A potential new phase of massive star formation

Abstract

Context. Due to the sparsity and rapid evolution of high-mass stars, a detailed picture of the evolutionary sequence of massive protostellar objects still remains to be drawn. Some of the early phases of their formation are so short that only a handful of objects throughout the Milky Way currently find themselves spending time in those phases. Aims. Star-forming regions going through the shortest stages of massive star formation will present different observational characteristics than most regions. By studying the dust continuum and line emission of such unusual clouds, one might be able to set strong constraints on the evolution of massive protostellar objects. Methods. We present a detailed analysis of the G345.88-1.10 hub filament system, a newly discovered star-forming cloud that hosts an unusually bright bipolar infrared nebulosity at its centre. We used archival continuum observations from Herschel, WISE, Spitzer, 2MASS, and SUMSS in order to fully characterise the morphology and spectral energy distribution of the region. We further made use of APEX 12 CO(2-1), 13 CO(2-1), C 18 O(2-1) and H30α observations to investigate the presence of outflows and map the kinematics of the cloud. Finally, we performed RADMC-3D radiative transfer calculations to constrain the physical origin of the central nebulosity.Results. At a distance of 2.26 +0.30 −0.21 kpc, G345.88-1.10 exhibits a network of parsec-long converging filaments. At the junction of these filaments lie four infrared-quiet fragments. H1 is the densest fragment (with M=210 M , R eff = 0.14 pc) and sits right at the centre of a wide (opening angle of ∼ 90±15 o ) bipolar nebulosity where the column density reaches local minima. The 12 CO(2-1) observations of the region show that these infrared-bright cavities are spatially associated with a powerful molecular outflow that is centred on the H1 fragment. Negligible radio continuum and no H30α emission is detected towards the cavities, seemingly excluding that ionising radiation drives the evolution of the cavities. Radiative transfer calculations of an embedded source surrounded by a disc and/or a dense core are unable to reproduce the observed combination of a low-luminosity ( 500 L ) central source and a surrounding highluminosity (∼ 4000 L ) mid-infrared-bright bipolar cavity. This suggests that radiative heating from a central protostar cannot be responsible for the illumination of the outflow cavities. Conclusions. This is, to our knowledge, the first reported object of this type. The rarity of objects like G345.88-1.10 is likely related to a very short phase in the massive star and/or cluster formation process that was so far unidentified. We discuss whether mechanical energy deposition by one episode or successive episodes of powerful mass accretion in a collapsing hub might explain the observations. While promising in some aspects, a fully coherent scenario that explains the presence of a luminous bipolar cavity centred on an infrared-dark fragment remains elusive at this point.

SOFIA Observations of 30 Doradus. II. Magnetic Fields and Large-scale Gas Kinematics

“…This reveals that the gravitational instability likely sets in relatively low gas density in 30 Dor cloud in general, and the north experiences it at a slightly lower density than that of the south because its power-law tail pops up earlier. The gravitational collapse in parsec scale has been proposed in various studies (e.g., Hartmann & Burkert 2007;Peretto et al 2006Peretto et al , 2013Schneider et al 2010;Jackson et al 2019;Bonne et al 2022b). Another note is that the gravitational collapse in the south is much more compact than that in the north.…”

The SOFIA FEEDBACK Legacy Survey Dynamics and Mass Ejection in the Bipolar H ii Region RCW 36

“…B ν (T d ) is the Planck function at a specific dust temperature T d . In order to calculate the dust temperature map, the method presented in Peretto et al (2016) and Bonne et al (2022), based on the intensity ratio of 70 μm (after smoothing to the resolution of the 160 μm data) and 160 μm, is used. From this dust temperature map, it is then possible to calculate the optical depth and the column density (Draine 2003).…”

Unveiling the Formation of the Massive DR21 Ridge

“…This opens the question of how massive stars can form. Based on observations of molecular clouds that form massive stars, it was proposed that some largescale dynamics, partly driven by self-gravity, can provide the fast concentration of mass necessary to form massive stars (e.g., Peretto et al 2006Peretto et al , 2013Peretto et al , 2014Hartmann & Burkert 2007;Galván-Madrid et al 2010;Schneider et al 2010Schneider et al , 2015Csengeri et al 2011aCsengeri et al , 2011bWyrowski et al 2012Wyrowski et al , 2016Beuther et al 2015;Williams et al 2018;Jackson et al 2019;Bonne et al 2022a).…”