Reconstructing the three-dimensional distribution of dark matter from weak-lensing observations is a central but highly ill-posed inverse problem in cosmology. Unlike standard 3D reconstruction with multiple viewpoints, we observe the universe from a single line of sight, through noisy shape distortions of galaxies with uncertain distances, so meaningful recovery of the 3D matter field requires strong prior assumptions. Existing methods either produce point estimates with handcrafted priors or use neural ensembles for approximate Bayesian uncertainty, and struggle to capture the non-Gaussian, filamentary structure of the cosmic web. With the advent of new high-resolution cosmological simulations, we now have an alternative source of prior knowledge that captures the nonlinear statistics of structure formation with far greater fidelity than analytic prescriptions. We leverage these simulations to build a new dataset \texttt{Conicus3D}, which enables us to learn a data-driven diffusion-model prior capturing the full 3D distribution of dark matter structure across cosmic time. Building on recent plug-and-play approaches, we modify a diffusion-based posterior sampling scheme to the 3D weak-lensing setting, combining the learned prior with a differentiable physical forward model. On realistic simulations targeting a modern weak lensing survey, our approach yields substantially improved 2D and 3D reconstruction accuracy over baseline methods. Moreover, it produces posterior samples whose statistics closely track the underlying simulations, while remaining robust to moderate shifts in cosmology.

Current and upcoming large-scale structure surveys are pushing toward increasingly wide angular coverage, where wide-angle effects (arising from the varying line of sight across the curved sky) become critical for accurate modeling of the three-dimensional galaxy power spectrum. At the same time, these survey's broader redshift reach makes the effects of redshift evolution (beyond the effective-redshift approximation) non-negligible on large radial scales. Additional observational effects such as the survey window function and integral constraints also become significant on these large scales, necessitating a careful theoretical treatment to robustly constrain local primordial non-Gaussianities and relativistic effects. In this work, we present a consistent and accurate theoretical framework for modeling the commonly used power spectrum multipoles (PSM) on large scales using the discrete spherical Fourier-Bessel (dSFB) basis. This basis ensures numerical stability and allows an exact separation between angular and radial modes. Using the dSFB basis, we study the impact of wide-angle effects and redshift evolution on the PSM, and incorporate the effects of window function convolution and integral constraints. We validate our PSM modeling using lognormal mocks under radial integral constraints with realistic survey geometries, demonstrating the readiness of our framework for application to all-sky galaxy surveys.

The Spherical Fourier-Bessel (SFB) basis, in separating the angular and radial modes of the power spectrum, permits a targeted identification and mitigation of systematics in clustering surveys while retaining more cosmological signal than traditional bases. We demonstrate this principle on the eBOSS DR16 LRG and QSO samples, identifying modes which may be contaminated by systematics. Our initial inference on the LRG sample yields an fNL value consistent with zero, while the QSO value is in slight tension with zero. Using the SFB basis, we vary the selection of angular and radial modes to search for inconsistencies in the inferred value of fNL, an indicator of underlying systematics. In the QSO sample, we find evidence (p < 0.005 compared to the same cuts on EZMocks) of a systematic afflicting large physical scales, which is consistent with residual stellar contamination; we also find evidence (p < 0.05) for an unknown systematic in the QSO and LRG samples at the approximate angular plate and imaging scale of eBOSS.

SPHEREx is a NASA mission designed to perform an all-sky spectroscopic survey in the 0.75-5 mu m wavelength range. Its primary science objectives are to investigate: (1) inflationary cosmology; (2) the history of galaxy formation; and (3) the abundance of molecular ices-critical for prebiotic chemistry-found on the surfaces of interstellar dust grains within planet-forming regions. This paper focuses on the third theme, the SPHEREx Ices Investigation, for which SPHEREx is conducting a spectroscopic survey of nearly 10 million preselected sources throughout the Milky Way and Magellanic Clouds, to characterize their ice absorption features. By selecting targets based on infrared color, spatial isolation, and brightness, the Ices Investigation secures high-signal-to-noise-ratio spectra across a broad range of astrophysical environments that are relatively free of spectral contamination. Rather than attempting to decompose each spectrum into its individual ice components, the Ices Investigation prioritizes accurate measurements of the integrated optical depths of key molecular ice absorption features. This approach enables statistically powerful correlation studies between ice abundances and environmental parameters-including extinction, temperature, gas composition, radiation field strength, cosmic-ray flux, and star formation activity. The data pipeline developed for this purpose incorporates machine learning for continuum estimation, drawing on both SPHEREx and ancillary data sets. Ultimately, the expansive spectral archive produced by SPHEREx, combined with targeted follow-up from facilities like JWST, will transform our understanding of Galactic ice formation, evolution, abundance, and their inheritance into planetary systems and prebiotic inventories.

We present a composite spectrum of ∼ 61,000 type 1 SDSS QSOs (median z ≈ 1.26), constructed using SPHEREx spectrophotometric data and covering a rest-frame wavelength range of 0.14-4.5 μm. The SPHEREx mission surveys the entire sky in 102 near-infrared spectral channels spanning 0.75-5.0 μm with a spectral resolution of R ≈ 35-130, providing a unique dataset for building a statistically robust QSO composite. We find that the UV and optical continuum of the resulting composite can be described by a power law, f_ν∝ ν^α_ν, with a best-fit spectral index of α_ν= -0.10, while the near-infrared continuum is well-fit with a spectral index of -1.46. The power-law indices in both the optical and near-infrared regimes strongly depend on properties of QSOs, such that more luminous QSOs tend to exhibit flatter UV/optical and steeper near-infrared continua compared to those of less luminous ones. The IR-to-optical flux ratio decreases with increasing AGN luminosity, consistent with the predictions of the receding torus model. The line ratios of broad emission lines, including Hα, Paβ, and Paα, are in good agreement with predictions from Case B recombination, suggesting that internal extinction is almost negligible. The equivalent widths of these emission lines are proportional to AGN luminosity, contrary to the trend expected from the Baldwin effect. Finally, the shape of the composite is sensitive to host-galaxy contamination, which must be considered when utilizing this QSO composite for subsequent scientific applications.

We present map-making methodologies and preliminary spectral data cubes for SPHEREx, a NASA Explorer mission that launched in March 2025 and has been performing an all-sky near-infrared spectral survey. The SPHEREx instrument observes from 0.75 to 5.0 microns with a spectral resolution ranging from 35 to 130 and a pixel size of 6.15". We define a nominal set of 102 wavelength channels, each of which maps the entire sky approximately twice per year. Among the main mission goals is an investigation of the cosmic history of galaxy formation through intensity mapping of the extragalactic background light (EBL), which is a primary motivation for the map maker described in this work. The SPHEREx dataset contains a wealth of additional mapping targets, e.g., resolved galaxies and nebulae and diffuse clouds of Galactic dust and gas, which display strong spectral features such as hydrogen recombination lines, molecular-hydrogen lines and emission from polycyclic aromatic hydrocarbons (PAHs). We describe how our map maker handles these various cases, how to mitigate foregrounds such as zodiacal light and upper-atmospheric emission and how to monitor and mitigate systematics and signal loss. Our maps are produced both in tangent-plane projection and in full-sky HEALPix format. Specialized maps will be released to accompany future publications from the SPHEREx Science Team, and a public mosaic tool will be made available by the NASA/IPAC Infrared Science Archive (IRSA).

We present preliminary SPHEREx maps of diffuse Galactic emission tracing polycyclic aromatic hydrocarbons (PAHs) and ionized hydrogen gas, and we study their relationship across the Galactic plane. Since its launch in early 2025, the SPHEREx space telescope has been conducting an all-sky near-infrared spectral survey from 0.75 to 5.0 mu m. We produce a large-scale map of the 3.3 mu m PAH emission feature, which is bright and detectable throughout the Galactic plane, and find a strong correlation with the thermal dust radiance measured by Planck. We also trace ionized hydrogen gas by producing a map of Brackett-alpha emission at 4.05 mu m. By combining the two maps, we identify extended shells of PAH emission associated with photodissociation regions surrounding ionized gas. We construct a PAH abundance map and find a significant anticorrelation between PAH abundance and ionized hydrogen, indicating systematic PAH depletion within ionized gas regions across the Galactic plane and demonstrating that ionizing radiation is a dominant driver of PAH abundance variations. These early SPHEREx results provide a large-scale view of PAHs and ionized hydrogen and a preview of the capability of the mission to map diffuse emission in the interstellar medium.

We model the impact of source confusion on photometry and the resulting spectrophotometric redshifts for SPHEREx, a NASA Medium-Class Explorer that is carrying out an all-sky near-infrared spectral survey. Spectral confusion from untargeted background galaxies degrades sensitivity and introduces a spectral bias. Using interpolated spectral energy distributions (SEDs) from the COSMOS2020 catalog, we construct a Monte Carlo library of confusion spectra that captures the cumulative impact from faint galaxies. By injecting confusion realizations into galaxy SEDs and performing forced photometry at known source positions, we quantify photometric and redshift error and bias. For our current expected selection of sources for the cosmology analysis, we find typical 1 sigma confusion levels range from 0.8-3.8 mu Jy across 0.75-5.0 mu m. While negligible at full-sky survey depth, spectral confusion becomes significant in the SPHEREx deep fields, reducing the number of intermediate-precision redshifts and inducing a small systematic overestimation in redshift. In parallel, we also model targeted source blending from beam overlaps, which contributes additional photometric noise without systematic redshift bias, provided that positions are known exactly. Together, confusion and blending vary with the depth of the selected reference sample, revealing a trade-off, where deeper selections reduce confusion but increase blending-induced noise. Our methodology informs optimization of the SPHEREx source selection strategy and future treatments of stellar source blending and confusion.

The Spectro Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx) is conducting the first all-sky near-infrared spectral survey spanning 0.75-5.0 mu m with resolving power R approximate to 35-130. Linear variable filters mounted in front of six H2RG detectors produce a position-dependent spectral response across the focal plane. This paper presents the ground-based spectral calibration of SPHEREx, including the cryogenic apparatus, optical configuration, measurement strategy, analysis pipeline, and resulting calibration products. Monochromatic wavelength scans are used to derive the spectral response function, band center, and resolving power for every pixel. Band centers are measured to better than 1 nm for Bands 1 through 4 (0.75-3.82 mu m) and better than 10 nm for Bands 5 and 6 (3.82-5.0 mu m). Out-of-band leakage is negligible for detectors above 1.64 mu m and is present at the percent level below this wavelength. The resolving power is measured to within 5% and agrees with design expectations to within 10%. An on-sky spectrum of the Cat's Eye Nebula (NGC 6543) constructed from repeated observations provides in-flight verification and shows agreement between ground-calibrated response and astrophysical emission features. Calibration products, including per-pixel band center and resolving power maps, are released through IPAC to support community use of SPHEREx data. The absolute spectral calibration will continue to improve through in-flight measurements, with further reductions in uncertainty expected for the longest-wavelength bands.

Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx), a NASA Explorer satellite launched on 2025 March 11, is carrying out the first all-sky near-infrared spectral survey. The satellite observes in 102 spectral bands from 0.75 to 5.0 mu m with a resolving power ranging from lambda/Delta lambda = 35-130 in 6 .'' 2 pixels. The observatory obtains a 5 sigma depth of 19.5-19.9 AB mag for 0.75 < lambda < 3.8 mu m with lambda/Delta lambda similar to 40 and 17.8-18.8 AB mag for 3.8 < lambda < 5.0 mu m with lambda/Delta lambda similar to 120 after mapping the full sky four times over two years. Scientifically, SPHEREx will produce a large galaxy redshift survey over the full sky to constrain the amplitude of inflationary non-Gaussianity. The observations will produce two deep spectral maps near the ecliptic poles that use intensity mapping to probe the evolution of galaxies over cosmic history. By mapping the depth of infrared absorption features over the Galactic plane, SPHEREx will comprehensively survey the abundance and composition of water and other biogenic ice species in the interstellar medium. The project will release initial data rapidly in the form of spectral images, and specialized data products over the life of the mission as the surveys proceed. The science team will also produce spectral catalogs of planet-bearing and low-mass stars, solar system objects, and galaxy clusters three years after launch. We describe the design of the instrument and spacecraft, which flow from the core science requirements. Finally, we present an initial evaluation of the satellite's in-flight performance and key characteristics.

The bispectrum of galaxy distribution remains an underutilized statistic in cosmological data analysis. This can be attributed to mathematical and computational challenges associated with a proper modeling of the signal and its covariance. While recent theoretical advances have made it possible to analytically model the bispectrum signal and covariance using perturbation theory, a fully non-Gaussian analytical treatment of the covariance for a realistic survey with window remains elusive. The full bispectrum covariance of observed galaxies is a non-Gaussian six-point function with each of its legs convolved with a complex window function. Although it has so far proven intractable, the problem is well-posed. In this article, we present the derivation, implementation, and validation of a numerical routine for the analytic calculation of the bispectrum covariance for a spherical window, carried out by a large language model (LLM). The derivation uncovered terms that vanish in the windowless case but that dominate the covariance for triangles with survey scale modes. As a development benchmark for the implementation, we used the sample covariance of the halo bispectrum measured from 6000 fiducial Quijote halo catalogs in real space. Over several iterations of refinement, the LLM converged on a regime-specific numerical scheme for the covariance matrix calculation, mixing exact and approximate approaches, resulting in a highly optimized, tractable and accurate covariance across scales and shapes, using only tree-level models for the input polyspectra. Closing the loop still required human expertise, which illustrates what human-AI collaboration in research may look like in the near term.

We explore the sensitivity of weak lensing surveys to gravitational waves (GWs) emitted by inspiraling supermassive black hole binaries (SMBHBs) in the nanohertz to microhertz frequency band, bridging the gap between pulsar timing arrays and space-based interferometers. Building on the formalism for GW-induced shear distortions, we develop a signal-to-noise framework that incorporates survey characteristics such as cadence, angular resolution, and depth. We model the effective galaxy population to evaluate the noise power spectral density and derive characteristic strain sensitivity curves. Applying this framework to both LSST-like and idealized survey configurations, we show that current surveys are limited by angular resolution and measurement noise, while an idealized, cosmic-variance-limited survey could in principle probe this frequency range. We emphasize that such sensitivity requires observational capabilities far beyond those of existing or planned facilities, and our results should be interpreted as an ultimate limit on the information accessible through weak lensing measurements.

The NASA SPHEREx satellite was launched in 03/2025 to survey the full sky between 0.75 - 5.0 um. The image processing of SPHEREx H2RG detectors includes real-time flagging of transient events during integration. SPHEREx follows a polar orbit passing over the South Atlantic Anomaly (SAA) zone multiple times daily, where the transient counts reach as high as >80

We present a simulation-driven assessment of the performance of the SPHEREx pipeline for galaxy cluster science, focusing on photometry, source blending, survey depth, and photometric redshift accuracy. To do that, we compile a sample of eight galaxy clusters spanning a wide redshift range (z ≈ 0.02-1.1) and develop an end-to-end pipeline. We use the ancillary data from the DESI Legacy Survey and COSMOS survey, and generate realistic mock SPHEREx observations with the SPHEREx Sky Simulator. By performing forced photometry on these images with The Tractor, we quantify the characteristic biases and uncertainties relevant to cluster science. We find that the photometry is generally unbiased, but source blending is the primary driver of catastrophic outliers, particularly when the combined flux of neighbors is comparable to the flux of targets. Measuring the effective survey depth, we find that SPHEREx detects members down to K_s≈ 20 AB (5σ), 7-9 mag fainter than the brightest cluster galaxy (BCG) in nearby clusters but only 1-2 mag for clusters at z ∼ 1, where the BCG itself has faded close to this depth. Despite these challenges, we demonstrate that SPHEREx can achieve a photometric redshift precision of σ_NMAD≈ 0.003-0.01 for cluster galaxies with an appropriate sample selection based on brightness or signal-to-noise. Combining the redshifts of quality-selected members, we recover cluster redshifts with a bias of |Δz|/(1+z) < 0.002 and a scatter of σ≈ 0.002 at z ≲ 0.5, meeting the precision required for cluster cosmology.

Polycyclic aromatic hydrocarbons (PAHs) are responsible for a variety of near- and mid-infrared spectral features in Galactic and extragalactic sources. A feature at 1.05 mu m arising from electronic transitions in PAH cations is predicted by laboratory experiments but has never been observationally confirmed. We conduct a dedicated search for this feature in absorption on a highly extinguished sight line toward BD+40 4223, a blue supergiant in Cyg OB2, using the TripleSpec spectrograph at Palomar Observatory. We place a 5 sigma upper limit on the feature strength of Delta tau(1.05)/A(V) < 5.6 & times; 10(-3), ruling out theoretical estimates with >10 sigma significance. We constrain the effective temperature of BD+40 4223 to be log(10)(T-eff)=4.41 +/- 0.03 and infer that it is veiled by 6.39 +/- 0.05 mag of visual extinction, consistent with but more constraining than previous determinations. As dust on the sight line toward BD+40 4223 appears typical of the diffuse interstellar medium, this nondetection challenges existing models of PAH material properties and/or charge distribution

We present measurements of near-infrared (NIR) terrestrial airglow produced by helium and oxygen in the exosphere as observed by SPHEREx. Using eight months of survey data obtained from a 680 km low-Earth orbit, emission from HeI λ10830, OI λ8446, and OI λ11287 is mapped with both global spatial and multi-season temporal coverage. These measurements are obtained along upward looking lines of sight as part of the astrophysical survey, in contrast to conventional nadir-viewing Earth remote sensing, which probes the behavior of low-density material in the thermo- and exosphere. We describe an analytical framework to extract atmospheric emission lines in the presence of astrophysical backgrounds including stars, resolved galaxies, and the diffuse Zodiacal light. The resulting global measurements reveal temporal variability over the survey period and systematic dependencies on geographic location. We interpret these variations in the context of the variable Solar illumination and seasonal effects. SPHEREx, an astrophysical space observatory, is demonstrated to be a promising new platform for monitoring NIR airglow and investigating its coupling to Solar activity and global geophysical processes.

The SPHEREx all-sky survey has now measured the R∼40-100 infrared spectra of thousands of nearby brown dwarfs in the chemically rich 0.75-5 μm range. The survey's wide spectral coverage and high S/N permits flux measurements that capture several broadband molecular absorption features, and upwards of 80% of the total bolometric luminosity of most brown dwarfs. Atmospheric models are known to yield systematic disagreements in the inferred temperatures and radii of brown dwarfs, necessitating benchmarking against observations. In this work, we present SPHEREx spectra across a broad sequence of 37 nearby field brown dwarfs, ranging from L0 to Y4 (∼2500-250 K) and compare them to theoretical expectations. We additionally compile spectra for separate low-gravity and low-metallicity objects, and show how they trend with constant spectral type. We fit the measured spectra to the well-known forward model grids Sonora Diamondback, Elf Owl, BT-Settl, ATMO2020 and ATMO2020++ and compare their goodness-of-fit as a function of wavelength, spectral type, and treatment of clouds and chemistry. We find that the models continue to struggle to simultaneously fit the J/H/K peaks and the 4 μm opacity window, especially in L/T transition objects. The largest deviations appear around the chemistry-sensitive CO_2 and CO features. Despite these offsets, the models broadly capture their trends across the L/T transition, with the observed sample of field dwarfs strongly preferring the weak vertical mixing (k_zz = 10^4 cm^2s^-1) Elf Owl models over strong mixing. The spectra shown here along with future SPHEREx data will help guide improvements to models.

We present some of the first infrared spectral maps acquired by SPHEREx. These maps, which to our knowledge are the largest of their type ever compiled in the near-infrared, reveal multiple strong lines due to interstellar ices and polycyclic aromatic hydrocarbons (PAHs) throughout the Cygnus X and North American Nebula regions. The maps emphasize the strongest features arising from the 3 mu m H2O, 4.27 mu m CO2, and 4.67 mu m CO lines and the 3.28 mu m PAH feature, all of which are detected over large areas with complex and filamentary spatial distributions. The ice absorption maps of H2O and CO2 in particular broadly trace dense, cold, and well-shielded regions across Cygnus X, consistent with the established picture of efficient ice formation in dense molecular clouds. The interstellar ice features are also detected abundantly in diffuse absorption over wide areas. The relative strengths of the H2O and CO2 features vary among different lines of sight, indicating possible differences in local physical conditions or chemical variations. The 3.28 mu m PAH emission correlates with the emission from the 7.7 and 11.2 mu m features but shows small differences that may trace the grain-size distribution and variations in the ambient UV field. SPHEREx all-sky spectral imaging-only a small fraction of which is showcased in this work-will support numerous science investigations, including the structure of the Galaxy, the physics of the interstellar medium, and the chemistry of stars.

The three-dimensional galaxy power spectrum is a powerful probe of primordial non-Gaussianity (PNG) and additional general relativistic (GR) effects on large scales, which can be constrained by current and upcoming large-scale structure surveys. In this work, we forecast the measurability of local PNG and linear-order relativistic effects in the spherical Fourier-Bessel (SFB) power spectrum for DESI, Euclid, and SPHEREx surveys. A Chebyshev-decomposition scheme is employed to accelerate the multi-tracer SFB power-spectrum calculations. Fisher forecasts establish baseline constraints and test the sensitivity of f_ NL constraints to SFB mode cuts and to the marginalization over primordial cosmological parameters, while simulated Bayesian inference is used to quantify the impact and measurability of relativistic effects. We find that neglecting GR effects can bias f_ NL constraints at the 1-3σ level for Euclid and SPHEREx. The degeneracy between GR and PNG terms is strongly tracer dependent, with the degradation of σ(f_ NL) ranging from a few percent to nearly a factor of two when the GR amplitudes are varied. Lensing can be detected at high significance for several tracers, while multi-tracer analyses substantially improve the measurability of the Doppler term. Assuming GR, we show that relativistic clustering partially breaks the exact b_ϕf_ NL product degeneracy present in Newtonian linear power-spectrum analyses, although the resulting b_ϕ constraints remain weak for the survey configurations considered. The joint PNG-GR inference consistently propagates uncertainty in b_ϕ into the marginalized f_ NL constraint. This firmly establishes the path toward extracting cosmological information from ultra-large-scale galaxy clustering.