LERMA UMR8112

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



Accueil > en > Research > Galaxies and Cosmology

Galaxies and Cosmology

par Françoise Combes - publié le , mis à jour le

This pole has several themes of research, which can be gathered in :

  1. The early universe : inflation, cosmic backgrounds, reionization
  2. Dark matter : Cold, warm or modified gravity ?
  3. Galaxy formation : high-z early galaxies, secular evolution and mergers
  4. Black holes and galaxies : AGN, starbursts, symbiotic growth and feedback
  5. Star formation efficiency, history and stellar populations

See Activities of the group for more details

The pole Galaxies and Cosmology includes a group working on the cosmic microwave background (CMB), who has a major role in the Planck mission, another group working on the standard model of the Universe, the inflation theory compared to observations. Another team studies through numerical simulations the epoch of reionization of the Universe (EoR, cf Fig 1), and in particular the preparation of SKA (Embrace prototype, key projects on pathfinders, etc..). Pioneering work has been done on cooling flows and the presence of cold molecular gas near the brightest cluster galaxies. The nature of dark matter, and investigation on alternative theories of modified gravity have been probed through galaxy dynamics and observations. A thorough study of AGN fueling and feedback has been carried out, addressing black hole growth history and galaxy evolution.

Figure 1 : Simulations de l’émission HI-21cm pendant l’Epoque de Réionisation (EoR). Exemple de surface de section du cône de lumière à 21-cm : dTb à partir de la simulation brute (à gauche) , dTb avec le bruit et la résolution de SKA (milieu) et dTb avec le bruit et la résolution de LOFAR (à droite). Les couleurs montrent la température de brilliance différentielle Tb en mK.

Another team works both on the observation of local galaxies, the physics of galaxies in clusters, galaxies at high redshift (cf Fig 2), and on the dynamical theories for the evolution and formation of galaxies, on large-scale star formation and the cosmic star formation history.
Multi-wavelengths observations are used extensively, in the millimeter and centimeter with the instruments of IRAM, the VLA and now ALMA since 2011-12, infrared and far-infrared with the satellites Spitzer and Herschel, optical and near-infrared with the CFHT and ESO. Team members are leaders in key programs, such as the NUGA consortium on the IRAM interferometer, the consortium PrimGal on the VLT, or major programs at IRAM (which will be completed by NOEMA in the near future) on distant galaxies, and the observation of galaxies at large z with APEX, Plateau de Bure and ALMA, which data are now frequently arriving to the various groups. One group is actively preparing for the SKA.

Figure 2 : Un des objets de l’échantillon dans le Grand Programme PHIBSS de l’IRAM PdB à z = 1.2 A gauche : Superposition de la carte de CO (en rouge, obtenue avec l’interféromètre de l’IRAM), avec les images en bande I (en vert) et la bande V (en bleu) obtenues avec le télescope spatial Hubble. La raie CO(3-2), décalée vers le rouge à 2 mm, a été observée avec une résolution angulaire de 0,6 "x0.7" (indiqué par l’ellipse grise hachurée). A droite : Champ de vitesse de la galaxie : bleu indique la vitesse négative (côté en approche), et la vitesse rouge positif (côté en récession).

One specialty of the pole is also heavy numerical simulations, and the team competed at a very high level in the HORIZON project program of formation of galaxies in a cosmological context. Always larger and more impressive simulations are now going on with the supercomputers at GENCI (Curie at CEA, IDRIS, CINES), and locally use of the meso-center and local momentum cluster is favoring the exploitation and post-processing.

Figure 3 : La galaxie spirale barrée NGC 1433, cartographiée avec ALMA en CO(3-2). The trou noir central super-massif est un noyau actif (AGN), qui rejette du gaz moléculaire, et modère la formation d’étoiles.

Voir en ligne : Activities of the group

Séminaires à venir

Vendredi 16 novembre 2018, 14h00
Salle de l'atelier, Paris
Quantum walks and astrophysical plasmas
Fabrice DEBBASCH
UPMC, LERMA, Paris
résumé :
Quantum walks (QWs) have been first considered by Feynman in the 1940's and later introduced systematically in the 1990's in the context of quantum information. These discrete automata are a universal quantum computation tool and their first experimental realisation is less than 10 years old (2009).

I will present some of the research conducted at the LERMA since 2012. I will explain that QWs can be viewed as models of Dirac fermions (electrons etc.) interacting with gauge fields like EM fields and gravitation and that QWs can be used to build self-consistent many body theories. These results pave the way towards new numerical simulations and laboratory experiments modelling astrophysical and cosmological relativistic quantum plasmas through QWs.
 
Vendredi 30 novembre 2018, 14h00
Salle de l'atelier, Paris
Multiscale star-formation in the Ophiuchus Molecular Cloud: from molecular clouds to brown-dwarfs formation
Bilal LADJELATE
IRAM
résumé :
From molecular clouds to stars, every step of the evolution of young stars can be observed in the submillimetric range. The Herschel Space Telescope observed, as part of the Herschel Gould Belt Survey, many molecular clouds. When these molecular clouds are fragmenting, dense prestellar cores accumulating dust and gas are forming and contracting. We performed a census of prestellar dense cores in the Ophiuchus Molecular Cloud, which appear to be coupled with filamentary structures, as part of the paradigm of star-formation inside interstellar filaments. The region was not previously known as filamentary, despite the observation of protostellar alignments. This molecular cloud is under the heavy feedback of active stars nearby seen in the structure of the molecular cloud. Oph B-11, detected with interferometric observations, is a brown dwarf precursor, which final mass will not be important enough for the final star to burn hydrogen. Their formation mechanism is not well constrained, we must find and characterize a first candidate pre-brown dwarf. Oph B-11 was detected along a nearby shock, we characterize chemically. Moreover, higher resolution studies with ALMA show a structured molecular environment and help us constrain the mechanism of formation of this kind of objects. These observations show a series of shocks in different tracers, spatially coincident with the detected position of the pre-brown dwarf, in favour of the gravo- turbulent scenario for the formation of brown dwarfs. I will discuss the legacy of Herschel in the Ophiuchus region in the filament paradigm of star-formation, and the future of these studies with the advent of new instruments, like NIKA2 and its polarimetry facility.
 
Vendredi 21 décembre 2018, 14h00
Salle de l'atelier, Paris
Astrochemistry in star forming regions : new modeling approaches
Emeric BRON
IRAM/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.
 
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