Intergalactic Medium Research Articles

On the Andromeda-Milky Way Future Encounter: Thrice Faster Over Time

This inquiry accurately provides an analytical solution of the orbital free-falling time for the system of galaxies Andromeda-Milky Way within a non-expanding tired-light-dominated framework. The mathematical and physical background involves a two-body problem based on the orbital dynamics in which, in the first scenario, the gravitational interaction between local galaxies dominates over the expanding space. The latter is the standard astrophysical approach undertaken by public fund-based universities all over the world. However, in the second alternative scenario, Andromeda’s blueshift has to be corrected for the apparent recession velocity provided by the photon energy loss as a result of multiple interactions between photons and crystallized electrons through the intergalactic medium provided by a Tired Light, specifically, a New Tired Light process. This leads towards a substantial temporal deviation between the classic research approach and this unconventional and independent mindset. Hence, the outcome gives out a disagreement consisting in an orbital free-falling time equal to 1.7 rather than 4.5 billion years. Accordingly, the encounter of the two main galaxies of the Local Group will occur much earlier than estimated thus far. Accordingly, this implies an urgent shift in the scientific mindset as well as a course change in the application of the boundary conditions into forthcoming computational methods.

JADES: Primaeval Lyman-α emitting galaxies reveal early sites of reionisation out to redshift z ∼ 9

Abstract Given the sensitivity of the resonant Lyman-α (Lyα) transition to absorption by neutral hydrogen, observations of Lyα emitting galaxies (LAEs) have been widely used to probe the ionising capabilities of reionisation-era galaxies and their impact on the intergalactic medium (IGM). However, prior to JWST our understanding of the contribution of fainter sources and of ionised ‘bubbles’ at earlier stages of reionisation remained uncertain. Here, we present the characterisation of three exceptionally distant LAEs at z > 8, newly discovered by JWST/NIRSpec in the JADES survey. These three similarly bright (MUV ≈ −20 mag) LAEs exhibit small Lyα velocity offsets from the systemic redshift, ΔvLy$α$ ≲ 200 km s−1, yet span a range of Lyα equivalent widths (15 Å, 31 Å, and 132 Å). The former two show moderate Lyα escape fractions ($f_\text{esc, {Ly$\alpha $}} \approx 10\%$), whereas Lyα escapes remarkably efficiently from the third ($f_\text{esc, {Ly$\alpha $}} \approx 72\%$), which moreover is very compact (half-light radius of 90 ± 10 pc). We find these LAEs are low-mass galaxies dominated by very recent, vigorous bursts of star formation accompanied by strong nebular emission from metal-poor gas. We infer the two LAEs with modest fesc, Ly$α$, one of which reveals evidence for ionisation by an active galactic nucleus, may have reasonably produced small ionised bubbles preventing complete IGM absorption of Lyα. The third, however, requires a ∼3 physicalMpc bubble, indicating faint galaxies have contributed significantly. The most distant LAEs thus continue to be powerful observational probes into the earlier stages of reionisation.

The cooler past of the intracluster medium in TNG-Cluster

Abstract The intracluster medium (ICM) today is comprised largely of hot gas with clouds of cooler gas of unknown origin and lifespan. We analyze the evolution of cool gas (temperatures ≲ 104.5 K) in the ICM of 352 galaxy clusters from the TNG-Cluster simulations, with present-day mass ∼1014.3 − 15.4 M⊙. We follow the main progenitors of these clusters over the past ∼13 billion years (since z ≲ 7) and find that, according to TNG-Cluster, the cool ICM mass increases with redshift at fixed cluster mass, implying that this cooler past of the ICM is due to more than just halo growth. The cool cluster gas at z ≲ 0.5 is mostly located in and around satellite galaxies, while at z ≳ 2 cool gas can also accrete via filaments from the intergalactic medium. Lower-mass and higher-redshift clusters are more susceptible to cooling. The cool ICM mass correlates with the number of gaseous satellites and inversely with the central supermassive black hole (SMBH) mass. The average number of gaseous satellites decreases since z = 2, correlating with the decline in the cool ICM mass over cosmic time, suggesting a link between the two. Concurrently, kinetic SMBH feedback shifts the ICM temperature distribution, decreasing the cool ICM mass inside-out. At z ≈ 0.5, the predicted Mg ii column densities are in the ballpark of recent observations, where satellites and other halos contribute significantly to the total Mg ii column density. Suggestively, a non-negligible amount of the ICM cool gas forms stars in-situ at early times, reaching ∼102 M⊙ yr−1 and an Hα surface brightness of ∼10−17 erg s−1 cm−2 arcsec−2 at z ≈ 2, detectable with Euclid and JWST.

Measurements of the thermal and ionization state of the intergalactic medium during the cosmic afternoon

Abstract We perform the first measurement of the thermal and ionization state of the intergalactic medium (IGM) across 0.9 < z < 1.5 using 301 Lyα absorption lines fitted from 12 archival HST STIS quasar spectra. We employ the machine-learning-based inference method that uses joint Doppler parameter - column density ($b-N_{{\rm {H\,{\small I}}}{}}$) distributions obtained from Lyα forest decomposition. Our results show that the H i photoionization rates, $\Gamma _{{\rm{H\,{\small I}}}{}}$, agree with recent UV background synthesis models, with $\log (\Gamma _{{\rm{H\,{\small I}}}}/\text{s}^{-1})={-11.79}^{+0.18}_{-0.15}$, ${-11.98}^{+0.09}_{-0.09}$, and ${-12.32}^{+0.10}_{-0.12}$ at z = 1.4, 1.2, and 1 respectively. We obtain the IGM temperature at the mean density, T0, and the adiabatic index, γ, as [log (T0/K), γ] = [${4.13}^{+0.12}_{-0.10}$, ${1.34}^{+0.10}_{-0.15}$], $[{3.79}^{+0.11}_{-0.11}$, ${1.70}^{+0.09}_{-0.09}]$ and $[{4.12}^{+0.15}_{-0.25}$, ${1.34}^{+0.21}_{-0.26}]$ at z = 1.4, 1.2 and 1. Our measurements of T0 at z = 1.4 and 1.2 are consistent with the trend predicted from previous z < 3 temperature measurements and theoretical expectations, where the IGM cools down after He ii reionization in the absence of any non-standard heating. However, our T0 measurement at z = 1 shows unexpectedly high IGM temperature. Given the relatively large uncertainty in these measurements, where $\sigma _{T_0} \sim 5000$ K, mostly emanating from the limited size of our dataset, we can not conclude whether the IGM cools down as expected. Lastly, we generate mock datasets to test the constraining power of future measurement with larger datasets. The results demonstrate that, with redshift pathlength Δz ∼ 2 for each redshift bin, three times the current dataset, we can constrain the T0 of IGM within 1500K, which would be sufficient to constrain the IGM thermal history at z < 1.5 conclusively.

A SPectroscopic Survey of Biased Halos In the Reionization Era (ASPIRE): JWST Supports Earlier Reionization around [O iii] Emitters

Understanding when and how reionization happened is crucial for studying the early structure formation and the properties of the first galaxies in the Universe. At z > 5.5, the observed intergalactic medium (IGM) optical depth shows a significant scatter, indicating an inhomogeneous reionization process. However, the nature of the inhomogeneous reionization remains debated. A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE) is a JWST Cycle 1 program that has spectroscopically identified >400 [O iii] emitters in 25 quasar fields at z > 6.5. Combined with deep ground-based optical spectroscopy of ASPIRE quasars, the ASPIRE program provides the current largest sample for IGM-galaxy connection studies during cosmic reionization. We present the first results of IGM effective optical depth measurements around [O iii] emitters using 14 ASPIRE quasar fields. We find the IGM transmission is tightly related to reionization era galaxies to the extent that a significant excess of Lyα transmission exists around [O iii] emitters. We measure the stacked IGM effective optical depth of IGM patches associated with [O iii] emitters and find they reach the same IGM effective optical depth at least d z ∼ 0.1 ahead of those IGM patches where no [O iii] emitters are detected, supporting earlier reionization around [O iii] emitters. Our results indicate an enhancement in IGM Lyα transmission around [O iii] emitters at scales beyond 25 h −1 cMpc, consistent with the predicted topology of reionization from fluctuating UV background models.

Fast Radio Bursts as Standard Candles for Cosmology

Recently, fast radio bursts (FRBs) have become a thriving field in astronomy and cosmology. Due to their extragalactic and cosmological origin, they are useful to study the cosmic expansion and the intergalactic medium (IGM). In the literature, the dispersion measure (DM) of FRB has been considered extensively. It could be used as an indirect proxy of the luminosity distance dL of FRB. The observed DM contains the contributions from the Milky Way (MW), the MW halo, IGM, and the host galaxy. Unfortunately, IGM and the host galaxy of FRB are poorly known to date, and hence the large uncertainties of DMIGM and DMhost in DM plague the FRB cosmology. Could we avoid DM in studying cosmology? Could we instead consider the luminosity distance dL directly in the FRB cosmology? We are interested to find a way out for this problem in the present work. From the lessons of calibrating type Ia supernovae (SNIa) or long gamma-ray bursts (GRBs) as standard candles, we consider a universal subclassification scheme for FRBs, and there are some empirical relations for them. In the present work, we propose to calibrate type Ib FRBs as standard candles by using a tight empirical relation without DM. The calibrated type Ib FRBs at high redshifts can be used like SNIa to constrain the cosmological models. We also test the key factors affecting the calibration and the cosmological constraints. Notice that the results are speculative, since they are based on simulations for the future (instead of now). We stress that the point in the present work is just to propose a viable method and a workable pipeline using type Ib FRBs as standard candles for cosmology in the future.

The COS CGM Compendium. V. The Dichotomy of O vi Associated with Low- and High-metallicity Cool Gas at z < 1

We analyze the O vi content and kinematics for 126 H i-selected absorbers at 0.14 ≲ z ≲ 0.73 for which the metallicities of their cool photoionized phase have been determined. We separate the absorbers into 100 strong Lyα forest systems (SLFSs with 15 ≲ log N(H i) < 16.2) and 26 partial Lyman Limit systems (pLLSs with 16.2 ≤ log N(H i) ≤ 17.2). The sample is drawn from the COS CGM Compendium (CCC) and has O vi coverage in signal-to-noise ratio ≥ 8 Hubble Space Telescope/COS G130M/G160M QSO spectra, yielding a 2σ completeness level of logN (O vi) ≥ 13.6. The O vi detection rates differ substantially between low-metallicity (LM; [X/H] ≤ −1.4) and high-metallicity (HM; [X/H] > −1.4) SLFSs, with 20% and 60% detection rates, respectively. The O vi detection frequency for the HM and LM pLLSs is, however, similar at ∼60%. The SLFSs and pLLSs without detected O vi are consistent with the absorbing gas being in a single phase, while those with O vi trace multiphase gas. We show that the O vi velocity widths and column densities have different distributions in LM and HM gas. We find a strong correlation between O vi column density and metallicity. The strongest ( logN (O vi) ≳ 14) and broadest O vi absorbers are nearly always associated with HM absorbers, while weaker O vi absorbers are found in both LM and HM absorbers. From comparisons with galaxy-selected and blind O vi surveys, we conclude absorbers with logN (O vi) ≳ 14 most likely arise in the CGM of star-forming galaxies. Absorbers with weak O vi likely trace the extended CGM or intergalactic medium, while those without O vi likely originate in the intergalactic medium.

Osaka Feedback Model. III. Cosmological Simulation CROCODILE

We introduce our new cosmological simulation data set CROCODILE, executed using the GADGET4-Osaka smoothed particle hydrodynamics code. This simulation incorporates an updated supernova (SN) feedback model of Y. Oku et al. and an active galactic nuclei (AGN) feedback model. A key innovation in our SN feedback model is the integration of a metallicity- and redshift-dependent, top-heavy initial mass function. Our SN model introduces a new consideration that results in an order of magnitude difference in the energy injection rate per unit stellar mass formed at high redshift. The CROCODILE data set is comprehensive, encompassing a variety of runs with diverse feedback parameters. This allows for an in-depth exploration of the relative impacts of different feedback processes in galactic evolution. Our initial comparisons with observational data, spanning the galaxy stellar mass function, the star formation main sequence, and the mass–metallicity relation, show promising agreement, especially for the Fiducial run. These results establish a solid foundation for our future work. We find that SN feedback is a key driver in the chemical enrichment of the intergalactic medium (IGM). Additionally, the AGN feedback creates metal-rich, bipolar outflows that extend and enrich the circumgalactic medium and IGM over a few Mpc scales.

QSO MUSEUM

Extended Lyα emission is routinely found around single quasars across cosmic time. However, few studies have investigated how such emission changes in fields with physically associated quasar pairs, which should reside in dense environments and are predicted to be linked through intergalactic filaments. We present VLT/MUSE snapshot observations (45 minutes/source) to unveil extended Lyα emission on scales of the circumgalactic medium (CGM) around the largest sample of physically associated quasar pairs to date, encompassing eight pairs (14 observed quasars) at z ∼ 3 with an i-band magnitude between 18 and 22.75, corresponding to absolute magnitudes Mi(z = 2) between −29.6 and −24.9. The pairs are either at close (∼50–100 kpc, five pairs) or wide (∼450–500 kpc, three pairs) angular separation and have velocity differences of Δv ≤ 2000 km s−1. We detected extended emission around 12 of the 14 targeted quasars and investigated the luminosity, size, kinematics, and morphology of these Lyα nebulae. On average, they span about 90 kpc and are 2.8 × 1043 erg s−1 bright. Irrespective of the quasars’ projected distance, the nebulae often (∼45%) extend toward the other quasar in the pair, leading to asymmetric emission whose flux-weighted centroid is at an offset position from any quasar location. We show that large nebulae are preferentially aligned with the large-scale structure, as traced by the direction between the two quasars, and conclude that the cool gas (104 K) in the CGM traces well the direction of cosmic web filaments. Additionally, the radial profile of the Lyα surface brightness around quasar pairs can be described by a power law with a shallower slope (∼−1.6) with respect to single quasars (∼−2), indicative of increased CGM densities out to large radii and/or an enhanced contribution from the intergalactic medium (IGM) due to the dense environments expected around quasar pairs. The sample presented in this study contains excellent targets for ultra-deep observations to directly study filamentary IGM structures in emission. This work demonstrates that a large snapshot survey of quasar pairs will pave the way to direct statistical study of the IGM.

The twisted jets and magnetic fields of the extended radio galaxy 4C 70.19

Context. The appearance of the jets and lobes of some radio galaxies makes it difficult to assign them to a known class of objects. This is often due to the activity of the central engine and/or interactions with the environment, as well as projection effects. Aims. We analyse the radio data for an apparently asymmetric radio source 4C 70.19, which is associated with the giant elliptical galaxy NGC 6048. The source shows distorted radio jets and lobes, one of which bends by 180°. The aim of our study is to explain the nature of the observed distortions. Methods. We used LOFAR, Effelsberg, and VLA radio data in a wide range of frequencies. At high frequencies, we also used radio polarimetry to study the properties of the magnetic fields. Additionally, we made use of optical, infra-red, and X-ray data. Results. Polarisation data suggest shearing of the magnetic fields at points where the jets bend. The low-frequency LOFAR map at 145 MHz, as well as the sensitive single-dish Effelsberg map at 8.35 GHz, reveal previously undetected diffuse emission around the source. The rotation measure (RM) derived from the polarimetric data allowed us to estimate the density of the medium surrounding the source, which agrees with typical densities of the intergalactic medium or the outer parts of insterstellar halos. Conclusions. We propose that the southern jet is bent in the same manner as the northern one, but that it is inclined to the sky plane. Both these bends are likely caused by the orbital motion within the galaxy group, as well as interactions with the intergalactic medium. Our analyses suggest that, despite its complex morphology, 4C 70.19 seems to be intrinsically symmetric with a physical extent of up to 600 kpc, and that the diffuse emission detected in our high-sensitivity maps is related to radio plumes that are expanding behind the source.

Spectral reconstruction for radiation hydrodynamic simulations of galaxy evolution

Radiation from stars and active galactic nuclei (AGN) plays an important role in galaxy formation and evolution, and profoundly transforms the intergalactic, circumgalactic, and interstellar medium (IGM, CGM, and ISM). On-the-fly radiative transfer (RT) has started being incorporated in cosmological simulations, but the complex evolving radiation spectra are often crudely approximated with a small number of broad bands with piece-wise constant intensity and a fixed photo-ionisation cross-section. Such a treatment is unable to capture the changes to the spectrum as light is absorbed while it propagates through a medium with non-zero opacity. This can lead to large errors in photo-ionisation and heating rates. In this work we present a novel approach of discretising the radiation field at discrete photon energies, at the edges of the typically used photo-ionising bands, in order to capture the power-law slope of the radiation field. In combination with power-law approximations for the photo-ionisation cross-sections, this model allows us to self-consistently combine radiation from sources with different spectra and accurately follow the ionisation states of primordial and metal species through time. The method is implemented in GASOLINE2 in connection with TREVR2, a fast reverse ray tracing algorithm with 𝒪(Nactive log2 N) scaling. We compare our new piece-wise power-law reconstruction to the piece-wise constant method in calculating the primordial chemistry photo-ionisation and heating rates under an evolving UV background (UVB) and stellar spectrum, and find that our method reduces errors significantly, by up to two orders of magnitude in the case of HeII ionisation. We apply our new spectral reconstruction method in RT post-processing of a cosmological zoom-in simulation, MUGS2 g1536, including radiation from stars and a live UVB, and find a significant increase in total neutral hydrogen (HI) mass in the ISM and the CGM due to shielding of the UVB and a low escape fraction of the stellar radiation. This demonstrates the importance of RT and an accurate spectral approximation in simulating the CGM-galaxy ecosystem.

JWST/NIRSpec Observations of Lyman α Emission in Star-forming Galaxies at 6.5 ≲ z ≲ 13

We present an analysis of JWST Lyα spectroscopy of z ≳ 6.5 galaxies, using observations in the public archive covering galaxies in four independent fields: Great Observatories Origins Deep Survey (GOODS)-N, GOODS-S, A2744, and the Extended Groth Strip (EGS). We measure the Lyα emission line properties for a sample of 210 z ≃ 6.5–13 galaxies, with redshifts confirmed independently of Lyα in all cases. We present three new detections of Lyα emission in JWST spectra, including a large equivalent width (EW; =143 Å) Lyα emitter (LAE) with strong C iv emission (EW = 21 Å) at z = 7.1 in GOODS-N. We measure the redshift-dependent Lyα EW distribution across our sample. We find that strong Lyα emission (EW > 25 Å) becomes increasingly rare at earlier epochs, suggesting that the transmission of Lyα photons decreases by 4× between z ≃ 5 and z ≃ 9. We describe potential implications for the intergalactic medium neutral fraction. There is significant field-to-field variance in the LAE fraction. In contrast to the three other fields, the EGS shows no evidence for reduced transmission of Lyα photons at z ≃ 7–8, suggesting a significantly ionized sight line may be present in the field. We use available NIRCam grism observations from the First Reionization Epoch Spectroscopically Complete Observations survey to characterize overdensities on large scales around known LAEs in the GOODS fields. The strongest overdensities appear linked with extremely strong Lyα detections (EW > 50 Å) in most cases. Future Lyα spectroscopy with JWST has the potential to constrain the size of ionized regions around early galaxy overdensities, providing a new probe of the reionization process.

Evidence of Extreme Ionization Conditions and Low Metallicity in GHZ2/GLASS-Z12 from a Combined Analysis of NIRSpec and MIRI Observations

GHZ2/GLASS-z12, one of the most distant galaxies found in JWST observations, has been recently observed with both the NIRSpec and MIRI spectrographs, establishing a spectroscopic redshift z spec = 12.34 and making it the first system at z > 10 with complete spectroscopic coverage from rest-frame UV to optical wavelengths. This galaxy is identified as a strong C iv λ1549 emitter (EW = 46 Å) with many other detected emission lines, such as N iv] λ1488, He ii λ1640, O iii] λ λ1661,1666, N iii] λ1750, C iii] λ λ1907,1909, [O ii] λ λ3726,3729, [Ne iii] λ3869, [O iii] λ λ4959,5007, and Hα, including a remarkable detection of the O iii Bowen fluorescence line at rest frame λ = 3133 Å. We analyze in this paper the joint NIRSpec + MIRI spectral data set. Combining six optical strong-line diagnostics (namely R2, R3, R23, O32, Ne3O2, and Ne3O2Hd), we find extreme-ionization conditions, with log10 ([O III] λ λ4959,5007/[O II] λ λ3726,3729) = 1.39 ± 0.19 and log10 ([Ne III] λ3869/[O II] λ λ3726,3729) = 0.37 ± 0.18 in stark excess compared to typical values in the interstellar medium (ISM) at lower redshifts. These line properties are compatible either with an active galactic nucleus (AGN) or with a compact, very dense star-forming environment (ΣSFR ≃ 102–103 M ⊙ yr−1 kpc−2 and ΣM* ≃ 104–105 M ⊙ pc−2), with a high ionization parameter (log10(U) =−1.75 ± 0.16), a high ionizing photon production efficiency log(ξion)=25.7−0.1+0.3 , and a low gas-phase metallicity (also confirmed by the direct, T e method) ranging between 4% and 11% Z ⊙, indicating a rapid chemical enrichment of the ISM in the past few megayears. These properties also suggest that a substantial amount of ionizing photons (∼10%) are leaking outside of GHZ2 and starting to reionize the surrounding intergalactic medium, possibly due to strong radiation-driven winds. The general lessons learned from GHZ2 are the following: (i) the UV-to-optical combined nebular indicators are broadly in agreement with UV-only or optical-only indicators; (ii) UV+optical diagnostics fail to discriminate between an AGN and star formation in a low-metallicity, high-density, and extreme-ionization environment; and (iii) comparing the nebular line ratios with local analogs may be approaching its limits at z ≳ 10, as this approach is potentially challenged by the unique conditions of star formation experienced by galaxies at these extreme redshifts.

On the Physical Nature of Lyα Transmission Spikes in High-redshift Quasar Spectra

We investigate Lyman-alpha (Lyα) transmission spikes at 5.2 < z < 6.8 using synthetic quasar spectra from the “Cosmic Reionization on Computers” simulations. We focus on understanding the relationship between these spikes and the properties of the intergalactic medium (IGM). Disentangling the complex interplay between IGM physics and the influence of galaxies on the generation of these spikes presents a significant challenge. To address this, we employ Explainable Boosting machines, an interpretable machine learning algorithm, to quantify the relative impact of various IGM properties on the Lyα flux. Our findings reveal that gas density is the primary factor influencing absorption strength, followed by the intensity of background radiation and the temperature of the IGM. Ionizing radiation from local sources (i.e., galaxies) appears to have a minimal effect on Lyα flux. The simulations show that transmission spikes predominantly occur in regions of low gas density. Our results challenge recent observational studies suggesting the origin of these spikes in regions with enhanced radiation. We demonstrate that Lyα transmission spikes are largely a product of the large-scale structure, of which galaxies are biased tracers.

The Metallicity Dilution in Local Massive Early-type Galaxies

We derive a sample of 114 Baldwin–Phillips–Terlevich-diagram star-forming and Wide-field Infrared Survey Explorer (WISE) low-star-formation-rate early-type galaxies (ETGs) by utilizing the criterion W2 − W3 < 2.5 (where W2 and W3 are the wavelengths of 4.6 and 12 μm in the WISE four bands) and cross matching the Galaxy Zoo 1 and the catalog of the Sloan Digital Sky Survey (SDSS) Data Release 7 Max Planck Institute for Astrophysics-Johns Hopkins University emission-line measurements. We find that ∼28% of our ETGs exhibit a metallicity that is at least 2 standard deviation (0.26 dex) below the mass–metallicity (MZ) relation of star-forming galaxies (SFGs) from the SDSS. We demonstrate that almost all of our ETGs locate below the “main sequence” of SFGs. We find that these ETGs with larger metallicity deviation from the MZ relation tend to have lower SFR and redder color. By exploring the dilution properties of these massive ETGs, we report that the dilution effect may be mainly attributed to the inflow of metal-poor gas from mergers/interaction or the intergalactic medium.

The JWST-PRIMAL archival survey. A JWST/NIRSpec reference sample for the physical properties and Lyman-alpha absorption and emission of ~ 600 galaxies at z = 5:0 - 13:4

One of the surprising early findings with has been the discovery of a strong ``roll-over'' or a softening of the absorption edge of in a large number of galaxies at \(z 6\), in addition to systematic offsets from photometric redshift estimates and fundamental galaxy scaling relations. This has been interpreted as strong cumulative damped absorption (DLA) wings from high column densities of neutral atomic hydrogen ( signifying major gas accretion events in the formation of these galaxies. To explore this new phenomenon systematically, we assembled the PRImordial gas Mass AssembLy (PRIMAL) legacy survey of 584 galaxies at $z=5.0-13.4$, designed to study the physical properties and gas in and around galaxies during the reionization epoch. We characterized this benchmark sample in full and spectroscopically derived the galaxy redshifts, metallicities, star formation rates, and ultraviolet (UV) slopes. We defined a new diagnostic, the damping parameter to measure and quantify the net effect of emission strength, the fraction in the intergalactic medium, or the local column density for each source. The survey is based on the spectroscopic DAWN Archive (DJA-Spec). We describe DJA-Spec in this paper, detailing the reduction methods, the post-processing steps, and basic analysis tools. All the software, reduced spectra, and spectroscopically derived quantities and catalogs are made publicly available in dedicated repositories. We find that the fraction of galaxies showing strong integrated DLAs with $N_ HI $ only increases slightly from $ 60&lt;!PCT!&gt;$ at $z 6$ up to $ 65-90&lt;!PCT!&gt;$ at $z&gt;8$. Similarly, the prevalence and prominence of emission is found to increase with decreasing redshift, in qualitative agreement with previous observational results. Strong emitters (LAEs) are predominantly found to be associated with low-metallicity and UV faint galaxies. By contrast, strong DLAs are observed in galaxies with a variety of intrinsic physical properties, but predominantly at high redshifts and low metallicities. Our results indicate that strong DLAs likely reflect a particular early assembly phase of reionization-era galaxies, at which point they are largely dominated by pristine gas accretion. At $z=8-10$, this gas gradually cools and forms into stars that ionize their local surroundings, forming large ionized bubbles and producing strong observed emission at $z&lt;8$.

Impact of the Epoch of Reionization sources on the 21-cm bispectrum

The morphology of the 21-cm signal emitted by the neutral hydrogen present in the intergalactic medium (IGM) during the Epoch of Reionization (EoR) depends both on the properties of the sources of ionizing radiation and on the underlying physical processes within the IGM. Variation in the morphology of the IGM 21-cm signal due to the different sources of the EoR is expected to have a significant impact on the 21-cm bispectrum, which is one of the crucial observable statistics that can evaluate the non-Gaussianity present in the signal and which can be estimated from radio interferometric observations of the EoR. Here we present the 21-cm bispectrum for different reionization scenarios assuming different simulated models for the sources of reionization. We also demonstrate how well the 21-cm bispectrum can distinguish between different IGM 21-cm signal morphologies, arising due to the differences in the reionization scenarios, which will help us shed light on the nature of the sources of ionizing photons. Our estimated large-scale bispectrum for all unique k-triangle shapes shows a significant difference in the magnitude and sign across different reionization scenarios. Additionally, our focused analysis of bispectrum for a few specific k-triangle shapes (e.g. squeezed-limit, linear, and shapes in the vicinity of the squeezed-limit) shows that the large scale 21-cm bispectrum can distinguish between reionization scenarios that show inside-out, outside-in and a combination of inside-out and outside-in morphologies. These results highlight the potential of using the 21-cm bispectrum for constraining different reionization scenarios.

Charting the Lyman-α escape fraction in the range 2.9 &lt; z &lt; 6.7 and consequences for the LAE reionisation contribution

Context. The escape of Lyman-α photons at redshifts greater than two is an ongoing subject of study and an important quantity to further understanding of Lyman-α emitters (LAEs), the transmission of Lyman-α photons through the interstellar medium and intergalactic medium, and the impact these LAEs have on cosmic reionisation. Aims. This study aims to assess the Lyman-α escape fraction, fesc, Lyα, over the redshift range 2.9 &lt; z &lt; 6.7, focusing on Very Large Telescope/Multi Unit Spectroscopic Explorer (VLT/MUSE) selected, gravitationally lensed, intrinsically faint LAEs. These galaxies are of particular interest as the potential drivers of cosmic reionisation. Methods. We assessed fesc, Lyα in two ways: through an individual study of 96 LAEs behind the A2744 lensing cluster, with James Webb Space Telescope/Near-Infrared Camera (JWST/NIRCam) and HST data, and through a study of the global evolution of fesc, Lyα using the state-of-the-art luminosity functions for LAEs and the UV-selected ‘parent’ population (dust-corrected). We compared these studies to those in the literature based on brighter samples. Results. We find a negligible redshift evolution of fesc, Lyα for our individual galaxies; it is likely that it was washed out by significant intrinsic scatter. We observed a more significant evolution towards higher escape fractions with decreasing UV magnitude and fit this relation. When comparing the two luminosity functions to derive fesc, Lyα in a global sense, we saw agreement with previous literature when integrating the luminosity functions to a bright limit. However, when integrating using a faint limit equivalent to the observational limits of our samples, we observed enhanced values of fesc, Lyα, particularly around z ∼ 6, where fesc, Lyα becomes consistent with 100% escape. This indicates for the faint regimes we sampled that galaxies towards reionisation tend to allow very large fractions of Lyman-α photons to escape. We interpret this as evidence of a lack of any significant dust in these populations; our sample is likely dominated by young, highly star-forming chemically unevolved galaxies. Finally, we assessed the contribution of the LAE population to reionisation using our latest values for fesc, Lyα and the LAE luminosity density. The dependence on the escape fraction of Lyman continuum photons is strong, but for values similar to those observed recently in z ∼ 3 LAEs and high-redshift analogues, LAEs could provide all the ionising emissivity necessary for reionisation.

Comparing sampling techniques to chart parameter space of 21 cm global signal with Artificial Neural Networks

Understanding the first billion years of the universe requires studying two critical epochs: the Epoch of Reionization (EoR) and Cosmic Dawn (CD). However, due to limited data, the properties of the Intergalactic Medium (IGM) during these periods remain poorly understood, leading to a vast parameter space for the global 21cm signal. Training an Artificial Neural Network (ANN) with a narrowly defined parameter space can result in biased inferences. To mitigate this, the training dataset must be uniformly drawn from the entire parameter space to cover all possible signal realizations. However, drawing all possible realizations is computationally challenging, necessitating the sampling of a representative subset of this space. This study aims to identify optimal sampling techniques for the extensive dimensionality and volume of the 21cm signal parameter space. The optimally sampled training set will be used to train the ANN to infer from the global signal experiment. We investigate three sampling techniques: random, Latin hypercube (stratified), and Hammersley sequence (quasi-Monte Carlo) sampling, and compare their outcomes. Our findings reveal that sufficient samples must be drawn for robust and accurate ANN model training, regardless of the sampling technique employed. The required sample size depends primarily on two factors: the complexity of the data and the number of free parameters. More free parameters necessitate drawing more realizations. Among the sampling techniques utilized, we find that ANN models trained with Hammersley Sequence sampling demonstrate greater robustness compared to those trained with Latin hypercube and Random sampling.

Dispersion and rotation measures from fast radio burst (FRB) host galaxies based on the TNG50 simulation

Context. Fast radio bursts (FRBs) are poised to become important cosmological tools in the near future, as the number of observed FRBs is increasing rapidly with multiple surveys underway. A large sample of FRBs will soon have available dispersion measures (DMs) and rotation measures (RMs), which can be used to study the cosmic baryon density and the intergalactic magnetic field. However, the observed DM and RM of FRBs consists of multiple contributions that must be quantified to estimate the DM and RM of the intergalactic medium (IGM). Aims. In this paper, we estimate one such contribution to DM and RM, namely, of FRB host galaxies. We show how this contribution changes with redshift, galaxy type, and the stellar mass of the galaxies. We also investigate its dependence on galaxy inclination and on an FRB’s offset from the center of the galaxy. Methods. Using the TNG50 simulation of the IllustrisTNG project, we selected 16 500 galaxies at redshifts of 0≤ ɀ ≤2, with stellar masses in the range of 9 ≤ log(M*/M⊙) ≤ 12. In each galaxy, we calculated the DM and RM contributions of 1000 sightlines; from these, we constructed the DM and RM probability density functions (PDFs). Results. We find that the rest frame DM distributions of all galaxies at a given redshift can be fitted by a log normal function and its median and width increase as a function of redshift. The rest-frame RM distribution is symmetric, with a median RMhost,rf=0 rad m–2 and it can be fitted by a combination of a Lorentzian and two Gaussian functions. The redshift evolution of the distribution width can be fitted by a curved power law. The parameters of these functions change for different subsets of galaxies with different stellar mass, inclination, and FRB offset. These changes are due to an increasing ne with redshift, SFR, and stellar mass. We do find a more ordered B field at lower ɀ compared to higher ɀ, as suggested by the presence of more galaxies with B field reversals and B fields dominated by random B field at higher ɀ. Conclusions. We estimated the FRB host DM and RM contributions, which can be used in the future to isolate the IGM contribution from the observed DM and RM of FRBs. We predict that to constrain a σRM,IGM of 2 rad m–2 to the 95% confidence level, we would need to observe 95 000 FRBs at ɀ = 0.5, but only 9 500 FRBs at ɀ = 2.