Distribution of Serpens South protostars revealed with ALMA

TL;DR

This study uses high-resolution ALMA observations to analyze the masses and spatial distribution of protostars in Serpens South, revealing primordial mass segregation and clustering in a young low-mass star-forming region.

Contribution

First ALMA-based detailed analysis of protostellar mass distribution and spatial segregation in Serpens South, demonstrating primordial mass segregation in a low-mass cluster.

Findings

Detected 52 protostellar sources with masses 0.002-0.9 solar masses.

Evidence of primordial mass segregation and clustering.

Higher-mass sources are concentrated near dense gas regions.

Abstract

Aims: We investigated the masses and spatial distributions of pre-stellar and protostellar candidates in the young, low-mass star forming region Serpens South, where active star formation is known to occur along a predominant filamentary structure. Previous observations used to study these distributions have been limited by two important observational factors: (1) sensitivity limits that leave the lowest-mass sources undetected, or (2) resolution limits that cannot distinguish binaries and/or cluster members in close proximity. Methods: Recent millimeter-wavelength interferometry observations can now uncover faint and/or compact sources in order to study a more complete population of protostars, especially in nearby ($D<500$ pc) clusters. Here we present ALMA observations of 1 mm (Band 6) continuum in a $3 \times 2$ arcminutes region at the center of Serpens South. Our angular resolution of $\sim1$ arcsec is equivalent to $\sim400$ au, corresponding to scales of envelopes and/or disks of protostellar sources. Results: We detect 52 sources with 1 mm continuum, and we measure masses of $0.002 - 0.9$ solar masses corresponding to gas and dust in the disk and/or envelope of the protostellar system. For the deeply embedded (youngest) sources with no IR counterparts, we find evidence of mass segregation and clustering according to: the Minimum Spanning Tree method, distribution of projected separations between unique sources, and concentration of higher-mass sources near to the dense gas at the cluster center. Conclusions: The mass segregation of the mm sources is likely primordial rather than dynamical given the young age of this cluster, compared with segregation time. This is the first case to show this for mm sources in a low-mass protostellar cluster environment.