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