arXiv subjects

Romain Teyssier

Publications and source records attributed to Romain Teyssier.

At least 73 records · Page 4Linked to original sources

arXiv2022

Toward fully compressible numerical simulations of stellar magneto-convection with the RAMSES code

Numerical simulations of magneto-convection have greatly expanded our understanding of stellar interiors and stellar magnetism. Recently, fully compressible hydrodynamical simulations of full-star models have demonstrated the feasibility of studying the excitation and propagation of pressure and internal gravity waves in stellar interiors, which would allow for a direct comparison with asteroseismological measurements. However, the impact of magnetic fields on such waves has not been taken into account yet in three-dimensional simulations. We conduct a proof of concept for the realization of three-dimensional, fully compressible, magneto-hydrodynamical numerical simulations of stellar interiors with the RAMSES code. We adapted the RAMSES code to deal with highly subsonic turbulence, typical of stellar convection, by implementing a well-balanced scheme in the numerical solver. We then ran and analyzed three-dimensional hydrodynamical and magneto-hydrodynamical simulations with different resolutions of a plane-parallel convective envelope on a Cartesian grid. Both hydrodynamical and magneto-hydrodynamical simulations develop a quasi-steady, turbulent convection layer from random density perturbations introduced over the initial profiles. The convective flows are characterized by small-amplitude fluctuations around the hydrodynamical equilibrium of the stellar interior, which is preserved over the whole simulation time. Using our compressible well-balanced scheme, we were able to model flows with Mach numbers as low as $\mathcal{M} \sim 10^{-3}$, but even lower Mach number flows are possible in principle. In the magneto-hydrodynamical runs, we observe an exponential growth of magnetic energy consistent with the action of a small-scale dynamo. (Abridged)

astro-ph.SR↗

arXiv2022

Turbulence Generation by Shock Interaction with a Highly Non-Uniform Medium

An initially planar shock wave propagating into a medium of non-uniform density will be perturbed, leading to the generation of post-shock velocity perturbations. Using numerical simulations we study this phenomenon in the case of highly-non-uniform density (order-unity normalized variance, $σ_ρ/\overlineρ \sim 1$) and strong shocks (shock Mach numbers $\overline{M}_s \gtrsim 10$). This leads to a highly disrupted shock and a turbulent post-shock flow. We simulate this interaction for a range of shock drives and initial density configurations meant to mimic those which might be presently achieved in experiments. Theoretical considerations lead to scaling relations, which are found to reasonably predict the post-shock turbulence properties. The turbulent velocity dispersion and turbulent Mach number are found to depend on the pre-shock density dispersion and shock speed in a manner consistent with the linear Richtymer-Meshkov instability prediction. We also show a dependence of the turbulence generation on the scale of density perturbations. The post-shock pressure and density, which can be substantially reduced relative to the unperturbed case, are found to be reasonably predicted by a simplified analysis that treats the extended shock transition region as a single normal shock.

physics.plasm-ph↗

arXiv2022

The driving mode of shock-driven turbulence

Turbulence in the interstellar medium (ISM) is crucial in the process of star formation. Shocks produced by supernova explosions, jets, radiation from massive stars, or galactic spiral-arm dynamics are amongst the most common drivers of turbulence in the ISM. However, it is not fully understood how shocks drive turbulence, in particular whether shock driving is a more solenoidal(rotational, divergence-free) or a more compressive (potential, curl-free) mode of driving turbulence. The mode of turbulence driving has profound consequences for star formation, with compressive driving producing three times larger density dispersion, and an order of magnitude higher star formation rate than solenoidal driving. Here, we use hydrodynamical simulations of a shock inducing turbulent motions in a structured, multi-phase medium. This is done in the context of a laser-induced shock, propagating into a foam material, in preparation for an experiment to be performed at the National Ignition Facility (NIF). Specifically, we analyse the density and velocity distributions in the shocked turbulent medium, and measure the turbulence driving parameter $b=(σ^{2 Γ}_{ρ/\langle ρ\rangle}-1)^{1/2} (1-σ_{ρ\langle ρ\rangle}^{-2})^{-1/2}\mathcal{M}^{-1}Γ^{-1/2}$ with the density dispersion $σ_{ρ/ \langle ρ\rangle}$, the turbulent Mach number $\mathcal{M}$, and the polytropic exponent $Γ$. Purely solenoidal and purely compressive driving correspond to $b \sim 1/3$ and $b \sim 1$, respectively. Using simulations in which a shock is driven into a multi-phase medium with structures of different sizes and $Γ< 1$, we find $b \sim 1$ for all cases, showing that shock-driven turbulence is consistent with strongly compressive driving.

astro-ph.GA↗

arXiv2022

A Subgrid Turbulent Mean Field Dynamo Model for Cosmological Galaxy Formation Simulations

Magnetic fields have been included in cosmological simulations of galaxy formation only recently, due to advances in numerical techniques and a better understanding of the galaxy formation physics. In this paper, we develop a new subgrid model for the turbulent dynamo that takes place in the supersonic interstellar medium in star-forming galaxies. It is based on a mean-field approach that computes the turbulent kinetic energy at unresolved scales (the so-called subgrid scales) and modifies the induction equation to account for the corresponding $α$ dynamo. Our subgrid model depends on one free parameter, the quenching parameter, that controls the saturation of the subgrid dynamo. Thanks to this mean-field approach, we can now model the fast amplification of the magnetic field inside turbulent star-forming galaxies, without relying on artificially strong initial fields or without using prohibitively expensive high-resolution simulations. We show that the evolution of the magnetic field in our zoom-in Milky Way-like galaxy is consistent with a simple picture, in which the field is in equipartition with the turbulent kinetic energy inside the star-forming disc, with a field strength around 10 $μ$G at low redshift, while at the same time strong galactic outflows fill the halo with a slightly weaker magnetic field, whose strength (10 nG) is consistent will the ideal MHD dilution factor. Our results are in good agreement with recent theoretical and numerical predictions. We also compare our simulation with Faraday depth observations at both low and high redshift, seeing overall good agreement with some caveats. Our model naturally predicts stronger magnetic fields at high redshift (around 100 $μ$G in the galaxy and 1 $μ$G in the halo), but also stronger depolarisation effects due to stronger turbulence at early time.

astro-ph.GA↗

arXiv2022

On the origin of surprisingly cold gas discs in galaxies at high redshift

We address the puzzling observational indications for very "cold" galactic discs at redshifts $z \gtrsim 3$, an epoch when discs are expected to be highly perturbed. Using a high-resolution cosmological zoom-in simulation, we identify such a cold disc at $z\sim 3.5$, with a rotation velocity to velocity dispersion ratio of $v_ϕ/σ_r \simeq 5$ for the total gas. It forms as a result of a period of intense accretion of co-planar, co-rotating gas via cold cosmic-web streams. This thin disc survives for $\sim 5$ orbital periods, after which it is disrupted by mergers and counter-rotating streams, longer but consistent with our estimate that a galaxy of this mass ($M_\star\sim10^{10}\mathrm{M_\odot}$) typically survives merger-driven spin flips for $\sim 2-3$ orbital periods. We find that $v_ϕ/σ_r$ is highly sensitive to the tracer used to perform the kinematic analysis. While it is $v_ϕ/σ_r \simeq 3.5$ for atomic HI gas, it is $v_ϕ/σ_r \simeq 8$ for molecular CO and H$_2$. This reflects the confinement of molecular gas to cold, dense clouds that reside near the disc mid-plane, while the atomic gas is spread into a turbulent and more extended thicker disc. The proposed mechanisms is a theoretical proposal that has not been validated yet with proper statistical measurements and it remains unclear whether it occurs frequently enough to explain the multiple discoveries of cold gas disks in high-z galaxies.

astro-ph.GA↗

arXiv2022

Internal dark matter structure of the most massive galaxy clusters since redshift 1

We investigate the evolution of the dark matter density profiles of the most massive galaxy clusters in the Universe. Using a `zoom-in' procedure on a large suite of cosmological simulations of total comoving volume of $3\,(h^{-1}\,\rm Gpc)^3$, we study the 25 most massive clusters in four redshift slices from $z\sim 1$ to the present. The minimum mass is $M_{500} > 5.5 \times 10^{14}$ M$_{\odot}$ at $z=1$. Each system has more than two million particles within $r_{500}$. Once scaled to the critical density at each redshift, the dark matter profiles within $r_{500}$ are strikingly similar from $z\sim1$ to the present day, exhibiting a low dispersion of 0.15 dex, and showing little evolution with redshift in the radial logarithmic slope and scatter. They have the running power law shape typical of the NFW-type profiles, and their inner structure, resolved to $3.8\,h^{-1}$ comoving kpc at $z=1$, shows no signs of converging to an asymptotic slope. Our results suggest that this type of profile is already in place at $z>1$ in the highest-mass haloes in the Universe, and that it remains exceptionally robust to merging activity.

astro-ph.CO↗

arXiv2022

Cosmology with one galaxy?

Galaxies can be characterized by many internal properties such as stellar mass, gas metallicity, and star-formation rate. We quantify the amount of cosmological and astrophysical information that the internal properties of individual galaxies and their host dark matter halos contain. We train neural networks using hundreds of thousands of galaxies from 2,000 state-of-the-art hydrodynamic simulations with different cosmologies and astrophysical models of the CAMELS project to perform likelihood-free inference on the value of the cosmological and astrophysical parameters. We find that knowing the internal properties of a single galaxy allow our models to infer the value of $Ω_{\rm m}$, at fixed $Ω_{\rm b}$, with a $\sim10\%$ precision, while no constraint can be placed on $σ_8$. Our results hold for any type of galaxy, central or satellite, massive or dwarf, at all considered redshifts, $z\leq3$, and they incorporate uncertainties in astrophysics as modeled in CAMELS. However, our models are not robust to changes in subgrid physics due to the large intrinsic differences the two considered models imprint on galaxy properties. We find that the stellar mass, stellar metallicity, and maximum circular velocity are among the most important galaxy properties to determine the value of $Ω_{\rm m}$. We believe that our results can be explained taking into account that changes in the value of $Ω_{\rm m}$, or potentially $Ω_{\rm b}/Ω_{\rm m}$, affect the dark matter content of galaxies. That effect leaves a distinct signature in galaxy properties to the one induced by galactic processes. Our results suggest that the low-dimensional manifold hosting galaxy properties provides a tight direct link between cosmology and astrophysics.

astro-ph.CO↗

arXiv2022

The Nature of High ${\rm [OIII]}_{\rm 88μm}$/${\rm [CII]}_{\rm 158μm}$ Galaxies in the Epoch of Reionization: Low Carbon Abundance and a Top-Heavy IMF?

ALMA observations of $z>6$ galaxies have revealed abnormally high [OIII]$_{\rm 88μm}$/[CII]$_{\rm 158μm}$ ratios and [CII]$_{\rm 158μm}$ deficits compared to local galaxies. Numerous solutions have been proposed including differences in C and O abundance ratios, observational bias, and differences in ISM properties. In order to elucidate the underlying physics that drives this high-redshift phenomenon, we employ SPHINX$^{20}$, a state-of-the-art, cosmological radiation-hydrodynamics simulation, that resolves detailed ISM properties of thousands of galaxies in the epoch of reionization. We find that the observed $z>6$ [OIII]-SFR and [CII]-SFR relations can only be reproduced when the C/O abundance ratio is $\sim8\times$ lower than Solar and the total metal production is $\sim4\times$ higher than that of a Kroupa IMF. This implies that high-redshift galaxies are potentially primarily enriched by low-metallicity core-collapse supernovae with a more top-heavy IMF. As AGB stars and type-Ia supernova begin to contribute to the galaxy metallicity, both the [CII]-SFR and [CII] luminosity functions are predicted to converge to observed values at $z\sim4.5$. While we demonstrate that ionisation parameter, LyC escape fraction, ISM gas density, and CMB attenuation all drive galaxies towards higher [OIII]/[CII], observed values at $z>6$ can only be reproduced with substantially lower C/O abundances compared to Solar. The combination of [CII] and [OIII] can be used to predict the values of ionisation parameter, ISM gas density, and LyC escape fraction and we provide estimates of these quantities for nine observed $z>6$ galaxies. Finally, we demonstrate that [OI]$_{\rm 63μm}$ can be used as a replacement for [CII] in high-redshift galaxies where [CII] is unobserved and argue that more observation time should be used to target [OI] at $z>6$. (Abridged)

astro-ph.GA↗

arXiv2021

ACACIA: a new method to produce on-the-fly merger trees in the RAMSES code

The implementation of ACACIA, a new algorithm to generate dark matter halo merger trees with the Adaptive Mesh Refinement (AMR) code RAMSES, is presented. The algorithm is fully parallel and based on the Message Passing Interface (MPI). As opposed to most available merger tree tools, it works on the fly during the course of the N body simulation. It can track dark matter substructures individually using the index of the most bound particle in the clump. Once a halo (or a sub-halo) merges into another one, the algorithm still tracks it through the last identified most bound particle in the clump, allowing to check at later snapshots whether the merging event was definitive, or whether it was only temporary, with the clump only traversing another one. The same technique can be used to track orphan galaxies that are not assigned to a parent clump anymore because the clump dissolved due to numerical over-merging. We study in detail the impact of various parameters on the resulting halo catalogues and corresponding merger histories. We then compare the performance of our method using standard validation diagnostics, demonstrating that we reach a quality similar to the best available and commonly used merger tree tools. As a proof of concept, we use our merger tree algorithm together with a parametrised stellar-mass-to-halo-mass relation and generate a mock galaxy catalogue that shows good agreement with observational data.

astro-ph.GA↗

arXiv2021

Eccentricity driving of pebble accreting low-mass planets

By means of high resolution hydrodynamical, three-dimensional calculations with nested-meshes, we evaluate the eccentricity reached by a low-mass, luminous planet embedded in an inviscid disc with constant thermal diffusivity and subjected to thermal forces. We find that a cell size of at most one tenth of the size of the region heated by the planet is required to get converged results. When the planet's luminosity is supercritical, we find that it reaches an eccentricity of order $10^{-2}$--$10^{-1}$, which increases with the luminosity and broadly scales with the disc's aspect ratio. Restricting our study to the case of pebble accretion, we incorporate to our model the dependence of the accretion rate of pebbles on the eccentricity. There is therefore a feedback between eccentricity, which determines the accretion rate and hence the planet's luminosity, and the luminosity, which yields the eccentricity attained through thermal forces. We solve for the steady state eccentricity and study how this quantity depends on the disc's turbulence strength parameter $α_z$, on the dimensionless stopping time of the pebbles $τ_s$, on the inward mass flux of pebbles and on the headwind (the difference between the gas velocity and the Keplerian velocity). We find that in general low-mass planets (up to a few Earth masses) reach eccentricities comparable to the disc's aspect ratio, or a sizeable fraction of the latter. Eccentric, low-mass protoplanets should therefore be the norm rather than the exception, even if they orbit far from other planets or from large scale disturbances in the disc.

astro-ph.EP↗

arXiv2021

Parameter inference with non-linear galaxy clustering: accounting for theoretical uncertainties

We implement EuclidEmulator (version 1), an emulator for the non-linear correction of the matter power spectrum, into the MCMC forecasting code MontePython. We compare the performance of Halofit, HMCode, and EuclidEmulator1, both at the level of power spectrum prediction and at the level of posterior probability distributions of the cosmological parameters, for different cosmological models and different galaxy power spectrum wave number cut-offs. We confirm that the choice of the power spectrum predictor has a non-negligible effect on the computed sensitivities when doing cosmological parameter forecasting, even for a conservative wave number cut-off of $0.2\,h\,{\rm Mpc}^{-1}$. We find that EuclidEmulator1 is on average up to $17\%$ more sensitive to the cosmological parameters than the other two codes, with the most significant improvements being for the Hubble parameter of up to $42\%$ and the equation of state of dark energy of up to $26\%$, depending on the case. In addition, we point out that the choice of the power spectrum predictor contributes to the risk of computing a significantly biased mean cosmology when doing parameter estimations. For the four tested scenarios we find biases, averaged over the cosmological parameters, of between 0.5 and 2$σ$ (from below $1σ$ up to $6σ$ for individual parameters). This paper provides a proof of concept that this risk can be mitigated by taking a well-tailored theoretical uncertainty into account as this allows to reduce the bias by a factor of 2 to 5, depending on the case under consideration, while keeping posterior credibility contours small: the standard deviations are amplified by a factor of $\leq1.4$ in all cases.

astro-ph.CO↗

arXiv2021

Efficient early stellar feedback can suppress galactic outflows by reducing supernova clustering

We present a novel set of stellar feedback models, implemented in the moving-mesh code Arepo, designed for galaxy formation simulations with near-parsec (or better) resolution. These include explicit sampling of stars from the IMF, allowing feedback to be linked to individual massive stars, an improved method for the modelling of H II regions, photoelectric heating from a spatially varying FUV field and supernova feedback. We perform a suite of 32 simulations of isolated $M_\mathrm{vir} = 10^{10}\,\mathrm{M_\odot}$ galaxies with a baryonic mass resolution of $20\,\mathrm{M_\odot}$ in order to study the non-linear coupling of the different feedback channels. We find that photoionization and supernova feedback are both independently capable of regulating star formation to the same level, while photoelectric heating is inefficient. Photoionization produces a considerably smoother star formation history than supernovae. When all feedback channels are combined, the additional suppression of star formation rates is minor. However, outflow rates are substantially reduced relative to the supernova only simulations. We show that this is directly caused by a suppression of supernova clustering by the photoionization feedback, disrupting star forming clouds prior to the first supernovae. We demonstrate that our results are robust to variations of our star formation prescription, feedback models and the gas fraction of the disk. Our results also imply that the burstiness of star formation and the mass loading of outflows may be overestimated if the adopted star particle mass is considerably larger than the mass of individual stars because this imposes a minimum cluster size.

astro-ph.GA↗

arXiv2021

Introducing SPHINX-MHD: The Impact of Primordial Magnetic Fields on the First Galaxies, Reionization, and the Global 21cm Signal

We present the first results from SPHINX-MHD, a suite of cosmological radiation-magnetohydrodynamics simulations designed to study the impact of primordial magnetic fields (PMFs) on galaxy formation and the evolution of the intergalactic medium during the epoch of reionization. The simulations are among the first to employ multi-frequency, on-the-fly radiation transfer and constrained transport ideal MHD in a cosmological context to simultaneously model the inhomogeneous process of reionization as well as the growth of PMFs. We run a series of $(5\,\text{cMpc})^3$ cosmological volumes, varying both the strength of the seed magnetic field ($B_0$) and its spectral index ($n_B$). We find that PMFs that have $n_B > -0.562\log_{10}\left(\frac{B_0}{1{\rm n}G}\right) - 3.35$ produce electron optical depths ($τ_e$) that are inconsistent with CMB constraints due to the unrealistically early collapse of low-mass dwarf galaxies. For $n_B\geq-2.9$, our constraints are considerably tighter than the $\sim{\rm n}G$ constraints from Planck. PMFs that do not satisfy our constraints have little impact on the reionization history or the shape of the UV luminosity function. Likewise, detecting changes in the Lya forest due to PMFs will be challenging because photoionisation and photoheating efficiently smooth the density field. However, we find that the first absorption feature in the global 21cm signal is a sensitive indicator of the properties of the PMFs, even for those that satisfy our $τ_e$ constraint. Furthermore, strong PMFs can marginally increase the escape of LyC photons by up to 25\% and shrink the effective radii of galaxies by $\sim44\%$ which could increase the completeness fraction of galaxy surveys. Finally, our simulations show that surveys with a magnitude limit of ${\rm M_{UV,1500}=-13}$ can probe the sources that provide the majority of photons for reionization out to $z=12$.

astro-ph.CO↗

arXiv2021

The AGORA High-resolution Galaxy Simulations Comparison Project. III: Cosmological zoom-in simulation of a Milky Way-mass halo

We present a suite of high-resolution cosmological zoom-in simulations to $z=4$ of a $10^{12}\,{\rm M}_{\odot}$ halo at $z=0$, obtained using seven contemporary astrophysical simulation codes widely used in the numerical galaxy formation community. Physics prescriptions for gas cooling, heating, and star formation, are similar to the ones used in our previous {\it AGORA} disk comparison but now account for the effects of cosmological processes. In this work, we introduce the most careful comparison yet of galaxy formation simulations run by different code groups, together with a series of four calibration steps each of which is designed to reduce the number of tunable simulation parameters adopted in the final run. After all the participating code groups successfully completed the calibration steps, we reach a suite of cosmological simulations with similar mass assembly histories down to $z=4$. With numerical accuracy that resolves the internal structure of a target halo, we find that the codes overall agree well with one another in e.g., gas and stellar properties, but also show differences in e.g., circumgalactic medium properties. We argue that, if adequately tested in accordance with our proposed calibration steps and common parameters, the results of high-resolution cosmological zoom-in simulations can be robust and reproducible. New code groups are invited to join this comparison by generating equivalent models by adopting the common initial conditions, the common easy-to-implement physics package, and the proposed calibration steps. Further analyses of the simulations presented here will be in forthcoming reports from our Collaboration.

astro-ph.GA↗

arXiv2021

Cosmological Magnetogenesis: The Biermann Battery during the Epoch of Reionization

We investigate the effect of the Biermann battery during the Epoch of Reionization (EoR) using cosmological Adaptive Mesh Refinement simulations within the framework of the SPHINX project. We develop a novel numerical technique to solve for the Biermann battery term in the Constrained Transport method, preserving both the zero divergence of the magnetic field and the absence of Biermann battery for isothermal flows. The structure-preserving nature of our numerical method turns out to be very important to minimise numerical errors during validation tests of the propagation of a Strömgren sphere and of a Sedov blast wave. We then use this new method to model the evolution of a 2.5 and 5 co-moving Mpc cosmological box with a state-of-the-art galaxy formation model within the RAMSES code. Contrary to previous findings, we show that three different Biermann battery channels emerge: the first one is associated with linear perturbations before the EoR, the second one is the classical Biermann battery associated with reionization fronts during the EoR, and the third one is associated with strong, supernova-driven outflows. While the two former channels generate spontaneously volume-filling magnetic fields with a strength on the order or below $10^{-20}$ G, the latter, owing to the higher plasma temperature and a marginally-resolved turbulent dynamo, reaches a field strength as high as $10^{-18}$ G in the intergalactic medium around massive haloes.

astro-ph.CO↗

arXiv2021

An arbitrary high-order Spectral Difference method for the induction equation

We study in this paper three variants of the high-order Discontinuous Galerkin (DG) method with Runge-Kutta (RK) time integration for the induction equation, analysing their ability to preserve the divergence free constraint of the magnetic field. To quantify divergence errors, we use a norm based on both a surface term, measuring global divergence errors, and a volume term, measuring local divergence errors. This leads us to design a new, arbitrary high-order numerical scheme for the induction equation in multiple space dimensions, based on a modification of the Spectral Difference (SD) method [1] with ADER time integration [2]. It appears as a natural extension of the Constrained Transport (CT) method. We show that it preserves $\nabla\cdot\vec{B}=0$ exactly by construction, both in a local and a global sense. We compare our new method to the 3 RKDG variants and show that the magnetic energy evolution and the solution maps of our new SD-ADER scheme are qualitatively similar to the RKDG variant with divergence cleaning, but without the need for an additional equation and an extra variable to control the divergence errors. [1] Liu Y., Vinokur M., Wang Z.J. (2006) Discontinuous Spectral Difference Method for Conservation Laws on Unstructured Grids. In: Groth C., Zingg D.W. (eds) Computational Fluid Dynamics 2004. Springer, Berlin, Heidelberg [2] Dumbser M., Castro M., Parés C., Toro E.F (2009) ADER schemes on unstructured meshes for nonconservative hyperbolic systems: Applications to geophysical flows. In: Computers & Fluids, Volume 38, Issue 9

math.NA↗

arXiv2021

Forming early-type galaxies without AGN feedback: a combination of merger-driven outflows and inefficient star formation

Regulating the available gas mass inside galaxies proceeds through a delicate balance between inflows and outflows, but also through the internal depletion of gas due to star formation. At the same time, stellar feedback is the internal engine that powers the strong outflows. Since star formation and stellar feedback are both small scale phenomena, we need a realistic and predictive subgrid model for both. We describe the implementation of supernova momentum feedback and star formation based on the turbulence of the gas in the RAMSES code. For star formation, we adopt the so-called multi-freefall model. The resulting star formation efficiencies can be significantly smaller or bigger than the traditionally chosen value of $1\%$. We apply these new numerical models to a prototype cosmological simulation of a massive halo that features a major merger which results in the formation of an early-type galaxy without using AGN feedback. We find that the feedback model provides the first order mechanism for regulating the stellar and baryonic content in our simulated galaxy. At high redshift, the merger event pushes gas to large densities and large turbulent velocity dispersions, such that efficiencies come close to $10\%$, resulting in large SFR. We find small molecular gas depletion time during the starburst, in perfect agreement with observations. Furthermore, at late times, the galaxy becomes quiescent with efficiencies significantly smaller than $1\%$, resulting in small SFR and long molecular gas depletion time.

astro-ph.GA↗

arXiv2020

EDGE: A new approach to suppressing numerical diffusion in adaptive mesh simulations of galaxy formation

We introduce a new method to mitigate numerical diffusion in adaptive mesh refinement (AMR) simulations of cosmological galaxy formation, and study its impact on a simulated dwarf galaxy as part of the 'EDGE' project. The target galaxy has a maximum circular velocity of 21 km/s but evolves in a region which is moving at up to 90 km/s relative to the hydrodynamic grid. In the absence of any mitigation, diffusion softens the filaments feeding our galaxy. As a result, gas is unphysically held in the circumgalactic medium around the galaxy for 320 Myr, delaying the onset of star formation until cooling and collapse eventually triggers an initial starburst at z=9. Using genetic modification, we produce 'velocity-zeroed' initial conditions in which the grid-relative streaming is strongly suppressed; by design, the change does not significantly modify the large scale structure or dark matter accretion history. The resulting simulation recovers a more physical, gradual onset of star formation starting at z=17. While the final stellar masses are nearly consistent ($4.8 \times 10^6\,M_\odot$ and $4.4\times 10^6\,M_\odot$ for unmodified and velocity-zeroed respectively), the dynamical and morphological structure of the z=0 dwarf galaxies are markedly different due to the contrasting histories. Our approach to diffusion suppression is suitable for any AMR zoom cosmological galaxy formation simulations, and is especially recommended for those of small galaxies at high redshift.

astro-ph.GA↗