This paper presents Owl-z, a Bayesian code aiming at identifying z ≥7 quasars in wide field optical and near-infrared surveys. By construction,the code can also be used to select objects that contaminate the high-z quasar population, i.e. brown dwarfs and early-type galaxies at intermediate redshifts. The code can be adapted for the selection of high-z galaxies, and although it has been tuned to the Euclid Wide Survey, it can be easily adapted to other photometric surveys. The code input data are the object's photometric data and its galactic longitude and latitude, and the code output data are the probabilities of the modelled populations of high-z quasars, brown dwarfs and early-type galaxies at intermediate redshift. As part of the validation, Owl-z could re-identify all spectroscopically confirmed quasars at z ≥7, demonstrating the code's versatility in applying to different photometric catalogues. The performance of Owl-z, based on a metric combining completeness and purity called F-measure, is analysed in the case of Euclid using simulated data in a wide range of redshifts (7 ≤z ≤12) and H-band Euclid magnitudes (18 ≤H_E ≤24.5). The results show that Owl-z reaches full performance for bright sources (H_E ≲22), independently of the redshift. We show that the probability threshold used to select promising quasar candidates can be adjusted after processing to fine-tune the F-measure value of candidates depending on their magnitude and redshift estimates. We show that for objects brighter than about two magnitudes above the survey detection limit, Owl-z provides a classification that will facilitate the optimisation of photometric and spectroscopic confirmation campaigns. In conclusion, Owl-z is a powerful public tool to help select high-z quasars, brown dwarfs or early-type galaxies at intermediate redshifts in Euclid or other wide-field surveys.

The current standard model of cosmology successfully describes a variety of measurements, but the nature of its main ingredients, dark matter and dark energy, remains unknown. Euclid is a medium-class mission in the Cosmic Vision 2015-2025 programme of the European Space Agency (ESA) that will provide high-resolution optical imaging, as well as near-infrared imaging and spectroscopy, over about 14,000 deg^2 of extragalactic sky. In addition to accurate weak lensing and clustering measurements that probe structure formation over half of the age of the Universe, its primary probes for cosmology, these exquisite data will enable a wide range of science. This paper provides a high-level overview of the mission, summarising the survey characteristics, the various data-processing steps, and data products. We also highlight the main science objectives and expected performance.

MOSAIC is the Multi-Object Spectrograph for the ESO-ELT (European Southern Observatory-Extremely Large Telescope). The Laboratoire d'Astrophysique de Marseille (LAM) is in charge of the "Assembly, Integration, Test and Verification (AIT/ V)" activities for both the Front-End channel level and the instrument level in Europe (LAM) and at the Telescope. AITV for AO instruments, in laboratory as well as at the telescope, always represent numerous technical challenges. We already started the preparation and planning for the Front-End and instrument AIT activities, from identification of needs, challenges, risks, to defining the optimal AIT strategy. In this paper, we present the state of this study and describe the MOSAIC AITV organization, give an overview of the Front-End and the Instrument MAIT flows. We also describe the visible and near-infrared channels MAIT flows as well as the different AITV responsibilities during the AITV phases both in Europe and in Chile.

Context. Faint, star-forming galaxies are likely to play a dominant role in cosmic reionisation. Great strides have been made in recent years to characterise these populations at high redshifts ( z > 3). Now, for the first time, with JWST photometry beyond 1 μm in the rest frame, we can derive accurate stellar masses and position these galaxies on the galaxy main sequence. Aims. We seek to assess the place of 96 individual Lyman- α emitters (LAEs) selected behind the A2744 lensing cluster with MUSE IFU spectroscopy on the galaxy main sequence. We also compare the derived stellar masses to Lyman- α luminosities and equivalent widths to better quantify the relationship between the Lyman- α emission and the host galaxy. Methods. These 96 LAEs lie in the redshift range of 2.9 < z < 6.7, with their range of masses extending down to 10 6 M ⊙ (over half with M ⋆ < 10 8 M ⊙ ). We used the JWST/NIRCam and HST photometric catalogues from the UNCOVER project, giving us excellent wavelength coverage from 450 nm to 4.5 μm. We also performed an SED fitting using CIGALE , fixing the redshift of the LAEs to the secure, spectroscopic value. This combination of photometric coverage with spectroscopic redshifts allows us to robustly derive stellar masses for these galaxies. Results. We found a main sequence relation for these low-mass LAEs of log SFR = (0.88 ± 0.07 − 0.030 ± 0.027 × t ) log M ⋆ − (6.31 ± 0.41 − 0.08 ± 0.37 × t ). This is in relative agreement with the best-fit results of prior collated studies; however, here we see a steeper slope and a higher normalisation. This indicates that low-mass LAEs towards the epoch of reionisation lie above the typical literature main sequence relations derived at lower redshift and higher masses. In addition, by comparing our results to UV-selected samples, we can see that while low-mass LAEs lie above these typical main sequence relations, they are likely not singular in this respect at these particular masses and redshifts. While low-mass galaxies have been shown to play a significant role in cosmic reionisation, our results point to the likelihood that LAEs hold no special position in this regard.

MOSAIC* is the multi-object spectrograph (MOS) for the ESO 39m European Extremely Large Telescope (ELT) approved to enter phase B at the of beginning 2023. MOSAIC combines visible and near-infrared channels, from resolved stars up to the most distant galaxies, with multi-object and multi-integral field spectroscopy capabilities. The NIR-spectrograph (130K-90K) is one sub-system of the NIR-channel, led by the Universidad Complutense de Madrid (UCM, Spain). The NIR Spectrograph (NIRSPEC) comprises 2 identical spectrographs, each one equipped with Teledyne H4RG science detectors (4kx4k, 15 mu m pixels). Each spectrograph operates at 130K (with detectors at 90K) and covers the 2 observing bands J (1 - 1.38 mu m) and H (1.43 - 1.85 mu m in low-resolution mode and 1.52 - 1.65 mu m in high-resolution mode). This paper presents the optical design of the NIRSPEC.

MOSAIC is the Multi-Object Spectrograph (MOS) for the 39m Extremely Large Telescope (ELT) of the European Southern Observatory (ESO), with unique capabilities in terms of multiplex, wavelength coverage and spectral resolution. It is a versatile multi-object spectrograph working in both the Visible and NIR domains, designed to cover the largest possible area (similar to 40 arcmin(2)) on the focal plane, and optimized to achieve the best possible signal-to-noise ratio on the faintest sources, from stars in our Galaxy to galaxies at the epoch of the reionization. In this paper we describe the main characteristics of the instrument, including its expected performance in the different observing modes. The status of the project will be briefly presented, together with the positioning of the instrument in the landscape of the ELT instrumentation. We also review the main expected scientific contributions of MOSAIC, focusing on the synergies between this instrument and other major ground-based and space facilities.

MOSAIC is a wide-field spectrograph, combining multiple-object spectroscopy and integral field units, to cover the ELT focal plane with a field-of-view of 7.8 a rcmin from the blue to the near-infrared, 3 90-1800nm. In the current Phase B design, AO is GLAO supported by four LGS in a fixed a sterism and with multiple NGS. Although the GLAO correction is modest compared to other ELT instrumentation, the use of the integrated M4/M5 correction elements and the existing LGS allows for an efficient de sign which is outlined. MOSAIC GLAO will use the ELT PFS guide-probes to compensate for high-frequency tip/tilt errors, greatly relaxing the requirements on the instrumental NGS sensors. The Phase A architecture used the same pick-off mirrors as the IFU instruments to feed the NGS-WFS from anywhere in the focal plane, which was mandatory for the proposed MOAO design. The reduced performance requirements at Phase B allows us to take advantage, instead, of the four 2 arcmin diameter field-of-view through the LGS cutouts, arranged in a square pattern at an off-axis distance of 3.75 a rcmin. In each LGS cutout, a wide-field-imager is implemented alongside one LGS WFS to acquire multiple NGS that supports both slow tip/tilt measurements, isolating instrument-Nasmyth flexure, solving for the a strometric distortion expected from errors in the ELT optical path, and supporting the alignment of MOS apertures with the field. The 1 atter is a key requirement for MOSAIC, 1 eading to 40 mas accuracy in MOS aperture positioning and 40 mas rotation displacement at the edge of the scientific field.

MOSAIC is an instrument for the Extremely Large Telescope (ELT). The instrument has started phase B, and apart from technical and financial requirements, MOSAIC has the additional requirement to investigate and minimise its environmental impact. The first step is to estimate the carbon footprint (and other effects) in a 'Life Cycle Analysis', for the instrument development up to Provisional Acceptance in Chile. This paper presents a preliminary analysis, aimed at identifying potential contributors to environmental impact. Investigated contributors are: materials, Full-Time-Equivalents, travel, and transport of the instrument. Not yet investigated (due to lack of information or certainty) are: electronics, test facilities and prototyping. Uncertainty in input data and conversion factors leads to error bars of a factor 2 or larger. Therefore, the outcome of the analysis can be used for internal comparison of contributors only, and it should not be used for comparison to other instruments or disciplines.

MOSAIC is the multi-object spectrograph (MOS) for the ESO 39m European Extremely Large Telescope (ELT) approved to enter phase B beginning 2023. MOSAIC combines visible and near-infrared channels, from resolved stars up to the most distant galaxies, with multi-object and multi-integral field spectroscopy capabilities. The NIR-spectrograph (130K-90K) is one sub-system of the NIR-channel, led by the Universidad Complutense de Madrid (UCM, Spain). It includes four camera modules delivered by the Laboratoire d'Astrophysique de Marseille (LAM, France) and equipped with Teledyne H4RG science detectors (4kx4k, 15 mu m pixels). The four modules distribute two identical cryogenic benches ensuring, on each, the spectral coverage of the two observing bands J (0.95 - 1.34 mu m) and H (1.43 1.80 mu m in LR mode and 1.52 - 1.63 mu m in HR mode). This paper presents the design of a cryogenic NIR camera prototype based on an athermal concept and details the ongoing AIT development for verification in the 0.95 - 1.34 mu m domain in relevant environment (ESO TRL5).

Context. The escape of Lyman-alpha photons at redshifts greater than two is an ongoing subject of study and an important quantity to further understanding of Lyman-alpha emitters (LAEs), the transmission of Lyman-alpha photons through the interstellar medium and intergalactic medium, and the impact these LAEs have on cosmic reionisation. Aims. This study aims to assess the Lyman-alpha escape fraction, f(esc, Ly alpha), over the redshift range 2.9 < z < 6.7, focusing on Very Large Telescope/Multi Unit Spectroscopic Explorer (VLT/MUSE) selected, gravitationally lensed, intrinsically faint LAEs. These galaxies are of particular interest as the potential drivers of cosmic reionisation. Methods. We assessed f(esc, Ly alpha) in two ways: through an individual study of 96 LAEs behind the A2744 lensing cluster, with James Webb Space Telescope/Near-Infrared Camera (JWST/NIRCam) and HST data, and through a study of the global evolution of f(esc, Ly alpha) using the state-of-the-art luminosity functions for LAEs and the UV-selected 'parent' population (dust-corrected). We compared these studies to those in the literature based on brighter samples. Results. We find a negligible redshift evolution of f(esc, Ly alpha) for our individual galaxies; it is likely that it was washed out by significant intrinsic scatter. We observed a more significant evolution towards higher escape fractions with decreasing UV magnitude and fit this relation. When comparing the two luminosity functions to derive f(esc, Ly alpha) in a global sense, we saw agreement with previous literature when integrating the luminosity functions to a bright limit. However, when integrating using a faint limit equivalent to the observational limits of our samples, we observed enhanced values of f(esc, Ly alpha), particularly around z similar to 6, where f(esc, Ly alpha) becomes consistent with 100% escape. This indicates for the faint regimes we sampled that galaxies towards reionisation tend to allow very large fractions of Lyman-alpha photons to escape. We interpret this as evidence of a lack of any significant dust in these populations; our sample is likely dominated by young, highly star-forming chemically unevolved galaxies. Finally, we assessed the contribution of the LAE population to reionisation using our latest values for f(esc, Ly alpha) and the LAE luminosity density. The dependence on the escape fraction of Lyman continuum photons is strong, but for values similar to those observed recently in z similar to 3 LAEs and high-redshift analogues, LAEs could provide all the ionising emissivity necessary for reionisation.

Context. Faint galaxies are theorised to have played a major role, perhaps the dominant role, in reionising the Universe. Their properties, as well as the Lyman-alpha emitter (LAE) fraction, X-LAE, could provide useful insights into this epoch.Aims. We used four clusters of galaxies from the Lensed Lyman-alpha MUSE Arcs Sample (LLAMAS) that also have deep HST photometry to select a population of intrinsically faint Lyman break galaxies (LBGs) and LAEs. We study the interrelation between these two populations, their properties, and the fraction of LBGs that display Lyman-alpha emission.Methods. The use of lensing clusters allows us to access an intrinsically faint population of galaxies, the largest such sample collected for this purpose: 263 LAEs and 972 LBGs with redshifts between 2.9 and 6.7, Lyman-alpha luminosities in the range 39.5 less than or similar to log(L-Ly alpha)(erg s(-1))less than or similar to 42, and absolute UV magnitudes in the range -22 less than or similar to M-1500 less than or similar to -12. In addition to matching LAEs and LBGs, we define an LAE+continuum sample for the LAEs that match with a continuum object that is not selected as an LBG. Additionally, with the use of MUSE integral field spectroscopy, we detect a population of LAEs completely undetected in the continuum.Results. We find a redshift evolution of X-LAE in line with literature results, with diminished values above z = 6. In line with past studies, we take this as signifying an increasingly neutral intervening intergalactic medium. When inspecting this redshift evolution with different limits on EWLy alpha and M-1500, we find that the X-LAE for the UV-brighter half of our sample is higher than the X-LAE for the UV-fainter half, a difference that increases at higher redshifts. This is a surprising result and can be interpreted as the presence of a population of low Lyman-alpha equivalent width (EWLy alpha), UV-bright galaxies situated in reionised bubbles and overdensities. This result is especially interesting in the context of similar, UV-bright, low EWLy alpha objects recently detected during and around the epoch of reionisation. For intrinsically fainter objects, we confirm the previously observed trend of LAEs among LBGs as galaxies with high star formation rates and low dust content, as well as the trend of the strongest LAEs having, in general, fainter M-1500 and steeper UV slopes.

Context. This paper presents a study of the galaxy Lyman-alpha luminosity function (LF) using a large sample of 17 lensing clusters observed by the Multi Unit Spectroscopic Explorer (MUSE) at the ESO Very Large Telescope (VLT). The magnification resulting from strong gravitational lensing by clusters of galaxies and MUSE spectroscopic capabilities allows for blind detections of LAEs without any photometric pre-selection, reaching the faint luminosity regime. Aims. The present work aims to constrain the abundance of Lyman-alpha emitters (LAEs) and quantify their contribution to the total cosmic reionization budget. Methods. We selected 600 lensed LAEs behind these clusters in the redshift range of 2.9 < z < 6.7, covering four orders of magnitude in magnification-corrected Ly-alpha luminosity (39.0 < log(L)[erg s(-1)] < 43.0). These data were collected behind lensing clusters, indicating an increased complexity in the computation of the LF to properly account for magnification and dilution effects. We applied a non-parametric V-max method to compute the LF to carefully determine the survey volume where an individual source could have been detected. The method used in this work follows the recipes originally developed in previous works, with some improvements to better account for the effects of lensing when computing the effective volume. Results. The total co-moving volume at 2.9 < z < 6.7 in the present survey is similar to 50 10(3) Mpc(3). Our LF points in the bright end (log(L) [erg s(-1)] > 42) are consistent with those obtained from blank field observations. In the faint luminosity regime, the density of sources is well described by a steep slope, alpha similar to -2 for the global redshift range. Up to log(L) [erg s(-1)] similar to 41, the steepening of the faint end slope with redshift, suggested in earlier works, is observed, but the uncertainties are still large. A significant flattening is observed towards the faintest end, for the highest redshift bins, namely, log(L)[erg s(-1)] < 41. Conclusions. When taken at face value, the steep slope at the faint-end causes the star formation rate density (SFRD) to dramatically increase with redshift, implying that LAEs could play a major role in the process of cosmic reionization. The flattening observed towards the faint end for the highest redshift bins still requires further investigation. This turnover is similar to the one observed for the UV LF at z >= 6 in lensing clusters, with the same conclusions regarding the reliability of current results. Improving the statistical significance of the sample in this low-luminosity high-redshift regime is a difficult endeavour that may lead to potentially valuable leads in understanding the process of reionization.

We present a study of the galaxy Lyman-alpha luminosity function (LF) using a sample of 17 lensing clusters observed by the MUSE/VLT. Magnification from strong gravitational lensing by clusters of galaxies and MUSE apabilities allow us to blindly detect LAEs without any photometric pre-selection, reaching the faint luminosity regime. 600 lensed LAEs were selected behind these clusters in the redshift range 2.942 are consistent with those obtained from blank field observations. In the faint luminosity regime, the density of sources is well described by a steep slope, $\alpha\sim-2$ for the global redshift range. Up to log(L)$\sim$41, the steepening of the faint end slope with redshift, suggested by the earlier work of DLV19 is observed, but the uncertainties remain large. A significant flattening is observed towards the faintest end, for the highest redshift bins (log$L$<41). Using face values, the steep slope at the faint-end causes the SFRD to dramatically increase with redshift, implying that LAEs could play a major role in the process of cosmic reionization. The flattening observed towards the faint end for the highest redshift bins still needs further investigation. This turnover is similar to the one observed for the UV LF at $z\geq6$ in lensing clusters, with the same conclusions regarding the reliability of current results (e.g.arXiv:1803.09747(N); arXiv:2205.11526(N)).

Studying the Luminosity Function of Lyman Alpha Emitters Selected Behind 17 Lensing Clusters from Multi-Unit Spectroscopic Explorer (MUSE/VLT) Observations.

We present the second data release of the MUSE Hubble UDF surveys, which includes the deepest spectroscopic survey ever performed. The MUSE data, with their 3D content, amazing depth, wide spectral range, and excellent spatial and medium spectral resolution, are rich in information. This update of the first release incorporates a new 141-hour adaptive-optics-assisted MXDF field (1' diameter FoV) in addition to the reprocessed 10-hour mosaic (3'x3') and the single 31-hour deep field (1'x1'). We have securely identified and measured the redshift of 2221 sources, an increase of 41% compared to the first release. With the exception of 8 stars, the collected sample consists of 25 nearby galaxies (z < 0.25), 677 OII emitters (z=0.25-1.5), 201 galaxies in the MUSE redshift desert range (z=1.5-2.8), and 1308 LAEs (z=2.8-6.7). This represents an order of magnitude more redshifts than the collection of all spectroscopic redshifts obtained before MUSE in the Hubble UDF area (2221 vs 292). At z > 3, the difference is even more striking, with a factor of 65 increase (1308 vs 20). We compared the measured redshifts against three published photometric redshift catalogs and find the photo-z accuracy to be lower than the constraints provided by photo-z fitting codes. 80% of the galaxies have an HST counterpart. They are on average faint, with a median magnitude of 25.7 and 28.7 for the OII and Ly-alpha emitters, respectively. SED fits show that these galaxies tend to be low-mass star-forming galaxies, with a median stellar mass of 6.2 10**8 M and a median SFR of 0.4 M/yr. 20% of our catalog, or 424 galaxies, have no HST counterpart. The vast majority of these new sources are high EQW z>2.8 LAEs that are detected by MUSE thanks to their bright and asymmetric broad Ly-alpha line. We release advanced data products, specific software, and a web interface to select and download data sets.

MOSAIC, the multi-object spectrograph (MOS) for the ESO 39m European Extremely Large Telescope (ELT), will combine visible and near-infrared observations with multi-object and multi-integral field spectroscopy capabilities. It will cover a wide panel of topics, from resolved stars up to the most distant galaxies. In the frame of the NIR spectrograph unit realization led by the Laboratoire d’Astrophysique de Marseille (LAM), this paper presents the ongoing development of a cryogenic (90-130 K) NIR camera prototype tested in the 0.77-1.063 µm wavelengths (I band) detailing the opto-mechanical design and the integration and verification strategies in accordance with validation in relevant environment (ESO TRL5).

This report is the result of a joint discussion between the Rubin and Euclid scientific communities. The work presented in this report was focused on designing and recommending an initial set of Derived Data products (DDPs) that could realize the science goals enabled by joint processing. All interested Rubin and Euclid data rights holders were invited to contribute via an online discussion forum and a series of virtual meetings. Strong interest in enhancing science with joint DDPs emerged from across a wide range of astrophysical domains: Solar System, the Galaxy, the Local Volume, from the nearby to the primaeval Universe, and cosmology.

We present an ALMA-Herschel joint analysis of sources detected by the ALMA Lensing Cluster Survey (ALCS) at 1.15 mm. Herschel/PACS and SPIRE data at 100–500 μm are deblended for 180 ALMA sources in 33 lensing cluster fields that are detected either securely (141 sources; in our main sample) or tentatively at S/N ≥ 4 with cross-matched HST/Spitzer counterparts, down to a delensed 1.15 mm flux density of ∼0.02 mJy. We performed far-infrared spectral energy distribution modeling and derived the physical properties of dusty star formation for 125 sources (109 independently) that are detected at >2σ in at least one Herschel band. A total of 27 secure ALCS sources are not detected in any Herschel bands, including 17 optical/near-IR-dark sources that likely reside at z = 4.2 ± 1.2. The 16th, 50th, and 84th percentiles of the redshift distribution are 1.15, 2.08, and 3.59, respectively, for ALCS sources in the main sample, suggesting an increasing fraction of z ≃ 1 − 2 galaxies among fainter millimeter sources (f 1150 ∼ 0.1 mJy). With a median lensing magnification factor of μ=2.6−0.8+2.6 , ALCS sources in the main sample exhibit a median intrinsic star formation rate of 94−54+84 M ⊙ yr−1, lower than that of conventional submillimeter galaxies at similar redshifts by a factor of ∼3. Our study suggests weak or no redshift evolution of dust temperature with L IR < 1012 L ⊙ galaxies within our sample at z ≃ 0 − 2. At L IR > 1012 L ⊙, the dust temperatures show no evolution across z ≃ 1–4 while being lower than those in the local universe. For the highest-redshift source in our sample (z = 6.07), we can rule out an extreme dust temperature (>80 K) that was reported for MACS0416 Y1 at z = 8.31.

Hydrogen Ly${\alpha}$ haloes (LAHs) are commonly used as a tracer of the circumgalactic medium (CGM) at high redshifts. In this work, we aim to explore the existence of Ly${\alpha}$ haloes around individual UV-selected galaxies, rather than around Ly${\alpha}$ emitters (LAEs), at high redshifts. Our sample was continuum-selected with F775W<=27.5, and spectroscopic redshifts were assigned or constrained for all the sources thanks to the deepest (100- to 140-hour) existing Very Large Telescope (VLT)/Multi-Unit Spectroscopic Explorer (MUSE) data with adaptive optics. The final sample includes 21 galaxies that are purely F775W-magnitude selected within the redshift range z=2.9-4.4 and within a UV magnitude range -20<=M1500<= -18, thus avoiding any bias toward LAEs. We tested whether galaxy's Ly${\alpha}$ emission is significantly more extended than the MUSE PSF-convolved continuum component. We find 17 LAHs and four non-LAHs. We report the first individual detections of extended Ly${\alpha}$ emission around non-LAEs. The Ly${\alpha}$ halo fraction is thus as high as $81.0^{+10.3}_{-11.2}$%, which is close to that for LAEs at z=3-6 in the literature. This implies that UV-selected galaxies generally have a large amount of hydrogen in their CGM. We derived the mean surface brightness (SB) profile for our LAHs with cosmic dimming corrections and find that Ly${\alpha}$ emission extends to 5.4 arcsec (~40 physical kpc at the midpoint redshift z=3.6) above the typical 1${\sigma}$ SB limit. The incidence rate of surrounding gas detected in Ly${\alpha}$ per one-dimensional line of sight per unit redshift, dn/dz, is estimated to be $0.76^{+0.09}_{-0.09}$ for galaxies with M1500<= -18 mag at z~3.7. Assuming that Ly${\alpha}$ emission and absorption arise in the same gas, this suggests, based on abundance matching, that LAHs trace the same gas as damped Ly${\alpha}$ systems (DLAs) and sub-DLAs.