arXiv subjects

Lucio Mayer

Publications and source records attributed to Lucio Mayer.

At least 73 records · Page 4Linked to original sources

arXiv2023

Molecular gas cloud properties at $z\simeq 1$ revealed by the superb angular resolution achieved with ALMA and gravitational lensing

Current observations favour that the massive ultraviolet-bright clumps with a median stellar mass of $\sim 10^7~M_{\odot}$, ubiquitously observed in $z\sim 1-3$ galaxies, are star-forming regions formed in-situ in galaxies. It has been proposed that they result from gas fragmentation due to gravitational instability of gas-rich, turbulent, high-redshift discs. We bring support to this scenario by reporting the new discovery of giant molecular clouds (GMCs) in the strongly lensed, clumpy, main-sequence galaxy, A521-sys1, at $z=1.043$. Its CO(4-3) emission was mapped with the Atacama Large Millimeter/submillimeter Array (ALMA) at an angular resolution of $0.19''\times 0.16''$, reading down to 30~pc thanks to gravitational lensing. We identified 14 GMCs, most being virialized, with $10^{5.9}- 10^{7.9}~M_{\odot}$ masses and a median $800~M_{\odot}~\rm{pc}^{-2}$ molecular gas mass surface density, that are, respectively, 100 and 10 times higher than for local GMCs. They are also characterized by 10 times higher supersonic turbulence with a median Mach number of 60. They end up to fall above the Larson scaling relations, similarly to the GMCs in another clumpy $z\simeq 1$ galaxy, the Cosmic Snake, although noteworthy differences between the two sets of high-redshift GMCs exist. Altogether they support that GMCs form with properties that adjust to the ambient interstellar medium conditions prevalent in the host galaxy whatever its redshift. The detected A521-sys1 GMCs are massive enough to be the parent gas clouds of stellar clumps, with a relatively high star-formation efficiency per free-fall time of $\sim 11$ per cent.

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arXiv2023

Direct collapse of exceptionally heavy black holes in the merger-driven scenario

We revisit the conditions present in supermassive discs (SMDs) formed by the merger of gas-rich, metal-enriched galaxies at red-shift $z\sim 10$. We find that SMDs naturally form hydrostatic cores which go through a rapidly accreting supermassive star phase, before directly collapsing into massive black holes via the general relativistic instability. The growth and collapse of the cores occurs within $\sim 5\times 10^5$ yr from the formation of the SMD, producing bright electromagnetic, neutrino and gravitational wave transients with a typical duration of a few minutes and, respectively, a typical flux and a typical strain amplitude at Earth of $\sim 10^{-8}$ erg s$^{-1}$ cm$^{-2}$ and $\sim4\times 10^{-21}$. We provide a simple fitting formula for the the resulting black hole masses, which range from a few $10^6$ M$_{\odot}$ to $10^8$ M$_{\odot}$ depending on the initial SMD configuration. Crucially, our analysis does not require any specific assumption on the thermal properties of the gas, nor on the angular momentum loss mechanisms within the SMD. Led by these findings, we argue that the merger-driven scenario provides a robust pathway for the rapid formation of supermassive black holes at $z > 6$. It provides an explanation for the origin of the brightest and oldest quasars without the need of a sustained growth phase from a much smaller seed. Its smoking gun signatures can be tested directly via multi-messenger observations.

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arXiv2022

Super-critical accretion of medium-weight seed black holes in gaseous proto-galactic nuclei

Accretion at sustained or episodic super-Eddington (SE) rates has been proposed as a pathway to grow efficiently light seeds produced by Pop-III stars. We investigate if SE accretion can be sustained onto a black hole (BH) with $M_{\odot} \sim 10^3$~M$_{\odot}$ in the centre of a gas-rich proto-galaxy at $z=15$. We perform high-resolution smoothed-particle hydrodynamical simulations, including two different sub-grid models for SE accretion, one based on the slim disc paradigm, and one inspired by recent radiation-magnetohydrodynamical simulations by Jiang and collaborators. Radiative feedback has the form of a thermal dump to surrounding gas particles, with the radiative efficiency being set according to the different SE accretion models. We find that, in all simulations, star formation, BH feedback, and interactions between clumps and the BH rapidly quench accretion after $\sim$1~Myr, irrespective of the sub-grid model used for accretion. Quenching is stronger in the model based on the simulations of Jiang and collaborators relative to the slim disc model because of its higher radiative efficiency. The SE growth phase is always very brief, lasting a few 0.1~Myr. In the most optimistic case, the BH reaches a mass of $\sim$10$^4$~M$_{\odot}$. We extrapolate the final BH masses from $z=15$ to $z\sim6$, assuming subsequent galaxy mergers will replenish the gas reservoir and trigger new cycles of SE accretion. We find that at most BH seeds would grow to $\sim$10$^6$~M$_{\odot}$, comparable to the mass of massive BHs in spiral galaxies such as the Milky Way, but falling short of the mass of the high-redshift quasars.

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arXiv2022

Realistic HI scale heights of Milky Way-mass galaxies in the FIREbox cosmological volume

Accurately reproducing the thin cold gas discs observed in nearby spiral galaxies has been a long standing issue in cosmological simulations. Here, we present measurements of the radially resolved HI scale height in 22 non-interacting Milky Way-mass galaxies from the FIREbox cosmological volume. We measure the HI scale heights using five different approaches commonly used in the literature: fitting the vertical volume density distribution with a Gaussian, the distance between maximum and half-maximum of the vertical volume density distribution, a semi-empirical description using the velocity dispersion and the galactic gravitational potential, the analytic assumption of hydrostatic equilibrium, and the distance from the midplane which encloses $\gtrsim$60 per cent of the HI mass. We find median HI scale heights, measured using the vertical volume distribution, that range from ~100 pc in the galactic centres to ~800 pc in the outskirts and are in excellent agreement with recent observational results. We speculate that the presence of a realistic multiphase interstellar medium, including cold gas, and realistic stellar feedback are the drivers behind the realistic HI scale heights.

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arXiv2022

The imprint of gas on gravitational waves from LISA intermediate-mass black hole binaries

We study the effect of torques on circular inspirals of intermediate-mass black hole binaries (IMBHBs) embedded in gas discs, wherein both BH masses are in the range $10^2$-$10^5~\rm{M}_\odot$, up to redshift $z = 10$. We focus on how torques impact the detected gravitational wave (GW) waveform in the frequency band of the Laser Interferometer Space Antenna (LISA) when the binary separation is within a few hundred Schwarzschild radii. For a sub-Eddington accretion disc with a viscosity coefficient $α=0.01$, surface density $Σ\approx10^5$ g cm$^{-2}$, and Mach number $\mathcal{M}_{\rm a}\approx80$, a gap, or a cavity, opens when the binary is in the LISA band. Depending on the torque's strength, LISA will observe dephasing in the IMBHB's GW signal up to either $z\sim5$ for high mass ratios ($q\approx0.1$) or to $z\sim7$ for $q\approx10^{-3}$. We study the dependence of the measurable dephasing on variations of BH masses, redshift, and accretion rates. Our results suggest that phase shift is detectable even in high-redshift ($z = 10$) binaries, provided that they experience super-Eddington accretion episodes. We investigate if the disc-driven torques can result in an observable `time-dependent' chirp mass with a simplified Fisher formalism, finding that, at the expected signal-to-noise ratio, the gas-induced variation of the chirp mass is too small to be detected. This work shows how perturbations of vacuum waveforms induced by gas should be strong enough to be detected by LISA for the IMBHB in the early inspiral phase. These perturbations encode precious information on the astrophysics of accretion discs and galactic nuclei. High-accuracy waveform models which incorporate these effects will be needed to extract such information.

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arXiv2022

TEMPus VoLA: the Timed Epstein Multi-pressure Vessel at Low Accelerations

The field of planetary system formation relies extensively on our understanding of the aerodynamic interaction between gas and dust in protoplanetary disks. Of particular importance are the mechanisms triggering fluid instabilities and clumping of dust particles into aggregates, and their subsequent inclusion into planetesimals. We introduce the Timed Epstein Multi-pressure vessel at Low Accelerations (TEMPusVoLA), which is an experimental apparatus for the study of particle dynamics and rarefied gas under micro-gravity conditions. This facility contains three experiments dedicated to studying aerodynamic processes, i) the development of pressure gradients due to collective particle-gas interaction, ii) the drag coefficients of dust aggregates with variable particle-gas velocity, iii) the effect of dust on the profile of a shear flow and resultant onset of turbulence. The approach is innovative with respect to previous experiments because we access an untouched parameter space in terms of dust particle packing fraction, and Knudsen, Stokes, and Reynolds numbers. The mechanisms investigated are also relevant for our understanding of the emission of dust from active surfaces such as cometary nuclei and new experimental data will help interpreting previous datasets (Rosetta) and prepare future spacecraft observations (Comet Interceptor). We report on the performance of the experiments, which has been tested over the course of multiple flight campaigns. The project is now ready to benefit from additional flight campaigns, to cover a wide parameter space. The outcome will be a comprehensive framework to test models and numerical recipes for studying collective dust particle aerodynamics under space-like conditions.

astro-ph.IM↗

arXiv2022

Multiply lensed star forming clumps in the A521-sys1 galaxy at redshift 1

We study the population of star-forming clumps in A521-sys1, a $\rm z=1.04$ system gravitationally lensed by the foreground ($\rm z=0.25$) cluster Abell 0521. The galaxy presents one complete counter--image with a mean magnification of $\rm μ\sim4$ and a wide arc containing two partial images of A521-sys1 with magnifications reaching $\rm μ>20$, allowing the investigations of clumps down to scales of $\rm R_{eff}<50$ pc. We identify 18 unique clumps with a total of 45 multiple images. Intrinsic sizes and UV magnitudes reveal clumps with elevated surface brightnesses, comparable to similar systems at redshifts $\rm z\gtrsim1.0$. Such clumps account for $\sim40\%$ of the galaxy UV luminosity, implying that a significant fraction of the recent star-formation activity is taking place there. Clump masses range from $\rm 10^6\ M_\odot$ to $\rm 10^9\ M_\odot$ and sizes from tens to hundreds of parsec, resulting in mass surface densities from $10$ to $\rm 10^3\ M_\odot\ pc^{-2}$, with a median of $\rm \sim10^2\ M_\odot\ pc^{-2}$. These properties suggest that we detect star formation taking place across a wide range of scale, from cluster aggregates to giant star-forming complexes. We find ages of less than $100$ Myr, consistent with clumps being observed close to their natal region. The lack of galactocentric trends with mass, mass density, or age and the lack of old migrated clumps can be explained either by dissolution of clumps after few $\sim100$ Myr or by stellar evolution making them fall below the detectability limits of our data.

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arXiv2022

From EMBER to FIRE: predicting high resolution baryon fields from dark matter simulations with Deep Learning

Hydrodynamic simulations provide a powerful, but computationally expensive, approach to study the interplay of dark matter and baryons in cosmological structure formation. Here we introduce the EMulating Baryonic EnRichment (EMBER) Deep Learning framework to predict baryon fields based on dark-matter-only simulations thereby reducing computational cost. EMBER comprises two network architectures, U-Net and Wasserstein Generative Adversarial Networks (WGANs), to predict two-dimensional gas and HI densities from dark matter fields. We design the conditional WGANs as stochastic emulators, such that multiple target fields can be sampled from the same dark matter input. For training we combine cosmological volume and zoom-in hydrodynamical simulations from the Feedback in Realistic Environments (FIRE) project to represent a large range of scales. Our fiducial WGAN model reproduces the gas and HI power spectra within 10% accuracy down to ~10 kpc scales. Furthermore, we investigate the capability of EMBER to predict high resolution baryon fields from low resolution dark matter inputs through upsampling techniques. As a practical application, we use this methodology to emulate high-resolution HI maps for a dark matter simulation of a L=100 Mpc/h comoving cosmological box. The gas content of dark matter haloes and the HI column density distributions predicted by EMBER agree well with results of large volume cosmological simulations and abundance matching models. Our method provides a computationally efficient, stochastic emulator for augmenting dark matter only simulations with physically consistent maps of baryon fields.

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arXiv2022

Presolar grain dynamics: creating nucleosynthetic variations through a combination of drag and viscous evolution

Meteoritic studies of solar system objects show evidence of nucleosynthetic heterogeneities that are inherited from small presolar grains (< 10 $μ$m) formed in stellar environments external to our own. The initial distribution and subsequent evolution of these grains are currently unconstrained. Using 3D, gas-dust simulations, we find that isotopic variations on the order of those observed in the solar system can be generated and maintained by drag and viscosity. Small grains are dragged radially outwards without size/density sorting by viscous expansion and backreaction, enriching the outer disc with presolar grains. Meanwhile large aggregates composed primarily of silicates drift radially inwards due to drag, further enriching the relative portion of presolar grains in the outer disc and diluting the inner disc. The late accumulation of enriched aggregates outside Jupiter could explain some of the isotopic variations observed in solar system bodies, such as the enrichment of supernovae derived material in carbonaceous chondrites. We also see evidence for isotopic variations in the inner disc that may hold implications for enstatite and ordinary chondrites that formed closer to the Sun. Initial heterogeneities in the presolar grain distribution that are not continuously reinforced are dispersed by diffusion, radial surface flows, and/or planetary interactions over the entire lifetime of the disc. For younger, more massive discs we expect turbulent diffusion to be even more homogenising, suggesting that dust evolution played a more central role in forming the isotopic anomalies in the solar system than originally thought.

astro-ph.EP↗

arXiv2022

The role of bars on the dynamical-friction driven inspiral of massive perturbers

In this paper, we systematically explore the impact of a galactic bar on the inspiral time-scale of a massive object (MO) within a Milky Way-like galaxy. We integrate the orbit of MOs in a multi-component galaxy model via a semi-analytical approach that accounts for dynamical friction generalized to rotationally supported backgrounds. We compare the MO evolution in a galaxy featuring a Milky Way-like rotating bar to the evolution within an analogous axisymmetric galaxy without the bar. In agreement with previous studies, we find that the bar presence may significantly affect the inspiral, sometimes making it shorter by a factor of a few, sometimes hindering it for a Hubble time. The erratic behaviour is mainly impacted by the relative phase at which the MO encounters the stronger bar-induced resonances. In particular, the effect of the bar is more prominent for initially in-plane, prograde MOs, especially those crossing the bar co-rotation radius or outer Lindblad resonance. In the barred galaxy, we find the sinking of the most massive MOs (>~10^7.5 Msun) approaching the galaxy from large separations (>~8 kpc) to be most efficiently hampered. Neglecting the effect of global torques associated with the non-symmetric mass distribution is thus not advisable even within an idealized, smooth galaxy model; we further note that spiral patterns are unlikely to affect the inspiral due to their transient and fluctuating nature. We speculate that the sinking efficiency of massive black holes involved in minor galaxy mergers may be hampered in barred galaxies, making them less likely to host a gravitational wave signal accessible to low-frequency detectors.

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arXiv2022

The Dawn of Disk Formation in a Milky Way-sized Galaxy Halo: Thin Stellar Disks at $z > 4$

We present results from \textsc{GigaEris}, a cosmological, $N$-body hydrodynamical "zoom-in" simulation of the formation of a Milky Way-sized galaxy halo with unprecedented resolution, encompassing of order a billion particles within the refined region. The simulation employs a modern implementation of smoothed-particle hydrodynamics, including metal-line cooling and metal and thermal diffusion. We focus on the early assembly of the galaxy, down to redshift $z=4.4$. The simulated galaxy has properties consistent with extrapolations of the main sequence of star-forming galaxies to higher redshifts and levels off to a star formation rate of $\sim$60$\, M_{\odot}$~yr$^{-1}$ at $z=4.4$. A compact, thin rotating stellar disk with properties analogous to those of low-redshift systems arises already at $z \sim 8$. The galaxy rapidly develops a multi-component structure, and the disk, at least at these early stages, does not grow "upside-down" as often reported in the literature. Rather, at any given time, newly born stars contribute to sustain a thin disk. The kinematics reflect the early, ubiquitous presence of a thin disk, as a stellar disk component with $v_ϕ/σ_R$ larger than unity is already present at $z \sim 9$--10. Our results suggest that high-resolution spectro-photometric observations of very high-redshift galaxies should find thin rotating disks, consistent with the recent discovery of cold rotating gas disks by ALMA. Finally, we present synthetic images for the JWST NIRCam camera, showing how the early disk would be easily detectable already at those early times.

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arXiv2022

Dirty waveforms: multiband harmonic content of gas-embedded gravitational wave sources

We analyse the effect of stochastic torque fluctuations on the orbital evolution and the gravitational wave (GW)emission of gas-embedded sources with intermediate and extreme mass ratios. We show that gas-driven fluctuations imprint additional harmonic content in the GWs of the binary system, which we dub dirty waveforms(DWs). We find three interesting observational prospects for DWs, provided that torque fluctuations do indeed persist beyond the resolution limit of current hydrodynamical simulations. Firstly, DWs can produce a significant stochastic GW background, comparable to other GW noise sources. Secondly, the energy flux implied by the additional harmonics can cause a detectable secular phase shift in Laser Interferometer Space Antenna (LISA) sources, even if the net torque fluctuations vanish when averaged over orbital time-scales. Lastly, the DWs of moderate-redshift nHz supermassive binaries detectable by pulsar timing arrays (PTAs) could be detectable in the mHz range, producing a new type of PTA-LISA multiband gravitational source. Our results suggest that searching for DWs and their effects can potentially be a novel way to probe the heaviest of black holes and the physics of the accretion discs surrounding them. We find these results to be a further confirmation of the many exciting prospects of actively searching for environmental effects within the data stream of future GW detectors.

astro-ph.HE↗

arXiv2021

A wide-orbit giant planet in the high-mass b Centauri binary system

Planet formation occurs around a wide range of stellar masses and stellar system architectures. An improved understanding of the formation process can be achieved by studying it across the full parameter space, particularly toward the extremes. Earlier studies of planets in close-in orbits around high-mass stars have revealed an increase in giant planet frequency with increasing stellar mass until a turnover point at 1.9 solar masses, above which the frequency rapidly decreases. This could potentially imply that planet formation is impeded around more massive stars, and that giant planets around stars exceeding 3 solar masses may be rare or non-existent. However, the methods used to detect planets in small orbits are insensitive to planets in wide orbits. Here we demonstrate the existence of a planet at 560 times the Sun-Earth distance from the 6-10 solar mass binary b Centauri through direct imaging. The planet-to-star mass ratio of 0.10-0.17% is similar to the Jupiter-Sun ratio, but the separation of the detected planet is ~100 times wider than that of Jupiter. Our results show that planets can reside in much more massive stellar systems than what would be expected from extrapolation of previous results. The planet is unlikely to have formed in-situ through the conventional core accretion mechanism, but might have formed elsewhere and arrived to its present location through dynamical interactions, or might have formed via gravitational instability.

astro-ph.EP↗

arXiv2021

Revised event rates for extreme and extremely large mass-ratio inspirals

One of the main targets of the Laser Interferometer Space Antenna (LISA) is the detection of extreme mass-ratio inspirals (EMRIs) and extremely large mass-ratio inspirals (X-MRIs). Their orbits are expected to be highly eccentric and relativistic when entering the LISA band. Under these circumstances, the inspiral time-scale given by Peters' formula loses precision and the shift of the last-stable orbit (LSO) caused by the massive black hole spin could influence the event rates estimate. We re-derive EMRIs and X-MRIs event rates by implementing two different versions of a Kerr loss-cone angle that includes the shift in the LSO, and a corrected version of Peters' time-scale that accounts for eccentricity evolution, 1.5 post-Newtonian hereditary fluxes, and spin-orbit coupling. The main findings of our study are summarized as follows: (1) implementing a Kerr loss-cone changes the event rates by a factor ranging between 0.9 and 1.1; (2) the high-eccentricity limit of Peters' formula offers a reliable inspiral time-scale for EMRIs and X-MRIs, resulting in an event rate estimate that deviates by a factor of about 0.9 to 3 when compared to event rates computed with the corrected version of Peters' time-scale and the usual loss-cone definition. (3) Event rates estimates for systems with a wide range of eccentricities should be revised. Peters' formula overestimates the inspiral rates of highly eccentric systems by a factor of about 8 to 30 compared to the corrected values. Besides, for e$_0 \lesssim$0.8, implementing the corrected version of Peters' formula would be necessary to obtain accurate estimates.

astro-ph.GA↗

arXiv2021

Improved gravitational radiation time-scales II: spin-orbit contributions and environmental perturbations

Peters' formula is an analytical estimate of the time-scale of gravitational wave (GW)-induced coalescence of binary systems. It is used in countless applications, where the convenience of a simple formula outweighs the need for precision. However, many promising sources of the Laser Interferometer Space Antenna (LISA), such as supermassive black hole binaries and extreme mass-ratio inspirals (EMRIs), are expected to enter the LISA band with highly eccentric ($e \gtrsim$ 0.9) and highly relativistic orbits. These are exactly the two limits in which Peters' estimate performs the worst. In this work, we expand upon previous results and give simple analytical fits to quantify how the inspiral time-scale is affected by the relative 1.5 post-Newtonian (PN) hereditary fluxes and spin-orbit couplings. We discuss several cases that demand a more accurate GW time-scale. We show how this can have a major influence on quantities that are relevant for LISA event-rate estimates, such as the EMRI critical semi-major axis. We further discuss two types of environmental perturbations that can play a role in the inspiral phase: the gravitational interaction with a third massive body and the energy loss due to dynamical friction and torques from a surrounding gas medium ubiquitous in galactic nuclei. With the aid of PN corrections to the time-scale in vacuum, we find simple analytical expressions for the regions of phase space in which environmental perturbations are of comparable strength to the effects of any particular PN order, being able to qualitatively reproduce the results of much more sophisticated analyses.

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arXiv2021

Revisiting dynamical friction: the role of global modes and local wakes

The orbital decay of a perturber within a larger system plays a key role in the dynamics of many astrophysical systems -- from nuclear star clusters or globular clusters in galaxies, to massive black holes in galactic nuclei, to dwarf galaxy satellites within the dark matter halos of more massive galaxies. For many decades, there have been various attempts to determine the underlying physics and time-scales of the drag mechanism, ranging from the local dynamical friction approach to descriptions based on the back-reaction of global modes induced in the background system. We present ultra-high-resolution $N$-body simulations of massive satellites orbiting a Milky Way-like galaxy (with $> 10^8$ particles), that appear to capture both the local "wake" and the global "mode" induced in the primary halo. We address directly the mechanism of orbital decay from the combined action of local and global perturbations and specifically analyze where the bulk of the torque originates.

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arXiv2021

An N-body population synthesis framework for the formation of moons around Jupiter-like planets

The moons of giant planets are believed to form in situ in Circumplanetary Discs (CPDs). Here we present an N-body population synthesis framework for satellite formation around a Jupiter-like planet, in which the dust-to-gas ratio, the accretion rate of solids from the Protoplanetary Disc, the number, and the initial positions of protosatellites were randomly chosen from realistic distributions. The disc properties were from 3D radiative simulations sampled in 1D and 2D grids and evolved semi-analytically with time. The N-body satellitesimals accreted mass from the dust component of the disc, interacted gravitationally with each other, experienced close-encounters, both scattering and colliding. With this improved modeling, we found that about $15\%$ of the resulting population is more massive than the Galilean one, and only $8.5\%$ were in resonances. The moons reach Europa's mass most frequently in $10^5$ years. In $10\%$ of the cases, moons are engulfed by the planet, and $1\%$ of the satellite-systems lose at least 1 Earth-mass into the planet, contributing to the giant planet's envelope's heavy element content. In $1\%$ of cases, we found eccentricities and inclinations of moons above 0.1. We examined the differences in outcome between the 1D and 2D disc models and used machine learning (Randomized Dependence Coefficient together with t-SNE) to compare our population with the Galilean system. Detecting our population around known transiting Jupiter-like planets via transits and TTVs would be challenging, but $14\%$ of the moons could be with an instrumental transit sensitivity of $10^{-5}$.

astro-ph.EP↗

arXiv2021

Formation of intermediate-mass planets via magnetically-controlled disk fragmentation

Intermediate mass planets, from Super-Earth to Neptune-sized bodies, are the most common type of planets in the galaxy. The prevailing theory of planet formation, core-accretion, predicts significantly fewer intermediate-mass giant planets than observed. The competing mechanism for planet formation, disk instability, can produce massive gas giant planets on wide-orbits, such as HR8799, by direct fragmentation of the protoplanetary disk. Previously, fragmentation in magnetized protoplanetary disks has only been considered when the magneto-rotational instability is the driving mechanism for magnetic field growth. Yet, this instability is naturally superseded by the spiral-driven dynamo when more realistic, non-ideal MHD conditions are considered. Here we report on MHD simulations of disk fragmentation in the presence of a spiral-driven dynamo. Fragmentation leads to the formation of long-lived bound protoplanets with masses that are at least one order of magnitude smaller than in conventional disk instability models. These light clumps survive shear and do not grow further due to the shielding effect of the magnetic field, whereby magnetic pressure stifles local inflow of matter. The outcome is a population of gaseous-rich planets with intermediate masses, while gas giants are found to be rarer, in qualitative agreement with the observed mass distribution of exoplanets.

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