More Like this

1. Constraints on the z ∼ 5 Star-forming Galaxy Luminosity Function From Hubble Space Telescope Imaging of an Unbiased and Complete Sample of Long Gamma-Ray Burst Host Galaxies

   https://doi.org/10.3847/1538-4357/ad2e93  

   Sears, Huei; Chornock, Ryan; Strader, Jay; Perley, Daniel A; Blanchard, Peter K; Margutti, Raffaella; Tanvir, Nial R (April 2024, The Astrophysical Journal)

   Abstract We present rest-frame UV Hubble Space Telescope imaging of the largest and most complete sample of 23 long-duration gamma-ray burst (GRB) host galaxies between redshifts 4 and 6. Of these 23, we present new WFC3/F110W imaging for 19 of the hosts, which we combine with archival WFC3/F110W and WFC3/F140W imaging for the remaining four. We use the photometry of the host galaxies from this sample to characterize both the rest-frame UV luminosity function (LF) and the size–luminosity relation of the sample. We find that when assuming the standard Schechter-function parameterization for the UV LF, the GRB host sample is best fit with $\alpha =-{1.30}_{-0.25}^{+0.30}$and $M_{*}=-{20.33}_{-0.54}^{+0.44}$mag, which are consistent with results based onz∼ 5 Lyman-break galaxies. We find that ∼68% of our size–luminosity measurements fall within or below the same relation for Lyman-break galaxies atz∼ 4. This study observationally confirms expectations that atz∼ 5 Lyman-break and GRB host galaxies should trace the same population and demonstrates the utility of GRBs as probes of hidden star formation in the high-redshift Universe. Under the assumption that GRBs unbiasedly trace star formation at this redshift, our nondetection fraction of 7/23 is consistent at the 95% confidence level with 13%–53% of star formation at redshiftz∼ 5 occurring in galaxies fainter than our detection limit ofM_1600Å≈ −18.3 mag. 

   more » « less
2. Modeling Galaxies in the Early Universe with Supernova Dust Attenuation

   https://doi.org/10.3847/2041-8213/add15d  

   McKinney, Jed; Cooper, Olivia R; Casey, Caitlin M; Muñoz, Julian B; Akins, Hollis; Lambrides, Erini; Long, Arianna S (May 2025, The Astrophysical Journal Letters)

   Abstract Supernovae (SNe) may be the dominant channel by which dust grains accumulate in galaxies during the first Gyr of cosmic time as formation channels important for lower-redshift galaxies, e.g., asymptotic giant branch stars and grain growth, may not have had sufficient time to take over. SNe produce fewer small grains, leading to a flatter attenuation law. In this work, we fit observations of 138 spectroscopically confirmedz > 6 galaxies adopting standard spectral energy distribution (SED) modeling assumptions and compare standard attenuation law prescriptions to a flat attenuation law. Compared to SMC dust, flat attenuation close to what may be expected from dust produced in SNe yields up to 0.5 mag higherA_Vand 0.4 dex larger stellar masses. It also finds better fits to the rest-frame UV photometry with lower ${\chi }_{\mathrm{UV}}^2$, allowing the observed UV luminosities taken from the models to be fainter by 0.2 dex on average. The systematically fainter observed UV luminosities for fixed observed photometry could help resolve current tension between the ionizing photon production implied by JWST observations and the redshift evolution of the neutral hydrogen fraction. Given these systematic effects and the physical constraint of cosmic time itself, fairly flat attenuation laws that could represent the properties of dust grains produced by SNe should be a standard consideration in fitting to the SEDs ofz > 6 galaxies. 

   more » « less
3. An empirical reionization history model inferred from the low-redshift Lyman continuum survey and the star-forming galaxies at z > 8

   https://doi.org/10.1093/mnras/stad3483  

   Lin, Yu-Heng; Scarlata, Claudia; Williams, Hayley; Chen, Wenlei; Kelly, Patrick; Langeroodi, Danial; Hjorth, Jens; Chisholm, John; Koekemoer, Anton M.; Zitrin, Adi; et al (November 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We present a new analysis of the rest-frame ultraviolet (UV) and optical spectra of a sample of three z > 8 galaxies discovered behind the gravitational lensing cluster RX J2129.4+0009. We combine these observations with z > 7.5 galaxies from the literature, for which similar measurements are available. As already pointed out in other studies, the high [O iii]λ5007/[O ii]λ3727 ratios (O32) and steep UV continuum slopes (β) are consistent with the values observed for low-redshift Lyman continuum emitters, suggesting that such galaxies contribute to the ionizing budget of the intergalactic medium. We construct a logistic regression model to estimate the probability of a galaxy being a Lyman continuum emitter based on the measured MUV, β, and O32. Using this probability and the UV luminosity function, we construct an empirical model that estimates the contribution of high-redshift galaxies to reionization. The preferred scenario in our analysis shows that at z ∼ 8, the average escape fraction of the galaxy population [i.e. including both LyC emitters (LCEs) and non-emitters] varies with MUV, with intermediate UV luminosity (−19 < MUV < −16) galaxies having larger escape fraction. Galaxies with faint UV luminosity (−16 < MUV < −13.5) contribute most of the ionizing photons. The relative contribution of faint versus bright galaxies depends on redshift, with the intermediate UV galaxies becoming more important over time. UV bright galaxies, although more likely to be LCEs at a given log(O32) and β, contribute the least of the total ionizing photon budget. 

   more » « less
4. Probing Ultralate Reionization: Direct Measurements of the Mean Free Path over 5 < z < 6

   https://doi.org/10.3847/1538-4357/aceef4  

   Zhu, Yongda; Becker, George D.; Christenson, Holly M.; D’Aloisio, Anson; Bosman, Sarah E. I.; Bakx, Tom; D’Odorico, Valentina; Bischetti, Manuela; Cain, Christopher; Davies, Frederick B.; et al (September 2023, The Astrophysical Journal)

   Abstract The mean free path of ionizing photons,λ_mfp, is a critical parameter for modeling the intergalactic medium (IGM) both during and after reionization. We present direct measurements ofλ_mfpfrom QSO spectra over the redshift range 5 <z< 6, including the first measurements atz≃ 5.3 and 5.6. Our sample includes data from the XQR-30 VLT large program, as well as new Keck/ESI observations of QSOs nearz∼ 5.5, for which we also acquire new [Cii] 158μm redshifts with ALMA. By measuring the Lyman continuum transmission profile in stacked QSO spectra, we find ${\lambda }_{\mathrm{mfp}}={9.33}_{-1.80}^{+2.06}$, ${5.40}_{-1.40}^{+1.47}$, ${3.31}_{-1.34}^{+2.74}$, and ${0.81}_{-0.48}^{+0.73}$pMpc atz= 5.08, 5.31, 5.65, and 5.93, respectively. Our results demonstrate thatλ_mfpincreases steadily and rapidly with time over 5 <z< 6. Notably, we find thatλ_mfpdeviates significantly from predictions based on a fully ionized and relaxed IGM as late asz= 5.3. By comparing our results to model predictions and indirectλ_mfpconstraints based on IGM Lyαopacity, we find that the evolution ofλ_mfpis consistent with scenarios wherein the IGM is still undergoing reionization and/or retains large fluctuations in the ionizing UV background well below redshift 6. 

   more » « less
5. Unveiling dark matter free streaming at the smallest scales with the high redshift Lyman-alpha forest

   https://doi.org/10.1103/PhysRevD.109.043511  

   Iršič, Vid; Viel, Matteo; Haehnelt, Martin G; Bolton, James S; Molaro, Margherita; Puchwein, Ewald; Boera, Elisa; Becker, George D; Gaikwad, Prakash; Keating, Laura C; et al (February 2024, Physical Review D)

   This study introduces novel constraints on the free streaming of thermal relic warm dark matter (WDM) from Lyman- $\alpha$forest flux power spectra. Our analysis utilizes a high resolution, high redshift sample of quasar spectra observed using the HIRES and UVES spectrographs ( $z=4.2–5.0$). We employ a Bayesian inference framework and a simulation-based likelihood that encompasses various parameters including the free streaming of dark matter, cosmological parameters, the thermal history of the intergalactic medium, and inhomogeneous reionization to establish lower limits on the mass of a thermal relic WDM particle of 5.7 keV (at 95% CL). This result surpasses previous limits from the Lyman- $\alpha$forest through reduction of the measured uncertainties due to a larger statistical sample and by measuring clustering to smaller scales ( $k_{\max }=0.2{\mathrm{km}}^{-1}\mathrm{s}$). The approximately two-fold improvement due to the expanded statistical sample suggests that the effectiveness of Lyman- $\alpha$forest constraints on WDM models at high redshifts are limited by the availability of high quality quasar spectra. Restricting the analysis to comparable scales and thermal history priors as in prior studies ( $k_{\max }<0.1{\mathrm{km}}^{-1}\mathrm{s}$) lowers the bound on the WDM mass to 4.1 keV. As the precision of the measurements increases, it becomes crucial to examine the instrumental and modeling systematics. On the modeling front, we argue that the impact of the thermal history uncertainty on the WDM particle mass constraint has diminished due to improved independent observations. At the smallest scales, the primary source of modeling systematic arises from the structure in the peculiar velocity of the intergalactic medium and inhomogeneous reionization. Published by the American Physical Society2024 

   more » « less