arXiv subjects

J. Schaye

Publications and source records attributed to J. Schaye.

At least 19 recordsLinked to original sources

arXiv2026

J-PAS & FLAMINGO: Cosmic voids and void galaxies in the gravitational landscape of photometric surveys

Photometric surveys offer a powerful way to map the large-scale structure of the Universe, but their redshift errors complicate the identification of cosmic voids, challenging studies of their environmental effect on galaxy properties. We present an approach to robustly identify dynamically relevant voids and void galaxies in galaxy mocks of the Javalambre Physics of the Accelerating Universe Astrophysical Survey (J-PAS), testing whether known trends in void galaxy properties survive photometric redshift errors. Using FLAMINGO mocks at z = 0.3 and mi < 20, we compare a FLAMINGO-based ideal (FBI) mock to a FLAMINGO-based JP mock with J-PAS-like redshift errors. We mitigate redshift errors using a quasi-gravitational potential field in the two galaxy mocks. We apply a watershed algorithm to the thresholded quasi-potential field to identify dynamically dominant voids, and define massive void galaxies alongside a comparison sample in high-density regions. Photometric errors lead to a slightly lower void abundance and a marginal shift toward larger, less spherical voids, but overall size and ellipticity distributions agree well between mocks. Their main impact is contamination of void interiors in the JP density profiles by galaxies scattered from high-density regions. We recover a reasonable number of FBI sample voids in the JP sample, with excellent size and shape agreement, occupying ~63% of the thresholded quasi-potential volume. In both mocks, void galaxies show lower stellar masses, bluer colours, and enhanced star formation relative to equal-mass galaxies in high-density regions. These results suggest a quasi-potential can mitigate redshift errors at the level expected for J-PAS, enabling identification of reliable, dynamically dominant voids that are less sensitive to small-scale noise. The massive void galaxy population shows the expected trends relative to high-density environments.

astro-ph.CO↗

arXiv2026

Bound or blown: the fate of hot gas in galaxy groups

The impact of AGN feedback on the hot gas content of galaxy groups remains a key uncertainty in galaxy formation and its connection to the large scale structure of the Universe. We aim to compare the XMM-Newton Group AGN Project (X-GAP) sample to the hydrodynamical FLAMINGO simulations, which span a wide range of AGN feedback prescriptions. We construct X-GAP analogues by forward-modelling the full selection function, including detection and observational systematics, and generate end-to-end XMM-Newton mock observations analysed consistently with the data. We study multiple observables, including the L--T and Mgas--T relations, number of groups, mean temperature, and velocity dispersion, accounting for their covariance. The forward model accurately recovers input luminosities, gas masses, and core-excised temperatures for regular systems, enabling direct comparison in observable space. The normalisation of the scaling relations is the best discriminator between feedback models, while cosmic variance introduces > 20% fluctuations in the number of detected systems, making counts alone a weak discriminator. Models with intermediate feedback strength provide the best agreement with X-GAP, with the fgas-2sigma model yielding the lowest tension of only 0.8sigma, while the most extreme feedback scenario (fgas-8sigma) is ruled out at > 4sigma. Our results indicate that the thermodynamic properties of galaxy groups favour feedback stronger than the fiducial FLAMINGO calibration, but disfavour the most ejective models. This highlights the importance of combining forward modelling and multi-observable constraints to probe the fate of hot baryons in low-mass haloes.

astro-ph.CO↗

arXiv2026

Euclid: Scaled-up little red dots and other sources with v-shaped spectral energy distributions at z>4

Little Red Dots (LRDs) are some the most intriguing galaxy populations recently identified at z>~4 with JWST. They constitute the most extreme class of a more abundant population of sources with `V-shaped' spectral energy distributions (SEDs) and compact morphologies, which includes also Little Blue Dots (LBDs). Finding brighter analogues to these sources requires surveying sky areas which are significantly larger than those covered with JWST. Euclid deep images are ideally suited for this purpose. We make use of Euclid near-infrared images, complemented by Spitzer Infrared Array Camera (IRAC) data, over 0.75 sq. deg. of the COSMOS field to select a sample of 233 sources with `V-shaped' SEDs at z>4. Out of those, we identify 16 sources with compactness >1sigma above the median of all z>4 galaxies, which we consider robust LRD/LBD candidates in our sample. The stellar masses of these 16 sources are in the range 10^{8.5} - 10^{10.5} Msun, so they are significantly more massive than typical JWST-selected LRDs/LBDs. Interestingly, half of them are about as old as the Universe at their redshifts. In addition, we find that the median photometric properties of the Euclid LRDs/LBDs are similar to those of the so-called Blue Dust-Obscured Galaxies (Blue DOGs). Less than 10% of all our `V-shaped' SED sources, including only one of the Euclid LBDs, correspond to known AGN. The latter mostly constitute a population disjoint to the `V-shaped' SED sources. Spectroscopic follow up of the Euclid LRDs/LBD candidates remains necessary to probe whether they host BLAGN as fainter analogues do and whether constitute a transition phase from these fainter sources to standard AGN.

astro-ph.GA↗

arXiv2026

Resolving circumgalactic gas flows around a z$\approx$3.6 quasar using MUSE and ALMA

The formation and evolution of galaxies is regulated by the exchange of gas with the surrounding large-scale structures on circum- and intergalactic scales. Yet, little is known about the complex processes shaping the cycle of baryons in and out of galaxies. In this work, we present a multiline study of the gas surrounding a $z\approx3.66$ quasar known to host one of the brightest Ly$\alpha$ nebulae at high redshift, MUSE Quasar Nebula 04 (MQN04). By combining a high-resolution MUSE detection of non-resonant HeII emission with a precise measurement of the redshift of the quasar host via the ALMA CO(4-3) line, we study the kinematics of the cool ionized gas down to $\approx1\rm\,kpc$ from the quasar. The MUSE observations reveal complex clumpy structures as well as diffuse emission extended over $\approx100\,{\rm kpc}$ and blueshifted by $\approx 0-800\,{\rm km\,s^{-1}}$ relative to the quasar systemic redshift, suggesting that the circumgalactic medium is highly asymmetric. The analysis of the HeII/Ly$\alpha$ line ratio, and the presence of a low-column density ($\approx10^{14.6}~\rm cm^{-2}$) HI absorber along the quasar sightline suggests that MQN04 resides in a highly ionized medium. This is also supported by the gas kinematics, which, except in the most central region, shows consistent velocity shifts across the different tracers, indicative of relatively weak radiative transfer effects. Based on its morphology and kinematics, we conclude that the extended HeII emission may arise from merger-driven tidal stripping or inflows of gas illuminated by the quasar radiation. On comoving megaparsec scales, we discover a large concentration ($\delta\approx41$) of star-forming galaxies lying within $|\Delta v_{\rm QSO}| \leq1000\rm\,km\,s^{-1}$ from the quasar. MQN04 is therefore one of the most overdense environments discovered at this epoch.

astro-ph.GA↗

arXiv2026

Impact and interplay of $\Lambda$CDM analysis choices for LSST cosmic shear

We forecast cosmological parameter constraints for a cosmic shear analysis of the Rubin Observatory Legacy Survey of Space and Time (LSST), defining an analysis framework that can accurately recover the $\Lambda$CDM model in the presence of astrophysical and data-related systematics. When accounting for our present uncertainty on the suppression of the non-linear matter power spectrum through baryon feedback, we find that the error on the composite parameter $S_8=\sigma_8\sqrt{\Omega_{\rm m}/0.3}$ almost doubles compared to an LSST analysis which neglects this astrophysical phenomenon. After the first year of observations, LSST will extend beyond the magnitude limit of existing representative spectroscopic calibration samples, requiring photometric redshifts to be calibrated using an alternative strategy. Adopting literature measurements of the reduced redshift calibration precision found from galaxy cross-correlation techniques, combined with current levels of baryon feedback uncertainty, we forecast final year LSST cosmic shear constraints that barely improve upon the first year analysis. This forecast therefore serves as encouragement to the community to develop methodology and observations to constrain models of baryon feedback and enhance photometric redshift calibration at depths where spectroscopy is unrepresentative. With tight priors on both these systematic terms, we forecast that LSST cosmic shear can deliver constraints on $S_8$ that are more than five times as constraining as existing cosmic shear surveys.

astro-ph.CO↗

arXiv2026

Intrinsic alignments in the FLAMINGO simulations with two-point statistics

Intrinsic alignments are a major astrophysical contaminant for next generation large-sky surveys like Euclid and LSST. Large hydrodynamic simulations are crucial for informing the alignment modelling for these surveys. We measure position-position and position-shape correlations of a Luminous Red Galaxy sample from the FLAMINGO suite of hydrodynamical simulations, measuring the alignment signal for more than 4.9 million galaxies at redshift 0. We jointly model the clustering and alignment correlations to provide the tightest constraints on the alignment amplitude to date from a hydrodynamic simulation. We find that both the Non-Linear Alignment (NLA) and the more complex Tidal Alignment Tidal Torquing (TATT) models provide good fits to the data. We compare the measured $A_1$ amplitude to observational data and find good agreement. We measure the dependence of the NLA and TATT free parameters on halo mass. We also introduce a mass-dependent TATT model, TATT-M, by finding empirical relations between the halo mass and the TATT parameters. This allows us to fit TATT with only one parameter, $A_1$, with $A_2/A_1$ being a constant and $A_{1\delta}/A_1$ being a function of halo mass. Using a Bayesian approach, we find that TATT-M is very strongly preferred by the data over NLA. Using the baryonic feedback variations of the FLAMINGO simulation suite, we test whether the TATT parameters are sensitive to feedback. Variations in AGN and supernova feedback do not significantly change the alignment amplitude beyond the change associated with the dependence of galaxy stellar mass on the strength of feedback. Our results inform the IA modelling for upcoming surveys by providing guidance on model choices, priors and sensitivities to feedback.

astro-ph.CO↗

arXiv2025

Euclid Quick Data Release (Q1): Identification of massive galaxy candidates at the end of the Epoch of Reionisation

Probing the presence and properties of massive galaxies at high redshift is one of the most critical tests for galaxy formation models. In this work, we search for galaxies with stellar masses M* > 10^10.25 Msun at z in [5,7], i.e., towards the end of the Epoch of Reionisation, over a total of ~23 deg^2 in two of the Euclid Quick Data Release (Q1) fields: the Euclid Deep Field North and Fornax (EDF-N and EDF-F). In addition to the Euclid photometry, we incorporate Spitzer Infrared Camera (IRAC) and ground-based optical data to perform spectral energy distribution (SED) fitting, obtaining photometric redshifts and derived physical parameters. After applying rigorous selection criteria, we identify a conservative sample of 145 candidate massive galaxies with M* > 10^10.25 Msun at z in [5,7], including 5 objects with M* > 10^11 Msun. This makes for a surface density of about 6.3 deg^-2 at z in [5,7], which should be considered a lower limit because of the current depth of the Euclid data (H_E < 24, 5 sigma in Q1). We find that the inferred stellar masses are consistent with galaxy formation models with standard star-formation efficiencies. These massive galaxies have colour excess E(B-V) values up to 0.75, indicating significant dust attenuation in some of them. In addition, half of the massive galaxies have best-fit ages comparable to the age of the Universe at those redshifts, which suggests that their progenitors were formed very early in cosmic time. About 78% of the massive galaxies lie on the star-forming main sequence (MS) in the SFR-M* plane, ~12% are found in the starburst region, and 10% in the transition zone between the MS and starbursts. We find no significant evidence for outshining or AGN contamination that could account for the elevated specific star-formation rates (sSFR) observed in the ~12% of galaxies classified as starbursts.

astro-ph.GA↗

arXiv2025

Euclid Quick Data Release (Q1). Quenching precedes bulge formation in dense environments but follows it in the field

(Abridged) The bimodality between star-forming discs and quiescent spheroids requires the existence of two main processes: the galaxy quenching and the morphological transformation. In this paper, we aim to understand the link between these processes and their relation with the stellar mass of galaxies and their local environment. Taking advantage of the first data released by the Euclid Collaboration, covering more than 60 deg2 with space-based imaging and photometry, we analyse a mass-complete sample of nearly one million galaxies in the range 0.25 10^{9.5} M_\odot$. We divide the sample into four sub-populations of galaxies, based on their star-formation activity and morphology. We then analyse the physical properties of these populations and their relative abundances in the stellar mass vs. local density plane. Together with confirming the passivity-density relation and the morphology-density relation, we find that quiescent discy galaxies are more abundant in the low-mass regime of high-density environment. At the same time, star-forming bulge-dominated galaxies are more common in field regions, preferentially at high masses. Building on these results and interpreting them through comparison with simulations, we propose a scenario where the evolution of galaxies in the field significantly differs from that in higher-density environments. The morphological transformation in the majority of field galaxies takes place before the onset of quenching and is mainly driven by secular processes taking place within the main sequence, leading to the formation of star-forming bulge-dominated galaxies as intermediate-stage galaxies. Conversely, quenching of star formation precedes morphological transformation for most galaxies in higher-density environments. This causes the formation of quiescent disc-dominated galaxies before their transition into bulge-dominated ones.

astro-ph.GA↗

arXiv2025

Euclid: An emulator for baryonic effects on the matter bispectrum

Understanding the impact of baryonic processes such as star formation and active galactic nuclei (AGN) feedback on matter clustering is crucial to ensure precise and unbiased cosmological inference. Most theoretical models of baryonic effects to date focus on two-point statistics, neglecting higher-order contributions. This work develops a fast and accurate emulator for baryonic effects on the matter bispectrum, a key non-Gaussian statistic in the nonlinear regime. We employ high-resolution $N$-body simulations from the BACCO suite and apply a combination of cutting-edge techniques such as cosmology scaling and baryonification to efficiently span a large cosmological and astrophysical parameter space. A deep neural network is trained to emulate baryonic effects on the matter bispectrum measured in simulations, capturing modifications across various scales and redshifts relevant to Euclid. We validate the emulator accuracy and robustness using an analysis of \Euclid mock data, employing predictions from the state-of-the-art FLAMINGO hydrodynamical simulations. The emulator reproduces baryonic suppression in the bispectrum to better than 2$\%$ for the $68\%$ percentile across most triangle configurations for $k \in [0.01, 20]\,\mathrm{i}h\mathrm{Mpc}^{-1}$ and ensures consistency between cosmological posteriors inferred from second- and third-order weak lensing statistics. These results demonstrate that our emulator meets the high-precision requirements of the Euclid mission for at least the first data release and provides reliable forecasts of the cosmological information contained in the small-scale matter bispectrum. This underscores the potential of emulation techniques to bridge the gap between complex baryonic physics and observational data, maximising the scientific output of Euclid.

astro-ph.CO↗

arXiv2025

Euclid Quick Data Release (Q1). A first view of the star-forming main sequence in the Euclid Deep Fields

The star-forming main sequence (SFMS) is a tight relation observed between stellar masses and star formation rates (SFR) in a population of galaxies. This relation is observed at different redshifts, in various morphological, and environmental domains, and is key to understanding the underlying relations between a galaxy budget of cold gas and its stellar content. Euclid Quick Data Release 1 (Q1) gives us the opportunity to investigate this fundamental relation in galaxy formation and evolution. We complement the Euclid release with public IRAC observations of the Euclid Deep Fields, improving the quality of recovered photometric redshifts, stellar masses, and SFRs, as is shown both with simulations and a comparison with available spectroscopic redshifts. From Q1 data alone, we recover more than $\sim 30\,\mathrm{k}$ galaxies with $\log_{10} (M_\ast/M_\odot) > 11$, giving a precise constraint of the SFMS at the high-mass end. We investigated the SFMS, in a redshift interval between $0.2$ and $3.0$, comparing our results with the existing literature and fitting them with a parameterisation taking into account the presence of a bending of the relation at the high-mass end, depending on the bending mass, $M_0$. We find good agreement with previous results in terms of $M_0$ values, and an increasing trend for the relation scatter at higher stellar masses. We also investigate the distribution of physical (e.g. dust absorption, $A_V$, and formation age) and morphological properties (e.g., Sérsic index and radius) in the SFR--stellar mass plane, and their relation with the SFMS. These results highlight the potential of Euclid in studying the fundamental scaling relations that regulate galaxy formation and evolution in anticipation of the forthcoming Data Release 1.

astro-ph.GA↗

arXiv2025

Unbiased estimates of the shapes of haloes using the positions of satellite galaxies

The shapes of dark matter haloes are sensitive to both cosmology and baryon physics, but are difficult to measure observationally. A promising way to constrain them is to use the positions of satellite galaxies as tracers of the underlying dark matter, but there are typically too few galaxies per halo for reliable shape estimates, resulting in biased shapes. We present a method to model sampling noise to correct for the shape bias. We compare our predicted median shape bias with that obtained from the FLAMINGO suite of simulations and find reasonable agreement. We check that our results are robust to resolution effects and baryonic feedback. We also explore the validity of our bias correction at various redshifts and we discuss how our method might be applied to observations in the future. We show that median projected halo axis ratios are on average biased low by 0.31 when they are traced by only 5 satellites. Using the satellite galaxies, the projected host halo axis ratio can be corrected with a residual bias of ~ 0.1, by accounting for sampling bias. Hence, about two-thirds of the projected axis ratio bias can be explained by sampling noise. This enables the statistical measurement of halo shapes at lower masses than previously possible. Our method will also allow improved estimates of halo shapes in cosmological simulations using fewer particles than currently required.

astro-ph.CO↗

arXiv2025

MusE GAs FLOw and Wind (MEGAFLOW) XII. Rationale and design of a MgII survey of the cool circum-galactic medium with MUSE and UVES: The MEGAFLOW Survey

We present the design, rationale, properties and catalogs of the MusE Gas FLOw and Wind survey (MEGAFLOW), a survey of the cool gaseous halos of $z\sim1$ galaxies using low-ionization MgII absorption systems. The survey consists of 22 quasar fields selected from the Sloan Digital Sky Survey (SDSS) having multiple ($\geq3$) strong MgII absorption lines over the redshift range $0.3 1$, i.e. more than 60 galaxies per arcmin$^{2}$. They were identified using a dual detection algorithm based on both continuum and emission line objects. The achieved [OII] 50\%\ completeness is 3.7$\times 10^{-18}$ erg/s/cm$^2$ (corresponding to SFR$>0.01$ M$_\odot$ yr$^{-1}$ at $z=1$) using realistic mock [OII] emitters and the 50\%\ completeness is $m_{F775W}\approx26$ AB magnitudes for continuum sources. We find that (i) the fraction of [OII] emitting galaxies which have no continuum is $\sim15$\%; (ii) the success rate in identifying at least one galaxy within 500 km/s and 100 kpc is $\approx90$\%\ for MgII absorptions with $W_r^{2796}\gtrsim0.5$~Å; (iii) the mean number of galaxies per MgII absorption is $2.9\pm1.6$ within the MUSE field-of-view; (iv) of the 80 MgII systems at $0.3 10^9$ M$_\odot$, and star-formation rates $>1$ M$_\odot$ yr$^{-1}$.

astro-ph.GA↗

arXiv2024

The MUSE Extremely Deep Field: Classifying the Spectral Shapes of Lya Emitting Galaxies

The Hydrogen Lyman-alpha (Lya) line shows a large variety of shapes which is caused by factors at different scales, from the interstellar medium to the intergalactic medium. This work aims to provide a systematic inventory and classification of the spectral shapes of Lya emission lines to understand the general population of high-redshift Lya emitting galaxies (LAEs). Using the data from the MUSE eXtremely Deep Field, we select 477 galaxies at z=2.8-6.6. We develop a method to classify Lya emission lines in four spectral and three spatial categories, by combining a spectral analysis with a narrow-band image analysis. We measure spectral properties, such as the peak separation and the blue-to-total flux ratio. To ensure a robust sample for statistical analysis, we define a final unbiased sample of 206 galaxies by applying thresholds for signal-to-noise ratio, peak separation, and Lya luminosity. Our analysis reveals that between 32% and 51% of the galaxies exhibit double-peaked profiles. This fraction seems to evolve dependently with the Lya luminosity, while we don't notice a severe decrease of this fraction with redshift. A large amount of these double-peaked profiles shows blue-dominated spectra, suggesting unique gas dynamics and inflow characteristics in some high-redshift galaxies. Among the double-peaked galaxies, 4% are spurious detections. Around 20% out of the 477 sources of the parent sample lie in a complex environment, meaning there are other clumps or galaxies at the same redshift within a distance of 30kpc. Our results suggest that the Lya double-peak fraction may trace the evolution of IGM attenuation, but faintest galaxies are needed to be observed at high redshift. In addition, it is crucial to obtain secure systemic redshifts for LAEs to better constrain the nature of the double-peaks.

astro-ph.GA↗

arXiv2023

Lyman Continuum Leaker Candidates at $z\sim3-4$ in the HDUV Based on a Spectroscopic Sample of MUSE LAEs

In recent years, a number of Lyman continuum (LyC) leaker candidates at intermediate redshifts have been found, providing insight into how the Universe was reionised at early cosmic times. Here we identify new LyC leaker candidates at $z\approx 3-4.5$ and compare them to objects from the literature to get an overview of the different observed escape fractions and their relation to the properties of the Lyman $α$ (Ly$α$) emission line. The aim of this work is to test indicators for LyC leakage and to improve our understanding of the kind of galaxies from which LyC radiation can escape. We use data from the Hubble Deep Ultraviolet (HDUV) legacy survey to search for LyC emission based on a sample of $\approx 2000$ Ly$α$ emitters (LAEs) detected previously in two surveys with the Multi-Unit Spectroscopic Explorer (MUSE), MUSE-Deep and MUSE-Wide. Based on their known redshifts and positions, we look for potential LyC leakage in the WFC3/UVIS F336W band of the HDUV. The escape fractions are measured and compared based on spectral energy distribution (SED) fitting performed using the CIGALE software. We add twelve objects to the sample of known LyC leaker candidates, one of which was previously known, and compare their Ly$α$ properties to their escape fractions. We find escape fractions between $\sim 20\%$ and $\sim 90\%$, assuming a high transmission in the intergalactic medium (IGM). We show a method to use the number of LyC leaker candidates we find to infer the underlying average escape fraction of galaxies, which is $\approx 12\%$. Based on their Ly$α$ properties, we conclude that LyC leakers are not very different from other high-z LAEs and suggest that most LAEs could be leaking LyC even if this can not always be detected due to the direction of emission and the transmission properties of the IGM.

astro-ph.GA↗

arXiv2023

A case study of early galaxy cluster with the Athena X-IFU

Context: Observations of the hot gas in distant clusters of galaxies, though challenging, are key to understand the role of intense galaxy activity, super-massive black hole feedback and chemical enrichment in the process of massive halos assembly. Aims: We assess the feasibility to retrieve, using X-ray hyperspectral data only, the thermodymamical hot gas properties and chemical abundances of a $z=2$ galaxy cluster of mass M500=7 x $10^{13} M_{\odot}$, extracted from the Hydrangea hydrodynamical simulation. Methods: We create mock X-ray observations of the future X-ray Integral Field Unit (X-IFU) onboard the Athena mission. By forward-modeling the measured 0.4-1 keV surface brightness, the projected gas temperature and abundance profiles, we reconstruct the three-dimensional distribution for the gas density, pressure, temperature and entropy. Results: Thanks to its large field-of-view, high throughput and exquisite spectral resolution, one X-IFU exposure lasting 100ks enables reconstructing density and pressure profiles with 20% precision out to a characteristic radius of R500, accounting for each quantity's intrinsic dispersion in the Hydrangea simulations. Reconstruction of abundance profiles requires both higher signal-to-noise ratios and specific binning schemes. We assess the enhancement brought by longer exposures and by observing the same object at later evolutionary stages ($z=1-1.5$). Conclusions: Our analysis highlights the importance of scatter in the radially binned gas properties, which induces significant effects on the observed projected quantities. The fidelity of the reconstruction of gas profiles is sensitive to the degree of gas components mixing along the line-of-sight. Future analyses should aim at involving dedicated hyper-spectral models and fitting methods that are able to grasp the complexity of such three-dimensional, multi-phase, diffuse gas structures.

astro-ph.CO↗

arXiv2023

The contribution of faint Lyman-$α$ emitters to extended Lyman-$α$ halos constrained by MUSE clustering measurements

Detections of extended Ly$α$ halos (LAHs) around Ly$α$ emitters (LAEs) have lately been reported on a regular basis, but their origin is still under investigation. Simulation studies predict that the outer regions of the extended LAHs contain a major contribution from the Ly$α$ emission of faint, individually undetected LAEs. To address this matter from an observational angle, we use halo occupation distribution (HOD) modeling to reproduce the clustering of a spectroscopic sample of 1265 LAEs at $3<z<5$ from the MUSE-Wide survey. We integrate the Ly$α$ luminosity function (LF) to estimate the background surface brightness due to discrete faint LAEs. We then extend the HOD statistics inwards towards small separations and compute the factor by which the measured Ly$α$ surface brightness (SB) is enhanced by undetected close physical neighbors. We consider various clustering scenarios for the undetected sources and compare the corresponding radial profiles. The resulting inferred Ly$α$ SB of faint LAEs ranges between $(0.4-2)\times10^{20}\;\rm{erg}\;\rm{s}^{-1}~\rm{cm}^{-2}~\rm{arcsec}^{-2}$, with a very slow radial decline outwards. Our results suggest that the outer regions of observed LAHs ($R\gtrsim50$~pkpc) could indeed contain a strong component from external (but physically associated) LAEs, possibly even be dominated by them. Only for a relatively shallow faint-end slope of the Ly$α$ LF would this contribution from clustered LAEs become unimportant. We also confirm that the observed emission from the inner regions ($R\le20-30$~pkpc) is too bright to be significantly affected by clustering. We compare our findings with predicted profiles from simulations and find good overall agreement. We outline possible future measurements to further constrain the impact of discrete undetected LAEs on observed extended LAHs.

astro-ph.GA↗

arXiv2023

A comprehensive study on the relation between the metal enrichment of ionised and atomic gas in star-forming galaxies

We study the relation between the metallicities of ionised and atomic gas in star-forming galaxies at z=0-3 using the EAGLE cosmological, hydrodynamical simulations. This is done by constructing a dense grid of sightlines through the simulated galaxies and obtaining the star formation rate- and HI column density-weighted metallicities, Z_{SFR} and Z_{HI}, for each sightline as proxies for the metallicities of ionised and atomic gas, respectively. We find Z_{SFR} > Z_{HI} for almost all sightlines, with their difference generally increasing with decreasing metallicity. The stellar masses of galaxies do not have a significant effect on this trend, but the positions of the sightlines with respect to the galaxy centres play an important role: the difference between the two metallicities decreases when moving towards the galaxy centres, and saturates to a minimum value in the central regions of galaxies, irrespective of redshift and stellar mass. This implies that the mixing of the two gas phases is most efficient in the central regions of galaxies where sightlines generally have high column densities of HI. However, a high HI column density alone doesn't guarantee a small difference between the two metallicities. In galaxy outskirts, the inefficiency of the mixing of star-forming gas with HI seems to dominate over the dilution of heavy elements in HI through mixing with the pristine gas. We find good agreement between the available observational data and the Z_{SFR}-Z_{HI} relation predicted by the EAGLE simulations. Though, observed regions with a nuclear-starburst mode of star formation appear not to follow the same relation.

astro-ph.GA↗

arXiv2023

MusE GAs FLOw and Wind (MEGAFLOW) IX. The impact of gas flows on the relations between the mass, star formation rate and metallicity of galaxies

We study the link between gas flow events and key galaxy scaling relations: the relations between star formation rate (SFR) and stellar mass (the main sequence, MS), gas metallicity and stellar mass (the mass-metallicity relation, MZR) and gas metallicity, stellar mass and SFR (the fundamental metallicity relation, FMR). Using all star-forming galaxies (SFGs) in the 22 MUSE fields of the MusE GAs FLOw and Wind (MEGAFLOW) survey, we derive the MS, MZR and FMR scaling relations for 385 SFGs with $M = 10^8 - 10^{11.5}$ $M_\odot$ at redshifts 0.35 < z < 0.85. Using the MUSE data and complementary X-Shooter spectra at 0.85 < z < 1.4, we determine the locations of 21 SFGs associated with inflowing or outflowing circumgalactic gas (i.e. with strong MgII absorption in background quasar spectra) relative to these scaling relations. Compared to a control sample of galaxies without gas flows (i.e., without MgII absorption within 70 kpc of the quasar), SFGs with inflow events (i.e., MgII absorption along the major axis) are preferentially located above the MS, while SFGs with ouflow events (i.e., MgII absorption along the minor axis) are preferentially more metal rich. Our observations support the scenario in which gas accretion increases the SFR while diluting the metal content and where circumgalactic outflows are found in more metal-rich galaxies.

astro-ph.GA↗