116 Search Results

We present the cosmological analysis of the one-dimensional Lyman-α flux power spectrum from the first data release of the Dark Energy Spectroscopic Instrument (DESI). We capture the dependence of the signal on cosmology and intergalactic medium physics using an emulator trained on a cosmological suite of hydrodynamical simulations, and we correct its predictions for the impact of astrophysical contaminants and systematics, many of these not considered in previous analyses. We employ this framework to constrain the amplitude and logarithmic slope of the linear matter power spectrum at k$$_{★}$$ = 0.009 km$$^{-1}$$s and redshift z = 3, obtaining Δ$$^{2}$$$$_{★}$$ = 0.379more » ± 0.032 and n$$_{★}$$ = -2.309 ± 0.019 https://github.com/igmhub/cobaya_lya_p1d. The robustness of these constraints is validated through the analysis of mocks and a large number of alternative data analysis variations, with cosmological parameters kept blinded throughout the validation process. We then combine our results with constraints from DESI BAO and temperature, polarization, and lensing measurements from Planck, ACT, and SPT-3G to set constraints on ΛCDM extensions. While our measurements do not significantly tighten the limits on the sum of neutrino masses from the combination of these probes, they sharpen the constraints on the effective number of relativistic species, N$$_{eff}$$ = 3.02 ± 0.10, the running of the spectral index, α$$_{s}$$ = 0.0014 ± 0.0041, and the running of the running, β$$_{s}$$ = -0.0006 ± 0.0048, by a factor of 1.18, 1.27, and 1.90, respectively. We conclude by outlining the improvements needed to fully reach the level of confidence implied by these uncertainties.« less

We present a cosmological analysis combining full-shape (FS) clustering measurements from the Dark Energy Spectroscopic Instrument (DESI) DR1 with baryon acoustic oscillation (BAO) measurements from DESI DR2. To achieve a robust combination that accounts for the correlation between the two data releases, we employ the ShapeFit compression method and estimate the joint covariance using EZmocks. This compressed approach inherently mitigates the prior volume effects that have previously dominated Bayesian constraints from DESI data with minimal external priors. Consequently, we obtain — for the first time within a Bayesian framework — reliable DESI-only constraints on extensions to ΛCDM using only amore » Big Bang Nucleosynthesis prior on the baryon density and a wide prior on the spectral index. In flat ΛCDM, we find Ω$$_{m}$$ = 0.3035 ± 0.0085, h = 0.6876 ± 0.0059, and σ$$_{8}$$ = 0.822 ± 0.034. For the w$$_{0}$$waCDM dynamical dark energy model, we measure w$$_{0}$$ = -0.49 ± 0.25 and wa = -1.52 ± 0.77, improving constraints by ∼ 30% relative to the analogous DR1 measurement and reducing the discrepancy with ΛCDM to 1.4σ when compared to BAO only analyses. We also report competitive limits on the sum of neutrino masses and spatial curvature. This work demonstrates that the ShapeFit compression provides a prior-robust and computationally efficient pathway to constrain beyond-ΛCDM physics with large-scale structure.« less

The Dark Energy Spectroscopic Instrument (DESI) in its first Data Release (DR1) already provides more than 100,000 galaxies with relative distance measurements. The primary purpose of this paper is to perform the calibration of the zero-point for the DESI Fundamental Plane and Tully–Fisher relations, which allows us to measure the Hubble constant, H$$_{0}$$. This sample has a lower statistical uncertainty than any previously used to measure H$$_{0}$$, and we investigate the systematic uncertainties in absolute calibration that could limit the accuracy of that measurement. We improve upon the DESI Early Data Release Fundamental Plane H$$_{0}$$ measurement by (a) using amore » group catalog to increase the number of calibrator galaxies and (b) investigating alternative calibrators in the nearby Universe. Our baseline measurement calibrates to the SH0ES/Pantheon+ type Ia supernovae, and finds H$$_{0}$$ = 73.7 ± 0.06 (stat.) ± 1.1 (syst.) km s$$^{−1}$$ Mpc$$^{−1}$$. Calibrating to surface brightness fluctuation distances yields a similar H$$_{0}$$. We explore measurements using other calibrators, but these are currently less precise since the overlap with DESI peculiar velocity tracers is much smaller. In future data releases with an even larger peculiar velocity sample, we plan to calibrate directly to Cepheids and the tip of the red giant branch, which will enable the uncertainty to decrease towards a percent-level measurement of H$$_{0}$$. This will provide an alternative to supernovae as the Hubble flow sample for H$$_{0}$$ measurements.« less

Emission-line galaxies (ELGs) are an important tracer of baryon acoustic oscillations (BAOs) and large-scale structure at z > 1. In this work, we investigate the feasibility of using deep wide-area multiband imaging (e.g., from the Rubin Observatory) to efficiently select high-redshift ELGs. Using Hyper Suprime-Cam grizy photometry and COSMOS2020 many-band photometric redshifts, we design simple color cuts guided by a probabilistic random forest classifier to select galaxies at z = 1.1–1.6. We then empirically test and refine these color cuts using two samples of galaxies with deep spectroscopy and broad color coverage obtained with the Dark Energy Spectroscopic Instrument (DESI).more » Compared to DESI ELGs at z = 1.1–1.6, we achieve a higher redshift-measurement success rate (89% versus 69%), a much higher correct redshift-range success rate (84% versus 34%), and a far higher net surface density yield (1372 deg⁻² versus 660 deg⁻²). Combining our sample with current DESI ELGs would increase the net ELG number density by a factor of ∼2.5, moving it out of the shot-noise limited regime and reducing the uncertainties on the BAO scale parameter at z = 1.1–1.6 by a factor of ∼2 at the highest redshifts. We also test selections using shallower photometry and obtain qualitatively similar results.« less

We present the first measurement of local-type primordial non-Gaussianity from thecross-correlation between 1.2 million spectroscopically confirmed quasars from the first datarelease (DR1) of the Dark Energy Spectroscopic Instrument (DESI) and the Planck PR4 CMB lensingreconstructions. The analysis is performed in three tomographic redshift bins covering 0.8 < z <3.5, covering a sky fraction of ∼20%. We adopt a catalog-based pseudo-Cℓ estimatorand apply linear imaging weights validated on noiseless mocks. Compared to previous analyses usingphotometric quasar samples, our results benefit from the high purity of the DESI spectroscopicsample, the reduced noise of PR4 lensing, and the absence of excess large-scale powermore » in thespectroscopic quasar auto-correlation. Fitting simultaneously for the non-Gaussianity parameter f$$_{NL}$$ and the linear bias amplitude in each redshift bin, we obtain f$$_{NL}$$ = 2$$^{+28}$$$$_{-34}$$ for a response parameter p = 1.6, and f$$_{NL}$$ = 6$$^{+20}$$$$_{-24}$$ for p = 1.0. These results improve the constraints on f$$_{NL}$$ by ∼35% compared tothe previous analysis based on the Legacy Imaging Survey DR9. Additionally, we derive an optimalweighting scheme to maximize the constraining power. In this case, and assuming p = 1.6, we obtain f$$_{NL}$$ = 19$$^{+25}$$$$_{-31}$$. Our results demonstrate the statistical power of DESI quasars forprobing inflationary physics, and highlight the promise of future DESI data releases.« less

The calibration of tomographic redshift distributionsis essential for cosmological analysis of weak lensing data.In this work, we calibrate all four tomographic bins of the Hyper Suprime Camera (HSC) weak lensing catalog with the Dark Energy Spectroscopic Instrument (DESI) Data Release 1 and 2 using the clustering redshifts technique. We include z > 1.2 redshift sources such as emission line galaxies (ELG) and quasars (QSO) sources in our calibration, which were not available in the previous HSC calibration (Rau et al. (2022), Mon. Not. Roy. Astron. Soc. 524 (2023) 5109), allowing a complete calibration of all the redshift bins. We find the firstmore » tomographic bin exhibits a small shift towards low redshifts. The second bin is in good agreement with the photometric calibration, while third and fourth bin exhibit a shift towards higher redshifts. However, these shifts are considerably smaller than the shifts obtained in the HSC Year 3 cosmic shear analyses. We evaluate the impact of galaxy bias and magnification effects from all the samples on the measurements, finding them to be small, and we propose corrections to reduce them further. Specifically, we relax the assumption of linear bias and only assume no redshift evolution of the cross-correlation coefficient, allowing us to leverage smaller clustering scales. We model the redshift distributions with splines and compare our results to previous analyses as well as to other parameterizations found in literature. For the two high-redshift tomographic bins, we find the shifts to higher redshifts with respect to the measurements performed in Rau+2022 to be Δz$$_{3}$$ =-0.039$$^{+0.020}$$$$_{-0.021}$$ and Δz$$_{4}$$ = -0.048$$^{+0.012}$$$$_{-0.012}$$.« less

The intergalactic medium (IGM) around a quasar is shaped by its dense environment and by its excess ionizing radiation, which form a “quasar proximity zone” whose size and anisotropy depend on the quasar’s halo mass, luminosity, age, and radiation geometry. Using over 10,000 quasar pairs from the Dark Energy Spectroscopic Instrument (DESI) Year 1 data, with projected comoving separations r$$_{⊥}$$ < 2h$$^{−1}$$ Mpc, we investigate how the proximity zone of foreground quasars at z ∼ 2–3.5 affects Lyα absorption in their background quasars. The large DESI sample enables unprecedented precision in measuring this “transverse proximity” effect, allowing a detailed investigation of the signal’s dependencemore » on the projected separation of quasar pairs and the luminosity of the foreground quasar. We find that enhanced gas clustering near quasars dominates over their ionizing effect, leading to stronger absorption on neighboring sightlines. Under the assumption that quasar ionizing luminosity is isotropic and steady, we infer the IGM overdensity profile in the vicinity of quasars, finding overdensities as high as Δ ∼ 10 at comoving distance ∼1h$$^{−1}$$ Mpc from the most luminous systems. Surprisingly, however, we find no significant dependence of the proximity profile on the luminosity of the foreground quasar. This lack of luminosity dependence could reflect a cancellation between higher ionizing flux and higher gas overdensity, or it could indicate that quasar emission is highly time-variable or anisotropic, so that the observed luminosity does not trace the ionizing flux on nearby sightlines.« less

The standard cosmological analysis with the Lyα forest relies on a continuum fitting procedure that suppresses information on large scales and distorts the three-dimensional correlation function on all scales. In this work, we present the first cosmological forecasts without continuum fitting distortion in the Lyα forest, focusing on the recovery of large-scale information. Using idealized synthetic data, we compare the constraining power of the full shape of the Lyα forest auto-correlation and its cross-correlation with quasars using the baseline continuum fitting analysis versus the true continuum. We find that knowledge of the true continuum enables a ∼ 10% reduction inmore » uncertainties on the Alcock-Paczyński (AP) parameter and the matter density, Ω$$_{m}$$. We also explore the impact of large-scale information by extending the analysis up to separations of 240 h$$^{-1}$$Mpc along and across the line of sight. The combination of these analysis choices can recover significant large-scale information, yielding up to a ∼ 15% improvement in AP constraints. This improvement is analogous to extending the Lyα forest survey area by ∼ 40%.« less

The aim of this work is to construct mock galaxy catalogues that accurately reproduce theredshift evolution of galaxy number density, clustering statistics, and baryonic properties, suchas stellar mass for luminous red galaxies (LRGs) and absolute magnitude in the r-band for thebright galaxy sample (BGS), based on the first three years of observations from the Dark EnergySpectroscopic Instrument (DESI). To achieve this, we applied the subhalo abundance matching (SHAM)technique to the UchuuN-body simulation, which follows the evolution of 2.1 trillionparticles within a volume of 8 h$$^{-3}$$ Gpc$$^{3}$$, assuming a Planck base-ΛCDMcosmology. Using SHAM, we populated Uchuu subhalos with LRGs and BGS-BRIGHTmore » (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 andluminosity for each tracer. Our results show that the Uchuu BGS-BRIGHT and LRG mocksaccurately 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. Forthe 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-limitedsubsamples. We also find good agreement between the data and mocks in the dependence oflarge-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 theremainder of the survey, thereby enhancing our understanding of the galaxy-halo connection.« less

Reconstruction of the baryon acoustic oscillation (BAO) signal has been a standard procedure in BAO analyses over the past decade and has helped to improve the BAO parameter precision by a factor of ∼2 on average. The Dark Energy Spectroscopic Instrument (DESI) BAO analysis for the first year (DR1) data uses the “standard” reconstruction framework, in which the displacement field is estimated from the observed density field by solving the linearized continuity equation in redshift space, and galaxy and random positions are shifted in order to partially remove non-linearities.There are several approaches tosolving for the displacement field in real surveymore » data,including the multigrid (MG), iterative Fast Fourier Transform (iFFT), and iterative Fast Fourier Transform particle (iFFTP) algorithms. In this work, we analyze these algorithms and compare them with various metrics including two-point statistics and the displacement itself using realistic DESI mocks. We focus on three representative DESI samples, the emission line galaxies (ELG), quasars (QSO), and the bright galaxy sample (BGS), which cover the extreme redshifts and number densities, and potential wide-angle effects. We conclude that the MG and iFFT algorithms agree within 0.4% in post-reconstruction power spectrum on BAO scales with the RecSym convention, which does not remove large-scale redshift space distortions (RSDs), in all three tracers. The RecSym convention appears to be less sensitive to displacement errors than the RecIso convention, which attempts to remove large-scale RSDs.However, iFFTP deviates from the first two; thus, we recommend against using iFFTP without further development. In addition, we provide the optimal settings for reconstruction for five years of DESI observation.The analyses presented in this work pave the way for DESI DR1 analysis as well as future BAO analyses.« less