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1. A SPectroscopic Survey of Biased Halos in the Reionization Era (ASPIRE): Spectroscopically Complete Census of Obscured Cosmic Star Formation Rate Density at z  = 4–6

   https://doi.org/10.3847/1538-4357/ad9d0e  

   Sun, Fengwu; Wang, Feige; Yang, Jinyi; Champagne, Jaclyn B; Decarli, Roberto; Fan, Xiaohui; Bañados, Eduardo; Cai, Zheng; Colina, Luis; Egami, Eiichi; et al (January 2025, The Astrophysical Journal)

   Abstract We present a stringent measurement of the dust-obscured star formation rate density (SFRD) atz= 4–6 from the ASPIRE JWST Cycle-1 medium and ALMA Cycle-9 large program. We obtained JWST/NIRCam grism spectroscopy and ALMA 1.2 mm continuum map along 25 independent quasar sightlines, covering a total survey area of  ∼35 arcmin²where we search for dusty star-forming galaxies (DSFGs) atz= 0–7. We identify eight DSFGs in seven fields atz= 4–6 through the detection of Hαor [O iii]λ5008 lines, including fainter lines such as Hβ, [O iii]λ4960, [N ii]λ6585, and [S ii]λλ6718,6733 for six sources. With this spectroscopically complete DSFG sample atz= 4–6 and negligible impact from cosmic variance (shot noise), we measure the infrared luminosity function (IRLF) down toL_IR ∼ 2 × 10¹¹L_⊙. We find flattening of IRLF atz= 4–6 towards the faint end (power-law slope $\alpha =0.59_{-0.45}^{+0.39}$). We determine the dust-obscured cosmic SFRD at this epoch to be $\log [{\rho }_{\mathrm{SFR},\mathrm{IR}}/(M_{\odot }{\mathrm{yr}}^{-1}{\mathrm{Mpc}}^{-3}\left)\right]=-1.52_{-0.13}^{+0.14}$. This is significantly higher than previous determinations using ALMA data in the Hubble Ultra Deep Field, which is void of DSFGs atz= 4–6 because of strong cosmic variance (shot noise). We conclude that the majority (66% ± 7%) of cosmic star formation atz ∼ 5 is still obscured by dust. We also discuss the uncertainty of SFRD propagated from far-IR spectral energy distribution and IRLF at the bright end, which will need to be resolved with future ALMA and JWST observations. 

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2. Morphologies of Galaxies at z ≳ 9 Uncovered by JWST/NIRCam Imaging: Cosmic Size Evolution and an Identification of an Extremely Compact Bright Galaxy at z ∼ 12

   https://doi.org/10.3847/1538-4357/acd44a  

   Ono, Yoshiaki; Harikane, Yuichi; Ouchi, Masami; Yajima, Hidenobu; Abe, Makito; Isobe, Yuki; Shibuya, Takatoshi; Wise, John H.; Zhang, Yechi; Nakajima, Kimihiko; et al (July 2023, The Astrophysical Journal)

   Abstract We present morphologies of galaxies atz≳ 9 resolved by JWST/NIRCam 2–5μm imaging. Our sample consists of 22 galaxy candidates identified by stringent dropout and photo-zcriteria in GLASS, CEERS, SMACS J0723, and Stephan’s Quintet flanking fields, one of which has been spectroscopically identified atz= 11.44. We perform surface brightness (SB) profile fitting with GALFIT for six bright galaxies with a signal-to-noise ratio = 10–40 on an individual basis and for stacked faint galaxies with secure point-spread functions (PSFs) of the NIRCam real data, carefully evaluating systematics by Monte Carlo simulations. We compare our results with those of previous JWST studies, and confirm that the effective radiir_eof our measurements are consistent with those of previous measurements atz∼ 9. We obtainr_e≃ 200–300 pc with the exponential-like profiles, Sérsic indexes ofn≃ 1–1.5, for galaxies atz∼ 12–16, indicating that the relation ofr_e∝ (1 +z)^sfor $s=-{1.22}_{-0.16}^{+0.17}$explains cosmic evolution overz∼ 0–16 for $\sim L_{z=3}^{*}$galaxies. One bright (M_UV= −21 mag) galaxy atz∼ 12, GL-z12-1, has an extremely compact profile withr_e= 39 ± 11 pc that is surely extended over the PSF. Even in the case that the GL-z12-1 SB is fit by active galactic nuclei + galaxy composite profiles, the best-fit galaxy component is again compact, $r_{\mathrm{e}}={48}_{-15}^{+38}$pc, which is significantly (>5σ) smaller than the typicalr_evalue atz∼ 12. Compared with numerical simulations, we find that such a compact galaxy naturally forms atz≳ 10, and that frequent mergers at the early epoch produce more extended galaxies following ther_e∝ (1 +z)^srelation. 

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3. Efficient Ionizers with Low H β + [O iii ] Equivalent Widths: JADES Spectroscopy of a Peculiar High-redshift Population

   https://doi.org/10.3847/1538-4357/adddb5  

   Laseter, Isaac H; Maseda, Michael V; Simmonds, Charlotte; Endsley, Ryan; Stark, Daniel; Bunker, Andrew J; Bhatawdekar, Rachana; Boyett, Kristan; Cameron, Alex J; Carniani, Stefano; et al (July 2025, The Astrophysical Journal)

   Abstract Early JWST photometric studies discovered a population of UV-faint ( $<{\mathit{L}}_{\mathrm{UV}}^{*}$)z ∼ 6.5–8 Lyman break galaxies with spectral energy distributions implying young ages (∼10 Myr) yet relatively weak Hβ+ [Oiii] equivalent widths (EW_{Hβ+ [Oiii]} ≈ 400 Å). These galaxies seemingly contradict the implicit understanding that young star-forming galaxies are ubiquitously strong Hβ+ [Oiii] emitters, i.e., extreme emission line galaxies (EW ≳750 Å). Low metallicities, high Lyman continuum escape fractions, and rapidly declining star formation histories have been proposed as primary drivers behind low Hβ+ [Oiii] EWs, but the blend of Hβ+ [Oiii] in photometric studies makes proving one of these scenarios difficult. We aim to characterize this peculiar population with deep spectroscopy from the JWST Advanced Deep Extragalactic Survey. We find that a significant subset of these galaxies atz ≳ 2 with modest Hβ+ [Oiii] EWs (≈300–600 Å) have high ionization efficiencies ( $\log {\xi }_{\mathrm{ion}}\gtrsim 25.5\mathrm{Hz}{\mathrm{erg}}^{-1}$). Suppressed [Oiii] EW values yet elevated Hαand HβEW values imply that the level of chemical enrichment is the primary culprit, supported by spectroscopic measurements of metallicities below 12 + log(O/H) ≈ 7.70 (0.1Z_⊙). We demonstrate that integrated Hβ+ [Oiii] selections (e.g., Hβ+ [Oiii] EW > 700 Å) exclude the most metal-poor efficient ionizers and favor (1) more chemically enriched systems with comparable extreme radiation fields and (2) older starbursting systems. In contrast, metallicity degeneracies are reduced in Hαspace, enabling the identification of these metal-poor efficient ionizers by their specific star formation rate. 

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4. SILVERRUSH. XIV. Ly α Luminosity Functions and Angular Correlation Functions from 20,000 Ly α Emitters at z  ∼ 2.2–7.3 from up to 24 deg ² HSC-SSP and CHORUS Surveys: Linking the Postreionization Epoch to the Heart of Reionization

   https://doi.org/10.3847/1538-4365/adb1c0  

   Umeda, Hiroya; Ouchi, Masami; Kikuta, Satoshi; Harikane, Yuichi; Ono, Yoshiaki; Shibuya, Takatoshi; Inoue, Akio K; Shimasaku, Kazuhiro; Liang, Yongming; Matsumoto, Akinori; et al (March 2025, The Astrophysical Journal Supplement Series)

   Abstract We present luminosity functions (LFs) and angular correlation functions (ACFs) derived from 18,960 Lyαemitters (LAEs) atz = 2.2−7.3 over a wide survey area of ≲24 deg²that are identified in the narrowband data of the HSC-SSP and CHORUS surveys. Confirming the large sample with 241 spectroscopically identified LAEs, we determine LyαLFs and ACFs in the brighter luminosity range down to 0.5L_⋆, and confirm that our measurements are consistent with previous studies but offer significantly reduced statistical uncertainties. The improved precision of our ACFs allows us to clearly detect one-halo terms at some redshifts, and provides large-scale bias measurements that indicate host halo masses of ∼10¹¹M_⊙overz ≃ 2−7. By comparing our LyαLF (ACF) measurements with reionization models, we estimate the neutral hydrogen fractions in the intergalactic medium to bex_Hi < 0.05 (= ${0.06}_{-0.03}^{+0.12}$) atz= 5.7 andx_Hi= $0.15_{-0.08}^{+0.10}$( ${0.21}_{-0.14}^{+0.19}$), $0.18_{-0.12}^{+0.14}$, and $0.75_{-0.13}^{+0.09}$atz= 6.6, 7.0, and 7.3, respectively. Our findings suggest that the neutral hydrogen fraction remains relatively low,x_Hi ≲ 0.2, atz = 5−7, but increases sharply atz > 7, reachingx_Hi ∼ 0.9 byz ≃ 8−9, as indicated by recent JWST studies. The combination of our results from LAE observations with recent JWST observations suggests that the major epoch of reionization occurred atz ∼ 7−8, likely driven by the emergence of massive sources emitting significant ionizing photons. 

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5. The Pan-STARRS1 z > 5.6 Quasar Survey. III. The z ≈ 6 Quasar Luminosity Function

   https://doi.org/10.3847/1538-4357/aca7ca  

   Schindler, Jan-Torge; Bañados, Eduardo; Connor, Thomas; Decarli, Roberto; Fan, Xiaohui; Farina, Emanuele Paolo; Mazzucchelli, Chiara; Nanni, Riccardo; Rix, Hans-Walter; Stern, Daniel; et al (January 2023, The Astrophysical Journal)

   Abstract We present thez≈ 6 type-1 quasar luminosity function (QLF), based on the Pan-STARRS1 (PS1) quasar survey. The PS1 sample includes 125 quasars atz≈ 5.7–6.2, with −28 ≲M₁₄₅₀≲ −25. With the addition of 48 fainter quasars from the SHELLQs survey, we evaluate thez≈ 6 QLF over −28 ≲M₁₄₅₀≲ −22. Adopting a double power law with an exponential evolution of the quasar density (Φ(z) ∝ 10^k(z−6);k= −0.7), we use a maximum likelihood method to model our data. We find a break magnitude of $M^{*}=-{26.38}_{-0.60}^{+0.79}\mathrm{mag}$, a faint-end slope of $\alpha =-{1.70}_{-0.19}^{+0.29}$, and a steep bright-end slope of $\beta =-{3.84}_{-1.21}^{+0.63}$. Based on our new QLF model, we determine the quasar comoving spatial density atz≈ 6 to be $n(M_{1450}<-26)={1.16}_{-0.12}^{+0.13}{\mathrm{cGpc}}^{-3}$. In comparison with the literature, we find the quasar density to evolve with a constant value ofk≈ −0.7, fromz≈ 7 toz≈ 4. Additionally, we derive an ionizing emissivity of ${ϵ}_{912}(z=6)={7.23}_{-1.02}^{+1.65}\times {10}^{22}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{Hz}}^{-1}{\mathrm{cMpc}}^{-3}$, based on the QLF measurement. Given standard assumptions, and the recent measurement of the mean free path by Becker et al. atz≈ 6, we calculate an Hiphotoionizing rate of Γ_{H I}(z= 6) ≈ 6 × 10⁻¹⁶s⁻¹, strongly disfavoring a dominant role of quasars in hydrogen reionization. 

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