UV Background Research Articles

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.

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.

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.

What Are the Pillars of Reionization? Revising the AGN Luminosity Function at z ∼ 5

In the past, high-z active galactic nuclei (AGNs) were given a minor role as possible drivers of reionization, despite initial evidence in favor of their large space densities at low luminosities by Chandra and the Hubble Space Telescope. Recent observations from JWST are finding relatively large numbers of faint AGNs at z > 4, convincingly confirming these early results. We present a sample of z ∼ 5 AGNs, both from wide, shallow ground-based surveys and from deep, pencil-beam observations from JWST, allowing us to estimate their space densities with unprecedented accuracy. The bright end (M 1450 < −26) of the z ∼ 5 AGN luminosity function is well constrained, with a rather steep slope. The faint end (M 1450 ≥ −22) indicates a high space density, the scatter is significant, and the knee (M 1450 ∼ −24) is mostly undetermined. Comparisons with state-of-the-art models find reasonable agreement with the observed AGN luminosity function at z = 5, while the predicted space density evolution at higher redshifts appears to be too fast with respect to observational constraints. Given the large variance at the faint end, we consider different options in fitting the luminosity functions and deriving the ionizing emissivity. Even in the most conservative scenario, the photoionization rate produced by z ∼ 5 AGNs is consistent with the ultraviolet background measurements. A slow evolution of the space density of faint AGNs is observed, indicating that active SMBHs are probably producing large amounts of ionizing photons at z > 6, well into the Epoch of Reionization. This is an important indication that high-z AGNs could be major contributors to the reionization of the Universe.

A measurement of the escaping ionising efficiency of galaxies at redshift 5

The escaping ionising efficiency from galaxies, $f_ esc ion $, is a crucial ingredient for understanding their contribution to hydrogen reionisation, but both of its components, $f_ esc $ and $ ion $, are extremely difficult to measure. We measured the average escaping ionising efficiency $ esc ion of galaxies at $z=5$ implied by the mean level of ionisation in the intergalactic medium via the Lyman-alpha forest. We used the fact that $ N ion UV f_ esc ion $, the product of the ionising output and the UV density $ UV $, can be calculated from the known average strength of the UV background and the mean free path of ionising photons. These quantities, as well as $ UV $, are robustly measured at $z We calculated the missing factor of $ esc ion at $z=5$ during a convenient epoch after hydrogen reionisation had been completed and the intergalactic medium had reached ionisation equilibrium but before bright quasars began to dominate the ionising photon production. Intuitively, our constraint corresponds to the required escaping ionising production from galaxies in order to avoid over- or under-ionising the Lyman-alpha forest. We obtained a measurement of $ esc ion /$erg $ at $z=5$ when integrating the $ UV $ down to a limiting magnitude $M_ lim =-11$. Our measurement of the escaping ionising efficiency of galaxies is in rough agreement with both observations of early galaxies and with most models.

Searching for the imprints of AGN feedback on the Lyman alpha forest around luminous red galaxies

ABSTRACT We explore the potential of using the low-redshift Lyman $\alpha$ (Ly $\alpha$) forest surrounding luminous red galaxies (LRGs) as a tool to constrain active galactic nuclei (AGNs) feedback models. Our analysis is based on snapshots from the Illustris and IllustrisTNG simulations at a redshift of $z=0.1$. These simulations offer an ideal platform for studying the influence of AGN feedback on the gas surrounding galaxies, as they share the same initial conditions and underlying code but incorporate different feedback prescriptions. Both simulations show significant impacts of feedback on the temperature and density of the gas around massive haloes. Following our previous work, we adjusted the UV background in both simulations to align with the observed number density of Ly $\alpha$ lines ($\rm dN/dz$) in the intergalactic medium and study the Ly $\alpha$ forest around massive haloes hosting LRGs, at impact parameters ($r_{\perp }$) ranging from 0.1 to 100 pMpc. Our findings reveal that $\rm dN/dz$, as a function of $r_{\perp }$, is approximately 1.5 to 2 times higher in IllustrisTNG compared to Illustris up to $r_{\perp }$ of $\sim 10$ pMpc. To further assess whether existing data can effectively discern these differences, we search for archival data containing spectra of background quasars probing foreground LRGs. Through a feasibility analysis based on these data, we demonstrate that ${\rm dN/dz} (r_{\perp })$ measurements can distinguish between feedback models of IllustrisTNG and Illustris with a precision exceeding 16$\sigma$. This underscores the potential of ${\rm dN/dz} (r_{\perp })$ measurements around LRGs as a valuable benchmark observation for discriminating between different feedback models.

Damping wings in the Lyman-α forest: A model-independent measurement of the neutral fraction at 5.4 &lt; z &lt; 6.1

Context. Recent observations have positioned the end point of the Epoch of Reionization (EoR) at a redshift of z ∼ 5.3. However, observations of the Lyman-α forest have not yet been able to discern whether reionization occurred slowly and late, with substantial neutral hydrogen persisting at a redshift of ∼6, or rapidly and earlier, with the apparent late end driven by the fluctuating ultraviolet background. Gunn-Peterson (GP) absorption troughs are solid indicators that reionization is not complete until z = 5.3, but whether they contain significantly neutral gas has not yet been proven. Aims. We aim to answer this question by directly measuring, for the first time, the neutral hydrogen fraction (xHI) at the end of the EoR (5 ≲ z ≲ 6) in high-redshift quasar spectra. Methods. For high neutral fractions, xHI ≳ 0.1, GP troughs exhibit damping wing (DW) absorption extending over 1000 km s−1 beyond the troughs. While conclusively detected in Lyman-α emission lines of quasars at z ≥ 7, DWs are challenging to observe in the general Lyman-α forest due to absorption complexities and small-scale stochastic transmission features. Results. We report the first successful identification of the stochastic DW signal adjacent to GP troughs at redshifts of z = 5.6 through careful stacking of the dark gaps in the Lyman-α forest (S/N = 6.3). We use the signal to present a measurement of the corresponding global xHI = 0.19 ± 0.07 (−0.16+0.11) at 1σ (2σ) at z = 5.6 and a limit of xHI &lt; 0.44 at z = 5.9. Conclusions. The detection of this signal demonstrates the existence of substantially neutral islands near the conclusion of the EoR, unequivocally signaling a late-and-slow reionization scenario.

Radio Observations of Tidal Disruption Events Around Direct Collapse Black Holes at Cosmic Dawn

Primordial haloes immersed within intermediate Lyman-Werner (LW) UV backgrounds are theorisedto be the seeds of supermassive primordial stars (SMSs) that could be the origin of the first quasars in our universe. Only extreme levels of LW fluxes however will destroy the molecular hydrogen H2 in these haloes, resulting in much less massive stars in the early stages of our universe. This investigation considers the collapse in haloes within weaker LW background that were much more common in the primordial universe, and allowed for the survival of some H2 within these haloes. The survival of H2 along with Tvir ∼ 104 K allows the atomic cooling of H2 to begin, triggering the baryonic collapse within these haloes. These flows are predicted to result in SMSs on the order of a few × 105 M⊙ before collapsing to a DCBH due to general relativistic instabilities within their cores. The stars formed through these mechanisms could be the origin seeds of intermediate mass black holes found within dwarf galaxies today, or even create a secondary tier of less massive but still highly luminous quasars at a redshift z &gt; 7. Some of these stars form in binaries and small clusters, raising the possibility of future detections of gravitational waves from BH mergers by LISA. This investigation considers the tidal disruption events (TDEs) of lower mass Pop III stars that form within the nuclear accretion disc of these DCBHs, the potential observation of these TDE afterglows in the radio, and thesubsequent identification of their host DCBHs. We find that the radio observation of the afterglow of 15 M⊙ and 40 M⊙ TDEs due to 104 M⊙ DCBHs would be visible up to z = 20 by SKA and ngVLA.

Entrainment of hot gas into cold streams: the origin of excessive star formation rates at cosmic noon

ABSTRACT We explore the evolution of cold streams from the cosmic web that feed galaxies through their shock-heated circumgalactic medium (CGM) at cosmic noon, $z\simeq 1-5$. In addition to the hydrodynamical instabilities and radiative cooling that we have incorporated in earlier works, we embed the stream and the hot CGM in the gravitational potential of the host dark matter halo, deriving equilibrium profiles for both. Self-gravity within the stream is tentatively ignored. We find that the cold streams gradually entrain a large mass of initially hot CGM gas that cools in the mixing layer and condenses onto the stream. This entrainment, combined with the acceleration down the gravitational potential well, typically triples the inward cold inflow rate into the central galaxy, compared to the original rate at the virial radius, which makes the entrained gas the dominant source of gas supply to the galaxy. The potential sources for the hot gas to be entrained are recycled enriched gas that has been previously ejected from the galaxy, and fresh virial-shock-heated gas that has accumulated in the CGM. This can naturally elevate the star formation rate in the galaxy by a factor of $\sim 3$ compared to the gas accretion rate onto the halo, thus explaining the otherwise puzzling observed excess of star formation at cosmic noon. When accounting for self-shielding of dense gas from the ultraviolet background, we find that the energy radiated from the streams, originating predominantly from the cooling of the entrained gas, is consistent with observed Lyman-$\alpha$ blobs around galaxies.

Impact of Self-shielding Minihalos on the Lyα Forest at High Redshift

Dense gas in minihalos with masses of 106−108 M ⊙ can shield themselves from reionization for ∼100 Myr after being exposed to the UV background. These self-shielded systems, often unresolved in cosmological simulations, can introduce strong absorption in quasar spectra. This paper is the first systematic study on the impact of these systems on the Lyα forest. We first derive the H i column density profile of photoevaporating minihalos by conducting 1D radiation–hydrodynamics simulations. We utilize these results to estimate the Lyα opacity from minihalos in a large-scale simulation that cannot resolve self-shielding. When the ionization rate of the background radiation is 0.03 × 10−12 s−1, as expected near the end of reionization at z ∼ 5.5, we find that the incidence rate of damped Lyα absorbers increases by a factor of ∼2−4 compared to at z = 4.5. The Lyα flux is, on average, suppressed by ∼3% of its mean due to minihalos. The absorption features enhance the 1D power spectrum up to ∼5% at k ∼ 0.1 h Mpc−1 (or 10−3 km−1 s), which is comparable to the enhancement caused by inhomogeneous reionization. The flux is particularly suppressed in the vicinity of large halos along the line-of-sight direction at separations of up to 10 h −1 Mpc at r ⊥ ≲ 2 h −1 Mpc. However, these effects become much smaller for higher ionizing rates (≳0.3 × 10−12 s−1) expected in the post-reionization Universe. Our findings highlight the need to consider minihalo absorption when interpreting the Lyα forest at z ≳ 5.5. Moreover, the sensitivity of these quantities to the ionizing background intensity can be exploited to constrain the intensity itself.

H i Lyα Emission from a Metal-poor Cool Stream Fueling an Early Dusty Starburst

The GAMA J0913−0107 system is a rare conjunction of a submillimeter galaxy (SMG) at z ≈ 2.7 and two background QSOs with projected separations <200 kpc. Previous high-resolution QSO absorption-line spectroscopy has revealed high H i column density, extremely metal-poor (∼1% solar) gas streams in the circumgalactic medium of the SMG. Here we present deep optical integral-field spectroscopy of the system with the Keck Cosmic Web Imager (KCWI). Reaching a 2σ surface brightness limit ≈10−19 erg s−1 cm−2 arcsec−2 with ∼2 hr of integration time, we detect a filamentary Lyα nebula stretching ∼180 kpc from the SMG intercepting both QSO sightlines. This Lyα filament may correspond to the same cool gas stream penetrating through the hot halo seen in the absorption. In contrast to Lyα nebulae around QSOs, there is no obvious local source for photoionization due to the massive dust content. While uncertain, we consider the possibility that the nebula is ionized by shocks induced by the infall, obscured star formation, and/or a boosted UV background. The SMG–QSOs conjunction multiplied the efficiency of the KCWI observations, allowing a direct comparison of Lyα nebulae in two distinct environments. We find that the nebulae around the QSOs are much brighter and show steeper surface brightness profiles than the SMG nebula. This is consistent with the additional photoionization and Lyα scattering provided by the QSOs. While illustrating the challenges of detecting Lyα nebulae around SMGs, our work also demonstrates that important insights can be gained from comparative studies of high-z Lyα nebulae.

Detection of Faint Sources by the UltraViolet Imaging Telescope Onboard AstroSat Using Poisson Distribution of Background

We present an improved approach for constructing the UV source catalogs using observations from the UltraViolet Imaging Telescope (UVIT) onboard AstroSat, by considering the Poisson distribution of the UV background. The method is tested extensively using fields that are not crowded, the Small Magellanic Cloud and M31 (Field 13). The results are compared with previous studies that used UVIT observations. This approach is successful in detecting fainter sources and produces a large number of new sources (∼15% –92% more). Most of the newly discovered UV sources fall in the faint end of the source distribution (m ≳ 22). The counterparts at other wavelengths are identified for most sources. This approach is more efficient for source detection and provides an opportunity to explore new classes of UV sources.

A Fluorescent Polymer for Facile One‐Step Writing of Polychromic Hidden Information in Flexible Films

AbstractA poly(para)phenylene conjugated polymer is developed to store information via a quick and facile optical writing method. After exposure to UV light, co‐fluorescence (films with two or more written emission colors –, i.e., “double‐on”) and “on‐off” states are written into the flexible polymer films. The hidden information is invisible under ambient lighting and can only be read with an appropriate light source, optical filter, and/or magnifier, thus providing a level of security for information encoded into the films. The physical and chemical mechanisms are discussed responsible for the rapid fluorescence changes that occur under UV exposure and demonstrate microscale multi‐colored artwork and hidden QR codes written into pliable and freestanding films. Depending on the preparation, the written patterns remained easily visible and stable after exposure to water and to ambient levels of UV background radiation.

Impact of Helium ii Resonant Absorption on the Ultraviolet Background Modeled in Three Dimensions

We implement a treatment of helium ii absorption and reemission into the Technicolor Dawn cosmological simulations to study its impact on the metagalactic ultraviolet background (UVB) in three dimensions. By comparing simulations with and without He ii reprocessing, we show that it weakens the mean UVB by ∼3 dex from z = 10–5 between 3.5 and 4 Ryd, where the He ii Lyman series resonance occurs. In overdense regions, the overall UVB amplitude is higher, and the impact of He ii reprocessing is weaker, qualitatively indicating an early start to He ii reionization near galaxies. Comparing our simulations to two popular one-dimensional UV models, we find good agreement up to 3 Ryd at z = 5. At higher energies, our simulation shows significantly greater He ii absorption because it accounts for He ii arising both in diffuse regions and in Lyman limit systems. By contrast, the comparison models account only for He ii in Lyman limit systems, which are subdominant prior to the completion of He ii reionization. The H i and He ii reionization histories are nearly unaffected by He ii reprocessing, although the cosmic star formation rate density is altered by up to 4%. The cosmic mass density of C iv is reduced by ∼2 dex when He ii is accounted for, while Si iv, C ii, Mg ii, Si ii, and O i are unaffected.

Impact of astrophysical effects on the dark matter mass constraint with 21 cm intensity mapping

ABSTRACT We present an innovative approach to constraining the non-cold dark matter model using a convolutional neural network (CNN). We perform a suite of hydrodynamic simulations with varying dark matter particle masses and generate mock 21 cm radio intensity maps to trace the dark matter distribution at z = 3 in the postreionization epoch. Our proposed method complements the traditional power-spectrum analysis. We compare the results of the CNN classification between the mock maps with different dark matter masses with those from the two-dimensional power spectrum of the differential brightness temperature map of 21 cm radiation. We find that the CNN outperforms the power spectrum. Moreover, we investigate the impact of baryonic physics on the dark matter model constraint, including star formation, self-shielding of H i gas, and ultraviolet background model. We find that these effects may introduce some contamination in the dark matter constraint, but they are insignificant compared to the system noise of the SKA instruments.

Role of ionizing background and galactic feedback in the redshift space clustering of O vi absorbers in hydrodynamical simulations

ABSTRACT We explore the effect of ionizing ultraviolet background (UVB) on the redshift space clustering of low-z (z ≤ 0.5) O vi absorbers using the Sherwood simulations incorporating ‘WIND’ (i.e. outflows driven by stellar feedback)-only and ‘WIND + AGN (active galactic nucleus)’ feedback. These simulations show positive clustering signals up to a scale of 3 Mpc. We find that the effect of feedback is restricted to small scales (i.e. ≤2 Mpc or ≈200 km s−1 at z ∼ 0.3) and ‘WIND’-only simulations produce a stronger clustering signal compared to simulations incorporating ‘WIND + AGN’ feedback. How the clustering signal is affected by the assumed UVB depends on the feedback processes assumed. For the simulations considered here, the effect of the UVB is confined to even smaller scales (i.e. &amp;lt;1 Mpc or ≈100 km s−1 at z ∼ 0.3). These scales are also affected by exclusion caused by line blending. Therefore, our study suggests that clustering at intermediate scales (i.e. 1–2 Mpc for simulations considered here) together with the observed column density distribution can be used to constrain the effect of feedback in simulations.

Precise density measurements of refractory metals over 3000 K: Revisiting UV imaging technique at ultrahigh temperatures

Precise density and thermal expansion measurements of refractory materials are extremely challenging due to the chemical reactions and thermal gradients at ultrahigh temperatures. The UV image technique has been successfully applied to the density measurements at high temperatures above 3000 K. However, intense radiation from the sample can blur the edge of the sample image, leading to uncertain measurements. In this study, we investigate the influence of the contrast between the UV background light and sample radiation (B–S) on density measurements. We find that lower B–S contrast can significantly affect the calibration factor that converts image pixels to real size, resulting in underestimated density with scattering and overestimated thermal expansion coefficients at ultrahigh temperatures. This result underscores the necessity of adequate B–S contrast to ensure the precision of density measurements using UV imaging methods for refractory materials beyond 3000 K. By considering the critical minimum value of the B–S contrast, we successfully measure the densities and thermal expansion coefficients of four refractory metal liquids (tungsten, rhenium, osmium, and tantalum) with the improved UV technique, which are crucial for high-temperature industries. This work will be valuable for other imaging methods measuring the thermophysical properties at ultrahigh temperatures.

E-XQR-30: The evolution of Mg ii, C ii, and O i across 2 &amp;lt; z &amp;lt; 6

ABSTRACT Intervening metal absorbers in quasar spectra at z &amp;gt; 6 can be used as probes to study the chemical enrichment of the Universe during the Epoch of Reionization. This work presents the comoving line densities (dn/dX) of low-ionization absorbers, namely, Mg ii (2796 Å), C ii (1334 Å), and O i (1302 Å) across 2 &amp;lt; z &amp;lt; 6 using the E-XQR-30 metal absorber catalogue prepared from 42 XSHOOTER quasar spectra at 5.8 &amp;lt; z &amp;lt; 6.6. Here, we analyse 280 Mg ii (1.9 &amp;lt; z &amp;lt; 6.4), 22 C ii (5.2 &amp;lt; z &amp;lt; 6.4), and 10 O i (5.3 &amp;lt; z &amp;lt; 6.4) intervening absorbers, thereby building up on previous studies with improved sensitivity of 50 per cent completeness at an equivalent width of W &amp;gt; 0.03 Å. For the first time, we present the comoving line densities of 131 weak (W &amp;lt; 0.3 Å) intervening Mg ii absorbers at 1.9 &amp;lt; z &amp;lt; 6.4 which exhibit constant evolution with redshift similar to medium (0.3 &amp;lt; W &amp;lt; 1.0 Å) absorbers. However, the cosmic mass density of Mg ii – dominated by strong Mg ii systems – traces the evolution of global star formation history from redshift 1.9 to 5.5. E-XQR-30 also increases the absorption path-length by a factor of 50 per cent for C ii and O i whose line densities show a rising trend towards z &amp;gt; 5, in agreement with previous works. In the context of a decline in the metal enrichment of the Universe at z &amp;gt; 5, the overall evolution in the incidence rates of absorption systems can be explained by a weak – possibly soft fluctuating – ultraviolet background. Our results, thereby, provide evidence for a late reionization continuing to occur in metal-enriched and therefore, biased regions in the Universe.

A comprehensive model for the formation and evolution of the faintest Milky Way dwarf satellites

ABSTRACT In this study, we modify the semi-analytic model galacticus in order to accurately reproduce the observed properties of dwarf galaxies in the Milky Way. We find that reproducing observational determinations of the halo occupation fraction and mass–metallicity relation for dwarf galaxies requires us to include H2 cooling, an updated ultraviolet background radiation model, and to introduce a model for the metal content of the intergalactic medium. By fine-tuning various model parameters and incorporating empirical constraints, we have tailored the model to match the statistical properties of Milky Way dwarf galaxies, such as their luminosity function and size–mass relation. We have validated our modified semi-analytic framework by undertaking a comparative analysis of the resulting galaxy–halo connection. We predict a total of $300 ^{+75} _{-99}$ satellites with an absolute V-band magnitude (MV) less than 0 within 300 kpc from our Milky Way analogues. The fraction of subhaloes that host a galaxy at least this bright drops to 50 per cent by a halo peak mass of ∼8.9 × 107 M⊙, consistent with the occupation fraction inferred from the latest observations of Milky Way satellite population.

Semi-analytic modelling of Pop. III star formation and metallicity evolution - I. Impact on the UV luminosity functions at z = 9 − 16

Abstract We implemented Population III (Pop. III) star formation in mini-halos within the meraxes semi-analytic galaxy formation and reionisation model, run on top of a N-body simulation with L = 10h−1 cMpc with 20483 particles resolving all dark matter halos down to the mini-halos (∼105M⊙). Our modelling includes the chemical evolution of the IGM, with metals released through supernova-driven bubbles that expand according to the Sedov-Taylor model. We found that SN-driven metal bubbles are generally small, with radii typically of 150 ckpc at z = 6. Hence, the majority of the first galaxies are likely enriched by their own star formation. However, as reionization progresses, the feedback effects from the UV background become more pronounced, leading to a halt in star formation in low-mass galaxies, after which external chemical enrichment becomes more relevant. We explore the sensitivity of the star formation rate density and stellar mass functions on the unknown values of free parameters. We also discuss the observability of Pop. III dominated systems with JWST, finding that the inclusion of Pop. III galaxies can have a significant effect on the total UV luminosity function at z = 12 − 16. Our results support the idea that the excess of bright galaxies detected with JWST might be explained by the presence of bright top-heavy Pop. III dominated galaxies without requiring an increased star formation efficiency.