The federation
Intranet
Projects of the Interstellaire team
The theme of the research group is the study of interstellar molecules, their birth, life and death, and as a tool to study the process of star formation. The group mostly focuses its study on the earliest phases of a solar-type forming planetary system with the goal to make a link with the most primitive objects of the Solar System and, consequently, the early phases of the Proto-Solar Nebula. Our major expertise is observations of the first phases of solar-type protostars and environments, accompanied by modelling and theoretical chemistry. To do so, we make an intense use of the world-class observatories of the discipline in the (sub)millimeter domain: IRAM 30m, NOEMA, ALMA and Herschel in the past.
Large projects led by group members
IRAM-30m LP ASAI (Astrochemical Surveys At Iram)
PIs: B. Lefloch & R. Bachiller
The project consists in unbiased high sensitivity spectral line surveys of the 1mm, 2mm and 3mm bands of ten sources representing the various phases and aspects of the early solar-type star forming process, with the IRAM 30m telescope. This unique, large and homogeneous observational dataset has allowed, for the first time, to highlight and constrain the chemical evolution occurring during the solar-type star forming process. Major results of ASAI include a complete census of the chemical richness and diversity of protostars, prestellar cores and protostellar shocks, which calls for not yet understood modes of star formation and chemical processes, as well as the detection of new molecular species in the interstellar medium.
IRAM/NOEMA LP SOLIS (Seeds Of Life In Space)
PIs: C. Ceccarelli & P. Caselli
The project focuses on the observations at high spatial resolution (100–1000 au) of interstellar Complex Organic Molecules (iCOMs) toward seven solar-type objects and environments with the goal to constrain observationally the chemical routes of this special class of molecules, which may have been inherited by the early Earth. The observations, completed in 2018, have already allowed us to understand the origin of the early Proto-Solar Nebula ionizing sources and the route of formation of formamide, a potentially crucial molecule in the appearance of life.
ALMA FAUST (Fifty AU STudies of the chemistry of the disk/envelope system of solar-like protostars)
PIs S.Yamamoto, C.Ceccarelli, C. Chandler, C.Codella, N.Sakai
The goal of the FAUST AlMA large project is to reveal and quantify the variety of chemical composition of the envelope/disk system at scales of 50 AU in a sample of Class 0 and I protostars representative of the chemical diversity observed at larger scales. The targeted molecular families include organic molecules, molecular ions, and deuterated molecules.
Other "small-size" observational projects are also carried by members of the group, as the first measurements of enhanced Cosmic-Ray (CR) induced ionization in molecular clouds close to Supernova-Remnants (SNRs) and emitting gamma-ray emission, proving the presence of freshly accelerated CR and the origin of them in the SNR shock. Another project also allows us to identify the physical, ionization and chemical structure of protostellar outflows and jets, with the first census of iCOMs and a detailed structure of an archetype protostellar shock and jet.
Astrochemistry theory and modeling
1- Interstellar grain surface studies: In the last five years, we have opened up a new research activity involving quantum chemistry computations on: (a) The binding energies and NIR spectral features of molecules. (b) The reactivity of radical-radical on the grain icy surfaces. (c) The hydrogenation of atoms/molecules, e.g. the formation of water. (d) The hydrogen–deuterium exchanges between water and organics in the ice phase.
2- Gas-phase chemistry: We do a systematic study of the reactions that could synthesize and/or destroy iCOMs in the gas-phase.
3- Astrochemical models: We have two major research axis: (a) We develop a new, state-of-art, astrochemical network, the University of Grenoble Astrochemical Network (UGAN) dedicated to the chemistry of nuclear spin isomers (ortho/para species). (b) We continue the development of the GRAINOBLE gas-grain code and its exploitation from protostellar objects to extragalactic clouds.
The theme of the research group is constraining star formation, using statistical observational studies of Galactic clouds forming high-mass stars and rich stellar clusters.
Large projects led by group members
A new scenario for the formation of high-mass stars
For several decades, we know that solar-type stars (0.1 - 2 M⊙) are formed by the gravitational collapse of a prestellar core. In the case of massive stars ( 10-100 M⊙), the earliest (prestellar and protostellar) phases leading to their formation are still very poorly known and no massive star formation scenario has reached, to date, a definite consensus. With this in mind, we conduct the Herschel/HOBYS key program and higher angular-resolution follow-up observations to systematically search for the direct progenitors of massive stars. In the framework of the Herschel/HOBYS key program, we discovered very high density clouds which are the privileged sites to form massive stars. These "ridges" or "hubs" would be formed by the collision and fusion of several filaments and would be further fed by the gas of less dense filaments still free-falling toward them (Louvet et al. 2016; Rayner et al. 2017). These results suggest a very close connection between the formation of (massive) stars and their parental cloud. Within these ridges/hubs, we also discovered a very small number of massive prestellar core candidates (Tigé et al 2017; Nony et al 2018), proving that the massive analogs of solar-type prestellar cores do not generally exist. As a result, we propose, for the formation of massive stars, an empirical evolutionary sequence in which the prestellar phase would be replaced by the simultaneous formation and growth in mass of filaments, cores, and protostars. This scenario is presented in the Annual Review of Astronomy and Astrophysics (Motte, Bontemps, & Louvet 2018a).
An updated view on the IMF origin with ALMA and MnGSeg
The origin of the stellar initial mass function (IMF) and its dependence or not with the galactic environments remain unresolved problems. In star-formation regions that have been studied for 20 years, the mass function of cloud cores (CMF) is remarkably similar to the canonical IMF. The form of the IMF would simply be inherited from that of the CMF and there would be a direct relationship between the mass of stars and that of cores. Studying the CMF in regions representative of the typical conditions of star formation in our Galaxy requires targeting clouds with very sensitive millimeter interferometers like ALMA and NOEMA. We thus started a Large Program with ALMA to constrain the CMF into regions of the Galactic arms. A first study in the W43 cloud revealed massive cores that largely outnumber low-mass cores when compared to the shape of the canonical IMF. This result is presented in the Nature Astronomy article (Motte, Nony, Louvet et al. 2018b). Do we underestimate the effects of the environment on the shape of the IMF and its origin?
A systematic studies of the CMF of a large sample of massive proto-clusters is done as part of the ALMA-IMF Large Program (PI F. Motte) and completed by NOEMA programs. The objective is to assess whether the relationship between the CMF and the IMF, as defined in nearby clouds, can be generalized to all environments of our Milky Way or even the Universe. The ALMA-IMF and NOEMA-IMF consortia verify this hypothesis by combining observations and numerical simulations. Our challenge is to improve the classic view of compact cores that separate from their environment by using gas mass inflows arising from larger scales plus outflows and multiplicity to determine the real "mass reservoir" of individual star-formation seeds. We notably developed a Multiscale non-Gaussian Segmentation (MnGSeg, see Robitaille et al. 2014, 2019) analysis technique based on Morlet wavelet transform to separate coherent structures such as filaments and cores from the fractal structure of clouds. This tool is used to investigate the coherent cloud structures associated to variations of the CMF that could be at the origin of the IMF.
The theme of the research group focusses on cosmology and early universe, with an emphasis on the realization of new submillimeter detectors including NIKA2 and CONCERTO.
Members
- N. Ponthieu
- F.-X. Désert
Large projects led by group members
NIKA2
The group is deeply involved the NIKA2 project. The New IRAM Kids Arrays (NIKA2) is the next generation continuum instrument installed at the 30m telescope of IRAM, at Pico Veleta (Spain). The latter is a follow-up instrument of space missions to which the group have contributed in the past, in terms of angular resolution (5 arcmin Planck to 11 arcsec NIKA2 at 1.2 mm) and wavelength coverage (500 micron Herschel to 1.2 and 2 mm NIKA2). The NIKA2 focal plane is fully sampled using Kinetic Inductance Detectors (KID), a novel superconducting detectors technology that provides at the same time high sensitivity and ease of multiplexing.
The instrument is already available to the astronomical community. The collaboration is in charge of 1300 hours of guaranteed time of observations, shared in 5 Large Programs. The group is co-PI of two of them (PIs: G. Lagache & Beelen and PI: Mayet). The first one addresses the physics of galaxy clusters via the detailed mapping of clusters detected by Planck via the Sunyaev-Zel’dovitch. The second one shed new light on star formation at high redshift and the evolution of dusty star forming galaxies, by mapping two deep fields with lots of ancillary data: GOODS-North and COSMOS.
NIKA2 also has the capacity to measure linear polarization at 1.2 mm. The group started to observe the Large Program on the role of the magnetic field in interstellar filaments and the whole star formation process (PI: Ph. André).
KISS/CONCERTO
PI: G. Lagache, LAM
CONCERTO is a new instrument to be installed at APEX/ESO in 2021. It is a spectrometer, based on a Martin-Puplett and a KID camera. It will map the 158 micron CII line at redshift up to 7-8 and therefore trace the history of galaxy evolution and reionization. The ancillary data, such as the maps of the various CO lines, will be an important legacy to the community. CONCERTO will then be an instrument open to the community and we are in charge of delivering the data analysis pipeline. KISS, a demonstrator for CONCERTO is already installed on an antenna of the QUIJOTE project in Tenerife and has acquired data during several runs since December 2018 that are key to help us build the data reduction pipeline and understand the systematic effects that are specific to this system.