odot }$. 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.

6 Pages, 2 Figures, 1 Table. Accepted for publication in MNRAS Letters