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1. A Spectral Atlas of Lyα Emitters at z = 5.7 and z = 6.6

   https://doi.org/10.3847/1538-4357/ad5674  

   Songaila, A; Cowie, L L; Barger, A J; Hu, E M; Taylor, A J (August 2024, The Astrophysical Journal)

   Abstract We present two uniformly observed spectroscopic samples of Lyαemitters (LAEs; 127 atz= 5.7 and 82 atz= 6.6), which we use to investigate the evolution of the LAE population at these redshifts. The observations cover a large field (44 deg²) in the North Ecliptic Pole, as well as several smaller fields. We have a small number of exotic LAEs in the samples: double-peaked Lyαprofiles; very extended red wings; and one impressive lensed LAE cross. We also find three broad-line active galactic nuclei. We compare the Lyαline width measurements at the two redshifts, finding that the lower-luminosity LAEs show a strong evolution of decreasing line width with increasing redshift, while the high-luminosity LAEs do not, with a transition luminosity of logL(Lyα) ≈ 43.25 erg s⁻¹. Thus, atz= 6.6, the high-luminosity LAEs may be producing large ionized bubbles themselves, or they may be residing in overdense galaxy sites that are producing such bubbles. In order to avoid losses in the red wing, the radius of the ionized bubble must be larger than 1 pMpc. The double-peaked LAEs also require transmission on the blue side. For the four atz= 6.6, we use models to estimate the proximity radii,R_a, where the ionizing flux of the galaxy is sufficient to make the surroundings have a low enough neutral fraction to pass the blue light. Since the requiredR_aare large, multiple ionizing sources in the vicinity may be needed. 

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2. 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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3. The Relationship between IGM Lyα Opacity and Galaxy Density near the End of Reionization

   https://doi.org/10.3847/1538-4357/acf450  

   Christenson, Holly M.; Becker, George D.; D’Aloisio, Anson; Davies, Frederick B.; Zhu, Yongda; Boera, Elisa; Nasir, Fahad; Furlanetto, Steven R.; Malkan, Matthew A. (September 2023, The Astrophysical Journal)

   Abstract Observed scatter in the Lyαopacity of quasar sightlines atz< 6 has motivated measurements of the correlation between Lyαopacity and galaxy density, as models that predict this scatter make strong and sometimes opposite predictions for how they should be related. Our previous work associated two highly opaque Lyαtroughs atz∼ 5.7 with a deficit of Lyαemitting galaxies (LAEs). In this work, we survey two of the most highly transmissive lines of sight at this redshift toward thez= 6.02 quasar SDSS J1306+0356 and thez= 6.17 quasar PSO J359-06. We find that both fields are underdense in LAEs within 10h⁻¹Mpc of the quasar sightline, somewhat less extensive than underdensities associated with Lyαtroughs. We combine our observations with three additional fields from the literature and find that while fields with extreme opacities are generally underdense, moderate opacities span a wider density range. The results at high opacities are consistent with models that invoke UV background fluctuations and/or late reionization to explain the observed scatter in intergalactic medium (IGM) Lyαopacities. There is tension at low opacities, however, as the models tend to associate lower IGM Lyαopacities with higher densities. Although the number of fields surveyed is still small, the low-opacity results may support a scenario in which the ionizing background in low-density regions increases more rapidly than some models suggest after becoming ionized. Elevated gas temperatures from recent reionization may also be making these regions more transparent. 

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4. UV and Lyα Halos of Lyα Emitters across Environments at z = 2.84*

   https://doi.org/10.3847/1538-4357/acbf30  

   Kikuta, Satoshi; Matsuda, Yuichi; Inoue, Shigeki; Steidel, Charles C.; Cen, Renyue; Zheng, Zheng; Yajima, Hidenobu; Momose, Rieko; Imanishi, Masatoshi; Komiyama, Yutaka (April 2023, The Astrophysical Journal)

   Abstract We present UV and Ly α radial surface brightness (SB) profiles of Ly α emitters (LAEs) at z = 2.84 detected with the Hyper Suprime-Cam on the Subaru Telescope. The depth of our data, together with the wide-field coverage including a protocluster, enable us to study the dependence of Ly α halos (LAHs) on various galaxy properties, including Mpc scale environments. UV and Ly α images of 3490 LAEs are extracted, and stacking the images yields SB sensitivity of ∼ 1 × 10 − 20 erg s − 1 cm − 2 arcsec − 2 in Ly α , reaching the expected level of optically thick gas illuminated by the UV background at z ∼ 3. Fitting of the two-component exponential function gives the scale-lengths of 1.56 ± 0.01 and 10.4 ± 0.3 pkpc. Dividing the sample according to their photometric properties, we find that, while the dependence of halo scale-length on environment outside of the protocluster core is not clear, LAEs in the central regions of protoclusters appear to have very large LAHs, which could be caused by combined effects of source overlapping and diffuse Ly α emission from cool intergalactic gas permeating the forming protocluster core irradiated by active members. For the first time, we identify UV halos around bright LAEs that are probably due to a few lower-mass satellite galaxies. Through comparison with recent numerical simulations, we conclude that, while scattered Ly α photons from the host galaxies are dominant, star formation in satellites evidently contributes to LAHs, and that fluorescent Ly α emission may be boosted within protocluster cores at cosmic noon and/or near bright QSOs. 

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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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