Investigating the physical conditions and gas dynamics of a molecular cloud with molecular lines : the Orion-B case

Séminaire IPAG de Maryvonne Gérin (LERMA), jeudi 1 juillet 2021, 11h00, IPAG seminar room

Molecules have long been thought to be versatile tracers of cold neutral media in the universe, from high-redshift galaxies to star forming regions and proto-planetary disks, because their internal degrees of freedom are controlled by physical conditions in their environments. However, the promise that molecular emission can be used to quantitatively probe the physical and chemical state of the interstellar medium is still hampered by the incomplete understanding of the complex physical and chemical structure of the interstellar gas, and its dynamical evolution.

In this talk, I will present The ORION-B project (Outstanding Radio-Imaging of OrioN-B), a Large Program of the IRAM 30m telescope, and discuss recent results obtained by the consortium.

  1. How to improve the quantitative estimate of the H2 column density based on the molecular line intensities (Gratier et al. 2021) ;
  2. How to estimate a reference precision on the column densities, excitation temperatures, centroid velocities and velocity dispersions of the three main CO isotopologues, 12CO, 13CO, C18O, with the help of the Cramer Rao Bound (CRB) technique (Roueff et al. 2021) ;
  3. How to quantify the velocity field around the filaments (Gaudel et al. 2021) ;
  4. How to identify the best tracers of the ionization fraction among hundreds of species included in
    models (Bron et al. 2021). 4) I will discuss the astrophysical consequences.

References :
– Bron et al. 2021, A&A, 645, 28B, "Tracers of the ionization fraction in dense and translucent gas. I. Automated exploitation of massive astrochemical model grids"
– Gratier et al. 2021, A&A, 645, 27G, "Quantitative inference of the H2 column densities from 3 mm molecular emission : case study towards Orion B"
– Gaudel et al. 2021 in prep "Kinematics around filamentary structures in the Orion B cloud"
– Roueff et al. 2021, A&A, 645, 26R, "C18O, 13CO, and 12CO abundances and
excitation temperatures in the Orion B molecular cloud. Analysis of the achievable precision in modeling spectral lines within the approximation of the local thermodynamic equilibrium"