IRAS 23385+6053: an embedded massive cluster in the making

Abstract

Context. This study is part of the project "CORE", an IRAM/NOEMA large program consisting of observations of the millimeter continuum and molecular line emission towards 20 selected high-mass star forming regions. The goal of the program is to search for circumstellar accretion disks, study the fragmentation process of molecular clumps, and investigate the chemical composition of the gas in these regions. Aims. We focus on IRAS 23385+6053, which is believed to be the least evolved source of the CORE sample. This object is characterized by a compact molecular clump that is IR dark shortward of 24 µm and is surrounded by a stellar cluster detected in the near-IR. Our aim is to study the structure and velocity field of the clump. Methods. The observations were performed at ∼1.4 mm and employed three configurations of NOEMA and additional single-dish maps, merged with the interferometric data to recover the extended emission. Our correlator setup covered a number of lines from well-known hot core tracers and a few outflow tracers. The angular (∼0. 45-0. 9) and spectral (0.5 km s −1 ) resolutions were sufficient to resolve the clump in IRAS 23385+6053 and investigate the existence of large-scale motions due to rotation, infall, or expansion. Results. We find that the clump splits into six distinct cores when observed at sub-arcsecond resolution. These are identified through their 1.4 mm continuum and molecular line emission. We produce maps of the velocity, line width, and rotational temperature from the methanol and methyl cyanide lines, which allow us to investigate the cores and reveal a velocity and temperature gradient in the most massive core. We also find evidence of a bipolar outflow, possibly powered by a low-mass star. Conclusions. We present the tentative detection of a circumstellar self-gravitating disk lying in the most massive core and powering a largescale outflow previously known in the literature. In our scenario, the star powering the flow is responsible for most of the luminosity of IRAS 23385+6053 (∼3000 L ). The other cores, albeit with masses below the corresponding virial masses, appear to be accreting material from their molecular surroundings and are possibly collapsing or on the verge of collapse. We conclude that we are observing a sample of star-forming cores that is bound to turn into a cluster of massive stars.

ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions – V. Hierarchical fragmentation and gas dynamics in IRDC G034.43+00.24

“…Quantitatively, the velocity pattern can be fitted with a Keplerian rotation curve around an M sin 2 θ ∼10-50 M protostar, where θ is defined as the inclination angle between the rotation axis and the line of sight. Although this range of masses is consistent with the luminosity (10 4.3 L ) and spectral type (B0) determined from the SED of the MM1-a core by Rathborne, Jackson, & Simon (2006), it is still rather small compared with the core's mass (∼ 200 M , see Table 1) and is inconsistent with the assumption of the Keplerian rotation that requires the gas mass to be negligible with respect to the central mass (e.g., Cesaroni et al 2019). This inconsistency can be alleviated if the rotating envelope is sufficiently inclined.…”

The evolution of temperature and density structures of OB cluster-forming molecular clumps

“…On the other hand, the inclusion of infall velocities to the observed linewidth may also cause the source which is undergoing collapse to appear seemingly unbound (e.g., Smith et al 2009). Infall motions of dense cores that have large α vir (∼5-8) are revealed by Cesaroni et al (2019), inside a massive cluster-forming clump. Giannetti et al (2017) suggest that CH 3 CCH is a reliable tracer for the kinematics of bulk gas structures in the massive clumps.…”

Multi-scale view of star formation in IRAS 21078+5211: from clump fragmentation to disk wind

“…The analysis of the continuum emission from cold dust shows a large variety in the fragmentation properties of the sample, from regions where a single massive core dominates to regions where as many as 20 cores, with comparable masses, are detected (Beuther et al 2018). In several CORE targets, employing dense-gas molecular tracers such as the CH 3 CN and CH 3 OH rotational transitions, LSR velocity (V LSR ) gradients are often detected towards the most massive cores of the cluster (Ahmadi et al 2018;Bosco et al 2019;Cesaroni et al 2019;Gieser et al 2019). Extending over typical linear scales of 1000 au, these V LSR gradients are interpreted in terms of the edge-on rotation of either a disk around a high-mass YSO or an unresolved binary (or multiple) system, or the combination of both motions.…”