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Highlights include:

Vernet, E., Cirasuolo, M. et al.: ELT M5 — The Lightweight Field Stabilisation Mirror
Rigaut, F., McDermid, R. et al.: MAVIS on the VLT: A Powerful, Synergistic ELT Complement in the Visible
Magrini, L., Smiljanic, R. et al.: The Journey of Lithium
Beccari, G., Boffin, H.: The Hypatia Colloquium: Early Career Astronomer Series at ESO

ADS BibCode: 2021Msngr.185....3V

Vernet, E., Cirasuolo, M., Pirard, J., Cayrel, M., Tamai, R., Zuluaga Ramírez, P., Araujo Hauck, C., Koehler, B., Bianca Marchet, F., Gonzalez, J., Tuti, M., and the ELT team

The Extremely Large Telescope (ELT) is at the core of ESO’s vision to deliver the largest optical and infrared telescope in the world. Following on from our previous Messenger articles we continue with the description of the optical elements of the ELT. In this article we focus on the quintenary mirror (M5), the field stabilisation unit. In combination with the M4 mirror, M5 is vital to delivering the sharp diffraction limited images needed for science by correcting for the vibrations of the telescope, wind shaking and the atmosphere. We describe the main characteristics of the M5, as well as the challenges and complexity of this unique field stabilisation unit and its design and manufacturing status.

ADS BibCode: 2021Msngr.185....7R

Rigaut, F., McDermid, R., Cresci, G., Agapito, G., Aliverti, M., Antoniucci, S., Balestra, A., Baruffolo, A., Beltramo-Martin, O., Bergomi, M., Bianco, A., Bonaglia, M., Bono, G., Bouret, J., Brodrick, D., Busoni, L., Capasso, G., Carolo, E., Chinellato, S., Colapietro, M., Content, R., Cranney, J., de Silva, G., D’Orsi, S., Ellis, S., Fantinel, D., Fusco, T., Galla, A., Gausachs, G., Gratadour, D., Greggio, D., Gullieuszik, M., Haguenauer, P., Haynes, D., Herrald, N., Horton, A., Kamath, D., Magrini, L., Marasco, A., Marafatto, L., Massari, D., McGregor, H., Mendel, T., Monty, S., Neichel, B., Pinna, E., Plantet, C., Portaluri, E., Robertson, D., Salasnich, B., Savarese, S., Schipani, P., Schwab, C., Smedley, S., Sordo, R., Ströbele, S., Vaccarella, A., Vassallo, D., Viotto, V., Waller, L., Zanutta, A., Zhang, H., Seemann, U., Kuntschner, H., Arsenault, R.

On 1 June 2021 ESO and a consortium of Australian, Italian and French institutions signed an agreement for the design and construction of the MCAO Assisted Visible Imager and Spectrograph (MAVIS). This Very Large Telescope (VLT) instrument will push the frontier of new astronomical instrument technologies to provide, for the first time, wide-field, diffraction-limited angular resolution at visible wavelengths. In combination with the VLT Adaptive Optics Facility, it will use multi- conjugate adaptive optics (MCAO) to feed a 4k × 4k imager covering 30 × 30 arcseconds, as well as an Integral Field Spectrograph (IFS). Angular resolution down to 18 milliarcseconds will be achieved at a wavelength of 550 nm (V band). The IFS will provide four spectral modes, with spectral resolutions from 4000 to over 15000 between 370 and 950 nm. This will enable a wide variety of science cases, spanning themes that include the emergence of the Hubble sequence, resolving the contents of nearby galaxies, star clusters over cosmic time and the birth, life, and death of stars and their planets. Delivering visible images and integral- field spectroscopy at an angular resolution two to three times better than that of the Hubble Space Telescope will make MAVIS a powerful complement at visible wavelengths to future facilities like the James Webb Space Telescope and the 30–40-metre-class ground-based telescopes currently under construction, which are all optimised for science at infrared wavelengths.

ADS BibCode: 2021Msngr.185...13W

van der Wel, A., Bezanson, R., D’Eugenio, F., Straatman, C., Franx, M., van Houdt, J., Maseda, M., Gallazzi, A., Wu, P., Pacifici, C., Barisic, I., Brammer, G., Munoz-Mateos, J., Vervalcke, S., Zibetti, S., Sobral, D., de Graaff, A., Calhau, J., Kaushal, Y., Muzzin, A., Bell, E., van Dokkum, P.

The Large Early Galaxy Astrophysics Census (LEGA-C) survey is the final Public Spectroscopic Survey to be completed with the now-retired VIsible Multi-Object Spectrograph (VIMOS) instrument at ESO’s Very Large Telescope (VLT). Its aim is to characterise with high precision and for a very large sample the stellar population and kinematic properties of galaxies at redshifts 0.6 < z < 1, providing a first assessment of the star formation histories, the absolute mass scale, and the stellar kinematic structure of galaxies at large lookback times (7 gigayears ago). This article coincides with the third and final data release but mostly focuses on the large variety of scientific results achieved so far.

ADS BibCode: 2021Msngr.185...18M

Magrini, L., Smiljanic, R., Lagarde, N., Franciosini, E., Pasquini, L., Romano, D., Randich, S., Gilmore, G.

After more than ten years and six data releases, the Gaia–ESO spectroscopic survey has come to an end. Gaia–ESO provides an extremely rich database of stellar parameters, radial velocities, and chemical abundances of more than 100 000 stars, amongst which the abundance of lithium can be considered one of the main products. Lithium is perhaps the most enigmatic of the elements, with several open issues regarding its nucleosynthesis and its evolution in stars and in the Galaxy. Gaia–ESO observations are allowing such issues to be addressed, by providing lithium abundances in stars from the pre-main sequence, through the main sequence, up to the red giant branch and the helium- burning red clump phase, over a wide range of masses. In the present work, we discuss the journey of lithium on the surface of evolved stars, using Gaia–ESO data for both field and cluster stars. We focus on the impact of extra mixing and possible lithium enrichment during the helium-burning phase. We briefly comment on the implications that these results may have for models of the chemical evolution of lithium in the Galaxy.

ADS BibCode: 2021Msngr.185...23B

Beccari, G., Boffin, H.

At a time when most planned international conferences, science events and seminars had been postponed or cancelled because of the COVID-19 pandemic, ESO decided to organise a new series of talks aimed at fostering the visibility of, and promoting the work of, astronomers at an early stage of their career: the Hypatia Colloquium.

ADS BibCode: 2021Msngr.185...26G

George, E., Serra, B., Prod’homme, T., Arko, M., Lemmel, F., Kelman, B.

The Detector Modelling (DeMo) workshops aim to bring together a community of scientists and engineers who are interested in modelling detector effects and simulating detectors for astronomy. The first such workshop was held online over three afternoons from 14 to 16 June 2021. The three afternoons were organised around blocks of contributed talks from the community covering a wide range of detector topics such as detector effects like persistence and radiation damage, instru- ments covering a wide range of astronomical wavelengths from X-ray to the optical and infrared, and detectors used in other fields like particle physics. In addition to the scientific programme, the workshop featured a tutorial series on how to use the Pyxel detector simulation framework and how to contribute to Pyxel.

ADS BibCode: 2021Msngr.185...28M

Millour, F., Meilland, A., Matter, A., Mella, G., Bourgès, L., Paladini, C., Tallon-Bosc, I., Tallon, M., Soulez, F., Buscher, D., Mérand, A., Benisty, M., van Boekel, R., Cruzalèbes, P., Defrère, D., Domiciano de Souza, A., Filho, M., Garcia, P., Hönig, S., Ligi, R., Maccotta, C., McKean, J., Patru, F., Perraut, K., Pott, J., Spang, A., Rousset, S.

Very Large Telescope Inerferometer (VLTI) schools have nearly a 20-year history and have trained a significant fraction of today’s optical interferometrists who use high-angular-resolution techniques on a regular basis. Very early in the development of the VLTI, training was identified by the community as a necessary tool, as the expertise in optical long-baseline interferometry was limited to a few groups in France and Germany (in those early years the UK was not an ESO member state). The first VLTI school took place in Les Houches, France, in 2002 and since then VLTI schools have been organised in several locations (France, Germany, Hungary, Poland, Portugal) roughly every two years, the previous one being held in 2018 in Lisbon. The VLTI schools are funded and coordinated through the European Interferometry Initiative (Eii).

ADS BibCode: 2021Msngr.185...31H

Hatziminaoglou, E., Popping, G., Zwaan, M.

The properties of the interstellar medium (ISM) of the highest-redshift galaxies and quasars provide important indications of the complex interplay between the accretion of baryons onto galaxies, the physics that drives the build-up of stars out of this gas, the subsequent chemical evolution and feedback processes and the reionisation of the Universe. The Atacama Large Millimeter/submillimeter Array (ALMA) continues to play a pivotal role in the characterisation of the ISM of high-redshift galaxies. Observations of the dust continuum emission, atomic fine-structure and molecular lines arising from high-redshift galaxies are now carried out routinely, providing ever more constraints on the theoretical models of galaxy formation and evolution in the early Universe. The European Astronomical Society’s EAS 2021 symposium dedicated to the exploration of the high-redshift Universe with ALMA provided a forum for the observational and theoretical high-redshift ALMA communities to exchange their views and recent results in this rapidly evolving field.

ADS BibCode: 2021Msngr.185...35H

Häußler, B., Pompei, E., Jaffé, Y.

In April 2021 more than 200 participants gathered on Zoom for a meeting to discuss what we have learned about galaxy evolution using spectroscopic surveys, and to pay a special tribute to the Visible Multi-Object Spectrograph (VIMOS), which carried out some of the largest spectroscopic galaxy surveys to date and helped to pave the way for ongoing and future facilities. Despite being delayed twice and having to be adapted to an online format, the meeting was well received and many high- impact results were presented by a diverse body of participants. We present the organisation, lessons learned, and legacy of this workshop.

ADS BibCode: 2021Msngr.185...39M

Mroczkowski, T., Stroe, A., Chasiotis-Klingner, S.

Galaxy clusters are both important cosmological probes and the large-scale environments influencing galaxy evolution. Processes such as ram pressure stripping, active galactic nucleus feedback and mergers, both on smaller galaxy-galaxy scales and larger cluster-cluster or cluster-subcluster scales play a major role in temporarily boosting and eventually throttling star formation in massive galaxies. The early assembly of galaxy clusters in particular remains a crucial phase for investigation. But it is a difficult one to probe, owing to their redshifts and the messy astrophysical processes involved in so-called “protoclusters”, defined as as-yet unvirialised massive assemblies of galaxies, gas, and large dark matter overdensities that will one day form into bona fide galaxy clusters. This second workshop in the Galaxy Cluster Formation series, GCF2021, followed many advances in the field of study covering merging clusters, high-z protoclusters, and cluster assembly since the first workshop, held in 2017, GCF2017.

ADS BibCode: 2021Msngr.185...42E

Heida, M., Scicluna, P.

The Messenger Issue 185