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A High-Resolution View on Galaxy Formation with VLT/MUSE – FOGHAR

The History of Galaxies during the Last Ten Billion Years

The FOGHAR project consisted in exploiting the Guranteed Time Observations of MUSE, an integral field spectrograph that has been operating on the Very Large Telescope since the summer of 2014, in order to improve our understanding of the processes of galaxy formation and evolution, thanks to the sensitivity, spatial resolution, and angular resolution of this cutting-edge instrument.

Tracking the formation and evolution of galaxies in relation with their environment

The issue is to understand how the baryonic matter assembles as time goes on to form galaxies, at what rate stars form in them, and how galaxies exchange gas with their environment. In this perspective, three questions are being intensively investigated: 1) the study of the emitters of the Lyman alpha line at 121.6 nm, redshifted into the visible or the near infrared, which are galaxies during their first ages (1-2 billion years); ii) the dynamics of intermediate-redshift galaxies, observed on a time span of 5-10 billion years, when the morphological types form and when most of the star formation and the chemical enrichment takes place; and finally iii) the gas exchanges of galaxies with their environment, by observing absorbers in the lines-of-sight of quasars. The goal is to write up the consistent history of galaxy formation, and to compare it with the theoretical efforts of modelling and numerical simulations. More specifically, we would like to know whether galaxies at z>6 are responsible for reionisation, and to understand what triggers the peak of stellar formation at z=1.5.

Large extragalactic surveys which aim at answering the above-mentioned questions are affected by various problems: as a matter of fact, it is necessary to select galaxies in previously obtained images before performing spectroscopic observations which provide us with important information such as their distance, their dynamics or their chemical composition. The integral field spectrograph MUSE, built by an European consortium led by France, was installed in 2014 at the Very Large Telescope of the European Southern Observatory (ESO) to achieve spectroscopic observations without previous pre-selection. MUSE benefits from a wide field of view, an excellent spectral and spatial resolution (assisted by Adaptive Optics since 2017) and an unprecedented sensitivity. The FOGHAR project conducted deep surveys with unequalled performances during tens of observing nights.

The team of the FOGHAR project detected a large population of Lyman alpha emitters that were invisible until now, and could produce enough UV to explain the reionisation. The project also enabled several breakthroughs: the best mass model for clusters, the measure of the metallicity gradients and the dynamics of the ionised gas and stars for a significant sample of intermediate-redshift galaxies, the way matter assembled within galaxies, and how galaxies merged, and what quantity of gas they exchanged with their environment. These pioneering works are going to continue in the forthcoming years.

The results of FOGHAR will be useful to launch follow-up observing campaigns of the deep fields and sources of interest with other cutting-edge instruments (VLT/KMOS for the near IR, ALMA for the submm), and to prepare observations of some deep fields with JWST/NIRSpec.The observing runs of deep fields will go on until 2021.

The team of the FOGHAR project produced 32 papers in refereed scientific journals, and about forty international communications. The results were also presented in 7 press releases. A 35 min movie « MUSE the Cosmic Time Machine » has been shot, and many public outreach lectures were given.

The FOGHAR project (ANR-13-BS05-0010) is a project of fundamental research coordinated by the Centre de Recherche Astrophysique de Lyon (UMR 5574). It associates the Institut de Recherche en Astrophysique et Planétologie of Toulouse (UMR 5277). The project started on January 1, 2014, for a total duration of 60 months. It benefitted from an ANR grant amounting to € 591 760, for an overall cost of about M€ 3.7.

In the era of precision cosmology, we still need to understand how intergalactic gas flows into the potential wells of galaxy haloes, how it transforms into stars, and how stars eject gas, metals and energy feedback into the interstellar and/or intergalactic medium (IGM). Ideally, these processes have to be followed from the first galaxies and the reionization phase between redshifts 15 and 7, through the early mass assembly of building blocks, when the universe was typically 1-2 Gyr old, down to the formation of the Hubble sequence of morphological types seen in the local universe.

MUSE, a 2nd generation instrument for the VLT, will probe the deep universe like never before. Thanks to its sensitivity and multiplex power, this revolutionary giant 3D spectrograph will allow us to constrain and test scenarios of galaxy formation with unprecedented precision. MUSE will start its operations in 2013, assisted by adaptive optics from mid-2015. MUSE will obtain 90,000 spectra per exposure at an average resolution R=3000 on the full visible wavelength range 4800—9300 Å in a 1 arcmin2 field-of-view, with an excellent overall throughput and stability that will facilitate very long integrations.

Because no similar instrument currently exists in the world with such multiplex capabilities and sensitivity at this level of spatial and spectral resolution, we intend to make major progress in the knowledge of galaxy formation processes along the following axes: the characterization of the end of reionization (6<z<6.7), the census of star-forming objects and of the mass assembly of galaxies at 2.8<z<6 through the study of Lyman-alpha emitters (LAE) and Lyman Break Galaxies, the detection of possible emitting intergalactic medium and cold gas filamentary flows at z=3 (and maybe beyond) though cooling radiation and/or fluorescence, the formation of the Hubble sequence through gas dynamics and metals at z<1.5, and the study of feedback and outflow processes though observation of absorption lines in intervening material along the line-of-sight of bright QSOs. <br />
The MUSE European consortium is granted 255 nights of Guaranteed Time Observations (GTO), to be conducted at a rate of 20 observing nights per semester, on a typical period of 6 years. Most of the GTO will be spent in a “wedding-cake” strategy of shallow, medium-deep, and deep extragalactic surveys. This proposal is submitted by the French science team of the MUSE consortium, to exploit these deep extragalactic surveys and set new constraints on fundamental issues related to galaxy formation. MUSE GTO will be exploited jointly between the consortium institutes, leading to a collaborative but also competitive process. Given the significant investment made by France (CRAL and IRAP) for building MUSE, this proposal is of paramount importance for maintaining a leadership position of the French team on these topics, and for warranting a proportionate scientific return.

The scientific program of this ANR project is organized in work packages (WP). WP0 is the supervising WP. WP1 is the leading WP that deals with data management, from acquisition to exploitable catalogues. WP2, 3 and 4 respectively deal with high-redshift galaxies, intermediate-redshift galaxies, and the IGM. WP5 will develop theoretical tools, and lead synthesis at the end of the project. WP6 (public outreach) will accompany the project from beginning to end, especially through the making of a movie, exhibitions and lectures, for the general audience and high-school pupils. This project is scheduled for the 2014-2017 period. The resources that are needed to achieve this program are two 3-yr post-doctoral positions which are essential for the success of WP2, 3, and 4, computer and hard disk equipment (for data processing, analysis, storage and interpretation), travel costs, and subcontracting. The associated cost amounts to 591 760 € (569 000 € plus 4 % accounting costs).

Project coordination

Bruno GUIDERDONI (Centre de Recherche Astrophysique de Lyon)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.


CRAL Centre de Recherche Astrophysique de Lyon
IRAP Institut de Recherche en Astrophysique et Planétologie

Help of the ANR 591,760 euros
Beginning and duration of the scientific project: December 2013 - 48 Months

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