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1. Surface Brightness Profile of Lyman-α Halos out to 320 kpc in HETDEX

   https://doi.org/10.3847/1538-4357/ac5cb8  

   Lujan_Niemeyer, Maja; Komatsu, Eiichiro; Byrohl, Chris; Davis, Dustin; Fabricius, Maximilian; Gebhardt, Karl; Hill, Gary J; Wisotzki, Lutz; Bowman, William P; Ciardullo, Robin; et al (April 2022, The Astrophysical Journal)

   Abstract We present the median-stacked Lyman-α (Lyα) surface brightness profiles of 968 spectroscopically selected Lyαemitting galaxies (LAEs) at redshifts 1.9 <z< 3.5 in the early data of the Hobby-Eberly Telescope Dark Energy Experiment. The selected LAEs are high-confidence Lyαdetections with high signal-to-noise ratios observed with good seeing conditions (point-spread function FWHM <1.″4), excluding active galactic nuclei. The Lyαluminosities of the LAEs are 10^42.4–10⁴³erg s⁻¹. We detect faint emission in the median-stacked radial profiles at the level of $(3.6\pm 1.3)\times {10}^{-20}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}{\mathrm{arcsec}}^{-2}$ from the surrounding Lyαhalos out tor≃ 160 kpc (physical). The shape of the median-stacked radial profile is consistent atr< 80 kpc with that of much fainter LAEs at 3 <z< 4 observed with the Multi Unit Spectroscopic Explorer (MUSE), indicating that the median-stacked Lyαprofiles have similar shapes at redshifts 2 <z< 4 and across a factor of 10 in Lyαluminosity. While we agree with the results from the MUSE sample atr< 80 kpc, we extend the profile over a factor of two in radius. Atr> 80 kpc, our profile is flatter than the MUSE model. The measured profile agrees at most radii with that of galaxies in the Byrohl et al. cosmological radiative transfer simulation atz= 3. This suggests that the surface brightness of a Lyαhalo atr≲ 100 kpc is dominated by resonant scattering of Lyαphotons from star-forming regions in the central galaxy, whereas atr> 100 kpc, it is dominated by photons from galaxies in surrounding dark matter halos. 

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2. Resolved Measurements of the CO-to-H ₂ Conversion Factor in 37 Nearby Galaxies

   https://doi.org/10.3847/1538-4357/ad23ed  

   Chiang_江, I-Da 宜達; Sandstrom, Karin M; Chastenet, Jérémy; Bolatto, Alberto D; Koch, Eric W; Leroy, Adam K; Sun_孙, Jiayi 嘉懿; Teng, Yu-Hsuan; Williams, Thomas G (March 2024, The Astrophysical Journal)

   Abstract We measure the CO-to-H₂conversion factor (α_CO) in 37 galaxies at 2 kpc resolution, using the dust surface density inferred from far-infrared emission as a tracer of the gas surface density and assuming a constant dust-to-metal ratio. In total, we have ∼790 and ∼610 independent measurements ofα_COfor CO (2–1) and (1–0), respectively. The mean values forα_{CO (2–1)}andα_{CO (1–0)}are ${9.3}_{-5.4}^{+4.6}$ and ${4.2}_{-2.0}^{+1.9}{M}_{\odot }{\mathrm{pc}}^{-2}{\left(\mathrm{K}\mathrm{km}{\mathrm{s}}^{-1}\right)}^{-1}$ , respectively. The CO-intensity-weighted mean is 5.69 forα_{CO (2–1)}and 3.33 forα_{CO (1–0)}. We examine howα_COscales with several physical quantities, e.g., the star formation rate (SFR), stellar mass, and dust-mass-weighted average interstellar radiation field strength ( $\overline{U}$ ). Among them, $\overline{U}$ , Σ_SFR, and the integrated CO intensity (W_CO) have the strongest anticorrelation with spatially resolvedα_CO. We provide linear regression results toα_COfor all quantities tested. At galaxy-integrated scales, we observe significant correlations betweenα_COandW_CO, metallicity, $\overline{U}$ , and Σ_SFR. We also find thatα_COin each galaxy decreases with the stellar mass surface density (Σ_⋆) in high-surface-density regions (Σ_⋆≥ 100M_⊙pc⁻²), following the power-law relations ${\alpha }_{\mathrm{CO}(2–1)}\propto {\mathrm{\Sigma }}_{\star }^{-0.5}$ and ${\alpha }_{\mathrm{CO}(1–0)}\propto {\mathrm{\Sigma }}_{\star }^{-0.2}$ . The power-law index is insensitive to the assumed dust-to-metal ratio. We interpret the decrease inα_COwith increasing Σ_⋆as a result of higher velocity dispersion compared to isolated, self-gravitating clouds due to the additional gravitational force from stellar sources, which leads to the reduction inα_CO. The decrease inα_COat high Σ_⋆is important for accurately assessing molecular gas content and star formation efficiency in the centers of galaxies, which bridge “Milky Way–like” to “starburst-like” conversion factors. 

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3. H i Properties of Field Galaxies at z  ≈ 0.2–0.6: Insights into Declining Cosmic Star Formation

   https://doi.org/10.3847/2041-8213/ae0d8b  

   DePalma, David; Gupta, Neeraj; Chen, Hsiao-Wen; Simcoe, Robert A; Balashev, Sergei; Boettcher, Erin; Cantalupo, Sebastiano; Chen, Mandy C; Combes, Françoise; Faucher-Giguère, Claude-André; et al (October 2025, The Astrophysical Journal Letters)

   Abstract We report statistically significant detection of Hi21 cm emission from intermediate-redshift (z ≈ 0.2–0.6) galaxies. By leveraging multisightline galaxy survey data from the Cosmic Ultraviolet Baryon Survey and deep radio observations from the MeerKAT Absorption Line Survey, we have established a sample of ≈6000 spectroscopically identified galaxies in 11 distinct fields to constrain the neutral gas content at intermediate redshifts. The galaxies sample a broad range in stellar mass, from $\log M_{\mathrm{star}}/M_{\odot }\approx 8$ to $\log M_{\mathrm{star}}/M_{\odot }\approx 11$ , with a median of ${〈\log M_{\mathrm{star}}/M_{\odot }〉}_{\mathrm{med}}\approx 10$ and a wide range in redshift fromz ≈ 0.24 toz ≈ 0.63 with a median of 〈z〉_med = 0.44. While no individual galaxies show detectable Hiemission, the emission line signal is detected in the stacked spectra of all subsamples at greater than 4σsignificance. The observed total Hi21 cm line flux translates to a Himass,M_{H I}≈10¹⁰M_⊙. We find a high Hi-to-stellar-mass ratio ofM_HI/M_star ≈ 6 for low-mass galaxies with $〈\log M_{\mathrm{star}}/M_{\odot }〉\approx 9.3$ (>3.7σ). For galaxies with $〈\log M_{\mathrm{star}}/M_{\odot }〉\approx 10.6$ , we findM_HI/M_star ≈ 0.3 (>4.7σ). In addition, the redshift evolution of Himass, 〈M_{H I}〉, in both low- and high-mass field galaxies, inferred from the stacked emission-line signal, aligns well with the expectation from the cosmic star formation history. This suggests that the overall decline in the cosmic star formation activity across the general galaxy population may be connected to a decreasing supply of neutral hydrogen. Finally, our analysis has revealed significant 21 cm signals at distances greater than 75 kpc from these intermediate-redshift galaxies, indicating a substantial reservoir of Higas in their extended surroundings. 

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4. A Uniform Analysis of Gas-phase Metallicity Evolution with 1–3 Gyr Time Sampling over the Past 12 Gyr

   https://doi.org/10.3847/1538-4357/ae4590  

   Jain, Shweta; Sanders, Ryan L; Khostovan, Ali Ahmad; Jones, Tucker; Shapley, Alice E; Reddy, Naveen A; Garcia, Alex M; Torrey, Paul; Coil, Alison (March 2026, The Astrophysical Journal)

   Abstract We present a systematic investigation of the evolution of the mass–metallicity relation (MZR) and fundamental metallicity relation (FMR) using uniform metallicity diagnostics across redshiftsz∼ 0 toz∼ 3.3. We present new Keck/Deep Imaging Multi-Object Spectrograph measurements of the [OII]λλ3726, 3729 emission line doublet for star-forming galaxies atz∼ 1.5 with existing measurements of redder rest-optical lines from the MOSFIRE Deep Evolution Field survey. These new observations enable uniform estimation of the gas-phase oxygen abundance using ratios of the [OII], Hβ, and [OIII] lines for mass-binned samples of star-forming galaxies in six redshift bins, employing strong line calibrations that account for the distinct interstellar medium ionization conditions atz< 1 andz> 1. We find that the low-mass power-law slope of the MZR remains constant over this redshift range with a value ofγ= 0.28 ± 0.01, implying the outflow metal loading factor ( ${\zeta }_{\text{out}}=\frac{Z_{\text{out}}}{Z_{\text{ISM}}}\frac{{\dot{M}}_{\text{out}}}{\text{SFR}}$ ) scales approximately as ${\zeta }_{\mathrm{out}}\propto M_{*}^{-0.3}$ out to at leastz∼ 3.3. The normalization of the MZR at 10¹⁰M_⊙decreases with increasing redshift at a rate of $d\log \left(\text{O/H}\right)/dz=-0.11\pm 0.01$ across the full redshift range. We find that any evolution of the FMR is smaller than 0.1 dex out toz∼ 3.3. We compare to cosmological galaxy formation simulations, and find that IllustrisTNG matches our measured combination of a nearly-invariant MZR slope, rate of MZR normalization decrease, and constant or very weakly evolving FMR. This work provides the most detailed view of MZR and FMR evolution from the present day through Cosmic Noon with a fine time sampling of 1−3 Gyr, setting a robust baseline for metallicity evolution studies atz> 4 with JWST. 

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5. Ly α Intensity Mapping in HETDEX: Galaxy-Ly α Intensity Cross-power Spectrum

   https://doi.org/10.3847/1538-4357/ae3a98  

   Lujan_Niemeyer, Maja; Komatsu, Eiichiro; Bernal, José Luis; Byrohl, Chris; Ciardullo, Robin; Curtis, Olivia; Farrow, Daniel J; Finkelstein, Steven L; Gebhardt, Karl; Gronwall, Caryl; et al (March 2026, The Astrophysical Journal)

   Abstract We present a measurement of the Lyαintensity mapping power spectrum from the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). We measure the cross-power spectrum of the Lyαintensity and Lyα-emitting galaxies (LAEs) in a redshift range of 1.9 ≤z≤ 3.5. We calculate the intensity from HETDEX spectra that do not contain any detected LAEs above a signal-to-noise ratio of 5.5. To produce a power spectrum model and its covariance matrix, we simulate the data using lognormal mocks for the LAE catalog and Lyαintensity in redshift space. The simulations include the HETDEX sensitivity, selection function, and mask. The measurements yield the product of the LAE bias, the intensity bias, the mean intensity of undetected sources, and the ratio of the actual and fiducial redshift-space distortion parameters, $b_{\mathrm{g}}{b}_I〈I〉{\overline{F}}_{\mathrm{RSD}}/{\overline{F}}_{\mathrm{RSD}}^{\mathrm{fid}}=$ (6.7 ± 3.1), (11.7 ± 1.4), and (8.3 ± 1.5) × 10⁻²²erg s⁻¹cm⁻²arcsec⁻²Å⁻¹in three redshift bins centered at $\overline{z}=2.1$ , 2.6, and 3.2, respectively. The results are reasonably consistent with cosmological hydrodynamical simulations that include Lyαradiative transfer. They are, however, significantly smaller than previous results from cross-correlations of quasars with Lyαintensity. These results demonstrate the statistical power of HETDEX for Lyαintensity mapping and pave the way for a more comprehensive analysis. They will also be useful for constraining models of Lyαemission from galaxies used in modern cosmological simulations of galaxy formation and evolution. 

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