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1. The Galaxy–Halo Connection of DESI Luminous Red Galaxies with Subhalo Abundance Matching

   https://doi.org/10.3847/1538-4357/ace76e  

   Berti, Angela M; Dawson, Kyle S; Dominguez, Wilber (August 2023, The Astrophysical Journal)

   Abstract We use subhalo abundance and age distribution matching to create magnitude-limited mock galaxy catalogs atz∼ 0.43, 0.52, and 0.63 withz-band and 3.4μmW1-band absolute magnitudes andr−zandr−W1 colors. From these magnitude-limited mocks, we select mock luminous red galaxy (LRG) samples according to the (r−z)-based (optical) and (r−W1)-based (infrared) selection criteria for the LRG sample of the Dark Energy Spectroscopic Instrument (DESI) survey. Our models reproduce the number densities, luminosity functions, color distributions, and projected clustering of the DESI Legacy Surveys that are the basis for DESI LRG target selection. We predict the halo occupation statistics of both optical and IR DESI LRGs at fixed cosmology and assess the differences between the two LRG samples. We find that IR-based SHAM modeling represents the differences between the optical and IR LRG populations better than using thezband and that age distribution matching overpredicts the clustering of LRGs, implying that galaxy color is uncorrelated with halo age in the LRG regime. Both the optical and IR DESI LRG target selections exclude some of the most luminous galaxies that would appear to be LRGs based on their position on the red sequence in optical color–magnitude space. Both selections also yield populations with a nontrivial LRG–halo connection that does not reach unity for the most massive halos. We find that the IR selection achieves greater completeness (≳90%) than the optical selection across all redshift bins studied. 

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2. Bayesian Component Separation for DESI LAE Automated Spectroscopic Redshifts and Photometric Targeting

   https://doi.org/10.3847/1538-4357/ae3f9a  

   Uzsoy, Ana_Sofía M; Saydjari, Andrew K; Dey, Arjun; Raichoor, Anand; Finkbeiner, Douglas P; Gawiser, Eric; Lee, Kyoung-Soo; Ahlen, Steven; Bianchi, Davide; Brooks, David; et al (March 2026, The Astrophysical Journal)

   Abstract Lyα emitters (LAEs) are valuable high-redshift cosmological probes traditionally identified using specialized narrowband photometric surveys. In ground-based spectroscopy, it can be difficult to distinguish the sharp LAE peak from residual sky emission lines using automated methods, leading to misclassified redshifts. We present a Bayesian spectral component separation technique to automatically determine spectroscopic redshifts for LAEs while marginalizing over sky residuals. We use visually inspected spectra of LAEs obtained using the Dark Energy Spectroscopic Instrument (DESI) to create a data-driven prior and can determine redshift by jointly inferring sky residual, LAE, and residual components for each individual spectrum. We demonstrate this method on 881 spectroscopically observedz = 2–4 DESI LAE candidate spectra and determine their redshifts with >90% accuracy when validated against visually inspected redshifts. Using the Δχ²value from our pipeline as a proxy for detection confidence, we then explore potential survey design choices and implications for targeting LAEs with medium-band photometry. This method allows for scalability and accuracy in determining redshifts from DESI spectra, and the results provide recommendations for LAE targeting in anticipation of future high-redshift spectroscopic surveys. 

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3. Golden and Silver Dark Sirens for Precise H ₀ Measurement with HETDEX

   https://doi.org/10.3847/1538-4357/ae6329  

   Dang, Yixuan; Gupta, Ish; Ciardullo, Robin; Mentuch_Cooper, Erin; Pandey, Shiksha; Davis, Dustin; More, Surhud; Gray, Rachel; Chen, Hsin-Yu; Farrow, Daniel J; et al (May 2026, The Astrophysical Journal)

   Abstract Gravitational waves (GWs) from compact binary coalescences arestandard sirensthat provide a direct measure of the source’s luminosity distance, enabling an independent measurement of the Hubble constant (H₀). While abright siren—a GW event with an identified electromagnetic (EM) counterpart—provided the first such constraint, most detections, currently dominated by black hole mergers, lack EM signatures. A measurement ofH₀is still possible with thesedark sirensby statistically associating GW events with galaxies in existing catalogs based on the sky localization. In this work, we explore the potential of two subsets of dark sirens categorized by their localization precision: ’golden’ dark sirens, defined by a sky area localization ≤0.1deg², and ’silver’ dark sirens, which are more common but less precisely localized (≤1deg²). Using thefifth internal data releaseof the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX), we assess the suitability of the Visible Integral-field Replicable Unit Spectrograph (VIRUS) for spectroscopic follow-up of dark sirens. VIRUS exposures of the standard HETDEX depth provide precise redshifts and exquisite completeness withinz= 0.2. After a single year of observations with the upgraded LIGO-A^#network, the combined sample of golden and silver dark sirens withz≤ 0.2 atH₀ = 70 km s⁻¹Mpc⁻¹and follow-up VIRUS observations can potentially yield a few-percent constraint onH₀. Our predictions suggest that spectroscopic redshift surveys such as HETDEX can play a key role in realizing high-precision cosmology with dark sirens in the near future. 

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4. DESI Emission-line Galaxies: Clustering Dependence on Stellar Mass and [O II ] Luminosity

   https://doi.org/10.3847/1538-4357/ae0036  

   Hagen, T; Dawson, K S; Zheng, Z; Aguilar, J; Ahlen, S; BenZvi, S; Bianchi, D; Brooks, D; Castander, F J; Claybaugh, T; et al (October 2025, The Astrophysical Journal)

   Abstract We measure the projected two-point correlation functions of emission-line galaxies (ELGs) from the Dark Energy Spectroscopic Instrument One-Percent Survey and model their dependence on stellar mass and [OII] luminosity. We select ∼180,000 ELGs with redshifts of 0.8 < z < 1.6, and define 27 samples according to cuts in redshift and both galaxy properties. Following a framework that describes the conditional [OII] luminosity–stellar mass distribution as a function of halo mass, we simultaneously model the clustering measurements of all samples at fixed redshift. Based on the modeling result, most ELGs in our samples are classified as central galaxies, residing in halos of a narrow mass range with a typical median of ∼10^12.2−12.4h⁻¹M_⊙. We observe a weak dependence of clustering amplitude on stellar mass, which is reflected in the model constraints and is likely a consequence of the 0.5 dex measurement uncertainty in the stellar mass estimates. The model shows a trend between galaxy bias and [OII] luminosity at high redshift (1.2 < z < 1.6) that is otherwise absent at lower redshifts. 

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5. ODIN: Confirmation and 3D Reconstruction of Six Massive Protoclusters at Cosmic Noon

   https://doi.org/10.3847/1538-4357/ae899d  

   Ortiz, Ashley; Ramakrishnan, Vandana; Lee, Kyoung-Soo; Dey, Arjun; Guo, Yucheng; Pinarski, Ethan; Raichoor, Anand; Valdes, Francisco; Aguilar, J; Ahlen, S; et al (August 2026, The Astrophysical Journal)

   Protoclusters represent sites of accelerated galaxy formation and extreme astrophysical activity characteristic of dense environments. Identifying massive protoclusters and mapping their spatial structures are therefore crucial for understanding how large-scale environment influences galaxy evolution. We combine wide-field Lyαimaging from the One-hundred-deg²DECam Imaging in Narrowbands survey with extensive Dark Energy Spectroscopic Instrument and ancillary spectroscopy across the extended COSMOS and XMM Large Scale Structure (LSS) fields (≈14 deg²) to search for massive protoclusters. We confirm six systems atz ≈ 2.4 and ≈ 3.1, including three newly identified structures and three which overlap with previously known structures and/or systems detected using other tracers. We reconstruct their three-dimensional structures, estimate descendant halo masses, and for one structure atz ≈ 3.12, demonstrate that overlapping narrowband filters (NB497 and N501) provide accurate redshift tomography for emission-line galaxies. One protocluster atz ≈ 2.45 overlaps with one of the LATIS tomographic fields, enabling direct comparison between galaxy and H ioverdensities traced by Lyαforest absorption. Another atz ≈ 3.12 hosts a massive quiescent galaxy (M_* ≈ 1.2 × 10¹¹M_⊙), suggesting that overdense environments may play a role in accelerating galaxy assembly and quenching. Comparing Lyαemission properties across environments, we find that protocluster galaxies exhibit higher median line fluxes and a deficit of faint emitters relative to the field. The effect is strongest when combining 2D and 3D density information, indicating that galaxies in the densest protocluster cores are most affected by environmental processes. This effect is stronger atz ≈ 3.1 than atz ≈ 2.4, suggesting possible redshift evolution. 

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