arXiv subjects

Jérémy Blaizot

Publications and source records attributed to Jérémy Blaizot.

At least 19 recordsLinked to original sources

arXiv2026

A hydrodynamical CLONE of the Virgo cluster: II. Confronting observed and synthetic galaxy population twins in a dense environment

Galaxy clusters offer powerful laboratories for studying galaxy evolution in dense environments. In this context, the Constrained LOcal and Nesting Environment (CLONE) project provides a zoom-in hydrodynamical simulation of the Virgo cluster, including active galactic nucleus and supernova feedback, with a resolution down to 350~pc, designed to mirror Virgo's observed properties. Previous work showed that this replica and Virgo share the same history, mass, and luminosity distributions including the central M87. This study examines several observational relations extending to lower stellar masses than previous synthetic-population studies: star formation density, (specific) star formation rate, metallicity, and quenched fraction of galaxies as a function of stellar mass and cluster-centric distance. Despite the slightly low metallicity and the sufficiently high quenched fraction, simulated galaxies reproduce key observational trends even without averaging or accounting for observational uncertainties, aside from the consideration of projection effects: At fixed stellar mass, cluster galaxies form fewer stars than field counterparts; Most galaxies are quenched, except for intermediate-mass or isolated galaxies; Low-mass galaxies are highly quenched, thus implying a sharp metallicity drop, and low metallicity does not imply youth; Quenching occurs earlier for the most massive and the smallest galaxies than for those of intermediate mass, at least until they enter the cluster; Quenched galaxies have undergone dark matter stripping; Gas depletion drives quenching, especially in low-mass galaxies and the farther from the cluster center they are. Overall, the synthetic population jointly reproduces multiple observational trends, making it a valuable tool to probe processes from jellyfish galaxies to cluster-core gas dynamics.[Abridged]

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arXiv2026

The SPHINX public data release. II. Using low-ionisation absorption lines and dust attenuation to predict Lyman continuum escape

Low-ionisation state (LIS) absorption lines, such as SiII 1526, are widely used to trace the properties of the interstellar medium (ISM) in galaxies. These lines provide crucial insights into galaxy evolution, including feedback mechanisms, metal enrichment, and the escape fraction of ionising photons ($f_{\rm{esc}}$). We expand our understanding of LIS absorption lines as diagnostic tools for ISM properties and $f_{\rm{esc}}$. Using the SPHINX20 cosmological radiation-hydrodynamics simulation, we generated a comprehensive synthetic dataset of LIS absorption lines and tested their predictive power for $f_{\rm{esc}}$ in star-forming galaxies. Synthetic SiII 1260 and SiII 1526 lines were computed with the radiative transfer code RASCAS, incorporating resonant scattering of photons, fluorescent emission, and interactions with dust grains. The simulated data enhance the public SPHINX20 dataset with high-resolution LIS lines for the full 1380 galaxies and ten viewing angles per galaxy. We analysed correlations between line properties, dust attenuation, and $f_{\rm{esc}}$. We also tested our predictions on observed data using the LzLCS and CLASSY surveys. We found a strong correlation between the dust-corrected residual flux of SiII 1526, $\tilde{R} \equiv \rm{R_{flux}^{1526}} \cdot 10^{-0.4A_{1500}}$, and $f_{\rm{esc}}$. We found $f_{\rm{esc}} \approx 1.041\tilde{R}^{1.887} - 0.002$, with small error bars. When we applied observational conditions, the error increased, but the escape fraction was still well recovered. We show by applying common tools for fitting the spectral energy distribution to our mock data that the inferred dust attenuation is often far from the correct value, with an underestimation of the attenuation when the effect of dust is strongest. Our results demonstrate that the residual flux of SiII 1526 is a powerful predictor of the escape fraction of ionising photons.

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arXiv2026

ARCHITECTS II: Impact of subgrid physics on the observable properties of the circumgalactic medium

Galaxy evolution is driven by star formation and stellar feedback on scales unresolved by current high-resolution cosmological simulations, requiring robust subgrid models. However, these models remain degenerate, often calibrated primarily to match observed stellar masses. To explore these degeneracies, we conduct three state-of-the-art cosmological zoom-in simulations of the same galaxy, each incorporating different subgrid models: mechanical feedback, a combination of mechanical and thermal feedback, and delayed cooling. We compare their circumgalactic media (CGM) through quasar absorption sightlines of HI, MgII, CIV, and OVI. Our findings demonstrate that despite producing galaxies with the same stellar masses, the models lead to distinct feedback modes and CGM properties. Column densities and covering fractions serve as effective diagnostics of subgrid models, with all four ions providing strong constraints as they trace diverse gas phases, exhibit complementary spatial distributions, and originate from different mechanisms. Although all simulations bracket observed column density distributions, direct comparisons are limited by scarce detections and significant scatter in absorption strengths. Covering fractions of weak absorbers provides the most robust constraints. All models fail to reproduce HI and MgII covering fractions, and delayed cooling overproduces OVI covering fractions, while the other models underproduce them. The simulation including mechanical feedback reproduces the observed CIV covering fractions well, whereas the other models show slight offsets. We argue that this discrepancy is likely driven by unresolved thermal structures for HI and MgII, and insufficient metals for CIV and OVI, arising from missing physics such as AGNs or cosmic rays.

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arXiv2026

ARCHITECTS I: Impact of subgrid physics on the simulated properties of the circumgalactic medium

Galaxy evolution is shaped by star formation and stellar feedback at scales unresolved by current high-resolution cosmological simulations. Precise subgrid models are thus necessary, and different approaches have been developed. However, they are degenerate and often primarily calibrated to reproduce stellar masses from observations. To explore these degeneracies, we perform three cosmological zoom-in radiation-hydrodynamics simulations of the same galaxy within a $5\times10^{11}\rm\ M_\odot$ dark matter halo at $z\sim1$, each with a different subgrid model: mechanical feedback, a combination of mechanical feedback and thermal feedback, and delayed cooling. We calibrate the simulations to match in stellar mass, isolating the effect of the models on the circumgalactic medium (CGM). Our findings demonstrate that despite producing galaxies with comparable stellar masses, the three models lead to distinct feedback modes, resulting in notable variations in the CGM properties. The delayed cooling run is dominated by ejective feedback and exhibits high burstiness, whereas mechanical and the hybrid models primarily feature preventive feedback, respectively acting at the galaxy and halo scales. Delayed cooling reduces the baryon mass to half the universal baryon fraction while mechanical feedback retains most baryons, with the hybrid model standing in between. Delayed cooling also ejects significantly more metals into the CGM than both other models. While for delayed cooling and mechanical feedback metals are almost evenly distributed in the CGM, they are concentrated around satellites in the hybrid model. These discrepancies emphasize the need to design an appropriate subgrid model to understand how stellar feedback regulates galaxy growth.

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arXiv2026

Radiation hydrodynamic simulation of the Haro 11 galaxy: the escape of LyC and Ly$α$ in a dwarf galaxy merger

The Haro 11 galaxy merger is the closest known Lyman Continuum (LyC) leaker and a strong Lyman-$α$ (Ly$α$) emitter, making it an important analogue of the high-$z$ galaxies that reionised the early Universe. To investigate how Haro 11's properties arise, we perform a radiation hydrodynamics simulation of the merger, and create mock observations of LyC, Ly$α$, and H$α$, from which we compute their luminosities ($L$) and escape fractions ($f_{\rm esc}$). We track these quantities along multiple sightlines as the two progenitor galaxies merge, from the first interaction until the system resembles present-day Haro 11. We find that $L$ and $f_{\rm esc}$ vary by 1-2 orders of magnitude for LyC due to sightline variations. At the two pericentre passages, the total $f_{\rm esc}^{\rm LyC}$ increases by roughly an order of magnitude. Conversely, $f_{\rm esc}^{\rm Lyα}$ shows a moderate increase at the pericentre passages, which affects the inference of LyC properties from Ly$α$. We attribute this to a displacement of the LyC-emitting stars relative to the \Lya-emitting gas, combined with an increased density from gas compression. Furthermore, $f_{\rm esc}^{\rm LyC}$ is boosted during star formation bursts, likely due to stellar feedback. As direct comparison with Haro 11, the simulation qualitatively matches its morphology and luminosities. We find that among the dense stellar knots, knot C is the main contributor to both intrinsic and escaping LyC emission. Additionally, the Ly$α$ spectra displays distinct features found in observations, implying similar gas conditions are present.

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arXiv2025

The impact of cosmic ray feedback during the epoch of reionisation

Galaxies form and evolve via a multitude of complex physics. In this work, we investigate the role of cosmic ray (CR) feedback in galaxy evolution and reionisation, by examining its impact on the escape of ionising radiation from galaxies. For this purpose, we present two Sphinx cosmological radiation-magneto-hydrodynamics simulations, allowing for the first time a study of the impact of CR feedback on thousands of resolved galaxies during the Epoch of Reionisation (EoR). The simulations differ in their feedback prescriptions: one adopts a calibrated strong supernova (SN) feedback, while the other simulation reduces the strength of SN feedback and includes CR feedback instead. We show that both comparably regulate star formation, reasonably match observations of high-redshift UV luminosity functions, and produce a similar amount of hydrogen ionising photons. In contrast to the model with strong SN feedback, the model with CRs lead to incomplete reionisation, which is in strong disagreement with observational estimates of the reionisation history. This is due to CR feedback shaping the ISM differently, filling with gas the low density cavities otherwise carved by SN explosions. As a result, this reduces the escape of ionising photons, at any halo mass, and primarily in the close vicinity of the stars. Our study indicates that CR feedback regulates galaxy growth during the EoR, but negatively affects reionisation, a tension which paves the way for further exploration and refinement of existing galaxy formation and feedback models. Such improvements are crucial in order to capture and understand the process of reionisation and the underlying evolution of galaxies through cosmic time.

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arXiv2025

Testing the AGN unified model with simulated emission lines from the circumgalactic medium (CGM)

The CGM around unobscured AGN has received much attention in recent years. Comparatively, nebulae associated with obscured AGN are less studied. Here, we simulate the Ly$α$, H$α$, and HeII nebulae around the two types of AGN at $z=2-3$ with ten massive systems from the FIRE simulations based on the unified model to show their differences and to test if they can be used to constrain the AGN model. We post-process the data with the CLOUDY and the Ly$α$ radiative transfer code, RASCAS. Overall, we find that the Ly$α$ nebulae around the unobscured AGN (type-I nebulae) and obscured AGN (type-II nebulae) do not exhibit significant differences in the luminosity, area, and HeII/Ly$α$ when the simulated cutout is set to the halo virial radius. Whereas, the type-II nebulae exhibit less symmetric morphologies, flatter surface brightness profiles, and larger emission line widths (at $R\geq 10$ kpc) than those of the type-I nebulae. These nebulae properties exhibit complicated correlations with the AGN, indicating that nebulae observations can be applied to constrain the AGN engine. However, independent observations on nebulae in the mentioned emissions are insufficient to test the unified model as a priori in observations is not possible to know the direction and opening angle of the ionization cone. We prompt that the joint observations of Ly$α$ nebulae and radio jets can help to reveal the ionization cone to probe the unified model. Our calculations suggest that this method requires $\geq 75$ type-II Ly$α$ nebulae with current instruments to reach a confidence level of $\geq 95\%$.

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arXiv2025

Jellyfish Galaxies in Magnetic Fields: Insights from Numerical Simulations

Jellyfish galaxies provide direct evidence of ram pressure stripping in cluster environments. We investigate the role of magnetic fields in the formation of jellyfish galaxies with a multiphase interstellar medium (ISM) using radiation magneto-hydrodynamic simulations. We impose magnetized (MHD) and non-magnetized (HD) winds on the gas-rich dwarf galaxies containing the magnetized or non-magnetized ISM. The MHD winds strip the disk gas more effectively than the HD winds because of the magnetic force acting against the local density gradient, which results in remarkably different ram pressure stripped features. The magnetic fields induced by the MHD winds generate a strong magnetic pressure, which forms smoothed disks and tail gas features. Since the stripped ISM in MHD wind cases travels while being nearly isolated from the intracluster medium (ICM), the stripped ISM mostly forms stars within 20~kpc of the galactic disks. In contrast, non-magnetized winds facilitate the efficient mixing of the stripped ISM with the ICM, resulting in the formation of abundant warm clouds that cool and collapse in the distant ($\sim50-100\,$kpc) tails at times of a few hundred Myr. Consequently, distant tail star formation occurs only in the HD wind runs. Finally, despite the different tail features, the star formation rates in the disk remain similar owing to the interplay between the increased gas stripping and the gas density increase in the disks of the MHD wind runs. These results suggest that the magnetized ICM may have a significant influence on jellyfish galaxies, whereas the magnetized ISM play a minor role.

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arXiv2025

MUSEQuBES: Connecting HI absorption with Ly$α$ emitters at $z \approx 3.3$

We present a comprehensive analysis of HI absorption around 96 lya emitters (LAEs) at $z\approx3.3$ (median lya luminosity $\approx10^{42}$ erg.s$^{-1}$). These LAEs were identified within 8 MUSE fields, each $1'\times1'$ on the sky and centered on a bright background quasar, as part of the MUSEQuBES survey. Using Voigt profile fitting for all HI absorbers detected within $\pm500$ km.$s^{-1}$ of these LAEs, we compiled a catalog of 800 HI absorption components. Our analysis shows that HI absorption is enhanced near the LAEs compared to the IGM. However, no trend is found between the column densities of HI absorbers and their impact parameters from the LAEs (spanning $\approx54$ to 260 pkpc). Additionally, all galaxies associated with Lyman-limit systems have impact parameters $>50$ pkpc from the quasar sightlines, suggesting that true absorber-hosts may be too faint to detect. The LAEs show an overall HI covering fraction (fc(HI)) of $\approx88\%$ for a threshold logN(HI)$=15$. Notably, at the same threshold, the pairs/group LAEs exhibit a $100\%$ HI covering fraction out to $\approx 250$ pkpc. In contrast, isolated LAEs consistently show a lower fc(HI) of $\approx80\%$. This environmental influence on fc(HI) is also evident up to $\approx 300$ km.$s^{-1}$ in differential bins of line-of-sight velocity. We find an anti-correlation between fc(HI) and the rest-frame lya-emission equivalent width (ew). Based on the lya-shell model, this could imply that gas-rich galaxies tend to reside in gas-rich environments or that the higher EW LAEs are more efficient at ionizing their surrounding medium.

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arXiv2024

A public grid of radiative transfer simulations for Lyman-alpha and metal lines in idealised galactic outflows

The vast majority of star-forming galaxies are surrounded by large reservoirs of gas ejected from the interstellar medium. Ultraviolet absorption and emission lines represent powerful diagnostics to constrain the cool phase of these outflows, through resonant transitions of hydrogen and metal ions. The interpretation of these observations is often remarkably difficult as it requires detailed modelling of the propagation of the continuum and emission lines in the gas. To this aim, we present a large public grid of about 20000 simulated spectra which includes HI Lyman-alpha (Lya) and five metal transitions associated with MgII, CII, SiII, and FeII that is accessible online at https://rascas.univ-lyon1.fr/app/idealised_models_grid/. The spectra have been computed with the RASCAS radiative transfer code for 5760 idealised spherical configurations surrounding a central point source emission, and characterised by their column density, Doppler parameter, dust opacity, wind velocity, as well as various density/velocity gradients. Designed to interpret Lya and metal line profiles, our grid exhibits a wide diversity of resonant absorption and emission features, as well as fluorescent lines. We illustrate how it can help better constrain wind properties by performing a joint modelling of observed Lya, CII, and SiII spectra. Using CLOUDY simulations and virial scaling relations, we show that Lya is expected to be a faithful tracer of the gas at T=10^4-10^5 K, even if the medium is highly-ionised. While CII is found to probe the same range of temperatures as Lya, other metal lines merely trace cooler phases (T=10^4 K). As their gas opacity strongly depends on gas temperature, incident radiation field, metallicity and dust depletion, we caution that optically thin metal lines do not necessarily originate from low HI column densities and may not accurately probe Lyman continuum leakage.

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arXiv2024

Spatially-resolved Spectroscopic Analysis of Ly$α$ Haloes: Radial Evolution of the Ly$α$ Line Profile out to 60 kpc

The extended Ly$α$ haloes (LAHs) have been found to be prevalent around high-redshift star-forming galaxies. However, the origin of the LAHs is still a subject of debate. Spatially resolved analysis of Ly$α$ profiles provides an important diagnostic. We analyse the average spatial extent and spectral variation of the circumgalactic LAHs by stacking a sample of 155 Ly$α$ emitters (LAEs) at redshift $3<z<4$ in the MUSE Extremely Deep Field. Our analysis reveals that, with respect to the Ly$α$ line of the target LAE, the peak of the Ly$α$ line at large distances becomes increasingly more blueshifted up to a projected distance of 60 kpc ($\approx 3 \times$ virial radius), with a velocity offset of $\approx$ 250 km/s. This trend is evident in both the mean and median stacks, suggesting that it is a general property of our LAE sample, which typically has a Ly$α$ luminosity $\mathrm{\approx 10^{41.1} erg\,s^{-1}}$. However, due to the absence of systemic redshift data, it remains unclear whether the Ly$α$ line peak at large projected distances is less redshifted compared to the inner regions or truly blueshifted with respect to the systemic velocity. We explore various scenarios to explain the large-scale kinematics of the Ly$α$ line.

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arXiv2024

Median Surface Brightness Profiles of Lyman-$α$ Haloes in the MUSE Extremely Deep Field

We present the median surface brightness profiles of diffuse Ly$α$ haloes (LAHs) around star-forming galaxies by stacking 155 spectroscopically confirmed Ly$α$ emitters (LAEs) at 3<z<4 in the MUSE Extremely Deep Field (MXDF), with median Ly$α$ luminosity $\mathrm{L_{Lyα} \approx 10^{41.1} erg\,s^{-1}}$. After correcting for a systematic surface brightness offset we identified in the datacube, we detect extended Ly$α$ emission out to a distance of 270 kpc. The median Ly$α$ surface brightness profile shows a power-law decrease in the inner 20 kpc, and a possible flattening trend at larger distance. This shape is similar for LAEs with different Ly$α$ luminosities, but the normalisation of the surface brightness profile increases with luminosity. At distances over 50 kpc, we observe strong overlap of adjacent LAHs, and the Ly$α$ surface brightness is dominated by the LAHs of nearby LAEs. We find no clear evidence of redshift evolution of the observed Ly$α$ profiles when comparing with samples at 4<z<5 and 5<z<6. Our results are consistent with a scenario in which the inner 20 kpc of the LAH is powered by star formation in the central galaxy, while the LAH beyond a radius of 50 kpc is dominated by photons from surrounding galaxies.

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arXiv2024

The Effect of Cosmic Rays on the Observational Properties of the CGM

The circumgalactic medium (CGM) contains information on the cumulative effect of galactic outflows over time, generally thought to be caused by feedback from star formation and active galactic nuclei. Observations of such outflows via absorption in CGM gas of quasar sightlines show a significant amount of cold ($\lesssim 10^4 \; \rm{K}$) gas which cosmological simulations struggle to reproduce. Here, we use the adaptive mesh refinement hydrodynamical code RAMSES to investigate the effect of cosmic rays (CR) on the cold gas content of the CGM using three zoom realizations of a $z=1$ star-forming galaxy with supernova mechanical feedback: one with no CR feedback (referred to as no-CR), one with a medium CR diffusion coefficient $κ= 10^{28} \; \rm{cm^{2}\; s^{-1}}$ (CR$-κ_{\rm med}$), and one with a high rate of diffusion of $κ= 3\times10^{29} \; \rm{cm^{2}\; s^{-1}}$ (CR$-κ_{\rm high}$). We find that, for CR$-κ_{\rm med}$, the effects of CRs are largely confined to the galaxy itself as CRs do not extend far into the CGM. However, for CR$-κ_{\rm high}$, the CGM temperature is lowered and the amount of outflowing gas is boosted. Our CR simulations fall short of the observed Mg II covering fraction, a tracer of gas at temperatures $\lesssim 10^4 \; \rm{K}$, but the CR$-κ_{\rm high}$ simulation is more in agreement with covering fractions of C IV and O VI, which trace higher temperature gas.

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arXiv2024

Linking Mg II and [O II] spatial distribution to ionizing photon escape in confirmed LyC leakers and non-leakers

The geometry of the neutral gas in and around galaxies is a key regulator of the escape of ionizing photons. We present the first statistical study aiming at linking the neutral and ionized gas distributions to the Lyman continuum (LyC) escape fraction (fesc(LyC)) in a sample of 22 confirmed LyC leakers and non-leakers at z~0.35 using the Keck Cosmic Web Imager (Keck/KCWI) and the Low Resolution Spectrograph 2 (HET/LRS2). Our integral field unit data enable the detection of neutral and low-ionization gas, as traced by Mg II, and ionized gas, as traced by [O II], extending beyond the stellar continuum for 7 and 10 objects, respectively. All but one object with extended Mg II emission also shows extended [O II] emission; in this case, Mg II emission is always more extended than [O II] by a factor 1.3 on average. Most of the galaxies with extended emission are non or weak LyC leakers (fesc(LyC) < 5%), but we find a large diversity of neutral gas configurations around these weakly LyC-emitting galaxies. Conversely, the strongest leakers (fesc(LyC) > 10%) appear uniformly compact in both Mg II and [O II] with exponential scale lengths <1 kpc. We also find a trend between fesc(LyC) and the spatial offsets of the nebular gas and the stellar continuum emission. Moreover, we find significant anti-correlations between the spatial extent of the neutral gas and the [O III]/[O II] ratio, and H$β$ equivalent width, as well as positive correlations with metallicity and UV size, suggesting that galaxies with more compact neutral gas sizes are more highly ionized. The observations suggest that strong LyC emitters do not have extended neutral gas halos and ionizing photons may be emitted in many directions. Combined with high ionization diagnostics, we propose the Mg II, and potentially [O II], spatial compactness are indirect indicators of LyC emitting galaxies at high-redshift.

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arXiv2023

Bipolar Outflows out to 10~kpc for Massive Galaxies at Redshift $z\approx 1$

Galactic outflows are believed to play a critical role in the evolution of galaxies by regulating their mass build-up and star formation. Theoretical models assumes bipolar shapes for the outflows that extends well into the circumgalctic medium (CGM), up to tens of kpc perpendicular to the galaxies. They have been directly observed in the local Universe in several individual galaxies, e.g., around the Milky Way and M82. At higher redshifts, cosmological simulations of galaxy formation predict an increase in the frequency and efficiency of galactic outflows due to the increasing star formation activity. Outflows are responsible for removing potential fuel for star formation from the galaxy, while at the same enriching the CGM and the intergalactic medium. These feedback processes, although incorporated as key elements of cosmological simulations, are still poorly constrained on CGM scales. Here we present an ultra-deep MUSE image of the mean MgII emission surrounding a sample of galaxies at z~1 that strongly suggests the presence of outflowing gas on physical scales of more than 10kpc. We find a strong dependence of the detected signal on the inclination of the central galaxy, with edge-on galaxies clearly showing enhanced MgII emission along the minor axis, while face-on galaxies display much weaker and more isotropic emission. We interpret these findings as supporting the idea that outflows typically have a bipolar cone geometry perpendicular to the galactic disk. We demonstrate that the signal is not dominated by a few outliers. After dividing the galaxy sample in subsamples by mass, the bipolar emission is only detected in galaxies with stellar mass $\mathrm{M_* \gtrsim 10^{9.5} M_\odot}$.

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arXiv2023

On the evolution of the size of Lyman alpha halos across cosmic time: no change in the circumgalactic gas distribution when probed by line emission

Lyman $α$ (Ly$α$) is now routinely used as a tool for studying high-redshift galaxies and its resonant nature means it can trace neutral hydrogen around star-forming galaxies. Integral field spectrograph measurements of high-redshift Ly$α$ emitters indicate that significant extended Ly$α$ halo emission is ubiquitous around such objects. We present a sample of redshift 0.23 to 0.31 galaxies observed with the Hubble Space Telescope selected to match the star formation properties of high-$z$ samples while optimizing the observations for detection of low surface brightness Ly$α$ emission. The Ly$α$ escape fractions range between 0.7\% and 37\%, and we detect extended Ly$α$ emission around six out of seven targets. We find Ly$α$ halo to UV scale length ratios around 6:1 which is marginally lower than high-redshift observations, and halo flux fractions between 60\% and 85\% -- consistent with high-redshift observations -- when using comparable methods. However, our targets show additional extended stellar UV emission: we parametrize this with a new double exponential model. We find that this parametrization does not strongly affect the observed Ly$α$ halo fractions. We find that deeper H$α$ data would be required to firmly determine the origin of Ly$α$ halo emission, however, there are indications that H$α$ is more extended than the central FUV profile, potentially indicating conditions favorable for the escape of ionizing radiation. We discuss our results in the context of high-redshift galaxies, cosmological simulations, evolutionary studies of the circumgalactic medium in emission, and the emission of ionizing radiation.

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arXiv2022

LyC escape from SPHINX galaxies in the Epoch of Reionization

We measure escape fractions, $f_{\rm esc}$, of ionizing radiation from galaxies in the SPHINX suite of cosmological radiation-hydrodynamical simulations of reionization, resolving halos with $M_{\rm vir} \gtrapprox 7.5 \times 10^7 \ M_{\odot}$ with a minimum cell width of $\approx 10$ pc. Our new and largest $20$ co-moving Mpc wide volume contains tens of thousands of star-forming galaxies with halo masses up to a few times $10^{11} \ M_{\odot}$. The simulated galaxies agree well with observational constraints of the UV luminosity function in the Epoch of Reionization. The escape fraction fluctuates strongly in individual galaxies over timescales of a few Myrs, due to its regulation by supernova and radiation feedback, and at any given time a tiny fraction of star-forming galaxies emits a large fraction of the ionizing radiation escaping into the inter-galactic medium. Statistically, $f_{\rm esc}$ peaks in intermediate-mass, intermediate-brightness, and low-metallicity galaxies ($M_{*} \approx 10^7 \ M_{\odot}$, $M_{1500} \approx -17$, $Z\lesssim 5 \times 10^{-3} \ Z_{\odot}$), dropping strongly for lower and higher masses, brighter and dimmer galaxies, and more metal-rich galaxies. The escape fraction correlates positively with both the short-term and long-term specific star formation rate. According to SPHINX, galaxies too dim to be yet observed, with $M_{1500} \gtrapprox -17$, provide about $55$ percent of the photons contributing to reionization. The global averaged $f_{\rm esc}$ naturally decreases with decreasing redshift, as predicted by UV background models and low-redshift observations. This evolution is driven by decreasing specific star formation rates over cosmic time.

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arXiv2022

Radiation-MagnetoHydrodynamics simulations of cosmic ray feedback in disc galaxies

Cosmic rays (CRs) are thought to play an important role in galaxy evolution. We study their effect when coupled to other important sources of feedback, namely supernovae and stellar radiation, by including CR anisotropic diffusion and radiative losses but neglecting CR streaming. Using the RAMSES-RT code, we perform the first radiation-magnetohydrodynamics simulations of isolated disc galaxies with and without CRs. We study galaxies embedded in dark matter haloes of $10^{10}$, $10^{11}$ and $10^{12}\, \rm M_{\odot}$ with a maximum resolution of $9 \,\rm pc$. We find that CRs reduce star formation rate in our two dwarf galaxies by a factor 2, with decreasing efficiency with increasing galaxy mass. They increase significantly the outflow mass loading factor in all our galaxies and make the outflows colder. We study the impact of the CR diffusion coefficient, exploring values from $κ= 10^{27}$ to $\rm 3\times 10^{29}\, cm^2\, s^{-1}$. With lower $κ$, CRs remain confined for longer on small scales and are consequently efficient in suppressing star formation, whereas a higher diffusion coefficient reduces the effect on star formation and increases the generation of cold outflows. Finally, we compare CR feedback to a calibrated 'strong' supernova feedback model known to sufficiently regulate star formation in high-redshift cosmological simulations. We find that CR feedback is not sufficiently strong to replace this strong supernova feedback. As they tend to smooth out the ISM and fill it with denser gas, CRs also lower the escape fraction of Lyman continuum photons from galaxies.

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