Detailed Analysis Of the Inter-Stellar Medium – DAOISM

Star formation in galaxies is the engine that drives cosmic evolution. Decades of observations have yielded diverse empirical rules about how it operates, but we still have no comprehensive, quantitative theory that encompasses the full range of physics and spatial scales involved. The 4-year project DAOISM (Deep Analysis Of the InterStellar Medium) is a collaborative project between observational astronomers, theoretical astrophysicists and data scientists that is developing advanced statistical methods and data analysis techniques for deployment on observations of the cold star-forming interstellar medium (ISM) in galaxies. The project combines state-of-the-art modelling, data from world-class facilities (ALMA, MUSE, IRAM), and original data science methods in order to answer key outstanding questions in star formation: How best to estimate local physical conditions? Which spectral line diagnostics best capture the star-forming capability of molecular gas in clouds and galaxies? How does galactic environment affect their physics and chemistry?

The essence of DAOISM is to build a detailed comprehensive understanding of the local Orion B cloud and use it to improve the interpretation of poorly resolved extragalactic observations that map how star formation proceeds across the diversity of galactic environments in the local Universe. Our approach combines statistical analysis, machine learning and Bayesian inversion of data based on state-of-the-art models.These new strategies are urgently needed since the latest astronomical data and physico-chemical models of the ISM now regularly attain a volume and complexity that are intractable to the simple correlation analysis methods employed in the field to date.

DAOISM leverages our team’s complementary state-of-the-art observational programs (co-PIs of ORION-B and PHANGS), ISM models (Meudon PDR code, time-dependent astrochemistry code) and data science expertise. The ORION-B project is an IRAM-30m Large Program imaging the Orion-B giant molecular cloud (GMC). The resulting unique wide-field hyper-spectral data cube (>30 molecular lines detected, ~820,000 pixels, ~240,000 spectral channels per pixel) enables an unprecedented characterization of the physical structure, chemistry and dynamics of a GMC, and their link to its star formation activity. PHANGS combines high resolution ALMA observations of molecular emission lines, VLT/MUSE observations of ionised gas lines, and Hubble Space Telescope imaging to deliver the first statistically robust description of the evolution of ~100,000 star-forming regions throughout the nearby galaxy population. A dedicated joint analysis of the PHANGS and ORION-B surveys is an exceptional opportunity to bridge Galactic and extragalactic star formation studies.

The DAOISM project is structured along three scientific work packages, progressing from a detailed description of the ISM physical and chemical properties that locally control star formation, to the development of advanced methods for revealing the best diagnostics for these parameters and processes in local as well as galaxy-scale measurements. By the end of the ANR-funding period, DAOISM will deliver: i) a comprehensive characterization of the physical, kinematic, chemical and magnetic structure of a typical GMC and of their relation to star formation and feedback processes, as well as new statistical methods adapted to the description and analysis of the magneto-turbulent cold ISM; ii) a new observing mode for the NOEMA interferometer allowing efficient large wide-field high resolution observations, iii) new tools for disentangling the emission contributed by physically distinct regions within a single resolution element, and for comparing resolved Galactic observations to spatially unresolved extragalactic data, a major roadblock for current extragalactic star formation studies.

All tools and codes developed by DAOISM will be made public.