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1. Shedding New Light on Weak Emission-line Quasars in the C iv–Hβ Parameter Space

   https://doi.org/10.3847/1538-4357/acd04d  

   Ha, Trung; Dix, Cooper; Matthews, Brandon M.; Shemmer, Ohad; Brotherton, Michael S.; Myers, Adam D.; Richards, Gordon T.; Maithil, Jaya; Anderson, Scott F.; Brandt, W N; et al (June 2023, The Astrophysical Journal)

   Abstract Weak emission-line quasars (WLQs) are a subset of type 1 quasars that exhibit extremely weak Lyα+ Nvλ1240 and/or Civλ1549 emission lines. We investigate the relationship between emission-line properties and accretion rate for a sample of 230 “ordinary” type 1 quasars and 18 WLQs atz< 0.5 and 1.5 <z< 3.5 that have rest-frame ultraviolet and optical spectral measurements. We apply a correction to the Hβ-based black hole mass (M_BH) estimates of these quasars using the strength of the optical Feiiemission. We confirm previous findings that WLQs’M_BHvalues are overestimated by up to an order of magnitude using the traditional broad-emission-line region size–luminosity relation. With thisM_BHcorrection, we find a significant correlation between Hβ-based Eddington luminosity ratios and a combination of the rest-frame Civequivalent width and Civblueshift with respect to the systemic redshift. This correlation holds for both ordinary quasars and WLQs, which suggests that the two-dimensional Civparameter space can serve as an indicator of accretion rate in all type 1 quasars across a wide range of spectral properties. 

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2. Too Quiet for Comfort: Local Little Red Dots Lack Variability over Decades

   https://doi.org/10.3847/1538-4357/ae6b89  

   Burke, Colin J; Stone, Zachary; Shen, Yue; Jiang, Yan-Fei (June 2026, The Astrophysical Journal)

   Abstract Several local (z ≲ 0.2) metal-poor dwarf active galactic nuclei (AGNs) have remarkably similar properties to those of high-redshift little red dots (LRDs), and are proposed to be local analogs of LRDs. We use long-term photometric and spectroscopic observations of three local LRDs spanning ∼20 yr to measure variability in their rest-frame optical continua and broad Hαemission lines. Using Zwicky Transient Facility light curves over a rest-frame ∼5 yr baseline, ther-band intrinsic rms variability is ${(9\times 10^{-5})}_{-9\times {10}^{-5}}^{+0.014}$ mag (J1022+0841), 0.025 ± 0.004 mag (J1025+1402) and 0.020 ± 0.005 mag (J1047+0739), indicating low intrinsic variability (<3%–4% at 3σ). These variability amplitudes are much lower than those for dwarf AGNs and more massive quasars. We constrain the broad Hαvariability to be less than a few percent, without significant profile changes, over a rest-frame baseline of ∼15 yr in J1025+1402 and J1047+0739, respectively. Local LRDs have exceptionally large Hαequivalent widths and Hα/Hβratios that far exceed the Case B recombination value, in contrast with normal broad-line AGNs. In the context of recent theoretical models of LRDs as dense gas-enshrouded massive black holes with super-Eddington accretion, our results suggest that the photosphere emission is long-term stable and the broad Balmer lines do not arise primarily by photoionization. This scenario is consistent with the lack of variability, large Hα/Hβratios, little dust extinction, and expected high gas density. Virial black hole mass estimates using broad Hαassuming photoionization are therefore highly questionable for LRDs. 

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3. First HETDEX Spectroscopic Determinations of Lyα and UV Luminosity Functions at z = 2–3: Bridging a Gap between Faint AGNs and Bright Galaxies

   https://doi.org/10.3847/1538-4357/ac1e97  

   Zhang, Yechi; Ouchi, Masami; Gebhardt, Karl; Mentuch Cooper, Erin; Liu, Chenxu; Davis, Dustin; Jeong, Donghui; Farrow, Daniel J.; Finkelstein, Steven L.; Gawiser, Eric; et al (November 2021, The Astrophysical Journal)

   Abstract We present Ly α and ultraviolet (UV)-continuum luminosity functions (LFs) of galaxies and active galactic nuclei (AGNs) at z = 2.0–3.5 determined by the untargeted optical spectroscopic survey of the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX). We combine deep Subaru imaging with HETDEX spectra resulting in 11.4 deg 2 of fiber spectra sky coverage, obtaining 18,320 galaxies spectroscopically identified with Ly α emission, 2126 of which host type 1 AGNs showing broad (FWHM > 1000 km s −1 ) Ly α emission lines. We derive the Ly α (UV) LF over 2 orders of magnitude covering bright galaxies and AGNs in log L Ly α / [ erg s − 1 ] = 43.3 – 45.5 (−27 < M UV < −20) by the 1/ V max estimator. Our results reveal that the bright-end hump of the Ly α LF is composed of type 1 AGNs. In conjunction with previous spectroscopic results at the faint end, we measure a slope of the best-fit Schechter function to be α Sch = − 1.70 − 0.14 + 0.13 , which indicates that α Sch steepens from z = 2–3 toward high redshift. Our UV LF agrees well with previous AGN UV LFs and extends to faint-AGN and bright-galaxy regimes. The number fraction of Ly α -emitting objects ( X LAE ) increases from M UV * ∼ − 21 to bright magnitude due to the contribution of type 1 AGNs, while previous studies claim that X Ly α decreases from faint magnitudes to M UV * , suggesting a valley in the X Ly α –magnitude relation at M UV * . Comparing our UV LF of type 1 AGNs at z = 2–3 with those at z = 0, we find that the number density of faint ( M UV > −21) type 1 AGNs increases from z ∼ 2 to 0, as opposed to the evolution of bright ( M UV < −21) type 1 AGNs, suggesting AGN downsizing in the rest-frame UV luminosity. 

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4. A GLIMPSE into the very faint end of the H β +[O III] λλ 4960,5008 luminosity function at z ∼ 7 – 9 behind Abell S1063

   https://doi.org/10.1051/0004-6361/202556868  

   Korber, Damien; Chemerynska, Iryna; Furtak, Lukas J; Atek, Hakim; Endsley, Ryan; Schaerer, Daniel; Chisholm, John; Kokorev, Vasily; Saldana-Lopez, Alberto; Adamo, Angela; et al (April 2026, Astronomy & Astrophysics)

   We used the ultra-deep GLIMPSE JWST/NIRCam survey to constrain the faint end of the [O III]+Hβluminosity function (LF) down to 10³⁹erg s⁻¹atz ∼ 7 − 9 behind the lensed Hubble Frontier Field galaxy cluster Abell S1063. We applied a spectral energy distribution fitting on a Lyman-break galaxy selected sample of 164 lensed galaxies and measured their combined Hβ+[O III]λλ4960, 5008 flux to build the emission line LF. We found a [O III]+HβLF with a faint-end slope (α= −1.78^+0.06_−0.06forz = 7 − 8 andα= −1.55^+0.11_−0.11forz = 8 − 9), which is flatter than the UV LF at similar redshifts (α ≤ −2) and suggests a lower number density of weak [O III]+Hβemitting galaxies at fixedM_UV. We analysed several possible explanations: (i) a decrease in the [O III]+Hβ-to-UV ratio due to bursty star formation histories (SFHs), (ii) the effect of metallicity on the [O III]-to-Hβratio, or (iii) signs of a faint-end turnover in the UV LF. Under the assumption of an evolving [O III]-to-Hβratio, we separated the contribution of [O III]λ5008 and Hβand obtained a flatter [O III]λ5008 LF (α= −1.66^+0.05_−0.05forz = 7 − 8 andα= −1.45^+0.09_−0.10forz = 8 − 9) but steeper HβLF ($$ \alpha=-1.95_{-0.08}^{+0.08} $$ forz = 7 − 8 andα= −1.68^+0.13_−0.14forz = 8 − 9). The combination of a decreasing metallicity and bursty SFH can reconcile the observed differences between the UV and [O III]+HβLF. By converting this LF into the ionising photon-production rateṄ_ion, we show that galaxies withL_Hα ≥ 10³⁹erg s⁻¹, that is, with a star formation rate (SFR) (Hα)  ≥  5 × 10⁻³M_⊙yr⁻¹) cause 31%−90% and 46%−156% of the ionising photon budget (at 7 < z < 8 and 8 < z < 9), when we assume a constant escape fraction of Lyman-continuum photon (f_esc = 0.14). The shape of the LF further shows the negligible contribution of faint galaxies to theṄ_ion. Additionally, we derived the cosmic star formation rate density (SFRD), finding results consistent with previous estimates. However, the sensitivity of GLIMPSE to lower SFRs reinforces the conclusion that very faint galaxies contribute very little toṄ_ionand the SFRD. Our results suggests that GLIMPSE has detected the bulk of the total [O III]+Hβemission from star-forming galaxies, and that galaxies below our detection limits are likely minor contributors to cosmic re-ionisation. 

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5. The Active Galactic Nuclei in the Hobby–Eberly Telescope Dark Energy Experiment Survey (HETDEX). II. Luminosity Function

   https://doi.org/10.3847/1538-4357/ac8054  

   Liu, Chenxu; Gebhardt, Karl; Cooper, Erin Mentuch; Zhang, Yechi; Schneider, Donald P.; Ciardullo, Robin; Davis, Dustin; Farrow, Daniel J.; Finkelstein, Steven L.; Gronwall, Caryl; et al (August 2022, The Astrophysical Journal)

   Abstract We present the Ly α emission line luminosity function (LF) of the active galactic nuclei (AGN) in the first release of the Hobby–Eberly Telescope Dark Energy Experiment Survey (HETDEX) AGN catalog. The AGN are selected either by emission line pairs characteristic of AGN or by a single broad emission line, free of any photometric preselections (magnitude/color/morphology). The sample consists of 2346 AGN spanning 1.88 < z < 3.53, covering an effective area of 30.61 deg 2 . Approximately 2.6% of the HETDEX AGN are not detected at >5 σ confidence at r ∼ 26 in the deepest r -band images we have searched. The Ly α line luminosity ranges from ∼10 42.3 to 10 45.9 erg s −1 . Our Ly α LF shows a turnover luminosity with opposite slopes on the bright end and the faint end: The space density is highest at L Ly α ∗ = 10 43.4 erg s −1 . We explore the evolution of the AGN LF over a broader redshift range (0.8 < z < 3); constructing the rest-frame ultraviolet (UV) LF with the 1450 Å monochromatic luminosity of the power-law component of the continuum (M 1450 ) from M 1450 ∼ −18 to −27.5. We divide the sample into three redshift bins ( z ∼ 1.5, 2.1, and 2.6). In all three redshift bins, our UV LFs indicate that the space density of AGN is highest at the turnover luminosity M 1450 * with opposite slopes on the bright end and the faint end. The M 1450 LFs in the three redshift bins can be well fit with a luminosity evolution and density evolution model: the turnover luminosity ( M 1450 * ) increases, and the turnover density (Φ*) decreases with increasing redshift. 

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