More Like this

1. (Nearly) Model-independent Constraints on the Neutral Hydrogen Fraction in the Intergalactic Medium at z ∼ 5–7 Using Dark Pixel Fractions in Lyα and Lyβ Forests

   https://doi.org/10.3847/1538-4357/aca678  

   Jin, Xiangyu; Yang, Jinyi; Fan, Xiaohui; Wang, Feige; Bañados, Eduardo; Bian, Fuyan; Davies, Frederick B.; Eilers, Anna-Christina; Farina, Emanuele Paolo; Hennawi, Joseph F.; et al (January 2023, The Astrophysical Journal)

   Abstract Cosmic reionization was the last major phase transition of hydrogen from neutral to highly ionized in the intergalactic medium (IGM). Current observations show that the IGM is significantly neutral atz> 7 and largely ionized byz∼ 5.5. However, most methods to measure the IGM neutral fraction are highly model dependent and are limited to when the volume-averaged neutral fraction of the IGM is either relatively low ( ${\overline{x}}_{\mathrm{H}\mathrm{I}}\lesssim {10}^{-3}$) or close to unity ( ${\overline{x}}_{\mathrm{H}\mathrm{I}}\sim 1$). In particular, the neutral fraction evolution of the IGM at the critical redshift range ofz= 6–7 is poorly constrained. We present new constraints on ${\overline{x}}_{\mathrm{H}\mathrm{I}}$atz∼ 5.1–6.8 by analyzing deep optical spectra of 53 quasars at 5.73 <z< 7.09. We derive model-independent upper limits on the neutral hydrogen fraction based on the fraction of “dark” pixels identified in the Lyαand Lyβforests, without any assumptions on the IGM model or the intrinsic shape of the quasar continuum. They are the first model-independent constraints on the IGM neutral hydrogen fraction atz∼ 6.2–6.8 using quasar absorption measurements. Our results give upper limits of ${\overline{x}}_{\mathrm{H}\mathrm{I}}(z=6.3)<0.79\pm 0.04$(1σ), ${\overline{x}}_{\mathrm{H}\mathrm{I}}(z=6.5)<0.87\pm 0.03$(1σ), and ${\overline{x}}_{\mathrm{H}\mathrm{I}}(z=6.7)<{0.94}_{-0.09}^{+0.06}$(1σ). The dark pixel fractions atz> 6.1 are consistent with the redshift evolution of the neutral fraction of the IGM derived from Planck 2018. 

   more » « less
2. The Luminosity Function and Clustering of H α Emitting Galaxies at z  ≈ 4−6 from a Complete NIRCam Grism Redshift Survey

   https://doi.org/10.3847/1538-4357/ae225e  

   Lin, Xiaojing; Egami, Eiichi; Sun, Fengwu; Zhang, Haowen; Fan, Xiaohui; Helton, Jakob M; Wang, Feige; Bunker, Andrew J; Cai, Zheng; Eisenstein, Daniel J; et al (January 2026, The Astrophysical Journal)

   Abstract We study the luminosity function (LF) and clustering properties of 888 Hαemitters (HAEs) at 3.75 < z < 6 in the GOODS-N field. The sample, built from JWST CONGRESS and FRESCO NIRCam grism surveys using a novel redshift assignment algorithm, spans ∼62 arcmin²and reachesL_Hα ∼ 10^41.2erg s⁻¹. We identify two prominent filamentary protoclusters atz ≈ 4.41 andz ≈ 5.19, hosting 98 and 144 HAEs, respectively. The observed HαLFs show similar shallow faint-end slopes for both protocluster and field galaxies at 3.75 < z < 5, and for the protocluster at 5 < z < 6 (α ≈ −1.2 to −1.3). In contrast, the field LF at 5 < z < 6 has a much steeper slope ( $\alpha =-1.87_{-0.23}^{+0.30}$), suggesting that protocluster galaxies atz > 5 are more evolved, resembling the populations at 3.75 < z < 5. The observed star formation rate density from Hαintegrated down to 0.45M_⊙yr⁻¹, is $0.050_{-0.003}^{+0.002}{M}_{\odot }{\mathrm{yr}}^{-1}{\mathrm{Mpc}}^{-3}$at 3.75 < z < 5 and $0.046_{-0.004}^{+0.006}{M}_{\odot }{\mathrm{yr}}^{-1}{\mathrm{Mpc}}^{-3}$at 5 < z < 6, with protoclusters contributing about 25% and 55%, respectively. This implies a large fraction of star formation atz> 4 occurs in protoclusters. For the first time, we conduct the star formation-rate-limited three-dimensional clustering analysis atz > 4. We find that the filamentary geometry of protoclusters flattens the power-law shape of the HAE autocorrelation functions, with slopes much shallower than the typically assumed value. The autocorrelation function of field HAEs has a correlation length of $r_0=4.61_{-0.68}^{+1.00}{h}^{-1}\mathrm{Mpc}$atz ≈ 4−5 and $r_0=6.23_{-1.13}^{+1.68}{h}^{-1}\mathrm{Mpc}$atz ≈ 5−6. Comparing the observed correlation functions with the UniverseMachinesimulation, we infer the dark matter (sub-)halo masses of HAEs to be $\log (M_h/M_{\odot })=11.0-11.2$atz ≈ 4−6, with a scatter of 0.4 dex. 

   more » « less
3. The FRB 20190520B Sight Line Intersects Foreground Galaxy Clusters

   https://doi.org/10.3847/2041-8213/acefb5  

   Lee, Khee-Gan; Khrykin, Ilya S; Simha, Sunil; Ata, Metin; Huang, Yuxin; Prochaska, J Xavier; Tejos, Nicolas; Cooke, Jeff; Nagamine, Kentaro; Zhang, Jielai (August 2023, The Astrophysical Journal Letters)

   Abstract The repeating fast radio burst FRB 20190520B is an anomaly of the FRB population thanks to its high dispersion measure (DM = 1205 pc cm⁻³) despite its low redshift ofz_frb= 0.241. This excess has been attributed to a large host contribution of DM_host≈ 900 pc cm⁻³, far larger than any other known FRB. In this paper, we describe spectroscopic observations of the FRB 20190520B field obtained as part of the FLIMFLAM survey, which yielded 701 galaxy redshifts in the field. We find multiple foreground galaxy groups and clusters, for which we then estimated halo masses by comparing their richness with numerical simulations. We discover two separateM_halo> 10¹⁴M_⊙galaxy clusters atz= 0.1867 and 0.2170 that are directly intersected by the FRB sight line within their characteristic halo radiusr₂₀₀. Subtracting off their estimated DM contributions, as well that of the diffuse intergalactic medium, we estimate a host contribution of ${\mathrm{D}\mathrm{M}}_{\mathrm{h}\mathrm{o}\mathrm{s}\mathrm{t}}={430}_{-220}^{+140}$or ${280}_{-170}^{+140}\mathrm{p}\mathrm{c}{\mathrm{c}\mathrm{m}}^{-3}$(observed frame), depending on whether we assume that the halo gas extends tor₂₀₀or 2 ×r₂₀₀. This significantly smaller DM_host—no longer the largest known value—is now consistent with Hαemission measures of the host galaxy without invoking unusually high gas temperatures. Combined with the observed FRB scattering timescale, we estimate the turbulent fluctuation and geometric amplification factor of the scattering layer to be $\tilde{F}G\approx 4.5–11{\left({\mathrm{pc}}^2\mathrm{km}\right)}^{-1/3}$, suggesting that most of the gas is close to the FRB host. This result illustrates the importance of incorporating foreground data for FRB analyses both for understanding the nature of FRBs and to realize their potential as a cosmological probe. 

   more » « less
4. 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. 

   more » « less
5. HST Observations of HD 166620 and τ Ceti: First UV Spectra of a Magnetic Grand Minimum Star and the Extent of τ Ceti’s Astrosphere

   https://doi.org/10.3847/1538-4357/ae315b  

   Wood, Brian E; Müller, Hans-Reinhard; Hartshorn, Dean; Redfield, Seth; Metcalfe, Travis S (February 2026, The Astrophysical Journal)

   Abstract We present new Hubble Space Telescope (HST) UV spectra of the K2 V star HD 166620, the first star clearly recognized to be in a “magnetic grand minimum” state analogous to the Sun’s “Maunder minimum” in the late 1600s. The stellar HILyαsurface fluxes are extremely low, about a factor of 2 below fluxes observed during solar minimum, and also significantly lower than those ofτCeti (G8 V) and HD 191408 (K2.5 V), two stars more similar to HD 166620 in spectral type and age (∼10 Gyr) than the Sun. TheτCeti data that are compared with HD 166620 include both old archival data and a new HST observation as well. The Lyαdata are used to confirm a nondetection of astrospheric Lyαabsorption for this star, suggesting a very weak wind with $\dot{M}<0.1$ ${\dot{M}}_{\odot }$. The very compact astrosphere inferred forτCeti indicates that the star’s debris disk is at least partly exposed to the interstellar medium (ISM), and we discuss possible consequences. 

   more » « less