LERMA UMR8112

Laboratoire d’Études du Rayonnement et de la Matière en Astrophysique et Atmosphères



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Interstellar Medium and Plasmas

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What processes drive the evolution of interstellar matter in the Milky Way and in other galaxies ? What roles do the turbulence, the magnetic field, the cosmic rays, and the radiation field play in this evolution ? Those fundamental questions for modern Astrophysics now appear at many spatial scales and for a great variety of environments : from the galactic scales where the diffuse gas collapse to form the precursors of new stars ; down to the scale of proto-planetary disks where the central star strongly interacts with the surrounding matter ; and even in the stars themselves where the transport mechanisms are still unknown. To study all these astronomical objects, the group « Interstellar Medium and Plasmas » of the LERMA combine theoretical works, numerical modeling, 3D simulations, and observations of interstellar environments at high spectral and angular resolutions.

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On the observational side, our group is specialized in the treatment and the analysis of the data obtained with the most advanced space and ground-based observatories. Our expertise is particularly strong in the infrared and sub-millimeter domains which reveal the emission of atoms, molecules and interstellar dust. We have therefore been deeply involved in the recent successes and findings of Herschel and Planck space observatories, which we now follow up by collecting data with the new generation of instruments (in particular, APEX, ALMA, and soon NOEMA).

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On the numerical side, the codes developed in our group are internationally renowned as state-of-the-art tools for the analysis of interstellar matter and the interpretation of observational data. Our expertise extends from the conception of 3D numerical simulations of magnetohydrodynamics, which we run using high-level computational capacities (e.g. PRACE, MesoPSL), to the development of advanced numerical models. The strength of those models, which we provide to the community through the ISM and jets platform, is to solve a great number of microphysical processes at play in the interstellar medium, with prescriptions based on the results of laboratory experiments and theoretical studies which are partly performed in our laboratory.


Select one of the following links to know more about our activities


1. Turbulence & magnetic field

2. Matter / photon interactions

3. Stellar plasmas and laboratory astrophysics

4. Prestellar cores

5. Protostars, debris & jets

6. Accretion & ejection in stars


Click here to access our publications

Séminaires à venir

Vendredi 21 décembre 2018, 14h00
Salle de l'atelier, Paris
Astrochemistry in star forming regions : new modeling approaches
Emeric BRON
LERMA
résumé :
Star-forming regions present rich infrared and millimeter spectra emitted by the gas exposed to the feedback of young stars. This emission is increasingly used to study the star formation cycle in other galaxies, but results from a complex interplay of physical and chemical processes : chemistry in the gas and on grain surfaces, (de)excitation processes of the atoms and molecules, heating and cooling balance,... Its understanding thus requires detailed astrochemical models that include the couplings between these processes. In this talk, I will present several examples where new modeling approaches of specific processes and their couplings proved crucial to solve persistent observational riddles : from the driving role of UV irradiation in the dynamics of photodissociation regions (PDR) to the efficient reformation of molecular hydrogen in these regions.
 
Mardi 15 janvier 2019, 11h00
Salle de l'atelier, Paris
ATTENTION jour ET heure inhabituels
Thresholds for Globular Cluster Formation and their Dominance of Star Formation in the Early-Universe
Bruce ELMEGREEN
IBM Research Division
résumé :
Young massive clusters (YMCs) are usually accompanied by lower-mass clusters and unbound stars with a total mass equal to several tens times the mass of the YMC. If this was also true when globular clusters (GCs) formed, then their cosmic density implies that most star formation before redshift ~2 made a GC that lasted until today. Star-forming regions had to change after this time for the modern universe to be making very few YMCs. Here we consider the conditions needed for the formation of a ~10^6 Msun cluster. These include a star formation rate inside each independent region that exceeds ~1 Msun/yr to sample the cluster mass function up to such a high mass, and a star formation rate per unit area of Sigma_SFR ~ 1 Msun/kpc^2/yr to get the required high gas surface density from the Kennicutt-Schmidt relation, and therefore the required high pressure from the weight of the gas. High pressures are implied by the virial theorem at cluster densities. The ratio of these two quantities gives the area of a GC-forming region, ~1 kpc^2, and the young stellar mass converted to a cloud mass gives the typical gas surface density of 500-1000 Msun/pc^2. Observations of star-forming clumps in young galaxies are consistent with these numbers, suggesting they formed today's GCs. Observations of the cluster cut-off mass in local galaxies agree with the maximum mass calculated from Sigma_SFR. Metal-poor stellar populations in local dwarf irregular galaxies confirm the dominant role of GC formation in building their young disks.
 
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