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The first generation of ELT instruments includes an optical-infrared high-resolution spectrograph, indicated as ELT-HIRES and recently christened ANDES (ArmazoNes high Dispersion Echelle Spectrograph). ANDES consists of three fibre-fed spectrographs ([U]BV, RIZ, YJH) providing a spectral resolution of $\sim$100,000 with a minimum simultaneous wavelength coverage of 0.4-1.8 $\mu$m with the goal of extending it to 0.35-2.4 $\mu$m with the addition of a U arm to the BV spectrograph and a separate K band spectrograph. It operates both in seeing- and diffraction-limited conditions and the fibre feeding allows several, interchangeable observing modes including a single conjugated adaptive optics module and a small diffraction-limited integral field unit in the NIR. Modularity and fibre-feeding allow ANDES to be placed partly on the ELT Nasmyth platform and partly in the Coud\'e room. ANDES has a wide range of groundbreaking science cases spanning nearly all areas of research in astrophysics and even fundamental physics. Among the top science cases, there are the detection of biosignatures from exoplanet atmospheres, finding the fingerprints of the first generation of stars, tests on the stability of Nature's fundamental couplings, and the direct detection of the cosmic acceleration. The ANDES project is carried forward by a large international consortium, composed of 35 Institutes from 13 countries, forming a team of almost 300 scientists and engineers which include the majority of the scientific and technical expertise in the field that can be found in ESO member states., Comment: SPIE astronomical telescope and instrumentation 2024, in press

State-of-the-art 19th century spectroscopy led to the discovery of quantum mechanics, and 20th century spectroscopy led to the confirmation of quantum electrodynamics. State-of-the-art 21st century astrophysical spectrographs, especially ANDES at ESO's ELT, have another opportunity to play a key role in the search for, and characterization of, the new physics which is known to be out there, waiting to be discovered. We rely on detailed simulations and forecast techniques to discuss four important examples of this point: big bang nucleosynthesis, the evolution of the cosmic microwave background temperature, tests of the universality of physical laws, and a real-time model-independent mapping of the expansion history of the universe (also known as the redshift drift). The last two are among the flagship science drivers for the ELT. We also highlight what is required for the ESO community to be able to play a meaningful role in 2030s fundamental cosmology and show that, even if ANDES only provides null results, such `minimum guaranteed science' will be in the form of constraints on key cosmological paradigms: these are independent from, and can be competitive with, those obtained from traditional cosmological probes., Comment: 31 pages, 6 figures; submitted to Experimental Astronomy on behalf of the ANDES Science Team; v2: matches accepted version

In spite of the advent of extremely large telescopes in the UV/optical/NIR range, the current generation of 8-10m facilities is likely to remain competitive at ground-UV wavelengths for the foreseeable future. The Cassegrain U-Band Efficient Spectrograph (CUBES) has been designed to provide high-efficiency (>40%) observations in the near UV (305-400 nm requirement, 300-420 nm goal) at a spectral resolving power of R>20,000, although a lower-resolution, sky-limited mode of R ~ 7,000 is also planned. CUBES will offer new possibilities in many fields of astrophysics, providing access to key lines of stellar spectra: a tremendous diversity of iron-peak and heavy elements, lighter elements (in particular Beryllium) and light-element molecules (CO, CN, OH), as well as Balmer lines and the Balmer jump (particularly important for young stellar objects). The UV range is also critical in extragalactic studies: the circumgalactic medium of distant galaxies, the contribution of different types of sources to the cosmic UV background, the measurement of H2 and primordial Deuterium in a regime of relatively transparent intergalactic medium, and follow-up of explosive transients. The CUBES project completed a Phase A conceptual design in June 2021 and has now entered the Phase B dedicated to detailed design and construction. First science operations are planned for 2028. In this paper, we briefly describe the CUBES project development and goals, the main science cases, the instrument design and the project organization and management., Comment: Proceedings for the HACK100 conference, Trieste, June 2022. arXiv admin note: substantial text overlap with arXiv:2208.01672

We compare the two largest galaxy morphology catalogues, which separate early and late type galaxies at intermediate redshift. The two catalogues were built by applying supervised deep learning (convolutional neural networks, CNNs) to the Dark Energy Survey data down to a magnitude limit of $\sim$21 mag. The methodologies used for the construction of the catalogues include differences such as the cutout sizes, the labels used for training, and the input to the CNN - monochromatic images versus $gri$-band normalized images. In addition, one catalogue is trained using bright galaxies observed with DES ($i<18$), while the other is trained with bright galaxies ($r<17.5$) and `emulated' galaxies up to $r$-band magnitude $22.5$. Despite the different approaches, the agreement between the two catalogues is excellent up to $i<19$, demonstrating that CNN predictions are reliable for samples at least one magnitude fainter than the training sample limit. It also shows that morphological classifications based on monochromatic images are comparable to those based on $gri$-band images, at least in the bright regime. At fainter magnitudes, $i>19$, the overall agreement is good ($\sim$95\%), but is mostly driven by the large spiral fraction in the two catalogues. In contrast, the agreement within the elliptical population is not as good, especially at faint magnitudes. By studying the mismatched cases we are able to identify lenticular galaxies (at least up to $i<19$), which are difficult to distinguish using standard classification approaches. The synergy of both catalogues provides an unique opportunity to select a population of unusual galaxies., Comment: 17 pages, 14 figures (1 appendix for galaxy examples including 3 figures)

In the era of Extremely Large Telescopes, the current generation of 8-10m facilities are likely to remain competitive at ground-UV wavelengths for the foreseeable future. The Cassegrain U-Band Efficient Spectrograph (CUBES) has been designed to provide high-efficiency (>40%) observations in the near UV (305-400 nm requirement, 300-420 nm goal) at a spectral resolving power of R>20,000 (with a lower-resolution, sky-limited mode of R ~ 7,000). With the design focusing on maximizing the instrument throughput (ensuring a Signal to Noise Ratio (SNR) ~20 per high-resolution element at 313 nm for U ~18.5 mag objects in 1h of observations), it will offer new possibilities in many fields of astrophysics, providing access to key lines of stellar spectra: a tremendous diversity of iron-peak and heavy elements, lighter elements (in particular Beryllium) and light-element molecules (CO, CN, OH), as well as Balmer lines and the Balmer jump (particularly important for young stellar objects). The UV range is also critical in extragalactic studies: the circumgalactic medium of distant galaxies, the contribution of different types of sources to the cosmic UV background, the measurement of H2 and primordial Deuterium in a regime of relatively transparent intergalactic medium, and follow-up of explosive transients. The CUBES project completed a Phase A conceptual design in June 2021 and has now entered the detailed design and construction phase. First science operations are planned for 2028., Comment: SPIE proceedings, SPIE Astronomical Telescopes + Instrumentation 2022, Montr\'eal, Canada; 20 pages, 13 figures, 2 tables

We present the goals, design, and first results of the MUSE Ultra Deep Field (MUDF) survey, a large programme using the Multi Unit Spectroscopic Explorer (MUSE) instrument at the ESO Very Large Telescope. The MUDF survey is collecting ~ 150 hours on-source of integral field optical spectroscopy in a 1.5 x 1.2 square arcmin region which hosts several astrophysical structures along the line of sight, including two bright z ~ 3.2 quasars with close separation (~ 500 kpc). Following the description of the data reduction procedures, we present the analysis of the galaxy environment and gaseous properties of seven groups detected at redshifts 0.5 < z < 1.5, spanning a large dynamic range in halo mass, log(Mh/Msun) ~ 11 - 13.5. For four of the groups, we find associated MgII absorbers tracing cool gas in high-resolution spectroscopy of the two quasars, including one case of correlated absorption in both sightlines at distance ~ 480 kpc. The absorption strength associated with the groups is higher than what has been reported for more isolated galaxies of comparable mass and impact parameters. We do not find evidence for widespread cool gas giving rise to strong absorption within these groups. Combining these results with the distribution of neutral and ionised gas seen in emission in lower-redshift groups, we conclude that gravitational interactions in the group environment strip gas from the galaxy haloes into the intragroup medium, boosting the cross section of cool gas and leading to the high fraction of strong MgII absorbers that we detect., Comment: 20 pages, 12 figures, 4 tables, Accepted for publication in MNRAS

We present first results from Multi Unit Spectroscopic Explorer (MUSE) observations at the Very Large Telescope in the MUSE Ultra Deep Field (MUDF), a $\approx 1.2\times 1.4$ arcmin$^2$ region for which we are collecting $\approx$200 hours of integral field spectroscopy. The $\approx 40$-hour observation completed to date reveals the presence of a group of three Ly$\alpha$ nebulae associated with a bright quasar pair at $z\simeq3.23$ with projected separation of $\approx 500\rm~kpc$. Two of the nebulae are physically associated with the quasars which are likely powering the Ly$\alpha$ emission, and extend for $\gtrsim 100~\rm kpc$ at a surface brightness level of $\approx 6\times 10^{-19}~\rm erg~s^{-1}~cm^{-2}~arcsec^{-2}$. A third smaller ($\approx$35 kpc) nebula lies at a velocity offset of $\approx 1550$ km s$^{-1}$. Despite their clustered nature, the two large nebulae have properties similar to those observed in isolated quasars and exhibit no sharp decline in flux at the current depth, suggesting an even more extended distribution of gas around the quasars. We interpret the shape and the alignment of the two brighter nebulae as suggestive of the presence of an extended structure connecting the two quasar host galaxies, as seen for massive galaxies forming within gas-rich filaments in cosmological simulations., Comment: MNRAS Letters in press, 3 figures, revised version: minor changes following proofs

Using galaxies as background light sources to map the Lya absorption lines is a novel approach to study Damped Lya Absorbers (DLAs). We report the discovery of an intervening z = 3.335 +- 0.007 DLA along a galaxy sight-line identified among 80 Lyman Break Galaxy (LBG) spectra obtained with our Very Large Telescope/Visible Multi-Object Spectrograph survey in the SSA22 field. The measured DLA neutral hydrogen (HI) column density is log (NHI/cm^{-2}) = 21.68 +- 0.17. The DLA covering fraction over the extended background LBG is > 70% (2 sigma), yielding a conservative constraint on the DLA area of > 1 kpc^2. Our search for a counterpart galaxy hosting this DLA concludes that there is no counterpart galaxy with star formation rate (SFR) larger than a few Msun yr^{-1}, ruling out an unobscured violent star formation in the DLA gas cloud. We also rule out the possibility that the host galaxy of the DLA is a passive galaxy with Mstar > 5 x 10^{10} Msun or a heavily dust-obscured galaxy with E(B-V) > 2. The DLA may coincide with a large-scale overdensity of the spectroscopic LBGs. The occurrence rate of the DLA is compatible with that of DLAs found in QSO sight-lines., Comment: 6 pages, 5 figures, accepted for publication in ApJ

We present the largest, publicly available, sample of Damped Lyman-$\alpha$ systems (DLAs) along Gamma-ray Bursts (GRB) line of sights in order to investigate the environmental properties of long GRBs in the $z=1.8-6$ redshift range. Compared with the most recent quasar DLAs sample (QSO-DLA), our analysis shows that GRB-DLAs probe a more metal enriched environment at $z\gtrsim3$, up to $[X/H]\sim-0.5$. In the $z=2-3$ redshift range, despite the large number of lower limits, there are hints that the two populations may be more similar (only at 90\% significance level). Also at \hiz, the GRB-DLA average metallicity seems to decline at a shallower rate than the QSO-DLAs: GRB-DLA hosts may be polluted with metals at least as far as $\sim 2$kpc from the GRB explosion site, probably due to previous star-formation episodes and/or supernovae explosions. This shallow metallicity trend, extended now up to $z\sim5$, confirms previous results that GRB hosts are star-forming and have, on average, higher metallicity than the general QSO-DLA population. Finally, our metallicity measurements are broadly consistent with the hypothesis of two channels of GRB progenitors, one of which is mildly affected by a metallicity bias. The metallicity evolution of modeled GRB hosts agrees reasonably well with our data up to intermediate redshift, while more data are needed to constrain the models at $z\gtrsim 4$., Comment: 28 pages, 4 figures, Accepted on ApJ

We build a sample of distant (D > 80 kpc) stellar halo stars with measured radial velocities. Faint ($20 < g <22$) candidate blue horizontal branch (BHB) stars were selected using the deep, but wide, multi-epoch Sloan Digital Sky Survey photometry. Follow-up spectroscopy for these A-type stars was performed using the VLT-FORS2 instrument. We classify stars according to their Balmer line profiles, and find 7 are bona fide BHB stars and 31 are blue stragglers (BS). Owing to the magnitude range of our sample, even the intrinsically fainter BS stars can reach out to D ~ 90 kpc. We complement this sample of A-type stars with intrinsically brighter, intermediate-age, asymptotic giant branch stars. A set of 4 distant cool carbon stars is compiled from the literature and we perform spectroscopic follow-up on a further 4 N-type carbon stars using the WHT-ISIS instrument. Altogether, this provides us with the largest sample to date of individual star tracers out to r ~ 150 kpc. We find that the radial velocity dispersion of these tracers falls rapidly at large distances and is surprisingly cold (sigma_r ~ 50-60 km/s) between 100-150 kpc. Relating the measured radial velocities to the mass of the Milky Way requires knowledge of the (unknown) tracer density profile and anisotropy at these distances. Nonetheless, by assuming the stellar halo stars between 50-150 kpc have a moderate density fall-off (with power-law slope alpha < 5) and are on radial orbits (sigma^2_t/sigma^2_r < 1), we infer that the mass within 150 kpc is less than 10^12 M_solar and suggest it probably lies in the range (5-10) x 10^11 M_solar. We discuss the implications of such a low mass for the Milky Way., Comment: 15 pages, 12 figures. Accepted for publication in MNRAS

We employ the Union compilation of Type Ia supernovae with a maximum likelihood analysis to search for a dark energy dipole. To approach this problem, we present a simple, computationally efficient, and largely model independent method. We opted to weight each SN by its observed error estimate, so poorly measured SNe that deviate substantially from the Hubble law do not produce spurious results. We find, with very low significance, a dipole in the cosmic acceleration directed roughly towards the cosmic microwave background dipole, but this is almost certainly coincidental., Comment: 7 pages, 6 figures, Accepted for publication in MNRAS

In an earlier paper, we presented the first evidence for a bow-shock nebula surrounding the X-ray binary LMC X-1 on a scale of ~15 pc, which we argued was powered by a jet associated with an accretion disk. We now present the first evidence for an ionization cone extending from an X-ray binary, a phenomenon only seen to date in active galactic nuclei (AGN). The ionization cone, detected in the HeII4686/Hbeta and [OIII]5007/Hbeta line ratio maps, aligns with the direction of the jet inferred from the bow-shock nebula. The cone has an opening angle ~45 deg and radial extent ~3.8 pc. Since the HeII emission cannot be explained by the companion O star, the gas in the ionization cone must be exposed to the `naked' accretion disk, thereby allowing us to place constraints on the unobservable ionizing spectrum. The energetics of the ionization cone give unambiguous evidence for an "ultraviolet - soft X-ray" (XUV) excess in LMC X-1. Any attempt to match the hard X-ray spectrum (>1keV) with a conventional model of the accretion disk fails to account for this XUV component. We propose two likely sources for the observed anisotropy: (1) obscuration by a dusty torus, or (2) a jet-blown hole in a surrounding envelope of circumstellar absorbing material. We discuss the implications of our discovery in the context of the mass-scaling hypothesis for accretion onto black holes and suggest avenues for future research., Comment: 4 pages, 4 figures, accepted for publication in ApJ Letters