Kyle Dawson

We present a multi-redshift Baryon Acoustic Oscillations (BAO) analysis of the DESI Data Release 2 (DR2) Lyman- α (Ly α ) forest, splitting the forest auto-correlation and its cross-correlation with quasars into three redshift bins. We obtain BAO measurements at effective redshifts z _eff = 2.13, 2.40, and 2.81 with ∼ 2.0–2.5% precision per bin in the radial and transverse directions, corresponding to ∼ 1.1–1.2% precision for the isotropic BAO measurement. Using the same data products and modeling framework as the DESI DR2 Ly α BAO analysis, we validate the pipeline on 400 synthetic datasets and find unbiased BAO recovery with well-calibrated uncertainties. The measurements show an increase in the isotropic dilation parameter D _V / r _d from 30.26 ± 0.39 to 32.22 ± 0.47 and in the Alcock-Paczyński parameter D _M / D _H from 3.96 ± 0.15 to 5.63 ^+0.22 _-0.24 . The Hubble distance D _H / r _d decreases from 9.40 ± 0.20 to 7.22 ± 0.17, providing a direct measurement of the expansion history consistent with ΛCDM and the expected matter-dominated scaling, with H ( z ) ∝ (1 + z ) ⁿ giving n = 1.34 ± 0.16. The redshift split also provides a self-consistent measurement of clustering evolution: the Ly α forest bias evolves as (1 + z ) ^γ with γ _α = 3.05 ± 0.16, the RSD parameter has a redshift evolution described by γ _β = -0.97 ± 0.26, and the quasar bias evolves with γ _Q = 1.56 ± 0.23, consistent with independent quasar clustering measurements. Combining these three-bin BAO measurements with DESI DR2 galaxy and quasar BAO measurements yields cosmological constraints consistent with the single-bin Ly α BAO analysis in flat ΛCDM and w ₀ w _a CDM and improves curvature constraints by ∼ 12% in ΛCDM+Ω _K .

We present constraints on cosmic structure growth from the analysis of galaxy clustering and galaxy–galaxy lensing with galaxies from the Dark Energy Spectroscopic Instrument (DESI) Data Release 1. Our analysis includes four samples drawn from the Bright Galaxy Survey (BGS) and the luminous red galaxy (LRG) target classes. Projected galaxy clustering measurements from DESI are supplemented with lensing data from the Dark Energy Survey (DES), the Kilo-Degree Survey (KiDS), and the Hyper Suprime-Cam (HSC) survey around the same targets. Our method relies on a simulation-based modeling framework using the AbacusSummit simulations and a complex halo occupation distribution model that incorporates assembly bias. We analyze scales down to 0.4 h ⁻¹ Mpc for clustering and 2.5 h ⁻¹ Mpc for lensing, leading to stringent constraints on S 8 = σ 8 Ω m / 0.3 and Ω _m when fixing other cosmological parameters to those preferred by the cosmic microwave background. We find S 8 = 0.79 7 − 0.024 + 0.023 and Ω _m = 0.292 ± 0.011 when using lensing measurements from DES and KiDS. Similarly, for HSC, we find S 8 = 0.79 1 − 0.021 + 0.020 and Ω _m = 0.300 ± 0.009 when assuming the best-fit photometric redshift offset suggested by the HSC collaboration. Overall, our results are in good agreement with other results in the literature while continuing to highlight the constraining power of nonlinear scales.

Using the first spectroscopic data release from the Dark Energy Spectroscopic Instrument (DESI DR1), we conduct the largest systematic search for active galactic nuclei (AGN) signatures in ≈1.7 million low-redshift (0.001 ≤ z ≤ 0.45) line-emitting galaxies. Based on the [N ii ]/H α versus [O iii ]/H β emission-line ratio diagnostic, we identify AGN in 314,245/1,211,573 (25.9%) high-mass ( log ( M ⋆ / M ⊙ ) > 9.5 ) and 9648/467,214 (2.1%) dwarf ( log ( M ⋆ / M ⊙ ) ≤ 9.5 ) galaxies. The AGN fraction in line-emitting galaxies increases monotonically with stellar mass, from ∼1.4% at the low-mass end to ∼93.3% at the high-mass end. Among these AGN, 17,949 exhibit broad H α emission (BL-AGN), which we use to estimate their black hole (BH) masses via single-epoch virial methods. Leveraging this large BL-AGN sample, we extend the M _BH − M _⋆ scaling relation down to log ( M ⋆ / M ⊙ ) ≈ 7.8 and log ( M BH / M ⊙ ) ≈ 4.4 . We find a bimodal distribution of galaxies in this space, characterized by two distinct empirical relations. The relation for galaxies with high stellar and BH masses extrapolates to overlap with the high-redshift overmassive BH candidates. Our results suggest at least two broad evolutionary pathways for these overmassive BHs and their host galaxies across cosmic time. With this paper, we release the EmFit value-added catalog, containing emission-line flux and width measurements for ∼7.4 million galaxies, the largest catalog with emission-line decomposition into narrow, broad, and outflow components to date. This work significantly expands upon the early DESI results and provides a statistical sample for probing the galaxy−BH connection in the low-mass galaxy regime.

We present a clustering analysis of Lyman- α emitters (LAEs) using spectroscopic observations from the Dark Energy Spectroscopic Instrument (DESI) of candidates selected from the Blanco/DECam Intermediate-Band Imaging Survey (IBIS). We measure the two-point correlation function and the power spectrum, including cross-correlations with DESI quasars. Using both analytical and halo occupation distribution (HOD) simulation-based modeling, we find a linear bias of b ∼ 2.31–2.62 for LAEs over the redshift range 2.26 < z < 3.41. The analytical modeling also provides constraints on the strength of radiative transfer effects, while the HOD analysis characterizes the LAE-halo connection across multiple models. Finally, we quantify the magnitude of non-perturbative clustering effects such as Fingers of God in the LAE population, providing essential input for the accurate modeling of LAE-based cosmological analyses in forthcoming high-redshift surveys such as DESI-II.

The One-hundred-deg ² DECam Imaging in Narrowbands (ODIN) survey is conducting the widest-field deep narrowband (NB) imaging of the equatorial and southern skies. ODIN uses three custom-built NB filters that sample Ly α -emitting galaxies (LAEs) within thin cosmic slices centered at z = 2.4, 3.1, and 4.5. In this work, we utilize extensive DESI spectroscopy of ODIN-selected galaxies in the COSMOS and XMM-LSS fields to validate our LAE selection. Exposures of 2–4 hr with DESI yielded redshift confirmation of 3075 ODIN LAE candidates with NB magnitudes brighter than 26 mag. Restricting to objects that yield high-confidence redshifts, the confirmation rates are (93%, 96%, 92%) at z = (2.4, 3.1, 4.5). The primary contaminants consist of active galactic nuclei at the expected Ly α- redshift range and lower redshifts (C iv , C iii ]), with the remainder being star-forming galaxies ([O ii ] and [O iii ]). We find minimal contamination from [O ii ] emitters in our sample (≲1%), implying that our rest-frame equivalent width (REW) > 20 Å NB excess photometry requirement is sufficient to remove them.

Deep spectroscopic samples can improve photometric redshift (photo- z ) estimates and reduce uncertainties on redshift distributions. Such improvements can increase the cosmological constraining power of large imaging-based experiments such as the Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST) and mitigate what may be a limiting systematic effect. We present results from the “DESI-Deep pilot” program, which was designed to assess the capability of the Dark Energy Spectroscopic Instrument (DESI) on the 4m Mayall telescope to measure redshifts of galaxies as faint as expected lensing samples for early LSST data ( m _i ≤ 24.5). We find that DESI is remarkably efficient at this task, with redshift success rates comparable to the results of observations from 10 m class telescopes with only ∼2 × longer integration time (rather than ∼8 × longer as would be expected from aperture-area scaling), while simultaneously achieving ∼30 times larger multiplexing. We also find that the signal-to-noise ratio of the spectra scales as expected for background-limited observations even for the longest exposure times (∼7 hr) and faintest targets in the program. These results demonstrate that DESI could provide the definitive redshift sample for the early years of LSST with a modest investment of observing time. Based upon the results of this program, we provide updated predictions for the time required to collect benchmark samples for photo- z training and calibration using a variety of spectroscopic facilities. Finally, we describe a potential “DESI-Deep” survey designed to train and calibrate photo- z ’s for imaging experiments, and provide forecasts of its impact on cosmological inference.

We present the first systematic spectroscopic observations of extragalactic transients from the Dark Energy Spectroscopic Instrument (DESI), as part of the DESI Transients Survey program. With 5000 fibers and an ∼8 deg ² field of view, we exploit DESI as a machine for the discovery and classification of transients. We present transient classifications from archival DESI data in Data Releases 1 and 2, relying on a combination of a secondary target program and serendipitous observations. We also present observations from the first 6 months of the DESI spare fiber program dedicated to transients. The program is run in coordination with a dedicated DECam time-domain survey, serving as a pathfinder for what we will be able to achieve in conjunction with the Rubin Observatory Legacy Survey of Space and Time (LSST). We classify over 250 transients, of which the majority were previously unclassified. The sample comprises thermonuclear and core-collapse supernovae and tidal disruption events (TDEs), including a TDE observed before its discovery in imaging. We demonstrate DESI’s ability to classify a population of faint transients down to r ∼ 22.5 mag during main survey operations, with negligible impacts on DESI’s main observations. With the start of Rubin LSST operations, we expect to classify O ( 1000 ) transients per year.

We present the first measurement of local-type primordial non-Gaussianity from the cross-correlation between 1.2 million spectroscopically confirmed quasars from the first data release (DR1) of the Dark Energy Spectroscopic Instrument (DESI) and the Planck PR4 CMB lensing reconstructions. 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- C _ℓ estimator and apply linear imaging weights validated on noiseless mocks. Compared to previous analyses using photometric quasar samples, our results benefit from the high purity of the DESI spectroscopic sample, the reduced noise of PR4 lensing, and the absence of excess large-scale power in the spectroscopic 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 to the previous analysis based on the Legacy Imaging Survey DR9. Additionally, we derive an optimal weighting 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 for probing inflationary physics, and highlight the promise of future DESI data releases.

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.

Using the Dark Energy Spectroscopic Instrument (DESI) Milky Way Survey, we examine the six-dimensional space of the anticenter region of the Milky Way stellar disk (150° < Galactic longitude < 220°) using 61,883 main-sequence turnoff stars. We focus on two well-known stellar overdensities in the anticenter: the Monoceros Ring (MRi) and Anticenter Stream (ACS). We find that the MRi overdensity has kinematic signatures consistent with a tidally induced spiral arm, a type of dynamic spiral arm created by an interaction with a satellite galaxy, most likely the Sagittarius dwarf spheroidal galaxy (Sgr). We use the kinematics of the MRi to calculate the two most recent passage times of Sgr, finding 0.25 ± 0.09 Gyr and 1.10 ± 0.23 Gyr from the present day. We validate that the ACS is kinematically decoupled from the MRi because they are moving in opposite radial and vertical directions. We find that the kinematics associated with the ACS extends beyond our defined overdensity. The features we see in the ACS region are likely part of a broader distribution of stars with the same kinematic signature as detected in other places, like the vertical wave in the outer disk and phase spiral.