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 (${\overline{x}}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}\lesssim {10}^{-3}$ ) or close to unity (${\overline{x}}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}\sim 1$ ). 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${\overline{x}}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}$ 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 Lyα and Lyβ forests, 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 ofx ¯ more »
mathvariant='normal'>HI ( z = 6.3 ) < 0.79 ± 0.04 (1σ ),${\overline{x}}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}(z=6.5)<0.87\pm 0.03$ (1σ ), and${\overline{x}}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}(z=6.7)<{0.94}_{-0.09}^{+0.06}$ (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.

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Authors:
Jin, Xiangyu ; Yang, Jinyi ; Fan, Xiaohui ; Wang, Feige ; Bañados, Eduardo ; Bian, Fuyan ; Davies, Frederick B. ; Eilers, Anna-Christina ; Farina, Emanuele Paolo ; Hennawi, Joseph F. ; Pacucci, Fabio ; Venemans, Bram ; Walter, Fabian
Publication Date:
2023-01-11
NSF-PAR ID:
10390899
Journal Name:
The Astrophysical Journal
Volume:
942
Issue:
2
Page Range or eLocation-ID:
Article No. 59
ISSN:
0004-637X
Publisher:
DOI PREFIX: 10.3847
Sponsoring Org:
National Science Foundation

Masterson, Megan
; McDonald, Michael
; Ansarinejad, Behzad
; Bayliss, Matthew
; Benson, Bradford A.
; Bleem, Lindsey E.
; Calzadilla, Michael S.
; Edge, Alastair C.
; Floyd, Benjamin
; Kim, Keunho J.
; et al
(
February 2023
, The Astrophysical Journal)

Abstract We present a multiwavelength analysis of the galaxy cluster SPT-CL J0607-4448 (SPT0607), which is one of the most distant clusters discovered by the South Pole Telescope atz = 1.4010 ± 0.0028. The high-redshift cluster shows clear signs of being relaxed with well-regulated feedback from the active galactic nucleus (AGN) in the brightest cluster galaxy (BCG). Using Chandra X-ray data, we construct thermodynamic profiles and determine the properties of the intracluster medium. The cool-core nature of the cluster is supported by a centrally peaked density profile and low central entropy (${K}_{0}={18}_{-9}^{+11}$ keV cm^{2} ), which we estimate assuming an isothermal temperature profile due to the limited spectral information given the distance to the cluster. Using the density profile and gas cooling time inferred from the X-ray data, we find a mass-cooling rate${\stackrel{\u0307}{M}}_{\mathrm{cool}}={100}_{-60}^{+90}\phantom{\rule{0.25em}{0ex}}{M}_{\odot}$ yr^{−1} . From optical spectroscopy and photometry around the [Oii ] emission line, we estimate that the BCG star formation rate is${\mathrm{SFR}}_{[\mathrm{O}\phantom{\rule{0.25em}{0ex}}\mathrm{II}]}={1.7}_{-0.6}^{+1.0}\phantom{\rule{0.25em}{0ex}}{M}_{\odot}$ yr^{−1} , roughly two orders of magnitude lower than the predicted mass-cooling rate. In addition, using ATCA radio data at 2.1 GHz, we measure a radio jet power${P}_{\mathrm{cav}}={3.2}_{-1.3}^{+2.1}\times {10}^{44}$ erg s^{−1} , which is consistent withmore » the X-ray cooling luminosity (${L}_{\mathrm{cool}}={1.9}_{-0.5}^{+0.2}\times {10}^{44}$ erg s^{−1} withinr _{cool} = 43 kpc). These findings suggest that SPT0607 is a relaxed, cool-core cluster with AGN-regulated cooling at an epoch shortly after cluster formation, implying that the balance between cooling and feedback can be reached quickly. We discuss the implications for these findings on the evolution of AGN feedback in galaxy clusters.

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Lehner, Nicolas
; Kopenhafer, Claire
; O’Meara, John M.
; Howk, J. Christopher
; Fumagalli, Michele
; Prochaska, J. Xavier
; Acharyya, Ayan
; O’Shea, Brian W.
; Peeples, Molly S.
; Tumlinson, Jason
; et al
(
September 2022
, The Astrophysical Journal)

Abstract We present the KODIAQ-Z survey aimed to characterize the cool, photoionized gas at 2.2 ≲z ≲ 3.6 in 202 Hi -selected absorbers with 14.6 ≤$\mathrm{log}{N}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}$ < 20 that probe the interface between galaxies and the intergalactic medium (IGM). We find that gas with$14.6\le \mathrm{log}{N}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}<20$ at 2.2 ≲z ≲ 3.6 can be metal-rich (−1.6 ≲ [X/H] ≲ − 0.2) as seen in damped Lyα absorbers (DLAs); it can also be very metal-poor ([X/H] < − 2.4) or even pristine ([X/H] < − 3.8), which is not observed in DLAs but is common in the IGM. For$16<\mathrm{log}{N}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}<20$ absorbers, the frequency of pristine absorbers is about 1%–10%, while for$14.6\le \mathrm{log}{N}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}\le 16$ absorbers it is 10%–20%, similar to the diffuse IGM. Supersolar gas is extremely rare (<1%) at these redshifts. The factor of several thousand spread from the lowest to highest metallicities and large metallicity variations (a factor of a few to >100) between absorbers separated by less than Δv < 500 km s^{−1} imply that the metals are poorly mixed in$14.6\le \mathrm{log}{N}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}<20$ gas. We show that these photoionized absorbers contribute to aboutmore » 14% of the cosmic baryons and 45% of the cosmic metals at 2.2 ≲z ≲ 3.6. We find that the mean metallicity increases withN _{Hi} , consistent with what is found inz < 1 gas. The metallicity of gas in this column density regime has increased by a factor ∼8 from 2.2 ≲z ≲ 3.6 toz < 1, but the contribution of the$14.6\le \mathrm{log}{N}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}<19$ absorbers to the total metal budget of the universe atz < 1 is a quarter of that at 2.2 ≲z ≲ 3.6. We show that FOGGIE cosmological zoom-in simulations have a similar evolution of [X/H] withN _{Hi} , which is not observed in lower-resolution simulations. In these simulations, very metal-poor absorbers with [X/H] < − 2.4 atz ∼ 2–3 are tracers of inflows, while higher-metallicity absorbers are a mixture of inflows and outflows.

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Chastenet, Jérémy
; Sutter, Jessica
; Sandstrom, Karin
; Belfiore, Francesco
; Egorov, Oleg V.
; Larson, Kirsten L.
; Leroy, Adam K.
; Liu, Daizhong
; Rosolowsky, Erik
; Thilker, David A.
; et al
(
February 2023
, The Astrophysical Journal Letters)

Abstract We present maps tracing the fraction of dust in the form of polycyclic aromatic hydrocarbons (PAHs) in IC 5332, NGC 628, NGC 1365, and NGC 7496 from JWST/MIRI observations. We trace the PAH fraction by combining the F770W (7.7μ m) and F1130W (11.3μ m) filters to track ionized and neutral PAH emission, respectively, and comparing the PAH emission to F2100W, which traces small, hot dust grains. We find the averageR _{PAH} = (F770W + F1130W)/F2100W values of 3.3, 4.7, 5.1, and 3.6 in IC 5332, NGC 628, NGC 1365, and NGC 7496, respectively. We find that Hii regions traced by MUSE Hα show a systematically low PAH fraction. The PAH fraction remains relatively constant across other galactic environments, with slight variations. We use CO+Hi +Hα to trace the interstellar gas phase and find that the PAH fraction decreases above a value of${\mathrm{I}}_{\mathrm{H}\alpha}/{\mathrm{\Sigma}}_{\mathrm{H}\mathrm{I}+{\mathrm{H}}_{2}}\sim {10}^{37.5}\phantom{\rule{0.25em}{0ex}}\mathrm{erg}\phantom{\rule{0.25em}{0ex}}{\mathrm{s}}^{-1}\phantom{\rule{0.25em}{0ex}}{\mathrm{kpc}}^{-2}\phantom{\rule{0.25em}{0ex}}{({M}_{\odot}\phantom{\rule{0.25em}{0ex}}{\mathrm{pc}}^{-2})}^{-1}$ in all four galaxies. Radial profiles also show a decreasing PAH fraction with increasing radius, correlated with lower metallicity, in line with previous results showing a strong metallicity dependence to the PAH fraction. Our results suggest that the process of PAH destruction in ionized gas operates similarlymore » across the four targets.

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Grošelj, Daniel
; Sironi, Lorenzo
; Beloborodov, Andrei M.
(
July 2022
, The Astrophysical Journal)

Abstract We perform particle-in-cell simulations to elucidate the microphysics of relativistic weakly magnetized shocks loaded with electron-positron pairs. Various external magnetizationsσ ≲ 10^{−4} and pair-loading factorsZ _{±} ≲ 10 are studied, whereZ _{±} is the number of loaded electrons and positrons per ion. We find the following: (1) The shock becomes mediated by the ion Larmor gyration in the mean field whenσ exceeds a critical valueσ _{L} that decreases withZ _{±} . Atσ ≲σ _{L} the shock is mediated by particle scattering in the self-generated microturbulent fields, the strength and scale of which decrease withZ _{±} , leading to lowerσ _{L} . (2) The energy fraction carried by the post-shock pairs is robustly in the range between 20% and 50% of the upstream ion energy. The mean energy per post-shock electron scales as${\overline{E}}_{\mathrm{e}}\propto {\left({Z}_{\pm}+1\right)}^{-1}$ . (3) Pair loading suppresses nonthermal ion acceleration at magnetizations as low asσ ≈ 5 × 10^{−6} . The ions then become essentially thermal with mean energy${\overline{E}}_{\mathrm{i}}$ , while electrons form a nonthermal tail, extending from$E\sim {\left({Z}_{\pm}+1\right)}^{-1}{\overline{E}}_{\mathrm{i}}$ to${\overline{E}}_{\mathrm{i}}$ . Whenσ = 0, particle acceleration is enhanced by the formation of intense magnetic cavities that populate the precursor during the late stages of shock evolution. Here,more » the maximum energy of the nonthermal ions and electrons keeps growing over the duration of the simulation. Alongside the simulations, we develop theoretical estimates consistent with the numerical results. Our findings have important implications for models of early gamma-ray burst afterglows.

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

Abstract Recently, the Hydrogen Epoch of Reionization Array (HERA) has produced the experiment’s first upper limits on the power spectrum of 21 cm fluctuations atz ∼ 8 and 10. Here, we use several independent theoretical models to infer constraints on the intergalactic medium (IGM) and galaxies during the epoch of reionization from these limits. We find that the IGM must have been heated above the adiabatic-cooling threshold byz ∼ 8, independent of uncertainties about IGM ionization and the radio background. Combining HERA limits with complementary observations constrains the spin temperature of thez ∼ 8 neutral IGM to 27 K$\u3008{\overline{T}}_{S}\u3009$ 630 K (2.3 K$\u3008{\overline{T}}_{S}\u3009$ 640 K) at 68% (95%) confidence. They therefore also place a lower bound on X-ray heating, a previously unconstrained aspects of early galaxies. For example, if the cosmic microwave background dominates thez ∼ 8 radio background, the new HERA limits imply that the first galaxies produced X-rays more efficiently than local ones. Thez ∼ 10 limits require even earlier heating if dark-matter interactions cool the hydrogen gas. If an extra radio background is produced by galaxies, we rule out (at 95% confidence) the combination of high radio and low X-raymore » luminosities ofL _{r,ν} /SFR > 4 × 10^{24} W Hz^{−1} ${M}_{\odot}^{-1}$ yr andL _{X} /SFR < 7.6 × 10^{39} erg s^{−1} ${M}_{\odot}^{-1}$ yr. The new HERA upper limits neither support nor disfavor a cosmological interpretation of the recent Experiment to Detect the Global EOR Signature (EDGES) measurement. The framework described here provides a foundation for the interpretation of future HERA results.

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