Abstracts of Large Programmes and Public Spectroscopic Surveys scheduled in Period 103

This list of OPC approved Large Programmes (LPs) is updated every observing period.




Asteroids in our solar system are metallic, rocky and/or icy objects, ranging in size from a few meters to a few hundreds of kilometers. Whereas we now possess constraints for the surface composition of most D$\geq$100 km primordial main-belt asteroids, little is known regarding their internal structure. Yet, this is a fundamental property whose characteristics result directly from (a) their formation location, (b) their time of formation, and (c) their collisional history. Characterizing the internal structure of the main compositional classes of asteroids would therefore allow us to address entirely new questions regarding the earliest stages of planetesimal formation and their subsequent collisional and dynamical evolution. To achieve this goal, we propose - for a modest amount of observing time ($\sim$3 nights/semester) - to carry out disk-resolved observations of a substantial fraction of all D$\geq$100 km main-belt asteroids (sampling the four main compositional classes) at high angular-resolution with VLT/SPHERE throughout their rotation. These observations will enable us to derive their volume (via their 3-D shape) which combined with already existing mass estimates will allow us to determine their bulk density and hence to characterize their internal structure. Such information will, in turn, provide unprecedented constraints on solar system formation models such as the Nice and Grand Tack models.




SPHERE, the VLT's new generation planet imager, provides exquisite exoplanet detection performance owing to a combination of high-order XAO correction, coronography, and differential imaging technics in visible and near-infrared. These capabilities enable the detection of faint planets at small angular separations from bright stars. The SHINE program for SPHERE High-contrast ImagiNg survey for Exoplanets, a significant component of the consortium Guaranteed Time Observations, is a large near-infrared survey of 400-600 young, nearby stars. The scientific goals are: i) to characterize known planetary systems (architecture, orbit, stability, luminosity, atmosphere); ii) to search for new planetary systems using SPHERE's unprecedented performance; and finally iii) to determine the occurrence and orbital and mass function properties of the wide-orbit, giant planet population as a function of the stellar host mass and age. Combined, the results will increase our understanding of planetary atmospheric physics and the processes of planetary formation and evolution. To explore the origin of planetary formation a small fraction of the GTO Large Programme is also devoted to the study of proto-planetary and debris disks, using a variety of SPHERE instrument modes optimized for these tasks.




We propose to take the next leap forward in our view of the universe through a \hour\ MUSE Ultra Deep Field (MUDF), which will stimulate progress in multiple fields of astrophysics by reaching the faintest flux limits ever obtained for emission lines. To maximise the science impact of the MUDF, we have selected the unique field \qso\ with two bright $z\sim 3.22$ quasars, separated by 500 kpc, which act as ``light bulbs'' to trace in absorption the distribution of the diffuse cosmic gas. The powerful synergy of absorption and emission diagnostics in the MUDF will allow us to: (i) redefine our view of the matter distribution at $z\sim3$, enabling the first detection of the cosmic web in emission; (ii) provide a definite picture of how the flow of gas inside halos shape the evolution of galaxies; (iii) open a new window to study the link between quasars and their environment by glimpsing at the assembly of a massive cluster during its infancy; (iv) obtain a new vantage point on how the Hubble sequence emerges from over 10 billion years of cosmic evolution in a rich dataset of over 400 galaxies between $z\sim 0-6.5$. The transformational MUDF will be a long-lasting legacy for the VLT, it will open a new discovery space, and it will be a prime spectroscopic survey that the ESO community will exploit in the coming decade in synergy with campaigns at world-class observatories like {\it JWST} and ALMA.




We request MUSE mosaics to map the star forming disks of 20 nearby galaxies. These data will be combined with in-hand PHANGS-ALMA high angular resolution CO data (17 galaxies from our programs plus 3 archival datasets). The aim of the proposal is to obtain for the first time a comprehensive view of the chemo-dynamical evolution of the star formation process across the different ISM environments present within a representative sample of nearby massive star forming main sequence galaxies . In particular we will (a) estimate the timescales of the star forming process (i.e. molecular cloud lifetimes, feedback lifetimes, feedback outflow velocities, star formation efficiencies, mass loading factors), (b) quantify the importance of star formation feedback in galactic disks, and (c) study chemical enrichment and mixing in radial and azimuthal direction (via $\sim$40,000 fully characterized HII regions). All these aspects will be linked to the local conditions under which star formation proceeds in disks (e.g. gravitational potential, ISM pressure, local dynamics, local radiation field and shielding), which at the same time are connected to global properties of galaxies such as the stellar mass, star formation rate, morphology, nuclear activity, and environment. Building this connection will inform the next generation of theoretical models and simulations, finally bridging the fields of star formation and galaxy evolution.




We propose to continue and complete our deep NaCo $L^{\prime}$-band coronagraphic angular differential imaging GTO survey for wide-separation giant planets around nearby young stars with circumstellar disks. Our main goal is the revelation and characterisation of the observationally not yet well-characterised wide-separation \mbox{($>$5-10\,au)} giant planet population during the time of formation and dynamical evolution. Our survey is therefore focused on stars with protoplanetary transition disks and with well-characterised debris disks, many of which show signatures of dynamical activity that could indicate the presence of giant planets. With the combination of $L^{\prime}$-band observations, the use of the AGPM coronagraph to minimise the inner working angle for bright stars, and a strategy for going significantly deeper than previous surveys, we optimise the sensitivity to both more embedded (younger) as well as cooler (lower-mass and older) planets than targeted by previous/other surveys. We also probe smaller separations, thus bridging the gap between orbital separations probed by RV and previous direct imaging surveys. Our GTO survey is distinguished from and complementary to other state-of-the-art exoplanet imaging surveys like SPHERE-SHINE by the focus on stars with planet formation-related circumstellar disks and by covering a different parameter range by exploiting the unique $L^{\prime}$-band capability of NaCo.




The most promising way to understand the complex process of planet formation is to study its outcomes in a range of formation environments, and evaluate how those environments influence the outcomes. Stellar mass and metallicity are two parameters that are known to have a significant impact on the prevalence of giant planets. The effects of metallicity are reasonably well studied, at least for Sun-like stars, while stellar mass dependencies have been more elusive, primarily due to technical difficulties. Here, we propose a large high-contrast imaging survey for 83 B-type stars in the Sco-Cen region. Sco-Cen is already being surveyed at $\sim$1--3~$M_{\rm sun}$ ($\sim$A/F/G-type) with direct imaging, and has been very fruitful due to a favourable proximity ($\sim$120--150~pc) and age ($\sim$10--16)~Myr. Scalings from lower-mass populations and previous imaging detections imply that B-type stars may be the richest hosts of detectable giant planets, but a large dedicated survey is required to uncover and characterize this hypothesized planet population. By comparing our B-star results to the existing surveys of $\sim$1--3~$M_{\rm sun}$ Sco-Cen members, we can eliminate dependencies of formation environments (including metallicity), and thus cleanly isolate stellar mass as the dominant parameter in our statistical study.




\veils, the VISTA Extragalactic Infrared Legacy Survey, is a new ESO Public Survey, covering 9 sqrdeg of extragalactic legacy fields with deep, cadenced observations. The innovative aspect of \veils\ is its design enabling the first wide-field $J$ and $Ks$-band extragalactic time domain survey. The goal of this time-domain survey is to use two independent standardisable candles -- type Ia supernovae and AGN dust time-lags -- to significantly improve constraints of cosmological parameters in a complementary way to BAO, weak lensing, or the CMB. In addition, we will search for new members of a recently discovered class of optically-elusive, infrared-bright transients. With the proposed Large Programme VOILETTE (= VEILS OptIcal Lightcurves of Extragalactic TransienT Events), we are seeking the crucial optical time-domain support to enable the transient science of \veils\ as the Dark Energy Survey is finishing. VOILETTE will use the VST to obtain cadenced $griz$ observations of the \veils\ fields to (1) discover, classify, and build light curves of new type Ia supernovae, (2) monitor the optical variability of AGN to determine dust time lags, and (3) support identification of infrared transients with and without an optical counterpart.




The closest massive star forming region, Sco-Cen, has been recognized in recent years as a unique niche for extrasolar planetary systems studies. Indeed, several extrasolar planets have been found by direct imaging in this association, as well as many debris disks, possible signposts of past giant and on-going terrestrial planet formation. A few systems orbit binary stars have been found, giving thus the opportunity to study planet formation and early dynamical evolution in a unique way. We propose a HARPS survey to search for planets with semi major axis less than typically 2 au around a sample of 112 young stars members of Sco-Cen, already observed or to be observed under SPHERE GTO. Coupling HARPS, SPHERE and GAIA data will allow a full exploration of each star environment, from a fraction of au to hundreds of AU. This will be the first exhaustive GP survey around stars with similar, well known ages, providing thus a detailed comparison with formation models. Other outputs of our program include a search for comet evaporation around our target stars, and the characterization of the stars themselves.




Planets orbiting both stars of a binary system -circumbinary planets- are challenging our understanding about how planets are assembled and how their orbits subsequently evolve. We aim to assess how similar and how different the orbital and physical properties of circumbinary planets are to the properties of planets orbiting single stars. Our detections will open a new window of investigation into a highly debated topic, and complement observations of circumbinary protoplanetary discs imaged with SPHERE and ALMA. \smallskip During 78 nights, our programme will turn HARPS on a unique and carefully selected sample of 40, bright, recently identified, single-line, low-mass, eclipsing binary systems. They have been discovered and characterised in the course of a 10-year long observing campaign. Composed of an F, G, or K + late-M pair, their mass ratios provide optimal conditions for high radial-velocity precision and accuracy, reaching a level where the detection of circumbinary planets with the mass of Neptune is feasible. Based on already discovered systems, we expect to find between 5 and 15 planetary systems orbiting our eclipsing binaries. Discovering them using the radial-velocity method also opens the door to study dynamical effects unique to circumbinary planets, to estimate their multiplicity, and to compute their true occurrence rate, information that has eluded {\it Kepler}.




The rotation curves of galaxies are still a major tool for determining the distribution of mass within galaxies. Their shapes and normalisation provide fundamental information for measuring the contribution of stars, gas and dark matter in galaxies' mass budgets, as well as their formation and evolution, Hubble type and environment. Recent results on the falling outer rotation curves of high-redshift galaxies suggest that massive galaxies at $z\sim$\,2 have dark matter fractions that are negligible. However, these results rely on stacking, and the three-dimensional renormalisation of the data cubes required has strong systematic effects on the resulting rotation curve shape. Indeed, flat curves can also be derived from the same data if the stack is weighted by stellar size rather than dynamical radius, leading to radically different conclusions about the dark matter content of galaxies at this epoch. Here, we propose to overcome these systematics by obtaining two deep (100-hr each) KMOS pointings to measure the H$\alpha$ rotation curves in 46 main-sequence galaxies at $z\approx1.5$ to radii extending up to (and beyond) six times the stellar disk-scale radius ($\sim$\,15\,kpc). We will use the data to measure the contribution of stars and dark matter on a galaxy-by-galaxy basis, to definitively determine to what extent high-redshift galaxies are either baryon or dark matter dominated all the way to their outer edges.




Giant planets are thought to form via core-accretion, whereby rocky/icy cores form early on in the protoplanetary disk, and then at a critical point attract gas from the disk to build up an atmosphere. The precise composition of the core, particularly the ice-mass fraction, tells us about the formation process and where in the protoplanetary disk the planet formed. In most cases the gaseous envelope hides this core, meaning we cannot determine its composition. However in situations where the planet is exposed to intense radiation, that gaseous envelope is lost, providing us with a unique opportunity to study the exposed core. We target cores by observing planets subject to gas evaporation, with orbital period $<5$d and radius between 1.8 and 4 $R_\oplus$. With this large program proposal, we want to measure the masses of up to 30 new planetary cores across the parameter space, studying the core composition, formation process and mass distribution statistically for the first time. This will in turn allow us to determine where in the disk these cores formed, and thus give us insight into where planet formation occurs and how far these planets migrated since their initial formation. We will source our targets initially from \textit{K2} planet discoveries, updating to include bright \textit{TESS} candidates from mid-P102 onwards. Our science goals can be met independently of \textit{TESS}, allowing the characterisation of 12 new cores using \textit{K2} targets alone.




Owing to their favorable planet-star contrast ratio, planets around small stars --whether transiting or not-- are top targets for follow-up characterization. Those that transit can be characterized with transmission and occultation spectroscopy whereas those that do not transit can be found closer, brighter and with larger separations, such that they will become amenable to characterization for the ELT. Our previous time allocation detected, confirmed or measured the masses of most known planets around bright M dwarfs. This proposal aims to continue that effort in the context of newly available and forthcoming instruments such as ESPRESSO, NIRPS, EXTRA and TESS. In particular, we propose : - to continue the sensus of nearby temperate planets amenable to characterization with the ELT (d$<$5pc) - to confirm, and then measure masses of new transit candidates identified by MEarth, K2, ExTrA and TESS - to refine RV orbits of known planets in view of their transit searches with MEarth, ExTrA, and CHEOPS Better masses are critical to understanding the formation and composition for many of the known super-Earths, which typically have much more precise radii than masses. New, smaller, cooler planets amenable to atmospheric characterisation will be most precious for upcoming JWST and ELT programs.




Multimessenger astronomy, the detection of an astrophysical source in more than one ``messenger'' (photons, gravitational waves, neutrinos), offers an entirely new way to study the Universe. The first detection of gravitational waves combined with electromagnetic radiation from the merger of a binary neutron star in August 2017 marks the start of a new era in which information about the behaviour of mass from gravitational waves are coupled with constraints on the transfer and release of energy from electromagnetic light. ESO facilities played a pivotal role in the discovery and characterisation of the counterpart, delivering spectacular photometric and spectroscopic sequences with great diagnostic power. Here we propose a comprehensive pan-European collaboration to observe gravitational wave sources identified in the year-long LIGO-Virgo observing run beginning in late 2018. These observations will determine the range of electromagnetic properties seen in compact object mergers and how these depend on the system parameters and viewing angle; assess the yields of heavy elements and determine if the mergers are indeed the dominant site for the synthesis of heavy elements; measure the structure of jets to demonstrate how mergers create short-duration gamma-ray bursts, and determine redshifts and independent electromagnetic distances, enhancing the science return for fundamental physics and cosmology.




During the past decade, the field of exoplanets moved from extended searches to statistical studies and characterisation of individual planets. The scientific driver of low-mass planets, possibly located in the `habitable zones' of their host stars, makes the obtention of precise measurements of planetary masses, radii and densities, a critical endeavour. High-fidelity spectroscopy and high-precision radial velocities are an essential technique to obtain these quantities, while also enabling for the atmospheric characterisation of these objects. In this proposal, we pursue one of the main science goals of the ESPRESSO GTO: the detection and characterisation of Earth-mass planets (possibly) inside the habitable zone of G, K and M stars. We address it with 3 sub-programmes: (1) An intensive search for habitable rocky planets, built on the HARPS(-N) experience, in a sample of the most suitable stars -- some of which already hosting planets -- in the solar neighbourhood. (2) A follow-up of the most challenging, i.e.\ low-mass candidates from K2 and the upcoming TESS mission by the Doppler technique, to obtain their precise densities. (3) A survey for exoplanetary atmospheres, in the footsteps of HARPS(-N), through transit and reflected-light spectroscopy, exploiting the unique spectroscopic capabilities of ESPRESSO and the collecting area of the UTs.




Most extensions of the Standard Physical Model predict a space-time variation of the fundamental physical constants. Examples include models where Dark Energy is in the form of a scalar field (quintessence), string and GUT theories. Absorption lines of intervening systems towards distant quasars are the most effective way to test the stability of the fine-structure constant $\alpha$ or the proton-to-electron mass ratio $\mu$. These tests require measurements of a tiny variation of the position of one or few lines with respect to other reference lines. Claims of variability have already been made but the signal, at the level of few ppm (part per million), is comparable to the value of possible instrumental systematics (2-10 ppm). ESPRESSO is a high spectral resolution, ultra stable spectrograph, delivering precise radial velocity measurements in the optical wavelengths and these fundamental physics tests have been one of its scientific drivers. Here, we use the GTO to collect spectra of a sample of 18 carefully selected, relatively bright and well studied QSOs to significantly improve current measurements of $\alpha$ as well as $\mu$ (when possible) with the aim to break the 1 ppm precision. The proposed observations will further test the universality of physical laws in an unexplored regime, which directly impact fundamental physics and theoretical cosmology.




We propose an ambitious program to characterize, in terms of mass, radius, and density, at least 20 small transiting planets (1--4\,R$_\oplus$). By determining planetary masses to better than 10-15\%, we will be able to distinguish between internal structure models, and determine whether these systems are silicate-based planets like our Moon, planets with an iron core like the Earth, or even denser systems like Mercury. We will do so by conducting HARPS radial velocity (RV) observations of planets detected to transit by the Transiting Exoplanet Survey Satellite (\textit{TESS}), scheduled for launch in April 2018. Our extensive experience with planet detection and characterization for the \textit{K2} mission, will allow our \textit{KESPRINT} team to carry out quick and efficient \textit{TESS} transiting planet detection and vetting, and carry out a systematic RV characterization campaign. The detailed characterization of small transiting planets, enabled by the bright stars to be observed by \textit{TESS}, is key to understand planet formation. Our observations will provide constraints on photo-evaporation models and models of planet formation, by investigating the core composition of super-Earth planets and ultra-short period planets (USPs) that have lost their atmospheres. We will further investigate the population of sub-Neptune planets and identify key targets for future atmospheric studies such as with the James Webb Space Telescope.




We propose to exploit ALMA continuum surveys of submillimetre sources in the UKIDSS/UDS, COSMOS and GOODS-S/ECDFS fields, which provide precise identifications and multiwavelength properties for $\sim$\,1,100 submillimetre galaxies (SMGs). SMGs represent a population of massive, strongly star-forming galaxies at $z\sim$\,1--4, which have been empirically claimed to have many of the properties expected for the progenitors of local spheroidal galaxies. To test this claim quantitatively and so determine their role in the formation of today's massive galaxies, we propose to target 545 ALMA-identified SMGs ($K_{\rm AB} \le$ 24) in 49 KMOS pointings across these three fields. These observations allow us to: 1) derive precise spectroscopic redshifts for the SMGs to measure their clustering and thus their halo masses; 2) study the dynamics and kinematics of ionised gas in a subset of $\sim$\,300 of the brightest SMGs to derive their dynamical masses and gas fractions; 3) compare SMG kinematics to less-active populations to test their triggering; 4) search for transition objects to probe the links between starburst and AGN at the era of peak activity of both populations. Near-infrared high-multiplex spectra from KMOS is the most efficient way to derive redshifts, spectral properties and dynamics (especially for the brighter examples at $z\leq$\,3--4) and thus understand SMG's place in the evolution of massive galaxies.




A new generation of wide-field sky surveys, some monitoring the sky several times per night, mean we are now in a golden era of transient astronomy. Gathering the ESO community working on supernovae (SNe) and unusual transients into one coherent team, PESSTO/ePESSTO has revolutionised the exploitation of these surveys, developing efficient synergies with multi-messenger experiments and making the NTT a crucial global facility (80+ papers). We have provided legacy datasets for the electromagnetic counterpart of gravitational waves, the lowest metallicity supernovae, supernovae in remote locations, and long-lived supernovae not explained by standard neutrino-driven explosions, as well as unveiled a diversity in the most luminous supernovae. We now propose `advanced'-ePESSTO (ePESSTO+), building on the success of our ePESSTO consortium and bridging the gap to the SOXS instrument that will arrive at the NTT in 2021. We will expand the scientific focus to include gravitational wave sources, transients that evolve on the timescale of a few days, and those with extreme energetics. We will focus on the most exciting new transient populations now being discovered by all-sky surveys such as the Zwicky Transient Facility, \textit{Gaia} and ATLAS. The current stream of transients provided by these surveys requires large spectroscopic follow-up which we, the ESO community, are well placed to lead. We will continue to make all reduced data public as we have done for ePESSTO.




Current planet detection methods struggle to find planets around hot stars. Discovering planets in this regime would provide crucial information on how planet occurrence scales with stellar mass. Radial velocity surveys of evolved A-type stars hint that giant planets on $\sim$au orbits in this regime could be up to 5x more common than around solar-type stars. The only way to confidently detect these planets is via differential astrometry of sub-arcsecond early-type binary stars. Using data from a previous VLTI pilot test, we demonstrate that $\sim$10 micro-arcsecond precision can be achieved in 1-hour observations. This precision is sufficient to detect the ``wobble" of a star from 2-10 M$_J$ planets on $\sim$au orbits. Monitoring a sample of binaries for 2-years would reveal these planets, making this project perfectly suited for the large programme. The expert control of pupil and astrometric baseline with GRAVITY at VLTI are essential for controlling systematics that dominate the CHARA array, while better sensitivity at VLTI allows us to target wider binaries where planet suppression at 1 au is not expected. We propose to begin a large survey using GRAVITY and the ATs to monitor bright early-type binary stars in order to detect giant planets within a few au of individual stars in the binary pair. With 10 epochs on each of our sample of 30 targets, we expect to detect 8$\pm$3 giant exoplanets assuming a top-heavy distribution of planets.




One of the most exciting opportunities offered by GRAVITY is to directly resolve the broad line region (BLR) of active galactic nuclei using spectro-astrometry. Since P99 we have been exploiting this capability to study the inner workings of AGN in the K-band on unprecedented micro-arcsecond (sub-pc) spatial scales. We have made the first interferometric detection of the BLR and found ordered rotation in the quasar 3C 273 (GRAVITY collab., Nature, in press) proving both the feasibility and value of such measurements. This proposal takes a major step forward by extending this capability to measure BLR radius, structure, and kinematics for a sample of objects spanning four orders of magnitude in luminosity. We will establish a new, GRAVITY-based radius-luminosity relation, thereby testing reverberation mapping methods and forming the basis for more robust black hole mass measurements in large samples in the local and distant Universe. From the same data, we will simultaneously measure the size and structure of the hot dust ``torus'' to understand its origin and physical connection to the BLR. Our team of observers and theorists has extensive experience in AGN science including interferometry and reverberation. We have developed the analysis and modeling tools needed to fully capitalize on such a unique data set.




As remnants of stars with initial masses of $\simeq0.8-8\,\Msun$, white dwarfs play a central role in our understanding of the evolution of planets, stars, the Galaxy, and the Universe as a whole. Because of their well constrained cooling ages white dwarfs can be used to constrain the local star formation history and to calibrate age-metallicity and age-rotation relations of main-sequence stars. Double-degenerates are common products of binary evolution, are a likely pathway towards SN~Ia explosions, and will define the low-frequency noise floor for space-based gravitational wave detections. Finally, white dwarfs accreting the debris of tidally disrupted planetesimals provide a unique window into the bulk composition of extra-solar planets. Because of their small (Earth-like) size, white dwarfs are intrinsically faint and have been difficult to identify. Making use of {\em Gaia}~DR2, we have defined the first volume-complete sample (40\,pc) of white dwarfs that is sufficiently large ($\simeq1200$ stars) for robust statistical analyses across all the science areas outlined above. While the {\em Gaia} data unambiguously identifies their white dwarf nature, follow-up spectroscopy is required to obtain accurate masses, temperatures, ages, photospheric abundances, magnetic field strenghts, and to probe for multiplicity. Here we request X-Shooter observations of all 219 newly identified remnants in the Southern hemisphere to fully characterise their physical properties, which we will use to address a wide range of stellar and exo-planetary science questions.




In this study we will investigate binary stellar evolution through the study of post-AGB binaries. These targets are surrounded by circumbinary disks that can be seen as second-generation protoplanetary disks. We want to take advantage of the near-infrared interferometric technique that is able to resolve the building blocks (circumbinary disk inner rim, inner binary, accretion signatures) of our targets. Our previous snapshot survey revealed a morphological complexity that geometrical models are not able to reproduce. We propose to unveil this complexity by using the full capability of the VLTI by imaging the continuum emission of 11 targets with PIONIER and locate the emission lines with GRAVITY. Our objectives are to \textit{1)} reveal the 3-dimensional morphology of the disk inner rim and constrain disk/binary interactions, \textit{2)} obtain the absolute distances, luminosities, and masses of the systems, \textit{3)} look for direct evidence for accretion from the circumbinary disk, \textit{4)} confirm the presence of a circum-secondary accretion disk in the whole sample, \textit{5)} study the origin of extended flux component, and \textit{6)} reveal a disk evolutionary sequence. Combining recent advances in aperture synthesis techniques with state-of-the-art 3-dimensional radiative transfer models of circumbinary disks will give us a sharp view on the structure and evolution of these second generation protoplanetary disks.




This VST monitoring program is part of an ongoing effort to measure $H_0$ to 1\% using the time delays in 40 strongly lensed quasars. This single-step technique needs no complex calibration and provides robust constraints on $H_0$. A 1\% measurement of $H_0$ will both clarify the current discrepancy in $H_0$ between CMB and local measurements with Cepheids and Supernovae and improve the FoM of any stage-IV survey by 40\%. In practice, we will carry out a high-cadence (daily) and high-SNR (1000) R-band monitoring to measure time delays in at least 6 systems to $<$2\% in 2 years, complementing our current monitoring with the MPIA 2.2m telescope. With the same VST data, we will build mass maps for each field with weak lensing, allowing to detect any mass clump along the lines-of-sights down to $\kappa_{ext}\sim0.02$. Together with existing and approved HST data, the VST time delays and weak lensing maps will add 6 new systems to the current H0LiCOW sample of 4 analyzed systems.




Over the last decade, a coherent picture of the Universe during the epoch of reionisation has started to emerge. High-redshift quasar spectra have undoubtedly been the most polyvalent tools in the exploration of the $z>5$ Universe. As the only sources sufficiently bright to enable high-SNR spectroscopy, much information has been extracted from their foreground sight-lines, their immediate environments, as well as on the AGN themselves. However, the amount of high-quality quasar spectra is still too small to robustly test and refine models: the field is ready to advance from an \textit{exploratory} regime to a \textit{precision} regime. \textbf{We propose to construct a public sample of 29 high-quality spectra of quasars at $5.8\lesssim z \lesssim 6.6$, quadrupling the existing data of such quality in this critical redshift range.} This sample will be a game changer for the study of many key aspects of the early Universe: the unfolding of the reionisation process, early metal enrichment, the nature of the first stars and galaxies, the environment of quasars, and the formation of early super-massive black holes. As quasar surveys are reaching maturity, this project will likely constitute the ultimate statistical sample of quasars at $z\gtrsim5.8$. Moreover, this program will possess a huge legacy value for the community at large, and lay the foundation for the exploration of the yet more distant Universe with JWST and the ELT.



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Last update: OPO - January14, 2019