arXiv subjects

Lucio Mayer

Publications and source records attributed to Lucio Mayer.

At least 19 recordsLinked to original sources

arXiv2026

Reconstructing stochastic gravitational-wave signals from flavour deconstruction with LISA

We investigate the reconstruction of a stochastic gravitational-wave background generated by a first-order phase transition in flavour-deconstruction models using the Laser Interferometer Space Antenna (LISA). In these scenarios, the spontaneous breaking of an extended flavour-non-universal gauge symmetry at the TeV scale can both generate the observed hierarchies of Standard Model fermion masses and mixing angles and induce a strong first-order phase transition. We consider representative benchmark points of the model, compute the corresponding thermodynamic transition parameters, and construct the resulting gravitational-wave spectra using a state-of-the-art sound-wave template. We then inject these spectra into simulated LISA data and perform Bayesian inference with SGWBinner, jointly reconstructing the cosmological signal, instrumental noise, and astrophysical foregrounds. We find that the strongest benchmark signal can be successfully reconstructed, whereas weaker signals are substantially degenerate with the unresolved extragalactic compact-binary foreground. We further show that tighter prior information on this foreground, motivated by observations with ground-based detectors, can reduce this degeneracy and improve signal reconstruction. Our results demonstrate that flavour-deconstruction models can produce signals accessible to LISA, while highlighting the importance of astrophysical-foreground modelling for their identification and characterization.

astro-ph.CO↗

arXiv2026

Emulating the complex galactic-scale orbital dynamics of LISA massive black hole pairs with normalizing flows

Massive black hole (MBH) pairs, formed in galaxy mergers, may coalesce in a burst of gravitational waves. Estimating the coalescence time-scales and rates is a long-standing astrophysical problem, essential to inform predictions for future gravitational-wave detectors such as the Laser Interferometer Space Antenna, but remains challenging: MBH orbital decay in realistic galactic environments is complex and stochastic, and non-axisymmetric structures such as stellar bars can perturb MBH pair dynamics, delaying or accelerating binary formation and undermining the assumption that dynamical friction alone sets the inspiral duration. Capturing this evolution requires simulations too expensive to run at population scale. Here we present an artificial-intelligence framework that emulates the galactic-scale orbital decay of an inspiralling MBH using conditional normalizing flows trained on a large suite of semi-analytical orbital integrations. Our model captures the evolution of secondary MBHs orbiting within multi-component galactic merger remnants featuring rotating stellar discs and bars, across a broad range of MBH masses, orbital configurations, and bar properties. The trained emulator reproduces the simulations' decay-time distributions while reducing computational cost by orders of magnitude. For the first time, we apply this model to galaxy populations drawn from a cosmological simulation, exploiting morphological information on barred and non-barred galaxies to infer MBH binary formation time-scales across cosmic time. Our results show that stellar bars can alter the distribution of MBH binary formation times. More broadly, this demonstrates how simulation-based, surrogate machine-learning emulators can unlock a class of astrophysical problems where the physics is well understood system-by-system but intractable at scale.

astro-ph.GA↗

arXiv2026

Too shy to spin? Cosmic wallflowers as proto-globular clusters

We investigate the rotational properties of star-forming clusters at $z \sim 7.6$ in the high-resolution simulation MassiveBlackPS, focusing on two formation channels: clusters forming in galactic discs via gravitational instability and isolated circumgalactic systems, referred to as cosmic wallflowers, born out of cosmic filaments. Using stellar kinematics, we compare their rotational velocities, $v_{\rm rot}$, and rotational support, $v/\sigma$, to study whether formation environment leaves a clear dynamical imprint. We find a clear separation, wherein cosmic wallflowers systematically have lower rotational velocities and span a wide range in $v/\sigma$, whereas the identified disc clusters are strongly rotation-dominated and extend to higher $v_{\rm rot}$. When combined with stellar surface densities, a subset of the low-$v_{\rm rot}$ cosmic wallflowers lie surprisingly close to the observed globular cluster population in the Milky Way, whereas disc clusters remain offset. Within the cosmic wallflower population, we identify two regimes: lower-density, weakly rotating systems that overlap with these globular cluster properties, and denser, more rotationally supported systems that likely follow a different evolutionary pathway, possibly linking them to the origin of massive black hole seeds at high redshift. We further find that the gas content correlates with this behaviour, with gas-rich cosmic wallflowers preferentially occupying this low-rotation regime. This all suggests that environment and baryonic content together play a key role in setting the initial dynamical state and possible fate of clusters. In particular, weakly rotating, gas-rich cosmic wallflowers emerge as natural proto-globular cluster candidates, potentially evolving towards present-day systems through angular momentum loss and dynamical heating.

astro-ph.GA↗

arXiv2026

Multi-messenger and Multi-band Studies of Massive Black Holes: the Synergies Between LISA and SKAO

Depending on its mass, the same gas-embedded massive black hole (BH) binary can emit gravitational waves (GWs) in one or more bands (nHz and mHz) concurrently, along with electromagnetic (EM) waves over the entire spectrum. The Square Kilometre Array Observatory (SKAO), thanks to its unparalleled sensitivity, will be pivotal in achieving coincident GW-EM (mHz-radio) and GW-GW (nHz-mHz) detections. We review the state-of-the-art predictions - achieved by means of numerical simulations and mock catalogues - of the numbers of detectable coincident GW-EM signals when employing the Laser Interferometer Space Antenna (LISA) and SKA-Mid. By exploiting the same underlying BH binary populations, to allow for a fairer comparison, we then assess the importance of a variety of EM models for the radio flares and jets, finding that the number of radio counterparts of LISA sources is relatively insensitive to the jet/flare model employed and to whether SKA-Mid AA* or AA4 is assumed. Additionally, we describe how SKAO - as part of a pulsar timing array (PTA) - and LISA will provide the opportunity to detect the first low-frequency, multi-band (nHz-mHz) GW detection of the same object. Supermassive BH binaries embedded in gas discs are subjected to hydrodynamical torques, causing perturbations that produce additional small-amplitude, higher-frequency GWs. The main carrier GWs may thus be identifiable as a deterministic signal by SKAO-era PTAs, while the higher-frequency harmonics would shine in LISA as stochastic signals. Correlating these multi-band GWs would provide unprecedented constraints on the environment of the most massive BHs.

astro-ph.HE↗

arXiv2026

The role of major mergers in triggering super-Eddington accretion

JWST observations have opened a new era in the exploration of the high-redshift Universe, revealing black holes (BHs) with masses of several million solar masses already at $z>8$, challenging our understanding of their growth mechanisms. In this context, super-Eddington (SE) accretion has emerged as a promising solution and has been widely adopted in both numerical simulations and semi-analytical models. In this work, we investigate whether a major merger between two relatively low-mass halos ($M_{\rm halo}\sim10^9\,\mathrm{M_\odot}$) at high redshift can trigger episodes of sustained SE accretion, with particular focus on the role of BH feedback. We employ state-of-the-art, high-resolution cosmological zoom-in simulations of a major merger at $z\sim11$. We explore different prescriptions for BH seeding and feedback, including physically motivated radiative and kinetic models (winds and jets) across the three main accretion regimes: advection-dominated accretion flows (ADAF), radiatively efficient sub-Eddington accretion, and SE accretion. For the relatively low-mass halos studied here, our feedback prescription efficiently suppresses gas accretion, preventing substantial BH growth. We find that, although the merger drives gas inflows towards the central regions, this is not sufficient to trigger sustained SE accretion. Post-merger SE accretion episodes are observed only when BH feedback is entirely switched off. Amongst the feedback channels considered, kinetic feedback is the primary mechanism regulating BH growth. Moreover, the only significant SE accretion episodes occur immediately after BH seeding, while the merger itself does not produce a substantial enhancement of the accretion rate.

astro-ph.GA↗

arXiv2026

Chaotic migration of LISA Extreme Mass Ratio Inspirals in a turbulent accretion disk: effect on waveform de-phasing

Gravitational wave (GW) detector LISA will observe near-coalescence extreme mass ratio inspirals (EMRIs), which typically form in galactic central accretion disks. Torques from the disk can alter the GW-driven inspiral trajectory of an embedded EMRI from the vacuum expectation, leading to potentially observable GW dephasing ($\Delta\psi_{\rm gas}$). So far, all studies compute $\Delta\psi_{\rm gas}$ for a thin, laminar disk, with negligible flow turbulence, whereby the disk exerts the well-understood linear torque ($T_{\rm lin}$). However, these disks must be turbulent due to magneto-rotational instability in the inner regions. Hence, we present a proof-of-concept general prescription for the turbulent torque ($T_{\rm turb}$) acting on an EMRI by modeling it as a Gaussian distribution around $T_{\rm lin}$, inspired by recent global simulations that study such torques. We compute $\Delta\psi_{\rm gas}$ for the ``golden'' circular EMRI with total source mass $M=10^6~{\rm M}_\odot$ and mass ratio $q=5\times10^{-5}$ in its final four-year evolution at redshift $z=0.276$ and signal-to-noise ratio (SNR) $=50$ by varying turbulence amplitude $C$ ($=1$ in the aforementioned study), maximum correlation timescale ($N_{\rm max}$), Eddington ratio ${\rm f}_{\rm Edd}$, disk aspect ratio $h_0$, and turbo-viscous coefficient $\alpha$ in a reasonable parameters space. For $N_{\rm max}=100$ orbits, we find that for $C\gtrsim{10}$, ${\rm f}_{\rm Edd}\gtrsim0.3$, $h_0\gtrsim0.03$, and $\alpha\gtrsim0.1$, dephasings due to $T_{\rm lin}$ are unobservable but could become detectable ($\Delta\psi_{\rm gas}>8/$SNR) if EMRIs experience turbulent torques. Hence, this work motivates running MHD simulations of accretion disks with embedded early-inspiral LISA EMRIs over long timescales to understand the imprint of the turbulent environment on their orbital parameters and gravitational waveforms.

astro-ph.GA↗

arXiv2026

Active moons in our Solar System and beyond -- Io, Europa, Enceladus, Triton, and exomoons

The outgassing signatures of Io, Europa, Enceladus, Triton, and Io-like exomoons are the focus of this review chapter. The rocky volcanic world of Io is unique in our Solar System, with plumes reaching to hundreds of kilometres in altitude. Io-like exomoons could leave signatures strong enough to be detected with ground-based telescopes. The icy moons Europa and Enceladus, with their subsurface oceans, are currently the best candidates for life. Triton is different in many ways and raises unexplored questions. Our knowledge of these active moons is derived from space- and ground-based observations. To understand their origin, we discuss moon formation in general, before examining evidence and signatures of plumes on these moons. Given the accessibility of subsurface oceanic material through the occurrence of plumes, we expand on possibilities to investigate biosignatures.

astro-ph.EP↗

arXiv2026

Giant Planet Formation by Disk Instability

The disk instability (DI) model for giant planet formation remains an attractive alternative in explaining the formation of giant planets at early times, giant planets at large radial distances, and giant planets orbiting M-stars. In this review, we present recent developments in the disk instability model including hydrodynamical as well as magneto-hydrodynamical (MHD) disk simulations, populations synthesis models, and simulations of clump-clump collisions. We also discuss advances in observations that can be used to constrain and test this formation scenario.

astro-ph.EP↗

arXiv2026

Dust Processing in Protoplanetary Discs From Infall to Dispersal: the Origin of Solar System Isotopic Heterogeneities

The nucleosynthetic heterogeneity between different asteroids and planets is well established. These isotopic variations manifest themselves at the part per millions level or larger, in isotopes that were synthesised in various stellar environments. To escape homogenisation, some of these isotopic signatures must have been preserved in dust, which ended up being heterogeneously distributed in the solar protoplanetary disc. The origin of the nucleosynthetic heterogeneity is still poorly constrained, potentially reflecting inherited isotope variations from the Sun's parental molecular cloud and/or processing and redistribution during the subsequent protoplanetary disc phase with thermal processing and size sorting as major processes. This chapter aims to provide a broad review of the dynamical, collisional, and thermal processes in protoplanetary discs -- from initial infall to gas dispersal -- that may have influenced the distribution and survival of the anomalous carrier phases, which finally accreted into asteroids and planets. While several of these mechanisms have been considered in past studies, they are often examined in isolation, which impedes the assessment of how their effects may be altered or amplified by additional disc processes. Size sorting in particular has received little attention, and here we highlight that this process likely occurred in the disc and can induce nucleosynthetic heterogeneity. By placing previous studies within the context of a comprehensive overview, we aim to clarify the broader physical framework in which anomalous carrier transport occurs and identify previously underexplored mechanisms that may have contributed to the final isotopic structure of the Solar System we see today.

astro-ph.EP↗

arXiv2026

Experimental evidence for granular shear-flow instability in the Epstein regime

Stability analysis of two-fluid protoplanetary disc models has enriched our understanding of how solids can grow into larger bodies called planetesimals. Dust particles entrained in a gas stream modify the flow, creating shear layers prone to instability. In such environments, drag occurs in the free-molecular (Epstein) regime. Recreating these two-phase flows on Earth is difficult due to gravity-driven buoyancy. Here, we use particle image velocimetry to study a low-pressure dust-gas mixture at Knudsen numbers up to 10 in microgravity. We observe a granular shear flow instability, characterized by a periodic velocity field, which can be modeled to first order as a Kelvin-Helmholtz (KH) instability. This behavior resembles a Kelvin-Helmholtz instability and provides a benchmark for two-fluid theories relevant to planet formation.

astro-ph.EP↗

arXiv2026

Cosmic wallflowers: the circumgalactic origins of isolated ultra-compact star clusters at $z>7$

The discovery of gravitationally lensed stellar clusters at high redshift with the James Webb Space Telescope (JWST) has revealed extremely compact, massive star-forming systems in galaxies at $z > 6$, providing a new window into early cluster formation. In this work, we investigate star cluster formation in the circumgalactic environments of gas-rich galaxies with stellar masses spanning between $\sim$$10^{8}$ - $10^{11}$ M$_{\odot}$ at $z > 7$, using the MassiveBlackPS cosmological hydrodynamical simulation with 2 pc resolution. We identify 55 baryon-dominated clusters forming outside galactic discs but within the virial radius of the primary halo. Star formation in these systems proceeds rapidly, reaching peak stellar surface densities above $10^{5}$ M$_{\odot}$ pc$^{-2}$, closely matching the compact clusters recently discovered by JWST in the lensed Cosmic Gems Arc at $z \approx 9.6$. Such extreme densities are a key pre-requisite to trigger runaway stellar collisions, indicating that a subset of our clusters would be a likely host of intermediate-mass black holes (IMBHs). We find that massive star clusters can form efficiently in the circumgalactic medium at early times through filament fragmentation, whereby high gas densities lead to rapid local collapse via a combination of thermal and gravitational instabilities. This formation pathway implies that some compact clusters formed in the quiet outskirts of forming galaxies rather than within their discs. Small variations in filament properties, including metallicity, density, and dark-matter content, influence the likelihood of a star cluster being able to form an IMBH seed. The formation of clusters in circumgalactic environments points to a potential evolutionary pathway connecting early off-disc clusters, present-day globular clusters, and the seeds of massive BHs.

astro-ph.GA↗

arXiv2026

Disc fragmentation. II. Ejection of low mass Free Floating Planets from growing binary systems

Observations indicate that disc fragmentation due to Gravitational Instability (GI) is the likely origin of massive companions to stars, such as giant planets orbiting M-dwarf stars, Brown Dwarf (BD) companions to FGK stars, and binary stars with separations smaller than 100 au. Additionally, we have recently showed that disc fragmentation in young rapidly evolving binary systems ejects an abundant population of massive Jupiter-mass Free-Floating Planets (FFPs). In this model, a massive disc around an initially single protostar undergoes GI and hatches a number of fragments; the most massive oligarch grows by runaway accretion into the secondary star. As the system rearranges itself from a single to a binary star configuration, a dramatic "pincer movement" by the binary ejects planets through dynamical interactions with the stars. Here we propose that the same scenario applies to an even more abundant population of smaller FFPs discovered by the microlensing surveys. Although disc fragmentation is usually believed to form only massive objects, several pathways for forming small core-dominated planets at separations of tens of au exist. We present results from three complementary simulation approaches, all of which confirm planet ejection efficiency as high as 0.5 for secondaries more massive than $\sim 10$\% of the primary star mass. On the other hand, Jovian mass planets migrate through the region of tens of au too rapidly to eject planets from that region. We discuss implications of this scenario, concluding that microlensing FFPs may be the most convincing evidence yet that disc fragmentation forms planets much less massive than Jupiter.

astro-ph.EP↗

arXiv2025

The LISA Astrophysics "Disc-IMRI" Code Comparison Project: Intermediate-Mass-Ratio Binaries in AGN-Like Discs

Upcoming space-based gravitational wave detectors such as LISA, the Laser Interferometer Space Antenna, will be sensitive to extreme- and intermediate-mass-ratio inspirals (EMRIs and IMRIs). These binaries are comprised of a supermassive black hole and a stellar-mass object or intermediate-mass black hole. Their detection will probe the structure of galactic nuclei and enable tests of general relativity. As these events will be observed over thousands of orbital cycles, they will be extremely sensitive to both the underlying spacetime and astrophysical environment, demanding exquisite theoretical models on both fronts to avoid biased or even erroneous results. In particular, many (E/)IMRIs are expected to occur within accretion discs around supermassive black holes, and the nonlinearities present when modeling these systems require numerical simulations. In preparation for future modeling of LISA sources, we have conducted a comparison between eight different hydrodynamical codes and applied them to the problem of a q = 10^{-4} mass ratio binary interacting with an accretion disc. Thicker discs appear more lenient, and all codes at sufficiently high resolutions are in good agreement with each other and analytical predictions. For thinner discs, beyond the reach of analytical models, we find substantial disagreement between 2D and 3D simulations and between different codes, including both the magnitude and sign of the torque. With time and energy efficiency in mind, codes that leverage moving meshes or grid-based Lagrangian remapping seem preferable, as do codes that can leverage graphical processing units and other energy-efficient hardware.

astro-ph.HE↗

arXiv2025

The AGORA High-resolution Galaxy Simulations Comparison Project. X: Formation and Evolution of Galaxies at the High-redshift Frontier

Recent observations from JWST have revealed unexpectedly luminous galaxies, exhibiting stellar masses and luminosities significantly higher than predicted by theoretical models at Cosmic Dawn. In this study, we present a suite of cosmological zoom-in simulations targeting high-redshift ($z \geq 10$) galaxies with dark matter halo masses in the range $10^{10} - 10^{11}\ {\rm M}_{\odot}$ at $z=10$, using state-of-the-art galaxy formation simulation codes (Enzo, Ramses, Changa, Gadget-3, Gadget-4, and Gizmo). This study aims to evaluate the convergence of the participating codes and their reproducibility of high-redshift galaxies with the galaxy formation model calibrated at relatively low redshift, without additional physics for high-redshift environments. The subgrid physics follows the AGORA CosmoRun framework, with adjustments to resolution and initial conditions to emulate similar physical environments in the early universe. The participating codes show consistent results for key galaxy properties (e.g., stellar mass), but also reveal notable differences (e.g., metallicity), indicating that galaxy properties at high redshifts are highly sensitive to the feedback implementation of the simulation. Massive halos (${\rm M}_{\rm halo}\geq5\times10^{10}\,{\rm M}_{\odot}$ at $z=10$) succeed in reproducing observed stellar masses, metallicities, and UV luminosities at $10\leq z\leq12$ without requiring additional subgrid physics, but tend to underpredict those properties at higher redshift. We also find that varying the dust-to-metal ratio modestly affects UV luminosity of simulated galaxies, whereas the absence of dust significantly enhances it. In future work, higher-resolution simulations will be conducted to better understand the formation and evolution of galaxies at Cosmic Dawn.

astro-ph.GA↗

arXiv2025

Tidal disruption events with SPH-EXA: resolving the return of the stream

In a tidal disruption event (TDE), a star is disrupted by the tidal field of a massive black hole, creating a debris stream that returns to the black hole, forms an accretion flow, and powers a luminous flare. Over the last few decades, several numerical studies have concluded that shock-induced dissipation occurs as the stream returns to pericentre (i.e., pre-self-intersection), resulting in efficient circularisation of the debris. However, the efficacy of these shocks is the subject of intense debate. We present high-resolution simulations (up to 10^10 particles) of the disruption of a solar-like star by a 10^6M_sun black hole with the new, GPU-based, smoothed-particle hydrodynamics code SPH-EXA, including the relativistic apsidal precession of the stellar debris orbits; our simulations run from initial disruption to the moment of stream self-intersection. With 10^8 particles - corresponding to the highest-resolution SPH simulations of TDEs in the pre-existing literature - we find significant, in-plane spreading of the debris as the stream returns through pericenter, in line with previous works that suggested this is a significant source of dissipation and luminous emission. However, with increasing resolution this effect is dramatically diminished, and with 10^10 particles there is effectively no change between the incoming and the outgoing stream widths. Our results demonstrate that the paradigm of significant dissipation of kinetic energy during pericentre passage is incorrect, and instead it is likely that debris circularisation is mediated by the originally proposed, stream-stream collision scenario.

astro-ph.HE↗

arXiv2025

Evidence for Supermassive Black Hole Binaries

We review the state of the evidence for the existence and observational appearance of supermassive black hole binaries. Such objects are expected from standard hierarchical galaxy evolution to form after two galaxies, each containing a supermassive black hole, have merged, in the centre of the merger remnant. A complex interaction is predicted to take place with stars and gas in the host galaxy, leading to observable signatures in weakly as well as actively accreting phases. Direct observational evidence is available and shows examples of dual active galactic nuclei from kpc scales down to parsec scales. Signatures of possibly closer supermassive black hole binaries may be seen in jetted black holes. The interaction with stars and gas in a galaxy significantly affects the hardening of the binary and hence contributes to uncertainties of the expected gravitational wave signal. The Laser Interferometer Space Antenna (LISA) should in the future detect actual mergers. Before the launch of LISA, pulsar timing arrays may have the best chance to detect a gravitational wave signal from supermassive black hole binaries. The first signs of the combined background of inspiralling objects might have been seen already.

astro-ph.HE↗

arXiv2025

Super-Eddington accretion in protogalactic cores

The presence of massive black holes (BHs) exceeding $10^9\,{\rm M}_{\odot}$ already at redshift $z > 6$ challenges standard models of BH growth. Super-Eddington (SE) accretion has emerged as a promising mechanism to solve this issue, yet its impact on early BH evolution in tailored numerical experiments remains largely unexplored. In this work, we investigate the growth of BH seeds embedded in a gas-rich, metal-poor protogalaxy at $z \sim 15$ using a suite of high-resolution hydrodynamical simulations that implement a slim-disc-based SE accretion model. We explored a broad parameter space, varying the initial BH mass, feedback efficiency, and spin. We find that SE accretion enables rapid growth in all cases, allowing BHs to accrete up to $10^5\,{\rm M}_{\odot}$ within a few $10^3$-$10^4$ years, independent of seed properties. Feedback regulates this process, both by depleting central gas and altering BH dynamics via star formation-driven potential fluctuations, yet even the strongest feedback regimes permit significantly greater growth than the Eddington-limited case. Growth stalls after less than $\sim$1 Myr due to local gas exhaustion, as no large-scale inflows are present in the adopted numerical setup. Our results show that SE accretion naturally leads to BHs that are overmassive relative to their host galaxy stellar content, consistent with JWST observations. We conclude that short low-duty-cycle SE episodes represent a viable pathway for assembling the most massive BHs observed at early cosmic times, even when starting from light seeds.

astro-ph.GA↗

arXiv2025

The Seven Dwarfs illuminated. The impact of radiation on dwarf galaxies and their circumgalactic medium

We present a high-resolution cosmological zoom-in simulation of a group of field dwarf galaxies which includes on-the-fly radiative transfer (RT) and is evolved to $z=0$. Emission from stars is included according to age-dependent spectra, and a redshift-dependent UV background. The inclusion of RT results in the formation of eight additional faint dwarf galaxies with stellar masses of $10^{4}$ M$_{\odot}$ to several $10^{5}$ M$_{\odot}$ and only old stellar populations, similar to the observed Ultra-Faint Dwarf galaxies. They formed before and during cosmic reionisation and were mostly quenched by $z \sim 3-4$. The simulated galaxies follow many observed scaling relations such as the stellar mass-halo mass relation, the mass-size relation, and the luminosity-velocity dispersion relation. For the more massive dwarf galaxies, radiative feedback suppresses star formation, making it less bursty and reducing explosive outflows. This consequently reduces the dark matter core sizes by a factor of 2-3, rendering the core sizes ($\sim$ 1 kpc) more consistent with observations. The distribution of HI in the circumgalactic medium (CGM) is ubiquitous with a covering fraction of unity within $R_{vir}$, in good agreement with observations. It is rather insensitive to radiative or SN feedback at $z=0$, but at $z>5$ it is much higher in the RT simulation. In contrast, the distribution of low ions like SiII is very compact and declines sharply beyond the ISM scale. CIV and OVI have a more extended distribution, but their column densities are generally below the detection limit. Radiative feedback leads to smaller column densities of the metal ions, partly due to the reduction of total metal production, and partly because hard photons from the stellar radiation escape the ISM and further ionise the CGM. The abundance of CIV is particularly sensitive to the latter effect.

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