We present a theoretical framework to derive redshift-dependent metallicity calibrations for galaxies at z=2-7. The ionization parameter (U) and gas pressure (P) in our approach are not assumed, but are predicted self-consistently. By combining the ASTRID cosmological simulation with stellar population synthesis (SPS) and MAPPINGS V photoionization modeling, we evolve young star clusters under an analytic wind-driven bubble model. This directly couples stellar feedback to the local ISM density, allowing region properties to emerge from the underlying physics rather than being treated as free parameters. The emission-line predictions are validated against observed star-formation rate indicators (deviation <0.05 dex) and the luminosity function. We derive calibrations for common optical (e.g. R23, O3N2, N2, O32) and UV (e.g. C3O3, N3O3) diagnostics. We find significant redshift evolution in these relations, driven primarily by changing ionization conditions. A Bayesian analysis quantifies calibration performance under varying signal-to-noise, enabling diagnostic recommendations as a function of redshift and data quality. The R23 calibration performs well at all redshifts with minimal error in our model, while nitrogen- and carbon-based calibrations are highly sensitive to the abundance enrichment process and should be used with caution. These results provide a practical framework for interpreting JWST spectroscopy and tracing chemical evolution from cosmic noon to the epoch of reionization.

The James Webb Space Telescope (JWST) has enabled dozens of high-z quasar host galaxy detections. Many of these observations imply galaxies with black holes that are overmassive compared to their low-z counterparts. However, the bright quasar point source removal can cause significant biases in recovered host magnitudes and stellar mass measurements due to the degeneracy in host galaxy and quasar light. We develop a statistical method to disentangle the quasar host galaxy stellar mass measurements from observational biases during the point source removal assuming the PSF is modelled perfectly. We use the BlueTides simulation to generate mock images and perform point source removal on thousands of simulated high-z quasar host galaxies, constructing corrected host magnitude posteriors. We find that removing a bright quasar in JWST photometry tends to either correctly recover or modestly misestimate host magnitudes, with a maximum magnitude underestimate of 0.2 mag. With our corrected magnitude posteriors, we perform SED fitting on each quasar host galaxy and compare the stellar mass measurement before and after the correction. We find that stellar mass estimates are generally robust, or misestimated by < 0.3 dex. We also find that the stellar masses of a subset of hosts (J0844-0132, J0911+0152, and J1146-0005) remain unconstrained, as key photometric bands provide only flux upper limits. Accounting for observational biases does not resolve the apparent mismatch between black hole and host galaxy growth at high-z, where some quasars appear to host overmassive black holes while others reside in relatively massive galaxies.

Where in the present-day Milky Way should we search for the remnants of its earliest stars? We address this question using the Dorcha (Gaelic for Dark; DUR-uh-khuh) suite: a set of 25 high-resolution, dark-matter-only cosmological zoom-in simulations of Milky Way analogue (MWA) haloes evolved to z=0. Of these, 15 are isolated and the rest are in pairs, similar to the MW and M31. By identifying and tagging the most bound material in high-redshift (z >= 5) progenitor haloes - those likely to host early star formation - we track the present-day phase-space distribution of this ancient component. We find that this material is highly centrally concentrated at z=0, with 90-100 per cent residing within r less than or similar to 15 h(-1) kpc. It exhibits steep density profiles (rho alpha r(-4)), low velocity dispersions (sigma(r) / sigma(max) less than or similar to 0.6), and radially biased orbits (beta greater than or similar to 0.5 for r greater than or similar to 0.1R(200)), consistent with a relaxed, centrally embedded population. These results hold across haloes with diverse formation histories and environments, suggesting that the dynamical signature of early progenitors is robust to later mergers and interactions. Our findings imply that the fossil record of the first generations of stars - including Population III and extremely metal-poor stars - should be sought in the innermost regions of the Milky Way, where they retain distinctive kinematic imprints. While these stellar populations may overlap, we caution that low metallicity does not uniquely identify ancient stars, nor vice versa. The Dorcha suite thus provides a physically motivated baseline for interpreting observations from Galactic Archaeology surveys targeting the bulge and inner halo.

We present four galaxy scale lenses discovered in two James Webb Space Telescope (JWST) blank-fields: the similar to 54 arcmin(2) of the PEARLS North-Ecliptic-Pole Time-Domain Field (NEP TDF) and in the similar to 90 arcmin(2) of CEERS. We perform the search by visual inspection of NIRCam photometric data, obtaining an initial list of 16 lens candidates. We down-select this list to five high-confidence lens candidates, based on lens modelling of the image configuration and photometric redshift measurements for both the source and the deflector. We compare our results to samples of lenses obtained in ground-based and space-based lens searches and theoretical expectations. We expect that JWST observations of field galaxies will yield approximately one galaxy scale lens every three to four NIRCam pointings of comparable depth to these observations ( similar to 9 arcmin(2) each). This shows that JWST, compared to other lens searches, can yield an extremely high number of secure lenses per unit area, with redshift and size distributions complementary to lens samples obtained from ground-based and wide-area surveys. We estimate that a single JWST pure-parallel survey of comparable depth could yield similar to 80 galaxy scale lenses, with a third of them having z(lens) > 1 and z(source) > 3.

We present JWST NIRSpec integral field spectroscopy observations of the z = 5.89 quasar NDWFS J1425+3254 from 0.6-5.3 mu m, covering the rest-frame ultraviolet and optical at a spectral resolution of R similar to 100. The quasar has a black hole mass of M-BH = (1.4(-1.0)(+3.1)) x 10(9) M-circle dot and an Eddington ratio of L-Bol/L-Edd = 0.3(-0.2)(+0.6), as implied from the broad Balmer H alpha and H beta lines. The quasar host has significant ongoing obscured star formation, as well as a quasar-driven outflow with velocity 6050(-630)(+460) km s(-1) and ionised outflow rate of 1650(-1230)(+130) M-circle dot yr(-1). This is possibly one of the most extreme outflows in the early Universe. The data also reveal that two companion galaxies are merging with the quasar host. The north-eastern companion galaxy is relatively old and very massive, with a luminosity-weighted stellar age of 65(-4)(+9) Myr, stellar mass of (3.6(-0.3)(+0.6))x10(11) M circle dot , and star-formation rate (SFR) of similar to 15-30 M-circle dot yr(-1). A bridge of gas connects this companion galaxy and the host, confirming their ongoing interaction. A second merger is occurring between the quasar host and a much younger companion galaxy to the south, with a stellar age of 6.7 +/- 1.8 Myr, stellar mass of (1.9 +/- 0.4)x10(10) M-circle dot, and SFR of similar to 40-65 M-circle dot yr(-1). There is also another galaxy in the field, likely in the foreground at z = 1.135, which could be gravitationally lensing the quasar with a magnification of 1 < mu < 2 and, thus, < 0.75 mag. Overall, the system is a 'train-wreck' merger of three galaxies, with star formation and extreme quasar activity that were likely triggered by these ongoing interactions.

We present [O III]/H-beta, emission-line flux ratio predictions for galaxies at z similar to 7-9 using the MAPPINGS V v5.2.0 photoionization modelling code combined with an analytic galaxy formation model. Properties such as pressure and ionization parameter that determine emission-line properties are thought to evolve towards high redshift. In order to determine the range of expected interstellar conditions we extend previous modelling of the star formation rate density (SFRD) function to calculate the metallicity and ionization parameter, and incorporate the potential impact of turbulence on the density of the interstellar medium. To validate our emission-line predictions, we calculate the [O III] line luminosity and its dependence on UV luminosity, as well as the flux ratio [O III]/H-beta, and its variation with the line luminosity, finding that both reproduce recent JWST observations from the FRESCO survey. We also use our model to predict the number counts of emission-line galaxies across a range of redshift as well as the dependence of [O III]/H-beta, on ionization parameter and metallicity. Finally, we show that the dependence of flux ratio on luminosity may provide a diagnostic of turbulent motion in galactic discs.

We investigate the detectability of Lyman-alpha(Ly alpha) emission from galaxies at the onset of cosmic reionization, aiming to understand the conditions necessary for detecting high-redshift sources like JADES-GS-z13-1-LA at z = 13. By integrating galaxy formation models with detailed intergalactic medium (IGM) reionization simulations, we construct high-redshift galaxy catalogues to model intrinsic Ly alpha profiles and assess their transmission through the IGM. For a galaxy with M-UV similar to-18.5 like JADES-GS-z13-1-LA, our fiducial model predicts a Ly alpha transmission of similar to 13 per cent and there is a probability of observing Ly alpha emission with an equivalent width > 40 angstrom of up to 10 per cent. We also explore how variations in the UV ionizing escape fraction, dependent on host halo mass or specific star formation rate, impact Ly adetectability. Our findings reveal that reionization morphology significantly influences detection chances - models where reionization is driven by low-mass galaxies can boost the detection probability to as much as 12 per cent, while those driven by massive galaxies tend to reduce ionized regions around faint emitters, limiting their detectability. Our findings remain robust when further accounting for stochastic star formation with the detection probability still spanning 3 per cent to 12 per cent. This study underscores the interplay between reionization morphology and intrinsic galaxy properties in interpreting high-redshift Ly alpha observations.

We present the discovery, and initial lensing analysis, of a high-redshift galaxy-galaxy lensing system within the JWST-PEARLS/HST-TREASUREHUNT North Ecliptic Pole Time Domain Field (designated NEPJ172238.9 + 655143.1). The lensing geometry shears a z = 3 . 6 +/- 0 . 1 star-forming galaxy into a near-Einstein ring with a radius of 0.92 arcsec, consisting of 4 images, around a foreground massive elliptical galaxy at z = 1 . 258 +/- 0 . 005. The system is fortuitously located within the NIRISS F200W footprint of the PEARLS survey, enabling spectroscopic identification of the 8500 & Aring; TiO band in the foreground galaxy and allowing tight constraints to be placed on the redshift of the background galaxy based on its continuum detection and lack of strong emission lines. We calculate magnification factors of 2 . 6 < < 8 . 4 for the four images and a total lensing mass of (4 . 08 +/- 0 . 07) x 10(11) M (R). SED fitting of the foreground elliptical galaxy within the Einstein radius reveals a stellar mass of 1 . 26 x 10(11 )M (R) under a Kroupa IMF, providing 31 percent of the estimated lensing mass. Employing simple scaling relations and assumptions, an NFW dark matter halo is found to provide the correct remaining mass within 0 . 12(-0.09)(+ 0.21) dex. However, if a modified IMF for elliptical galaxies is employed (e.g. bottom-heavy or bottom-and-top-heavy), stellar mass estimations increase and can account for the majority of the lensing mass, reducing the need for dark matter. This system further demonstrates the new discovery space that the combined wavelength coverage, sensitivity and resolution of James Webb Space Telescope (JWST) now enables.

Simulating Population (Pop.) III star formation in mini-halos in a large cosmological simulation is an extremely challenging task but it is crucial to estimate its impact on the 21cm power spectrum. In this work, we develop a framework within the semi-analytical code meraxes to estimate the radiative backgrounds from Pop. III stars needed for the computation of the 21cm signal. We computed the 21cm global signal and power spectrum for different Pop. III models varying star formation efficiency, initial mass function (IMF) and specific X-ray luminosity per unit of star formation (LX/SFR). In all the models considered, we find Pop. III stars have little to no impact on the reionization history but significantly affect the thermal state of the intergalactic medium (IGM) due to the strong injection of X-ray photons from their remnants that heat the neutral IGM at z ≥ 15. This is reflected not only on the 21cm sky-averaged global signal during the Cosmic Dawn but also on the 21cm power spectrum at z ≤ 10 where models with strong Pop. III X-ray emission have larger power than models with no or mild Pop. III X-ray emission. We estimate observational uncertainties on the power spectrum using 21cmsense and find that models where Pop. III stars have a stronger X-ray emission than Pop. II are distinguishable from models with no or mild Pop. III X-ray emission with 1000 hours observations of the upcoming SKA1-low.

The redshift and size distributions of galaxy scale strong lenses depend on the evolution of early-type galaxies (ETGs) in the redshift range 0.2<z<1. We use this dependence to constrain the velocity dispersion function (VDF) evolution from the Strong Lensing Legacy Survey (SL2S) sample of lenses. Our modeling of the lens population includes lens identifiability given survey parameters, and constrains the evolution of the VDF based on the redshift distributions of sources and lenses as well as the distribution of Einstein radii. We consider five different assumptions for the reference VDF at redshift zero and two sets of scaling relations for the VDF. We find that in all cases the observed lens sample favors a slow evolution of both the VDF normalization factor and the VDF characteristic velocity with redshift which is consistent with a VDF that is constant in redshift for z<1.

ABSTRACT The hosts of two low-luminosity high-z quasars, J2255+0251 and J2236+0032, were recently detected using JWST’s NIRCam instrument. These represent the first high-z quasar host galaxy stellar detections and open a new window into studying high-z quasars. We examine the implications of the measured properties of J2255+0251 and J2236+0032 within the context of the hydrodynamic simulation BlueTides at z = 6.5. We find that these observed quasars fall on the BlueTides stellar to black hole mass relation and have similar luminosities to the brightest simulated quasars. We predict their star formation rates, estimating approximately $10^{2-3}$${\rm M}_{\odot }\, \rm yr^{-1}$ for both quasar hosts. J2255+0251 and J2236+0032’s host galaxy radii also fall within estimates of the radii of the simulated host galaxies of similar luminosity quasars. We generate mock JWST NIRCam images of analogues to the observed quasars within BlueTides and perform a point source removal to illustrate both a qualitative and quantitative comparison of the measured and simulated radii and magnitudes. The quasar subtraction works well for similar luminosity quasars, and the recovered host images are consistent with what was observed for J2255+0251 and J2236+0032, further supporting the success of those observations. We also use our mock imaging pipeline to make predictions for the detection of J2255+0251 and J2236+0032’s hosts in upcoming JWST observations. We anticipate that the simulation analogues of future high-z quasar host discoveries will allow us to make accurate predictions of their properties beyond the capabilities of JWST.

The cosmological 21cm signal offers a potential probe of the early Universe and the first ionizing sources. Current experiments probe the spatially-dependent variance (Gaussianity) of the signal through the power spectrum (PS). The signal however is expected to be highly non-Gaussian due to the complex topology of reionization and X-ray heating. We investigate the non-Gaussianities of X-ray heating and reionization, by calculating the skew spectrum (SS) of the 21cm signal using MERAXES, which couples a semi-analytic galaxy population with semi-numerical reionization simulations. The SS is the cross-spectrum of the quadratic temperature brightness field with itself. We generate a set of seven simulations from $z = 30$ to $z = 5$, varying the halo mass threshold for hosting star-formation, the X-ray luminosity per star-formation rate, and the minimum X-ray energy escaping host galaxies. We find the SS is predominantly negative as a function of redshift, transitioning to positive towards the start of reionization, and peaking during the midpoint of reionization. We do not see a negative dip in the SS during reionization, likely due to the specifics of modelling ionization sources. We normalise the SS by the PS during reionization isolating the non-Gaussianities. We find a trough ($k\sim\,0.1\,\textrm{Mpc}^{-1}$) and peak ($k\sim\,0.4-1\,\textrm{Mpc}^{-1}$) in the normalised SS during the mid to late periods of reionization. These correlate to the ionization topology, and neutral islands in the IGM. We calculate the cosmic variance of the normalised SS, and find these features are detectable in the absence of foregrounds with the SKA_LOW.

Photometric wide-area observations in the next decade will be capable of detecting a large number of galaxy-scale strong gravitational lenses, increasing the gravitational lens sample size by orders of magnitude. To aid in forecasting and analysis of these surveys, we construct a flexible model based on observed distributions for the lens and source properties and test it on the results of past lens searches, including SL2S, SuGOHI and searches on the COSMOS HST and DES fields. We use this model to estimate the expected yields of some current and planned surveys, including Euclid Wide, Vera Rubin LSST, and Roman High Latitude Wide Area. The model proposed includes a set of free parameters to constrain on the identifiability of a lens in an image, allowing construction of prior probability distributions for different lens detection methods. The code used in this work is made publicly available.

We report evidence of galaxy assembly bias-the correlation between galaxy properties and biased secondary halo properties at fixed halo mass (M H)-in the stellar-to-halo mass relation for red central galaxies from the Sloan Digital Sky Survey. In the M H = 1011.5-1013.5 h -1 M circle dot range, central galaxy stellar mass (M *) is correlated with the number density of galaxies within 10 h -1 Mpc (delta 10), a common proxy for halo formation time. This galaxy assembly bias signal is also present when M H, M *, and delta 10 are substituted with group luminosity, galaxy luminosity, and metrics of the large-scale density field. To associate differences in delta 10 with variations in halo formation time, we fitted a model that accounts for (1) errors in the M H measured by the J. L. Tinker group catalog and (2) the level of correlation between halo formation time and M * at fixed M H. Fitting of this model yields that (1) errors in M H are similar to 0.15 dex and (2) halo formation time and M * are strongly correlated (Spearman's rank correlation coefficient similar to 0.85). At fixed M H, variations of similar to 0.4 dex in M * are associated with similar to 1-3 Gyr variations in halo formation time and galaxy formation time (from stellar population fitting). These results are indicative that halo properties other than M H can impact central galaxy assembly.

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 $L = 10 h^{-1}$ cMpc with 2048$^3$ particles resolving all dark matter halos down to the mini-halos ($\sim 10^5 M_\odot$). 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.

ABSTRACT Modeling the 21-cm global signal from the Cosmic Dawn is challenging due to the many poorly constrained physical processes that come into play. We address this problem using the semi-analytical code ‘Cosmic Archaeology Tool’ (cat). cat follows the evolution of dark matter haloes tracking their merger history and provides an ab initio description of their baryonic evolution, starting from the formation of the first (Pop III) stars and black holes (BHs) in mini-haloes at z > 20. The model is anchored to observations of galaxies and AGN at z < 6 and predicts a reionization history consistent with constraints. In this work, we compute the evolution of the mean global 21-cm signal between 4 ≤ z ≤ 40 based on the rate of formation and emission properties of stars and accreting BHs. We obtain an absorption profile with a maximum depth δTb = −95 mK at z ∼ 26.5 (54 MHz). This feature is quickly suppressed turning into an emission signal at z = 20 due to the contribution of accreting BHs that efficiently heat the intergalactic medium (IGM) at z < 27. The high-z absorption feature is caused by the early coupling between the spin and kinetic temperature of the IGM induced by Pop III star formation episodes in mini-haloes. Once we account for an additional radio background from early BHs, we are able to reproduce the timing and the depth of the EDGES signal only if we consider a smaller X-ray background from accreting BHs, but not the shape.

ABSTRACT The hyperfine 21-cm transition of neutral hydrogen from the early Universe (z > 5) is a sensitive probe of the formation and evolution of the first luminous sources. Using the Fisher matrix formalism we explore the complex and degenerate high-dimensional parameter space associated with the high-z sources of this era and forecast quantitative constraints from a future 21-cm power spectrum (21-cm PS) detection. This is achieved using $\rm {\small ERAXES}$, a coupled semi-analytic galaxy formation model and reionization simulation, applied to an N-body halo merger tree with a statistically complete population of all atomically cooled galaxies out to z ∼ 20. Our mock observation assumes a 21-cm detection spanning z ∈ [5, 24] from a 1000 h mock observation with the forthcoming Square Kilometre Array, and is calibrated with respect to ultraviolet luminosity functions (UV LFs) at z ∈ [5, 10], the optical depth of CMB photons to Thompson scattering from Planck, and various constraints on the IGM neutral fraction at z > 5. In this work, we focus on the X-ray luminosity, ionizing UV photon escape fraction, star formation, and supernova feedback of the first galaxies. We demonstrate that it is possible to recover five of the eight parameters describing these properties with better than 50 per cent precision using just the 21-cm PS. By combining with UV LFs, we are able to improve our forecast, with five of the eight parameters constrained to better than 10 per cent (and all below 50 per cent).

We give an overview and describe the rationale, methods, and first results from NIRCam images of the JWST “Prime Extragalactic Areas for Reionization and Lensing Science” (PEARLS) project. PEARLS uses up to eight NIRCam filters to survey several prime extragalactic survey areas: two fields at the North Ecliptic Pole (NEP); seven gravitationally lensing clusters; two high redshift protoclusters; and the iconic backlit VV 191 galaxy system to map its dust attenuation. PEARLS also includes NIRISS spectra for one of the NEP fields and NIRSpec spectra of two high-redshift quasars. The main goal of PEARLS is to study the epoch of galaxy assembly, active galactic nucleus (AGN) growth, and First Light. Five fields—the JWST NEP Time-Domain Field (TDF), IRAC Dark Field, and three lensing clusters—will be observed in up to four epochs over a year. The cadence and sensitivity of the imaging data are ideally suited to find faint variable objects such as weak AGN, high-redshift supernovae, and cluster caustic transits. Both NEP fields have sightlines through our Galaxy, providing significant numbers of very faint brown dwarfs whose proper motions can be studied. Observations from the first spoke in the NEP TDF are public. This paper presents our first PEARLS observations, their NIRCam data reduction and analysis, our first object catalogs, the 0.9–4.5 μ m galaxy counts and Integrated Galaxy Light. We assess the JWST sky brightness in 13 NIRCam filters, yielding our first constraints to diffuse light at 0.9–4.5 μ m. PEARLS is designed to be of lasting benefit to the community.

ABSTRACT Accuracy in the topology and statistics of a simulated epoch of reionization (EoR) are vital to draw connections between observations and physical processes. While full radiative transfer models produce the most accurate reionization models, they are highly computationally expensive, and are infeasible for the largest cosmological simulations. Instead, large simulations often include EoR models that are pre-computed via the initial density field, or post-processed where feedback effects are ignored. We introduce astrid-es, a resimulation of the astrid epoch of reionization 20 > z > 5.5 which includes an on-the-fly excursion-set reionization algorithm. astrid-es produces more accurate reionization histories without significantly impacting the computational time. This model directly utilizes the star particles produced in the simulation to calculate the EoR history and includes an ultraviolet (UV) background which heats the gas particles after their reionization. We contrast the reionization topology and statistics in astrid-es with the previously employed parametric reionization model, finding that in astrid-es, ionized regions are more correlated with galaxies, and the 21cm power spectrum shows an increase in large-scale power. We calculate the relation between the size of H ii regions and the UV luminosity of the brightest galaxy within them. Prior to the overlap phase, we find a power-law fit of log(R) = −0.314MUV − 2.550log(1 + z) + 7.408 with a standard deviation σR < 0.15 dex across all mass bins. We also examine the properties of haloes throughout reionization, finding that while the properties of haloes in the simulation are correlated with the redshift of reionization, they are not greatly affected by reionization itself.

Recent JWST observations have revealed an unexpected abundance of massive galaxy candidates in the early Universe, extending further in redshift and to lower luminosity than what had previously been found by sub-millimeter surveys. These JWST candidates have been interpreted as challenging the ΛCDM cosmology, but, so far, they have mostly relied only on rest-frame ultraviolet data and lacked spectroscopic confirmation of their redshifts. Here we report a systematic study of 36 massive dust-obscured galaxies with spectroscopic redshifts between z_ spec=5-9 from the JWST FRESCO survey. We find no tension with the ΛCDM model in our sample. However, three ultra-massive galaxies (logM_⋆/M_⊙ ≳11.0) require an exceptional fraction of 50 than even the most efficient galaxies at later epochs. The contribution from an active nucleus is unlikely because of their extended emission. Ultra-massive galaxies account for as much as 17 density at z∼5-6.