Simultaneous low- and high-mass star formation in a massive protocluster: ALMA observations of G11.92−0.61★

Abstract

We present 1.05 mm ALMA observations of the deeply embedded high-mass protocluster G11.92−0.61, designed to search for low-mass cores within the accretion reservoir of the massive protostars. Our ALMA mosaic, which covers an extent of ∼0.7 pc at sub-arcsecond (∼1400 au) resolution, reveals a rich population of 16 new millimetre continuum sources surrounding the three previously-known millimetre cores. Most of the new sources are located in the outer reaches of the accretion reservoir: the median projected separation from the central, massive (proto)star MM1 is ∼0.17 pc. The derived physical properties of the new millimetre continuum sources are consistent with those of low-mass prestellar and protostellar cores in nearby star-forming regions: the median mass, radius, and density of the new sources are 1.3 M ⊙ , 1600 au, and n H2 ∼10 7 cm −3 . At least three of the low-mass cores in G11.92−0.61 drive molecular outflows, traced by high-velocity 12 CO(3-2) (observed with the SMA) and/or by H 2 CO and CH 3 OH emission (observed with ALMA). This finding, combined with the known outflow/accretion activity of MM1, indicates that high-and low-mass stars are forming (accreting) simultaneously within this protocluster. Our ALMA results are consistent with the predictions of competitive-accretion-type models in which high-mass stars form along with their surrounding clusters.

The Seven Most Massive Clumps in W43-Main as Seen by ALMA: Dynamical Equilibrium and Magnetic Fields

“…A similar situation has also been seen in W43-MM1 (see Paper I and Motte et al 2018). Additional examples from other highmass star forming regions have been presented in the literature (Lu et al 2018;Sanhueza et al 2017;Cyganowski et al 2017;Zhang et al 2015;Frau et al 2014). This indicates that low mass stars are also being formed along high-mass stars and therefore, low mass and high mass star formation processes might be coupled.…”

ALMA Observations of Fragmentation, Substructure, and Protostars in High-mass Starless Clump Candidates

“…At a comparable distance of d = 3.37 +0.39 −0.32 kpc (derived from maser parallax Sato et al 2014) and total mass to the SCCs in this study, G11.92-0.61 is more evolved, coincident with several indicators of high-mass star formation, such as Class I & II CH 3 OH masers, H 2 O masers, a GLIMPSE Extended Green Object (Cyganowski et al 2008), numerous "hot core" molecular lines, and highvelocity collimated outflows. The sample of SCCs in this study complement the study of G11.92-0.61 in Cyganowski et al (2017) through ALMA observations at similar resolution and sensitivity for clumps in a less active evolutionary state. In contrast, we find no clear high-mass protostellar cores or high-mass protostars in our sample of SCCs, while numerous accreting low-mass protostars are observed, as evidenced by bipolar outflows in CO/SiO.…”

“…G28539, G29601), supports the presence of a distributed low-mass core population at the initial evolutionary phase for some systems. It is possible that depending on the initial level of support provided against fragmentation individual systems develop with varying degrees of hierarchy and segregation, and that the conclusions of Zhang et al (2015) and Cyganowski et al (2017) may both be correct for sources of different initial physical conditions.…”

The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars. I. Identifying and Characterizing the Protostellar Content of the OMC-2 FIR4 and OMC-2 FIR3 Regions

“…The uncertainty is, in part, because intermediate and high-mass stars are significantly more rare than low-mass stars. Furthermore, many examples of intermediate to high-mass protostars are at distances greater than 1 kpc (Cyganowski et al 2017;Motte et al 2018), and they are typically more deeply embedded than low-mass protostars making their characterization challenging (e.g., Orion BN-KL; Gezari et al 1998;De Buizer et al 2012;Ginsburg et al 2018). This typically large distance makes the identification and characterization of intermediate-mass protostars difficult, especially because multiplicity increases with stellar mass (e.g., van Kempen et al 2012;Duchêne & Kraus 2013;Moe & Di Stefano 2017).…”