arXiv subjects

Yi-Kuan Chiang

Publications and source records attributed to Yi-Kuan Chiang.

At least 19 recordsLinked to original sources

arXiv2026

The SPHEREx Instrument: Calibration, testing and performance measurements of the NIR spectroscopic surveyor from the laboratory to in-orbit commissioning

The SPHEREx near-infrared space telescope is an all-sky spectroscopic survey mission launched on March 12th, 2025 UTC. In addition to providing the community with a spectral database applicable to a wide range of investigations, it is optimized to address three core science goals: to survey the large scale structure of the Universe for signatures of non-Gaussianity during inflation; to conduct intensity mapping studies of the extragalactic background light for probing the history of galaxy evolution; and to survey the plane of the Milky Way for the prevalence and distribution of water and other biogenic ices. Each of these science goals imposes unique requirements on the performance of the instrument. We detail the design and testing strategies and report the performance results for the full instrument test campaign, ranging from component-level screening to in-orbit tests during the commissioning phase. The instrument, currently operating in full science survey mode, meets all of its driving requirements including optical performance, point source sensitivity, thermal stability and correlated noise minimization.

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arXiv2026

Spectral Map Making with SPHEREx

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).

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arXiv2026

Tomographer: End-to-end Redshift Distribution Estimation for Source Catalogs and Intensity Maps

Redshift information is central to nearly every extragalactic and cosmological application of sky surveys, yet only a small fraction of cataloged sources, and none of the photons forming diffuse backgrounds, have spectroscopic redshifts. Clustering-based redshift inference estimates the redshift distribution of an arbitrary dataset through spatial cross-correlation with a reference sample of known redshifts. It relies only on positional information, making it applicable to any tracer of large-scale structure, including source populations and diffuse intensity maps. Its broader adoption, however, has been limited by technical barriers: assembling and characterizing spectroscopic references, expensive pair-counting computations, theoretical corrections, and systematic control. To remove these barriers, we introduce Tomographer, an end-to-end clustering-redshift framework. The key design feature is a set of precomputed "activation maps" encoding the spatial pair information of 3 million SDSS spectroscopic galaxies and quasars up to $z\sim4$ over $10{,}000\,{\rm deg}^2$. This eliminates user-end pair counting, reducing computational scaling from $O(N\log N)$ to $O(1)$ map multiplications. Given a source catalog or intensity map, Tomographer returns the bias-weighted redshift distribution, $b(z)\,{\rm d}N/{\rm d}z(z)$ or $b(z)\,{\rm d}I/{\rm d}z(z)$. We validate the framework against samples with known redshifts, demonstrate accurate uncertainty estimates, and show robustness to survey footprint, spatially varying selection functions, beam smoothing, and foreground contamination. We showcase applications to source catalogs selected by flux, color, photometric redshift, morphology, or variability, and to intensity maps from radio to X-rays. Future Tomographer releases will incorporate additional wide-field spectroscopic reference samples as they become available.

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arXiv2026

CIBER $\times$ galaxy cross-correlations reveal a bright, low-redshift NIR background

We perform the first tomographic analysis of near-IR extragalactic background light (EBL) anisotropies, cross-correlating CIBER 1.1 and 1.8 $μ$m imager data with photometric galaxy catalogs from DESI Legacy Survey DR8 and Hyper-Suprime-Cam Ultra-Deep Survey. We measure significantly higher cross-power than expectations from an integrated galaxy light (IGL) model on scales $\ell < 2000$, concentrated at low redshift ($z\lesssim 0.6$). Cluster member galaxies and associated structure account for 15-20\% of the large-angle cross-power, indicating that group- and galaxy-scale halos contribute the bulk of the signal. Through a parametric halo model decomposition, we detect two-halo and one-halo clustering in cross-power at high significance, with amplitudes that decline smoothly across $z=0{-}1$. The inferred one-halo cross-power is of similar amplitude between DESI-LS and the deeper HSC catalog, implying a scenario in which low-redshift EBL fluctuations are amplified by contributions from lower-mass halos with satellites and/or diffuse intra-halo light (IHL). Converting our two-halo fits into estimates of $b_I \times dI/dz$, we find that standard IGL predictions underestimate our measurements, even when assuming an intensity bias as high as 3, similar to that of large SZ clusters, suggesting that a higher $dI/dz$ is required to reconcile observed discrepancies. Lastly, we find that correlated large-scale structure (LSS) at $z<1$ accounts for a substantial fraction of the CIBER auto-power reported in earlier work. These results identify low-redshift LSS as a significant and previously unappreciated contributor to near-IR EBL fluctuation measurements, setting the stage for cross-correlation science with CIBER-2, SPHEREx and a variety of LSS tracers.

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arXiv2026

Dynamical Test of Cosmic Acceleration: $k$-nearest Neighbor Cross Correlation of Cosmic Microwave Background and Cosmic Infrared Background

The physical origin of cosmic acceleration remains one of the central questions in modern cosmology. The integrated Sachs-Wolfe (ISW) and Rees-Sciama (RS) effects, which arise from the evolution of gravitational potentials, provide a dynamical test of cosmic acceleration. We measure the cross correlation between the Planck temperature map of the cosmic microwave background (CMB) and a foreground-free map of the $100\,μ\mathrm{m}$ cosmic infrared background (CIB) from Y.-K. Chiang (2023), using the $k$-nearest neighbor cumulative distribution function ($k$NN-CDF). As the CIB map is reconstructed from ${\sim}600$ million Wide-field Infrared Survey Explorer galaxies extending to $z\approx2.5$, the measurement is equivalent to a galaxy-CMB cross correlation. We find evidence for a positive cross correlation, rejecting the null hypothesis of no correlation at $p=0.02~(2.3σ)$ using the $χ^2$ test. We further quantify its amplitude with $A_{k\mathrm{NN}}$, defined relative to an assumed cosmological model, and obtain $A_{k\mathrm{NN}}=0.95\pm0.20~(4.8σ)$ with respect to $Λ\mathrm{CDM}$ mock data including the ISW and RS effects. The $k$NN-CDF analysis improves the detection significance by ${\sim}20\%$ over the two-point correlation function. We also explore evolving dark energy by constructing two tomographic maps from the full CIB map; the results are consistent with $Λ$CDM. Finer tomographic reconstruction of the CIB, for example from multiband data of SPHEREx, would further tighten constraints on evolving dark energy.

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arXiv2026

A UV-to-Near-infrared QSO Composite Spectrum from the SPHEREx All-Sky Survey

We present a composite spectrum of $\sim 61,000$ type 1 SDSS QSOs (median $z \approx 1.26$), constructed using SPHEREx spectrophotometric data and covering a rest-frame wavelength range of $0.14-4.5~μ$m. The SPHEREx mission surveys the entire sky in 102 near-infrared spectral channels spanning $0.75-5.0~μ$m with a spectral resolution of $R \approx 35-130$, 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, $f_ν\propto ν^{α_ν}$, 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 H$α$, Pa$β$, and Pa$α$, 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.

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arXiv2026

SPHEREx mapping of diffuse PAH and H II emission in the Galactic plane

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 microns. We produce a large-scale map of the 3.3-micron 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 microns. 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 preview the capability of the mission to map diffuse emission in the interstellar medium.

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arXiv2026

Backlighting the Cosmic Web with Fast Radio Bursts: An Anthology of Dispersion Measure Cross-Correlations with Large-Scale Structure and Baryon Tracers

Fast Radio Bursts (FRBs) probe baryons permeating the cosmic web through their dispersion measures (DMs), which encode the integrated electron density along cosmological sightlines. Using 3,455 unique FRB sources from CHIME/FRB with $\sim 15$ arcmin localizations, we present an anthology of DM correlations with tracers of large-scale structure and baryonic matter at redshifts $z \lesssim 1.5$. We measure statistically significant correlations at $2.6-5σ$ with ten probes, including galaxies ($2.8σ$), weak gravitational lensing ($2.6σ$), cosmic infrared background ($4.0σ$), cosmic microwave background (CMB) lensing ($3.3σ$), thermal Sunyaev Zel'dovich (tSZ) effect ($3.8σ$), X-ray emission tracing galaxy clusters ($5.0σ$) and superclusters ($3.3σ$), soft X-ray background (SXRB, $4.1σ$), and radio continuum emission ($3.2σ$). These measurements reveal a consistent picture in which FRB sightlines intersecting overdense environments carry systematically larger DMs. Correlations with hot-gas tracers provide additional leverage on the strength of feedback, as they are strongly weighted towards the dense, bound gas. The measured amplitude of tSZ$\times$DM and SXRB$\times$DM correlations are consistent with theoretical predictions of baryon distribution from a DM-$z$ relation-inferred model with moderate feedback at $\sim 0.5σ$ level. Weaker feedback scenario is ruled out at $\sim 3.5σ$ by the SXRB$\times$DM correlation. Taken together, these measurements constitute a quantitative multi-tracer foundation for a new era in which FRBs from next generation facilities, such as BURSTT, CHORD, DSA, and SKA, in harmony with other probes, will map the baryon content of the full extent of the cosmic web.

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arXiv2026

Spectral response of SPHEREx

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 to 5.0um with resolving power R~35 to 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 1nm for Bands 1 through 4 (0.75 to 3.82um) and better than 10nm for Bands 5 and 6 (3.82 to 5.0um). Out-of-band leakage is negligible for detectors above 1.64um 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.

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arXiv2026

SPHEREx Wide-Field Infrared Spectral Mapping of Interstellar Ices and Polycyclic Aromatic Hydrocarbons

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 $μ$m H$_2$O, 4.27 $μ$m CO$_2$, and 4.67 $μ$m CO lines and the 3.28 $μ$m PAH feature, all of which are detected over large areas with complex and filamentary spatial distributions. The ice absorption maps of H$_2$O and CO$_2$ 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 strength of the H$_2$O and CO$_2$ features varies among different lines of sight, indicating possible differences in local physical conditions or chemical variations. The 3.28 $μ$m PAH emission correlates with the emission from the 7.7 and 11.2 $μ$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, of which only a small fraction 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.

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arXiv2026

A Path to an All-Sky Survey with Roman

A deep, space-based, all-sky near-infrared survey carried out with the Nancy Grace Roman Space Telescope would constitute a foundational astronomical infrastructure for decades to come. In this white paper, we present a concrete and feasible path to imaging the entire sky at $\sim0.1''$ resolution, beginning with high-impact fields in Cycle 1 and scaling to ultra-wide coverage within the nominal mission. This first-epoch survey will reach $\mathrm{H}\sim25.5$ AB mag (5$σ$) and maximize synergies with contemporaneous observatories, while preserving substantial time for other ambitious Roman programs. We outline representative scheduling scenarios and an example Cycle 1 program that triples early Roman-LSST overlap and delivers high-value community data products such as LSST forced photometry, joint \textit{Gaia}-Roman astrometry, and catalogs of Galactic substructure, stong lenses, and other rare systems. The Cycle 1 program will lay the foundation for an eventual all-sky survey, while also delivering high-impact early science. We invite broad community participation in shaping and carrying out both the initial program and the long-term vision of an all-sky Roman survey.

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arXiv2026

Cosmic CO and [CII] backgrounds and the fueling of star formation over 12 Gyr

Molecular gas, modest in mass yet pivotal within the cosmic inventory, regulates baryon cycling as the immediate fuel for star formation. Across most of cosmic history, its reservoir has remained elusive, with only the tip of the iceberg revealed by luminous carbon monoxide (CO) emitting galaxies. Here we report the first detections of the mean cosmic CO background across its rotational ladder at 7$σ$, together with ionized carbon ([CII]) at 3$σ$, over $0<z<4.2$. This uses tomographic clustering of diffuse broadband intensities with reference galaxies, directly probing aggregate emission in the cosmic web. From CO(1-0) we infer the total molecular gas density, $Ω_{\rm H_2}$, finding it about twice that resolved in galaxy surveys. The global depletion time is $\sim$1 Gyr, shorter than the Hubble time, requiring sustained inflow. CO excitation links to star-formation surface density and, with depletion time, yields a super-linear Kennicutt-Schmidt law that appears universal. Together these results establish a global picture of galaxy growth fueled by a larger, short-lived molecular reservoir. The CO and [CII] detections mark a turning point for line-intensity mapping, replacing forecasts with empirical line strengths and defining sensitivity requirements for upcoming 3D experiments poised to open new windows on galaxy formation and cosmology.

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arXiv2025

The SPHEREx Satellite Mission

SPHEREx, a NASA explorer satellite launched on 11 March 2025, is carrying out the first all-sky near-infrared spectral survey. The satellite observes in 102 spectral bands from 0.75 to 5.0 um with a resolving power ranging from 35 to 130 in 6.2 arcsecond pixels. The observatory obtains a 5-sigma depth of 19.5 - 19.9 AB mag for 0.75 to 3.8 um and 17.8 - 18.8 AB mag for 3.8 to 5.0 um after mapping the full sky four times over two years. Scientifically, SPHEREx will produce a large galaxy redshift survey over the full sky, intended to constrain the amplitude of inflationary non-Gaussianity. The observations will produce two deep spectral maps near the ecliptic poles that will 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 initial data are rapidly released in the form of spectral images to the public. The project will release specialized data products over the life of the mission as the surveys proceed. The science team will also produce specialized spectral catalogs on planet-bearing and low-mass stars, solar system objects, and galaxy clusters 3 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 in-flight performance and key characteristics.

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arXiv2025

The Potential of the SPHEREx Mission for Characterizing Polycyclic Aromatic Hydrocarbon 3.3 μm Emission in Nearby Galaxies

Together with gas, stars, and supermassive black holes, dust is crucial in stellar and galaxy evolution. Hence, understanding galaxies' dust properties across cosmic time is critical to studying their evolution. In addition to photometric constraints on the absorption of blue light and its reemission at infrared wavelengths, dust grain properties can be explored spectroscopically via polycyclic aromatic hydrocarbon (PAH) emission bands in the mid-IR. The new SPHEREx space telescope conducts an all-sky spectrophotometric survey of stars and galaxies at wavelengths of 0.75-5$\,μ$m, making it ideal for studying the widespread presence of the 3.3$\,μ$m PAH emission across galaxy populations out to z ~ 0.4. In this paper, we simulated galaxy spectra to investigate SPHEREx's capability to study PAH emission in such galaxies. We find that for the all-sky survey the PAH 3.3$\,μ$m emission band flux can be measured to 30% accuracy at $\log(\rm M/{\rm M_\odot})>9.5$ and star formation rate (SFR) $> 1\,{\rm M_\odot\,yr^{-1}}$ at $z=0.1$, $\log(\rm M/{\rm M_\odot}) > 10.5$ and ${\rm SFR} > 10\,{\rm M_\odot\,yr^{-1}}$ at $z=0.2-0.3$, and $\log(\rm M/{\rm M_\odot})>11$ and ${\rm SFR} > 100\,{\rm M_\odot\,yr^{-1}}$ at $z=0.4$. For deep SPHEREx fields, a factor of ~10 deeper sensitivity limits can be reached. Overall, SPHEREx will enable the measurement of the 3.3$\,μ$m PAH band emission in several hundred thousand galaxies across the sky, providing a population study of the smallest dust grains ("nano grains") and radiation properties in massive galaxies in the nearby Universe.

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arXiv2025

Thermal Sunyaev-Zel'dovich Effect in the circumgalactic medium -- II: dependence on star formation

We measure thermal Sunyaev-Zel'dovich (tSZ) Effect in the circumgalactic medium (CGM) of $\approx$2.5 million $\rm M_{200}$=$\rm 10^{12-14}\,M_\odot$ WISE$\times$DESI galaxies out to $z$=1.2. We split the sample into quiescent (0.7 million) and star-forming (1.8 million) galaxies, exploring the relation between the thermal pressure of the CGM and star formation for the first time. We develop and implement a novel probabilistic approach to cross-correlate the galaxy catalog with the Atacama Cosmology Telescope+Planck data by taking into account the uncertainties in redshift, mass, and star formation rate. The S/N of the stacked Compton-$y$ value in the CGM varies from 4.9 to 18.5, depending on the sample size and the CGM signal strength within the relevant mass bin. We detect the CGM signal down to $\rm M_{200}=10^{12.3}\,M_\odot$, and provide stringent upper limit at $\rm M_{200}<10^{12.3}\,M_\odot$. The data fit well with the standard GNFW profile of thermal pressure and do not require a flatter or steeper profile. This suggests a significant impact of cooling and the absence of dominant feedback. In galaxies with $\rm M_{200}\approx10^{12.3-12.8}\,M_\odot$ halos, the volume filling CGM is likely the largest contributor to the $galactic$ baryons at their virial temperatures of $\sim$10$^{6-6.4}\rm\,K$. For $\rm M_{200}>10^{12.8}\,M_\odot$ halos, the most massive phase of the CGM is likely at a sub-virial temperature of $\rm\gtrsim 10^6\,K$. The thermal energy of the CGM of quiescent galaxies follows the self-similar relation with mass, but the star-forming galaxies deviate from this relation. This indicates that the impact of non-gravitational factors varies among halos of different degrees of star-forming activity.

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arXiv2025

Cosmic Infrared Background Tomography and a Census of Cosmic Dust and Star Formation

The cosmic far-infrared background (CIB) encodes dust emission from all galaxies and carries valuable information on structure formation, star formation, and chemical enrichment across cosmic time. However, its redshift-dependent spectrum remains poorly constrained due to line-of-sight projection effects. We address this by cross-correlating 11 far-infrared intensity maps spanning a 50-fold frequency range from Planck, Herschel, and IRAS, with spectroscopic galaxies and quasars from SDSS I-IV tomographically. We mitigate foregrounds using CSFD, a CIB-free Milky Way dust map. These cross-correlation amplitudes on two-halo scales trace bias-weighted CIB redshift distributions and collectively yield a $60σ$ detection of the evolving CIB spectrum, sampled across hundreds of rest-frame frequencies over $0 < z < 4$. We break the bias-intensity degeneracy by adding monopole information from FIRAS+Planck. The recovered spectrum reveals a dust temperature distribution that is broad, spanning the full range of host environments, and moderately evolving. Using low-frequency CIB amplitudes, we constrain cosmic dust density, $Ω_{\rm dust}$, which peaks at $z = 1$-$1.5$ and declines threefold to the present. Our broad spectral coverage enables a determination of the total infrared luminosity density to 0.04 dex statistical precision, tracing star-formation history with negligible cosmic variance across 90% of cosmic time. We find that cosmic star formation is 80% dust-obscured at $z = 0$ and 60% at $z = 4$. Our results, based on intensity mapping, are complete, requiring no extrapolation to faint galaxies or low-surface-brightness components. We release our tomographic CIB spectrum and redshift distributions as a public resource for future studies of the CIB, both as a cosmological matter tracer and CMB foreground.

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arXiv2025

Cosmic Ly$α$ Emission from Diffuse Gas

The Ly$α$ emission has emerged as a powerful tool for probing diffuse gas within the large-scale structure of the universe. In this paper, we investigate cosmic Ly$α$ emission by post-processing cosmological simulations from \texttt{IllustrisTNG} and \texttt{THESAN} project. Specifically, we calculate the Ly$α$ emission from galaxies, circum-galactic medium (CGM) and inter-galactic medium (IGM) across various redshifts. Our results show that IGM alone is significantly under the current observational upper limits. Meanwhile, CGM overshoots the observed galaxy contribution at $z \lesssim 0.5$ indicating that either the escape fraction for the inner CGM is less than unity or the current photoionization equilibrium treatment with an approximate self-shielding prescription is less accurate. The galaxy component also overshoots at low redshift, indicating that the escape fraction has strong evolution caused by an evolving halo mass function and dust growth distribution, that agrees with observationally inferred escape fractions. Furthermore, our findings suggest that the Ly$α$ emission from diffuse gas (CGM+IGM) peaked at $z \sim 4$ and diminishes toward lower redshift. The Ly$α$ emission from diffuse gas mainly originates through the collisional excitation of hot plasma. By comparing models with observation, our predicted Ly$α$ emission from diffuse gas remains $\sim 6$ times fainter than the observed cosmic Ly$α$ emission at $z=1-3$. However, future large telescopes may hold great promise to detect Ly$α$ emission from diffuse gas toward $z>3$.

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arXiv2024

SPHEREx: NASA's Near-Infrared Spectrophotmetric All-Sky Survey

SPHEREx, the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and ices Explorer, is a NASA MIDEX mission planned for launch in 2024. SPHEREx will carry out the first all-sky spectral survey at wavelengths between 0.75 micron and 5 micron with spectral resolving power ~40 between 0.75 and 3.8 micron and ~120 between 3.8 and 5 micron At the end of its two-year mission, SPHEREx will provide 0.75-to-5 micron spectra of each 6.2"x6.2" pixel on the sky - 14 billion spectra in all. This paper updates an earlier description of SPHEREx presenting changes made during the mission's Preliminary Design Phase, including a discussion of instrument integration and test and a summary of the data processing, analysis, and distribution plans.

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