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30/09/2019, 08:30
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30/09/2019, 09:10
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Prof. Sukyoung Yi (Yonsei University)30/09/2019, 09:20
Last year, I presented how the galaxies in New Horizon settle their galactic scale disc. More massive galaxies seem to have a settled disc earlier in the simulation, but it was not clear what is the main driver. This year I present a few pieces of information on the properties of galaxies, such as merger history, star formation rate, stellar feedback, black hole accretion and feedback, during...
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Ms Min-Jung Park (Yonsei University)30/09/2019, 09:40
Using the unprecedented high-resolution cosmological simulation, New Horizon, we have studied the origin of galactic structures: disk and spheroid. However, since New Horizon has only reached z=0.7, covering the first half of the cosmic time, it is not yet clear about the formation of the structures of local galaxies, including the Milky Way. Zooming in two individual galaxies in the field...
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Mr Sean Barrett (University of Oxford)30/09/2019, 10:00
In cosmological, radiation-hydrodynamics simulations of galaxy formation, chemical abundances and ionisation fractions are often determined by post-processing, which fails to capture the effect the chemical state has on the radiation field (by absorption and emission processes) and ultimately on the dynamics of the gas (by radiative cooling, and indirectly by other interactions with...
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Dr Garreth Martin (University of Arizona)30/09/2019, 10:50
Cosmological simulations provide an alternative way of probing populations of low-surface-brightness (LSB) objects, which make up the majority of galaxies in the Universe, but which remain poorly studied observationally. Making predictions for this sub-set of the galaxy population is important, since our current understanding of galaxy evolution is underpinned by the parts of the galaxy...
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Mr Ryan Jackson (University of Hertfordshire)30/09/2019, 11:10
Galaxy evolution studies have been dominated by objects that lie above the surface brightness (SB) limit of current wide surveys like the SDSS ( 23 mag/arcsec^2). However, hints of a much larger population of low-surface-brightness galaxies (LSBGs) have recently been discovered. State-of-the-art cosmological simulations, and new deep wide surveys, have begun to show that these galaxies might...
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Mr Michael Kretschmer (ICS Zurich)30/09/2019, 11:30
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...
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Dr Sugata Kaviraj (University of Hertfordshire)30/09/2019, 11:50
While AGN are considered to be key drivers of the evolution of massive galaxies, their potentially significant role in the dwarf-galaxy regime (M < 10^9 MSun) remains largely unexplored. We combine optical and infrared data, from the Hyper Suprime-Cam (HSC) and the Wide-field Infrared Explorer (WISE) respectively, to explore the properties of ~800 AGN in dwarfs at low redshift (z<0.3)....
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Jenny Sorce (CRAL)30/09/2019, 13:40
At about 15 Mpc from us, the Virgo cluster of galaxies is a formidable source of information to study cluster formation and galaxy evolution in this rich environment. Several observationally-based scenarios for the cluster formation arose within the past decade regarding the number and properties of the galaxies that entered the cluster recently and the nature of the last major merger that the...
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Mr Baptiste Faure (CEA)30/09/2019, 14:00
High redshift galaxies have a very different morphology than nearby ones. Indeed, the high gas fraction in such galaxies drives strong gravitational instabilities which lead to fragmentation and formation of giant star forming structures of masses up to $10^8$ and $10^9$ \msun often dubbed «giant clumps». Recent observations with high resolution questioned the existence of the giant clumps by...
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Dr Beckmann Ricarda (Institut d'Astrophysique de Paris)30/09/2019, 14:20
Extended filamentary nebulae of cold, dense gas are a striking feature or nearby galaxy clusters, but their formation mechanism and the processes which shape their morphology remain poorly understood. In this talk, I will present work investigating the condensation and evolution of this cold gas under the influence of a spin-driven AGN jet in a Perseus-like clusters.
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Mr Jacob Svensmark30/09/2019, 15:10
Dark matter dominates the properties of large cosmological structures such as galaxy clusters, and the mass profiles of the dark matter have been measured for these equilibrated structures for years using X-rays, lensing or galaxy velocities. A new method has been proposed, which should allow us to measure a dynamical property of the dark matter, namely the velocity anisotropy. For the gas a...
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Mr Marius Ramsoy (University of Oxford)30/09/2019, 15:30
Cold mode accretion filaments are extremely important in determining the morphology of galaxies at high redshifts, being responsible for transporting around 90% of a galaxy's mass and angular momentum. Unfortunately these structures are nearly invisible to current instruments despite numerous pieces of indirect evidence. With simulations however we can bypass these limitations to study their...
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Mr Donghyeon Khim (Yonsei University)30/09/2019, 15:50
We have explored star-gas misalignment using Horizon-AGN simulation and compared the result with Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. While stars and gas are expected to have aligned rotational axes in a galaxy, IFU observations found that about 11% of the observed galaxies are misaligned. Horizon-AGN showed the distribution of misalignment angles found by...
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Dr Joakim Rosdahl (Centre de Recherche Astrophysique de Lyon)01/10/2019, 09:00
The epoch of reionisation marks a major shift from a cold neutral Universe to a warm ionised one, a transition which was thought to be powered by UV radiation emitted from young massive stars in the first galaxies. Our understanding of this epoch is still limited: observationally we glimpse a handful of the most luminous galaxies existing at the end of the epoch, but with the advent of the...
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Mr Mathieu Chuniaud (CRAL)01/10/2019, 09:20
The epoch of reionization is the period during which the hydrogen present in the universe is entirely reionized, between z = 15 and z = 6. The nature of the sources of reionization is still a matter of debate. In this talk I will use the SPHINX simulation to characterize the properties of the galaxies that drive reionization. The SPHINX simulation focuses on the epoch of reionization and...
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Mr Pierre Ocvirk (Observatoire astronomique de Strasbourg)01/10/2019, 09:40
Cosmic Dawn II (CoDa II) is a new, fully-coupled radiation-hydrodynamics simulation of cosmic reionization and galaxy formation and their mutual impact, to redshift z < 6. With 4096^3 particles and cells in a (94 Mpc)^3 box, it is large enough to model global reionization and its feedback on galaxy formation while resolving all haloes above 10^8 Msun. To accomplish this massive numerical...
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Mr Joseph Lewis (Observatoire Astronomique de Strasbourg)01/10/2019, 10:00
A growing consensus seems to point towards the ionising UV light of galaxies having been the main driving force behind the reionisation process. I analysed the ionising photon contribution of galaxies to the intergalactic medium and its relation to galactic properties such as mass and star formation in the Cosmic Dawn II simulation, a new, massive, fully-coupled radiation-hydrodynamics...
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Mr Koki Kakiichi (University College London)01/10/2019, 10:50
The question of whether early star-forming galaxies generated sufficient Lyman continuum (LyC) photons to drive cosmic reionisation is one of the major challenge in modern cosmology. Recent deep HST UV imaging and spectroscopy have revealed a signature of LyC leakage along the lines-of-sight of Lyman-alpha emitting galaxies. The observed correlations between LyC escape fraction, Lyman alpha...
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Mr Taehwa Yoo (Yonsei University)01/10/2019, 11:10
The physical origin of low escape fractions of ionizing radiation derived from Lyman-break galaxies (LBGs) at $z\sim3$--$4$ is a puzzle in the theory of reionization. We perform idealized disk galaxy simulations to investigate how galactic properties, such as metallicity and gas mass, affect the escape of Lyman continuum (LyC) photons using radiation-hydrodynamic code, \texttt{RAMSES-RT}, with...
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Dr Peter Mitchell (Leiden Observatory)01/10/2019, 11:30
I will present scientific results from a Ramses-RT zoom-in simulation of a z=3 galaxy, run including the implementation of Monte Carlo tracer particles recently developed by Corentin Cadiou. I will show how tracer particles can be used to identify the Lagrangian origin of the gas emitting and scattering Lyman-alpha photons, and discuss how this informs the interpretation of recent observations...
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Mr Valentin Mauerhofer (University of Geneva)01/10/2019, 11:50
To understand the role of galaxies during the epoch of reionization, it is essential to know more about the values of the escape fractions of ionizing photons from those galaxies. Since the intergalactic medium was opaque to lyman continuum radiation during reionization, it will never be possible to observe directly the escape fraction, so we have to rely on indirect measurements. One...
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Ms Solène Chabanier (CEA Saclay)01/10/2019, 13:40
Neutral hydrogen in the IGM scatters light at 1216A producing an absorption spectrum that is observed on any background sources known as the Lyman-alpha forest. The fluctuations in the Lyman-alpha forest absorption can be used as a tracer of the varying density of intergalactic gas expected from the growth of structures from primordial fluctuations in the Universe. They can be accurately...
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Prof. Oliver Hahn (Lagrange/UCA/OCA)01/10/2019, 14:00
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Mr Bournaud Frederic (CEA Saclay)01/10/2019, 14:20
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Dr Jeremy Blaizot (CRAL)01/10/2019, 14:30
Community codes such as RAMSES face similar challenges regarding maintenance, upgrades, documentation, and user support, as classical observing instruments. They further face the issue of rapidly evolving platforms (e.g. computer centres buying GPUs), and have to manage a posteriori community developments. The French RAMSES community has been lobbying for RAMSES (and simulation codes in...
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Dr Neil Vaytet (European Spallation Source, Copenhagen, Denmark)01/10/2019, 15:20
I left the field of astrophysics a year ago and started working as a full-time software developer for the European Spallation Source, a large neutron physics facility current under construction in Lund (Sweden). I am involved in a sizeable project counting about 30 core developers, over 50 more casual developers, and ~2000 users. I will share my experiences on the methods we use to coordinate...
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Mr San Han (Yonsei University)01/10/2019, 15:40
Classic RAMSES code is purely written with MPI and not optimized for large simulations that use more than thousands of cores. We try to overcome this issue by adding OpenMP feature to RAMSES, implementing hybrid parallelism that takes advantage of both distributed and shared memory models. With the latest developed OpenMP version, we ran a small cosmological test simulation and it showed a...
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Prof. Romain Teyssier (University of Zurich)01/10/2019, 16:00
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Mr Eric Andersson (Lund Observatory)02/10/2019, 09:20
I am currently testing a model I have implemented in RAMSES which treats individual stars, both in isolated galaxies and cosmological context. In this talk, I will present a new star formation model that samples the IMF fast and accurately, hence allowing for a more sophisticated star-by-star treatment of stellar feedback processes. The model can currently trace stars down to 8 solar masses...
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Dr Maxime Delorme (University of Surrey)02/10/2019, 09:40
Modelling the formation and evolution of globular clusters in cosmological simulations is a notoriously difficult problem. Due to the extreme differences in scales in space and time required to resolve the star-by-star dynamics of the globular clusters, most simulations presently use sub-grid and semi-analytical models as prescriptions for the globular clusters. Moreover, even if this extreme...
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Dr William Chantereau (ARI (LJMU))02/10/2019, 10:00
Stars in old stellar clusters lose a non negligible amount of mass during their evolution. This material is then expected to build up a substantial intra-cluster medium. However, the observed gas content in these old stellar clusters is a couple of orders of magnitude below these expectations. We follow the evolution of the stellar wind material thanks to hydrodynamical simulations taking into...
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Dr Yohan Dubois (Institut d'Astrophysique de Paris)02/10/2019, 10:50
I will detail the implementation of cosmic rays (CR) in Ramses. This numerical method of CRs is based on a fluid description of CRs. The anisotropic diffusion of CRs along magnetic field lines is modeled with an implicit solver. CR streaming instability (CRs streaming down their own gradient at the Alfven velocity) can be solved within the implicit diffusion solver. The so-called diffuse shock...
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Prof. Taysun Kimm (Yonsei University)02/10/2019, 11:10
Strong radiation fields can change the ionization state of metals and hence cooling rates. In order to understand their effects on the momentum transfer from radiation and supernova feedback, we perform a suite of radiation-hydrodynamic simulations with radiation-modulated metal cooling. For this purpose, we pre-tabulate the metal cooling rates for a variety of spectral shapes and flux levels...
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Dr Rebekka Bieri (MPA)02/10/2019, 11:30
The interstellar medium (ISM) is notoriously difficult to reproduce in simulations. The standard approach models star formation following a Schmidt law and performs feedback with the same single instantaneous injections of the SN energy per stellar population particle. I will present an alternative method using sink particles to represent individual star clusters. This allows for each stellar...
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Mr Daniel Han (Yonsei University)02/10/2019, 11:50
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Mr Sigurd Jensen (Niels Bohr Institute)02/10/2019, 13:40
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Ms Tine Colman (ICS, University of Zurich)02/10/2019, 14:00
Understanding the stellar initial mass function has been a long standing problem in star formation. Recently, a new theory has been proposed that puts forward the idea that tidal forces caused by young stars prevent the formation of other stars within a certain radius. To study this, I ran a set of turbulent box simulations with ramses and analyzed the tidal field around new born stars. This...
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Dr Rajika Kuruwita (Niels Bohr Institute)02/10/2019, 14:20
I present theoretical work done using the AMR MHD code FLASH on the formation of binary stars and the evolution of their discs in these systems. I simulated the collapse of molecular cores until the formation of protostars and followed the early evolution of these systems. I investigated the influence that binarity has on the global evolution of a young stellar system, including looking at...
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Michael Küffmeier (Zentrum für Astronomie Heidelberg (ZAH))02/10/2019, 15:10
Stars form as a consequence of gravitational collapse in Giant Molecular Clouds. Contrary to models of individual stars forming due to the collapse of an isolated core, we account for the molecular cloud environment during the epoch of star and protoplanetary disk formation. Using zoom-in simulations with the magnetohydrodynamical codes RAMSES, we investigate the accretion process of young...
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Mr Noe Brucy (CEA)02/10/2019, 15:30
We run hydrodynamical simulations of protoplanetary disk to investigate the effects of a classical very simplified cooling model on disk fragmentation. The goals are to estimate the fragmentation boundary when using a Godunov scheme, probe convergence and build a simple analytical model.
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Mr Ugo Lebreuilly (CRAL)02/10/2019, 15:50
Dust grains are the building blocks of protoplanetary disks and planets. Dust regulates the thermal evolution of the disk through its opacity. In addition, it plays a major role in the coupling between the gas and the magnetic field, hence in the disk and jet formation. In observations, the polarized light emitted by the grains can be used to measure the magnetic fields orientation or to...
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