Fragmentation in the Serpens/Aquila Star-forming Region

TL;DR

This study uses ALMA observations and simulations to analyze fragmentation and star formation in dense cores within the Serpens/Aquila region, revealing starless cores and the influence of turbulence on core substructure.

Contribution

It provides new observational evidence of starless cores and tests turbulence-based models of core collapse with synthetic simulations.

Findings

Detection of two starless dense cores without protostars.

Simulation predictions match observed starless core detections.

Higher fragmentation correlates with increased multiplicity at smaller scales.

Abstract

We present a population study of Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 6 observations of the 100 most gravitationally unstable dense cores in Aquila using a simple mass versus size analysis. We identify 66 continuum sources from ALMA 12m observations at 106GHz and through comparisons with known protostellar catalogs; two of these detected dense cores appear to be completely starless, without any accompanying/nearby protostar detections. Additionally, we find nine other starless ALMA 12m detections within protostellar cores that have fragmented into a mixture of starless and protostellar substructures. We test the turbulent core collapse model by conducting synthetic observations of turbulent magnetohydrodynamical simulations of collapsing starless cores in order to predict how many starless cores should be detected given their central density and density profile. The simulations predict at least one (1.19) detection, consistent with our two detections of ALMA 12m emission within completely starless cores. We also use a combination of ALMA Compact Array Cycle 4 observations and the Herschel Gould Belt Survey data to analyze how mass is distributed on three distinct spatial scales, in order to understand how turbulence shapes the evolution of substructure development as dense cores collapse to form new star systems. We find an increase in multiplicity at the smallest scales when the parent larger-scale structure also has a higher degree of fragmentation.