Romain Teyssier | University of Zurich, Switzerland (original) (raw)

Papers by Romain Teyssier

Arxiv preprint arXiv:1108.0110, 2011

We develop a new sub-grid model for the growth of supermassive Black Holes (BHs) and their associ... more We develop a new sub-grid model for the growth of supermassive Black Holes (BHs) and their associated Active Galactic Nuclei (AGN) feedback in hydrodynamical cosmological simulations. Assuming that BHs are created in the early stages of galaxy formation, they grow by mergers and accretion of gas at a Eddington-limited Bondi accretion rate. However this growth is regulated by AGN feedback which we model using two different modes: a quasar-heating mode when accretion rates onto the BHs are comparable to the Eddington rate, and a radio-jet mode at lower accretion rates. In other words, our feedback model deposits energy as a succession of thermal bursts and jet outflows depending on the properties of the gas surrounding the BHs. We assess the plausibility of such a model by comparing our results to observational measurements of the coevolution of BHs and their host galaxy properties, and check their robustness with respect to numerical resolution. We show that AGN feedback must be a crucial physical ingredient for the formation of massive galaxies as it appears to be the only physical mechanism able to efficiently prevent the accumulation of and/or expel cold gas out of halos/galaxies and significantly suppress star formation. Our model predicts that the relationship between BHs and their host galaxy mass evolves as a function of redshift, because of the vigorous accretion of cold material in the early Universe that drives Eddington-limited accretion onto BHs. Quasar activity is also enhanced at high redshift. However, as structures grow in mass and lose their cold material through star formation and efficient BH feedback ejection, the AGN activity in the low-redshift Universe becomes more and more dominated by the radio mode, which powers jets through the hot circum-galactic medium.

The correlation between the large-scale distribution of galaxies and their spectroscopic properti... more The correlation between the large-scale distribution of galaxies and their spectroscopic properties at z=1.5 is investigated using the Horizon MareNostrum cosmological run. We have extracted a large sample of 105 galaxies from this large hydrodynamical simulation featuring standard galaxy formation physics. Spectral synthesis is applied to these single stellar populations to generate spectra and colours for all galaxies. We use

In this review, the equations of hydrodynamics, magnetohydrodynamics, and radiation hydrodynamics... more In this review, the equations of hydrodynamics, magnetohydrodynamics, and radiation hydrodynamics are presented, together with their corresponding nonideal source terms. I overview the current landscape of modern grid-based numerical techniques with an emphasis on numerical diffusion, which plays a fundamental role in stabilizing the solution but is also the main source of errors associated with these numerical techniques. I discuss in great detail the inclusion of additional important source terms, such as cooling and gravity. I also show how to modify classic operator-splitting techniques to avoid undesirable numerical errors associated with these additional source terms, in particular in the presence of highly supersonic flows. I finally present various mesh adaptation strategies that can be used to minimize these numerical errors. To conclude, I review existing astrophysical software that is publicly available to perform simulations for such astrophysical fluids.

Physical review. E, Statistical, nonlinear, and soft matter physics, 2001

Perturbation imprinting at a flat interface by a rippled shock has been observed in a laser hydro... more Perturbation imprinting at a flat interface by a rippled shock has been observed in a laser hydrodynamics experiment. A strong shock was driven through a three-layer target, with the first interface rippled, and the second flat. The chosen thickness of the second layer gave instability growth with opposite phases at the two interfaces, consistent with two-dimensional simulations and rippled shock theory.

The Astrophysical Journal, 2013

Star-forming disk galaxies at high redshift are often subject to violent disk instability, charac... more Star-forming disk galaxies at high redshift are often subject to violent disk instability, characterized by giant clumps whose fate is yet to be understood. The main question is whether the clumps disrupt within their dynamical timescale (≤ 50 Myr), like the molecular clouds in today's galaxies, or whether they survive stellar feedback for more than a disk orbital time (≈ 300 Myr) in which case they can migrate inward and help building the central bulge. We present 3.5-7 pc resolution AMR simulations of high-redshift disks including photo-ionization, radiation pressure, and supernovae feedback. Our modeling of radiation pressure determines the mass loading and initial velocity of winds from basic physical principles. We find that the giant clumps produce steady outflow rates comparable to and sometimes somewhat larger than their star formation rate, with velocities largely sufficient to escape galaxy. The clumps also lose mass, especially old stars, by tidal stripping, and the stellar populations contained in the clumps hence remain relatively young (≤ 200 Myr), as observed. The clumps survive gaseous outflows and stellar loss, because they are wandering in gas-rich turbulent disks from which they can re-accrete gas at high rates compensating for outflows and tidal stripping, overall keeping realistic and self-regulated gaseous and stellar masses. Our simulations produce gaseous outflows with velocities, densities and mass loading consistent with observations, and at the same time suggest that the giant clumps survive for hundreds of Myr and complete their migration to the center of highredshift galaxies, without rapid dispersion and reformation of clumps. These long-lived clumps can be involved in inside-out evolution and thickening of the disk, spheroid growth and fueling of the central black hole.

The Astrophysical Journal, 2009

THE ASTROPHYSICAL JOURNAL, 706:L192L196, 2009 November 20 ... C 2009. The American Astronomical ... more THE ASTROPHYSICAL JOURNAL, 706:L192L196, 2009 November 20 ... C 2009. The American Astronomical Society. All rights reserved. Printed in the USA ... GLOBULAR CLUSTER FORMATION WITHIN A COSMOLOGICAL CONTEXT ... AARON C. BOLEY, GEORGE LAKE, JUSTIN ...

The Astrophysical Journal, 2014

The Schmidt-Kennicutt relation links the surface densities of gas to the star formation rate in g... more The Schmidt-Kennicutt relation links the surface densities of gas to the star formation rate in galaxies. The physical origin of this relation, and in particular its break, i.e. the transition between an inefficient regime at low gas surface densities and a main regime at higher densities, remains debated. Here, we study the physical origin of the star formation relations and breaks in several low-redshift galaxies, from dwarf irregulars to massive spirals. We use numerical simulations representative of the Milky Way, the Large and the Small Magellanic Clouds with parsec up to subparsec resolution, and which reproduce the observed star formation relations and the relative variations of the star formation thresholds. We analyze the role of interstellar turbulence, gas cooling, and geometry in drawing these relations, at 100 pc scale. We suggest in particular that the existence of a break in the Schmidt-Kennicutt relation could be linked to the transition from subsonic to supersonic turbulence and is independent of self-shielding effects. This transition being connected to the gas thermal properties and thus to the metallicity, the break is shifted toward high surface densities in metal-poor galaxies, as observed in dwarf galaxies. Our results suggest that together with the collapse of clouds under self-gravity, turbulence (injected at galactic scale) can induce the compression of gas and regulate star formation.

We derive the transverse flux correlation function in the Lyman-alpha forest at z~2.1 from VLT-FO... more We derive the transverse flux correlation function in the Lyman-alpha forest at z~2.1 from VLT-FORS observations of a total of 32 pairs of quasars. The shape and correlation length of the transverse correlation function are in good agreement with the paradigm of intergalactic medium predicted in CDM-like models for structures formation. Using a sample of 139 Civ systems detected along the lines of sight toward the pairs of quasars we investigate the transverse correlation of metals on the same scales. We find that the correlation function is consistent with that of a randomly distributed population of Civ systems. However, we detect an important overdensity of systems in front of a quartet.

Monthly Notices of the Royal Astronomical Society, 2013

A large sample of cosmological hydrodynamical zoom-in simulations with Adaptive Mesh Refinement (... more A large sample of cosmological hydrodynamical zoom-in simulations with Adaptive Mesh Refinement (AMR) is analysed to study the properties of simulated Brightest Cluster Galaxies (BCGs). Following the formation and evolution of BCGs requires modeling an entire galaxy cluster, because the BCG properties are largely influenced by the state of the gas in the cluster and by interactions and mergers with satellites. BCG evolution is also deeply influenced by the presence of gas heating sources such as Active Galactic Nuclei (AGNs) that prevent catastrophic cooling of large amounts of gas. We show that AGN feedback is one of the most important mechanisms in shaping the properties of BCGs at low redshift by analysing our statistical sample of simulations with and without AGN feedback. When AGN feedback is included BCG masses, sizes, star formation rates and kinematic properties are closer to those of the observed systems. Some small discrepancies are observed only for the most massive BCGs, an effect that might be due to physical processes that are not included in our model.

Monthly Notices of the Royal Astronomical Society, 2008

To date, fully cosmological hydrodynamic disk simulations to redshift zero have only been underta... more To date, fully cosmological hydrodynamic disk simulations to redshift zero have only been undertaken with particle-based codes, such as GADGET, Gasoline, or GCD+. In light of the (supposed) limitations of traditional implementations of smoothed particle hydrodynamics (SPH), or at the very least, their respective idiosyncrasies, it is important to explore complementary approaches to the SPH paradigm to galaxy formation. We present the first high-resolution cosmological disk simulations to redshift zero using an adaptive mesh refinement (AMR)-based hydrodynamical code, in this case, RAMSES. We analyse the temporal and spatial evolution of the simulated stellar disks' vertical heating, velocity ellipsoids, stellar populations, vertical and radial abundance gradients (gas and stars), assembly/infall histories, warps/lopsideness, disk edges/truncations (gas and stars), ISM physics implementations, and compare and contrast these properties with our sample of cosmological SPH disks, generated with GCD+. These preliminary results are the first in our long-term Galactic Archaeology Simulation program.

Monthly Notices of the Royal Astronomical Society, 2006

We present the transverse flux correlation function of the Lyman-α forest in quasar absorption sp... more We present the transverse flux correlation function of the Lyman-α forest in quasar absorption spectra at z ∼ 2.1 from VLT-FORS and VLT-UVES observations of a total of 32 pairs of quasars; 26 pairs with separations in the range 0.6 < θ < 4 arcmin and 6 pairs with 4 < θ < 10 arcmin. Correlation is detected at the 3 σ level up to separations of the order of ∼4 arcmin (or ∼4.4h −1 Mpc comoving at z = 2.1 for Ω m = 0.3 and Ω Λ = 0.7). We have, furthermore, measured the longitudinal correlation function at a somewhat higher mean redshift (z = 2.39) from 20 lines of sight observed with high spectral resolution and high signal-tonoise ratio with VLT-UVES. We compare the observed transverse and longitudinal correlation functions to that obtained from numerical simulations and illustrate the effect of spectral resolution, thermal broadening and peculiar motions. The shape and correlation length of the correlation functions are in good agreement with those expected from absorption by the filamentary and sheet-like structures in the photoionized warm intergalactic medium predicted in CDM-like models for structures formation. Using a sample of 139 C IV systems detected along the lines of sight toward the pairs of quasars we also investigate the transverse correlation of metals on the same scales. The observed transverse correlation function of intervening C IV absorption systems is consistent with that of a randomly distributed population of absorbers. This is likely due to the small number of pairs with separation less than 2 arcmin. We detect, however, a significant overdensity of systems in the sightlines towards the quartet Q 0103−294A&B, Q 0102−2931 and Q 0102−293 which extends over the redshift range 1.5 ≤ z ≤ 2.2 and an angular scale larger than 10 arcmin. Associated systems are detected toward both quasars, at −1250 and −380 km s −1 relative to the QSO emission redshift toward, respectively, J 214501.6-303121 and J 214507.0-303046. A20 J 223850.1-295612−J 223850.9-295301 J 223850.9-295301 exhibits broad but shallow absorption lines of CIV and Lyman-α.

Astronomy & Astrophysics, 2011

Context. Stars, and more particularly massive stars, have a drastic impact on galaxy evolution. Y... more Context. Stars, and more particularly massive stars, have a drastic impact on galaxy evolution. Yet the conditions in which they form and collapse are still not fully understood. Aims. In particular, the influence of the magnetic field on the collapse of massive clumps is relatively unexplored, it is therefore of great relevance in the context of the formation of massive stars to investigate its impact. Methods. We perform high resolution, MHD simulations of the collapse of one hundred solar masses, turbulent and magnetized clouds, with the adaptive mesh refinement code RAMSES. We compute various quantities such as mass distribution, magnetic field, and angular momentum within the collapsing core and study the episodic outflows and the fragmentation that occurs during the collapse. Results. The magnetic field has a drastic impact on the cloud evolution. We find that magnetic braking is able to substantially reduce the angular momentum in the inner part of the collapsing cloud. Fast and episodic outflows are being launched with typical velocities of the order of 1-3 km s −1 , although the highest velocities can be as high as 20-40 km s −1 . The fragmentation in several objects is reduced in substantially magnetized clouds with respect to hydrodynamical ones by a factor of the order of 1.5-2. Conclusions. We conclude that magnetic fields have a significant impact on the evolution of massive clumps. In combination with radiation, magnetic fields largely determine the outcome of massive core collapse. We stress that numerical convergence of MHD collapse is a challenging issue. In particular, numerical diffusion appears to be important at high density and therefore could possibly lead to an overestimation of the number of fragments.

Astronomy & Astrophysics, 2014

Context. In Λ-CDM models, galaxies are thought to grow both through continuous cold gas accretion... more Context. In Λ-CDM models, galaxies are thought to grow both through continuous cold gas accretion coming from the cosmic web and episodic merger events. The relative importance of these different mechanisms at different cosmic epochs is nevertheless not yet well understood. Aims. We aim at addressing the questions related to galaxy mass assembly through major and minor wet merging processes in the redshift range 1 < z < 2, an epoch corresponding to the peak of the cosmic star formation history. A significant fraction of Milky Way-like galaxies are thought to have undergone an unstable clumpy phase at this early stage. We focus on the behavior of the young clumpy disks when galaxies are undergoing gas-rich galaxy mergers. Methods. Using the adaptive mesh refinement code RAMSES, we build the Merging and Isolated high-Redshift Adaptive mesh refinement Galaxies (MIRAGE) sample. It is composed of 20 mergers and 3 isolated idealized disks simulations, which sample disk orientations and merger masses. Our simulations can reach a physical resolution of 7 parsecs, and include: star formation, metal line cooling, metallicity advection, and a recent physically-motivated implementation of stellar feedback which encompasses OB-type stars radiative pressure, photo-ionization heating, and supernovae. Results. The star formation history of isolated disks shows stochastic star formation rate, which proceeds from the complex behavior of the giant clumps. Our minor and major gas-rich merger simulations do not trigger starbursts, suggesting a saturation of the star formation due to the detailed accounting of stellar feedback processes in a turbulent and clumpy interstellar medium fed by substantial accretion from the circum-galactic medium. Our simulations are globally close to the normal regime of the disk-like star formation on a Schmidt-Kennicutt diagram. The mass-size relation and its rate of evolution in the redshift range 1 < z < 2 matches observations, suggesting that the inside-out growth mechanisms of the stellar disk do not necessarily require to be achieved through a cold accretion.

Applied Physics Letters, 1999

In this letter, we present an experimental study of shock propagation in a decreasing density gra... more In this letter, we present an experimental study of shock propagation in a decreasing density gradient which is a common feature in many astrophysical objects. An original scheme for the targets has been designed to investigate the case of a discrete density step. Using foams in a wide density range (20-400 mg/cm-3), we obtained accurate data on shock acceleration at

Clefs CEA, 2009

... croissante. La simulation numé-rique des anneaux de Saturne (figure 4) illustre l'évolut... more ... croissante. La simulation numé-rique des anneaux de Saturne (figure 4) illustre l'évolution d'un système de corps gravitants et collisionnels. Les particules numé-riques modélisent les planétésimaux qui constituent les anneaux. ...