Eric Jullo

Modified gravity theories constitute viable alternatives to the standard cosmological model for explaining the observed late-time accelerated expansion of the Universe. The effective field theory of dark energy (EFTofDE) is an efficient framework to describe a wide range of such theories with a limited number of parameters. To robustly constrain these theories, high-resolution cosmological N -body simulations are required to obtain accurate predictions for the matter distribution on non-linear scales, which can then be quantitatively compared with clustering and weak gravitational lensing measurements from forthcoming galaxy surveys. We introduce two new N -body simulation codes for cosmologies governed by cubic luminal Horndeski gravity models of the EFTofDE under quasi-static approximation: PySCo-EFT , a fast Python-based particle-mesh code, and ECOSMOG-EFT , an accurate RAMSES -based code with adaptive mesh refinement. We used iterative solvers and multigrid schemes to solve for the additional scalar field equation in both codes, including the non-linear Vainshtein screening mechanism. The standard gravitational force was augmented by a fifth force from the scalar field. We present several validation and convergence tests of the codes. We obtained a sub 0.5% agreement with linear theory on large scales and a similar agreement between the two codes in particle-mesh mode for the power spectrum boost, although they implement different solvers. The dominant numerical effects on the matter power spectrum boost are finite mass resolution, finite-volume effects, refinement threshold, and starting redshift, but they are limited to below 2% at the largest wavenumbers, k = 10 h Mpc ⁻¹ , for the range of tested values. Finally, we investigated the impact of the EFTofDE parameters on the matter power spectrum ratios between EFTofDE and Lambda cold dark matter scenarios. Depending on the values of the EFTofDE parameters, the screening can play a negligible or dominant role compared to the often-used linearised field equations. Our codes provide tools for generating fast and accurate predictions of the impact of the EFTofDE on the clustering of matter, incorporating the non-linear Vainshtein screening mechanism.

The aim of this work is to construct mock galaxy catalogues that accurately reproduce the redshift evolution of galaxy number density, clustering statistics, and baryonic properties, such as stellar mass for luminous red galaxies (LRGs) and absolute magnitude in the r-band for the bright galaxy sample (BGS), based on the first three years of observations from the Dark Energy Spectroscopic Instrument (DESI). To achieve this, we applied the subhalo abundance matching (SHAM) technique to the Uchuu N -body simulation, which follows the evolution of 2.1 trillion particles within a volume of 8 h ^-3 Gpc ³ , assuming a Planck base-ΛCDM cosmology. Using SHAM, we populated Uchuu subhalos with LRGs and BGS-BRIGHT ( r < 19.5) galaxies up to redshift z = 1.1, assigning stellar masses to LRGs and luminosities to BGS galaxies (up to M _r ≤ 20). Furthermore, we analyzed the clustering dependence on stellar mass and luminosity for each tracer. Our results show that the Uchuu BGS-BRIGHT and LRG mocks accurately reproduce the observed redshift evolution of clustering, with better than 5% agreement for separations of 1 < r < 20 h ^-1 Mpc and below a 10% for 0.1 < r < 1 h ^-1 Mpc. For the Uchuu -LRG mock, we successfully captured the stellar mass dependence of clustering, while for the Uchuu -BGS mock, we replicated the clustering for various volume-limited subsamples. We also find good agreement between the data and mocks in the dependence of large-scale bias on luminosity for BGS-BRIGHT galaxies and on stellar mass for LRGs. Altogether, these results equip DESI with robust tools for generating high-fidelity lightcones for the remainder of the survey, thereby enhancing our understanding of the galaxy-halo connection.

We report spatially resolved measurements of cool gas traced by Mg II and Fe II absorption in the circumgalactic medium (CGM) of a star-forming galaxy at z ∼ 1 (G1). The fortuitous alignment of a background gravitational arc at z ∼ 2.4 provides seven closely spaced (∼6 kpc) transverse sightlines along the minor axis of G1, probing its CGM out to ∼50 kpc. This geometry allowed us to detect a galactic-scale outflow simultaneously in the down-the-barrel and transverse directions, where we detected blueshifted Mg II absorption lines along both types of sightlines, revealing a large-scale collimated wind. We measured blueshifted line-of-sight velocities of v _los ∼ 62 − 239 km s ⁻¹ and line-of-sight velocity dispersions of σ _los ∼ 53 − 133 km s ⁻¹ , suggesting a structure dominated by bulk motion. De-projection of v _los along the minor axis indicates that the outflow material barely approaches the escape velocity and is likely to be gravitationally bound to G1. We constrained an outflow opening angle θ _c ∼ 18° −25°, and a mass outflow rate of Ṁ _out ≳ 0.06 M _⊙ yr ⁻¹ , corresponding to a mass loading factor η ≳ 0.004, estimated within ∼10 − 50 kpc (∼0.05 − 0.3 R _vir ) of the galaxy centre. Our measurements, combined with previous arc tomography data along the major axis, indicate that normalizing impact parameters by galaxy B-band luminosity substantially reduces scatter in the established anti-correlation between Mg II equivalent width and impact parameter, while also diminishing possible excess of Mg II equivalent width towards the minor axis.

We present spectroscopic data of strong lenses and their source galaxies using the Keck Near-Infrared Echellette Spectrometer (NIRES) and the Dark Energy Spectroscopic Instrument (DESI), providing redshifts necessary for nearly all strong-lensing applications with these systems, especially the extraction of physical parameters from lensing modeling. These strong lenses were found in the DESI Legacy Imaging Surveys using residual neural networks and followed up by our Hubble Space Telescope program, with all systems displaying unambiguous lensed arcs. With NIRES, we target eight lensed sources at redshifts difficult to measure in the optical range and determine the source redshifts for six, between z _s = 1.675 and 3.332. DESI observed one of the remaining source redshifts, as well as an additional source redshift within the six systems. The two systems with nondetections by NIRES were observed for a considerably shorter 600 s at high airmass. Combining NIRES infrared spectroscopy with optical spectroscopy from our DESI Strong Lensing Secondary Target Program, these results provide the complete lens and source redshifts for six systems, a resource for refining automated strong lens searches in future deep- and wide-field imaging surveys and addressing a range of questions in astrophysics and cosmology.

In 2021 May the Dark Energy Spectroscopic Instrument (DESI) collaboration began a 5 yr spectroscopic redshift survey to produce a detailed map of the evolving three-dimensional structure of the Universe between z = 0 and z ≈ 4. DESI’s principal scientific objectives are to place precise constraints on the equation of state of dark energy, the gravitationally driven growth of large-scale structure, and the sum of the neutrino masses, and to explore the observational signatures of primordial inflation. We present DESI DR1, which consists of all data acquired during the first 13 months of the DESI main survey, as well as a uniform reprocessing of the DESI Survey Validation data, which were previously made public in the DESI Early Data Release. The DR1 main survey includes high-confidence redshifts for 18.7M objects, of which 13.1M are spectroscopically classified as galaxies, 1.6M as quasars, and 4M as stars, making DR1 the largest sample of extragalactic redshifts ever assembled. We summarize the DR1 observations, the spectroscopic data-reduction pipeline and data products, large-scale structure catalogs, value-added catalogs, and describe how to access and interact with the data. In addition to fulfilling its core cosmological objectives with unprecedented precision, we expect DR1 to enable a wide range of transformational astrophysical studies and discoveries.

ESA’s Euclid cosmology mission relies on the very sensitive and accurately calibrated spectroscopy channel of the Near-Infrared Spectrometer and Photometer (NISP). With three operational grisms in two wavelength intervals, NISP provides diffraction-limited slitless spectroscopy over a field of 0.57 deg ² . A blue grism, BG _E , covers the wavelength range 926–1366 nm at a spectral resolution (ℛ) of 440–900 for a 0.″5 diameter source with a dispersion of 1.24 nm px ⁻¹ . Two red grisms, RG _E , span 1206 to 1892 nm at ℛ = 550–740 and a dispersion of 1.37 nm px ⁻¹ . We describe the construction of the grisms as well as the ground testing of the flight model of the NISP instrument, where these properties were established.

We present the Dark Energy Spectroscopic Instrument (DESI) Strong Lens Foundry. We discovered ∼3500 new strong gravitational lens candidates in the DESI Legacy Imaging Surveys using residual neural networks (ResNet). We observed a subset (51) of our candidates using the Hubble Space Telescope (HST). Except for one ambiguous case, we have confirmed 50 of the 51 candidates to be strong lenses. We also briefly describe spectroscopic follow-up observations by DESI and Keck NIRES programs. From this very rich data set, a number of studies will be carried out, including evaluating the quality of the ResNet search candidates and lens modeling. In this paper, we present our initial effort in these directions. In particular, as a demonstration, we present the lens model for DESI-165.4754−06.0423, with imaging data from HST, and lens and source redshifts from DESI and Keck NIRES, respectively. In this effort, we have applied a fully forward-modeling Bayesian approach ( GIGA-Lens ), using multiple GPUs, to a strong lens with HST data, and achieved statistical convergence.