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1. Improved Constraints on the 21 cm EoR Power Spectrum and the X-Ray Heating of the IGM with HERA Phase I Observations

   https://doi.org/10.3847/1538-4357/acaf50  

   Abdurashidova, The HERA; Adams, Tyrone; Aguirre, James E.; Alexander, Paul; Ali, Zaki S.; Baartman, Rushelle; Balfour, Yanga; Barkana, Rennan; Beardsley, Adam P.; Bernardi, Gianni; et al (March 2023, The Astrophysical Journal)

   Abstract We report the most sensitive upper limits to date on the 21 cm epoch of reionization power spectrum using 94 nights of observing with Phase I of the Hydrogen Epoch of Reionization Array (HERA). Using similar analysis techniques as in previously reported limits, we find at 95% confidence that Δ²(k= 0.34hMpc⁻¹) ≤ 457 mK²atz= 7.9 and that Δ²(k= 0.36hMpc⁻¹) ≤ 3496 mK²atz= 10.4, an improvement by a factor of 2.1 and 2.6, respectively. These limits are mostly consistent with thermal noise over a wide range ofkafter our data quality cuts, despite performing a relatively conservative analysis designed to minimize signal loss. Our results are validated with both statistical tests on the data and end-to-end pipeline simulations. We also report updated constraints on the astrophysics of reionization and the cosmic dawn. Using multiple independent modeling and inference techniques previously employed by HERA Collaboration, we find that the intergalactic medium must have been heated above the adiabatic cooling limit at least as early asz= 10.4, ruling out a broad set of so-called “cold reionization” scenarios. If this heating is due to high-mass X-ray binaries during the cosmic dawn, as is generally believed, our result’s 99% credible interval excludes the local relationship between soft X-ray luminosity and star formation and thus requires heating driven by evolved low-metallicity stars. 

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2. First Results from HERA Phase I: Upper Limits on the Epoch of Reionization 21 cm Power Spectrum

   https://doi.org/10.3847/1538-4357/ac1c78  

   Abdurashidova, Zara; Aguirre, James E.; Alexander, Paul; Ali, Zaki S.; Balfour, Yanga; Beardsley, Adam P.; Bernardi, Gianni; Billings, Tashalee S.; Bowman, Judd D.; Bradley, Richard F.; et al (February 2022, The Astrophysical Journal)

   Abstract We report upper limits on the Epoch of Reionization 21 cm power spectrum at redshifts 7.9 and 10.4 with 18 nights of data (∼36 hr of integration) from Phase I of the Hydrogen Epoch of Reionization Array (HERA). The Phase I data show evidence for systematics that can be largely suppressed with systematic models down to a dynamic range of ∼10 9 with respect to the peak foreground power. This yields a 95% confidence upper limit on the 21 cm power spectrum of Δ 21 2 ≤ ( 30.76 ) 2 mK 2 at k = 0.192 h Mpc −1 at z = 7.9, and also Δ 21 2 ≤ ( 95.74 ) 2 mK 2 at k = 0.256 h Mpc −1 at z = 10.4. At z = 7.9, these limits are the most sensitive to date by over an order of magnitude. While we find evidence for residual systematics at low line-of-sight Fourier k ∥ modes, at high k ∥ modes we find our data to be largely consistent with thermal noise, an indicator that the system could benefit from deeper integrations. The observed systematics could be due to radio frequency interference, cable subreflections, or residual instrumental cross-coupling, and warrant further study. This analysis emphasizes algorithms that have minimal inherent signal loss, although we do perform a careful accounting in a companion paper of the small forms of loss or bias associated with the pipeline. Overall, these results are a promising first step in the development of a tuned, instrument-specific analysis pipeline for HERA, particularly as Phase II construction is completed en route to reaching the full sensitivity of the experiment. 

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3. The hydrodynamic response of small-scale structure to reionization drives large IGM temperature fluctuations that persist to z = 4

   https://doi.org/10.1093/mnrasl/slae067  

   Cain, Christopher; Scannapieco, Evan; McQuinn, Matthew; D’Aloisio, Anson; Trac, Hy (June 2024, Monthly Notices of the Royal Astronomical Society: Letters)

   ABSTRACT The thermal history and structure of the intergalactic medium (IGM) at $$z \ge 4$$ is an important boundary condition for reionization, and a key input for studies using the Ly $$\alpha$$ forest to constrain the masses of alternative dark matter candidates. Most such inferences rely on simulations that lack the spatial resolution to fully resolve the hydrodynamic response of IGM filaments and minihaloes to H i reionization heating. In this letter, we use high-resolution hydrodynamic + radiative transfer simulations to study how these affect the IGM thermal structure. We find that the adiabatic heating and cooling driven by the expansion of initially cold gas filaments and minihaloes sources significant small-scale temperature fluctuations. These likely persist in much of the IGM until $$z \le 4$$. Capturing this effect requires resolving the clumping scale of cold, pre-ionized gas, demanding spatial resolutions of $${\le} 2$$ $$h^{-1}$$kpc. Pre-heating of the IGM by X-rays can slightly reduce the effect. Our preliminary estimate of the effect on the Ly $$\alpha$$ forest finds that, at $$\log (k /[{\rm km^{-1} s}]) = -1.0$$, the Ly $$\alpha$$ forest flux power (at fixed mean flux) can increase $${\approx} 10~{{\ \rm per\ cent}}$$ going from 8 and 2 $$h^{-1}$$kpc resolution at $$z = 4{\!-\!}5$$ for gas ionized at $$z \ \lt\ 7$$. These findings motivate more careful analyses of how the effects studied here affect the Ly $$\alpha$$ forest. 

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4. Effects of Photoionization and Photoheating on Lyα Forest Properties from Cholla Cosmological Simulations

   https://doi.org/10.3847/1538-4357/abed5a  

   Villasenor, Bruno; Robertson, Brant; Madau, Piero; Schneider, Evan (May 2021, The Astrophysical Journal)

   Abstract The density and temperature properties of the intergalactic medium (IGM) reflect the heating and ionization history during cosmological structure formation, and are primarily probed by the Ly α forest of neutral hydrogen absorption features in the observed spectra of background sources. We present the methodology and initial results from the Cholla IGM Photoheating Simulation (CHIPS) suite performed with the graphics process unit–accelerated Cholla code to study the IGM at high, uniform spatial resolution maintained over large volumes. In this first paper, we examine the IGM structure in CHIPS cosmological simulations that include IGM uniform photoheating and photoionization models where hydrogen reionization is completed early or by redshift z ∼ 6. Comparing with observations of the large- and small-scale Ly α transmitted flux power spectra P ( k ) at redshifts 2 ≲ z ≲ 5.5, the relative agreement of the models depends on scale, with the self-consistent Puchwein et al. IGM photoheating and photoionization model in good agreement with the flux P ( k ) at k ≳ 0.01 s km −1 at redshifts 2 ≲ z ≲ 3.5. On larger scales, the P ( k ) measurements increase in amplitude from z ∼ 4.6 to z ∼ 2.2, faster than the models, and lie in between the model predictions at 2.2 ≲ z ≲ 4.6 for k ≈ 0.002–0.01 s km −1 . We argue that the models could improve by changing the He ii photoheating rate associated with active galactic nuclei to reduce the IGM temperature at z ∼ 3. At higher redshifts, z ≳ 4.5, the observed flux P ( k ) amplitude increases at a rate intermediate between the models, and we argue that for models where hydrogen reionization is completed late ( z ∼ 5.5–6), resolving this disagreement will require inhomogeneous or “patchy” reionization. We then use an additional set of simulations to demonstrate that our results have numerically converged and are not strongly affected by varying cosmological parameters. 

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5. Lyα Emission Line Profiles of Extreme [O iii]- emitting Galaxies at z ≳ 2: Implications for Lyα Visibility in the Reionization Era

   https://doi.org/10.3847/1538-4357/ad5ae0  

   Tang, Mengtao; Stark, Daniel P; Ellis, Richard S; Topping, Michael W; Mason, Charlotte; Li, Zhihui; Plat, Adèle (August 2024, The Astrophysical Journal)

   Abstract JWST observations have recently begun delivering the first samples of Lyαvelocity profile measurements atz> 6, opening a new window into the reionization process. Interpretation ofz≳ 6 line profiles is currently stunted by limitations in our knowledge of the intrinsic Lyαprofile (before encountering the intergalactic medium (IGM)) of the galaxies that are common atz≳ 6. To overcome this shortcoming, we have obtained resolved (R∼ 3900) Lyαspectroscopy of 42 galaxies atz= 2.1–3.4 with similar properties as are seen atz> 6. We quantify a variety of Lyαprofile statistics as a function of [Oiii]+Hβequivalent width (EW). Our spectra reveal a new population ofz≃ 2–3 galaxies with large [Oiii]+HβEWs (>1200 Å) and a large fraction of Lyαflux emerging near the systemic redshift (peak velocity ≃0 km s⁻¹). These spectra indicate that low-density neutral hydrogen channels are able to form in a subset of low-mass galaxies (≲1 × 10⁸M_⊙) that experience a burst of star formation (sSFR > 100 Gyr⁻¹). Other extreme [Oiii] emitters show weaker Lyαthat is shifted to higher velocities (≃240 km s⁻¹) with little emission near the line center. We investigate the impact the IGM is likely to have on these intrinsic line profiles in the reionization era, finding that the centrally peaked Lyαemitters should be strongly attenuated atz≳ 5. We show that these line profiles are particularly sensitive to the impact of resonant scattering from infalling IGM and can be strongly attenuated even when the IGM is highly ionized atz≃ 5. We compare these expectations against a new database ofz≳ 6.5 galaxies with robust velocity profiles measured with JWST/NIRSpec. 

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