Towards a unified theory of low- and high-mass star-formation


Traditionally, there is a theoretical and observational dichotomy in describing the star formation process: while low-mass clouds form distributed populations of solar-like stars, only high-mass clouds contain large stellar clusters and massive stars. However, increasing evidences suggest a smooth transition between these two regimes. So, does this classical distinction correspond to a real change of the cloud properties or is it artificially created by our observational techniques?The unprecedented sensitivity of the recent Herschel Space Observatory has revealed a high degree of internal organization of the gas and dust inside clouds prior to the formation of stars. Both low- and high- mass star-forming regions are typically found in association to filamentary gas structures. Several of these filamentary clouds exhibit an underlying substructure of fibers twisted in space forming complex bundels. Can these filaments within filaments (aka bundles of fibers) explain the internal substructure of regions of increasing complexity? Is, therefore, the internal structure of massive filaments a scaled-up version of their low-mass counterparts?

The Integral Shaped Filament in Orion. (Credit: ESO; link)

The Orion A cloud

The Orion A cloud, more than 60 pc long and with > 3×104 solar masses of gas, offers a unique opportunity to investigate the origin of stars along their entire mass spectrum. This giant molecular cloud harbors a total of ∼ 3000 young stars, most of them located in compact clusters and associations, including the massive Orion Nebula Cluster (ONC). This star-forming region is also recognized as a prototypical example of a filamentary cloud. The characteristics and properties of the resolved stellar populations and gas content of the Orion A cloud are usually employed as benchmarks for both low- and high-mass star formation theories.

Herschel dust emission (green) over the optical image (background) in the Orion A region. The upper panel shows the number of references per Galactic Longitude bin (Credit: Meingast et al 2016, ADS)

The ORION-4D survey

The ORION-4D survey aims to investigate the dynamical, physical, and chemical properties of the gas in the filamentary Orion A cloud. This project combines a new set of state-of-the-art single-dish (IRAM30m, EFF100m, and APEX12m) and interferometric (ALMA Cycles 3 & 4) observations for >400 hours of telescope time.

The ORION-4D survey will produce a unique set of large-scale, high-sensitivity molecular line observations of the entire Orion A cloud. Its wide spectral coverage includes observations of 30 molecular species (e.g., C18O, HCN, N2H+, NH3, etc), sensitive to different physical and dynamical properties of the gas (density, temperature, column density, chemical composition, velocity structure...). The unprecedented quality, resolution, and extension of the ORION-4D data will allow to simultaneously analyze the kinematic (2+1D) and chemical (+1D) properties of the gas at large-scales within this massive filamentary cloud.

Scientific Goals

The main goals of the ORION-4D survey are as follow:

  • Investigate the internal gas dynamics of massive filaments and its connection with their low-mass counterparts
  • Obtain statistical properties of filaments, fibers, and cores at cloud scales
  • Characterize the internal structure of clusters
  • Understand gas chemistry at large-scales
  • Develop new analysis techniques for the study of massive molecular clouds
  • Unify the description of low- and high-mass star-forming regions


This project is funded by NWO (Netherlands Organisation for Scientific Research).

Proj.ID: 639.041.644 (link)