Hydrodynamical Simulations of Extragalactic Jets

2001 ◽  
Vol 1 ◽  
pp. 75-87
Author(s):  
J.M. Martí
Keyword(s):  
Extragalactic Jets ◽  
Hydrodynamical Simulations

scholarly journals Is there enough star formation in simulated protoclusters?

2020 ◽  
Vol 501 (2) ◽  
pp. 1803-1822
Author(s):  
Seunghwan Lim ◽  
Douglas Scott ◽  
Arif Babul ◽  
David J Barnes ◽  
Scott T Kay ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
Star Formation History ◽  
Test Case ◽  
Numerical Resolution ◽  
Formation History ◽  
Order Of Magnitude ◽  
History Of ◽  
Hydrodynamical Simulations ◽  
Formation Efficiency

ABSTRACT As progenitors of the most massive objects, protoclusters are key to tracing the evolution and star formation history of the Universe, and are responsible for ${\gtrsim }\, 20$ per cent of the cosmic star formation at $z\, {\gt }\, 2$. Using a combination of state-of-the-art hydrodynamical simulations and empirical models, we show that current galaxy formation models do not produce enough star formation in protoclusters to match observations. We find that the star formation rates (SFRs) predicted from the models are an order of magnitude lower than what is seen in observations, despite the relatively good agreement found for their mass-accretion histories, specifically that they lie on an evolutionary path to become Coma-like clusters at $z\, {\simeq }\, 0$. Using a well-studied protocluster core at $z\, {=}\, 4.3$ as a test case, we find that star formation efficiency of protocluster galaxies is higher than predicted by the models. We show that a large part of the discrepancy can be attributed to a dependence of SFR on the numerical resolution of the simulations, with a roughly factor of 3 drop in SFR when the spatial resolution decreases by a factor of 4. We also present predictions up to $z\, {\simeq }\, 7$. Compared to lower redshifts, we find that centrals (the most massive member galaxies) are more distinct from the other galaxies, while protocluster galaxies are less distinct from field galaxies. All these results suggest that, as a rare and extreme population at high z, protoclusters can help constrain galaxy formation models tuned to match the average population at $z\, {\simeq }\, 0$.

scholarly journals The anisotropy of the power spectrum in periodic cosmological simulations

2021 ◽  
Vol 503 (4) ◽  
pp. 5638-5645
Author(s):  
Gábor Rácz ◽  
István Szapudi ◽  
István Csabai ◽  
László Dobos
Keyword(s):  
Dark Matter ◽  
Power Spectrum ◽  
Large Scale ◽  
Cold Dark Matter ◽  
Initial Conditions ◽  
Power Spectra ◽  
Cosmological Simulations ◽  
Spherical Collapse ◽  
Lower Amplitude ◽  
Hydrodynamical Simulations

ABSTRACT The classical gravitational force on a torus is anisotropic and always lower than Newton’s 1/r2 law. We demonstrate the effects of periodicity in dark matter only N-body simulations of spherical collapse and standard Lambda cold dark matter (ΛCDM) initial conditions. Periodic boundary conditions cause an overall negative and anisotropic bias in cosmological simulations of cosmic structure formation. The lower amplitude of power spectra of small periodic simulations is a consequence of the missing large-scale modes and the equally important smaller periodic forces. The effect is most significant when the largest mildly non-linear scales are comparable to the linear size of the simulation box, as often is the case for high-resolution hydrodynamical simulations. Spherical collapse morphs into a shape similar to an octahedron. The anisotropic growth distorts the large-scale ΛCDM dark matter structures. We introduce the direction-dependent power spectrum invariant under the octahedral group of the simulation volume and show that the results break spherical symmetry.

scholarly journals The effect of photoionizing feedback on the shaping of hierarchically-forming stellar clusters

2020 ◽  
Vol 499 (1) ◽  
pp. 668-680
Author(s):  
Alejandro González-Samaniego ◽  
Enrique Vazquez-Semadeni
Keyword(s):  
Star Formation ◽  
Early Stage ◽  
Stellar Clusters ◽  
Low Mass Stars ◽  
Transfer Scheme ◽  
Star Forming ◽  
Secondary Star ◽  
Low Mass ◽  
Hydrodynamical Simulations ◽  
Formation Efficiency

ABSTRACT We use two hydrodynamical simulations (with and without photoionizing feedback) of the self-consistent evolution of molecular clouds (MCs) undergoing global hierarchical collapse (GHC), to study the effect of the feedback on the structural and kinematic properties of the gas and the stellar clusters formed in the clouds. During this early stage, the evolution of the two simulations is very similar (implying that the feedback from low-mass stars does not affect the cloud-scale evolution significantly) and the star-forming region accretes faster than it can convert gas into stars, causing the instantaneous measured star formation efficiency (SFE) to remain low even in the absence of significant feedback. Afterwards, the ionizing feedback first destroys the filamentary supply to star-forming hubs and ultimately removes the gas from it, thus first reducing the star formation (SF) and finally halting it. The ionizing feedback also affects the initial kinematics and spatial distribution of the forming stars because the gas being dispersed continues to form stars, which inherit its motion. In the non-feedback simulation, the groups remain highly compact and do not mix, while in the run with feedback, the gas dispersal causes each group to expand, and the cluster expansion thus consists of the combined expansion of the groups. Most secondary star-forming sites around the main hub are also present in the non-feedback run, implying a primordial rather than triggered nature. We do find one example of a peripheral star-forming site that appears only in the feedback run, thus having a triggered origin. However, this appears to be the exception rather than the rule, although this may be an artefact of our simplified radiative transfer scheme.

scholarly journals Probing gas disc physics with LISA: simulations of an intermediate mass ratio inspiral in an accretion disc

2019 ◽  
Vol 486 (2) ◽  
pp. 2754-2765 ◽  
Author(s):  
A M Derdzinski ◽  
D D’Orazio ◽  
P Duffell ◽  
Z Haiman ◽  
A MacFadyen
Keyword(s):  
Small Deviation ◽  
Compact Object ◽  
Accretion Disc ◽  
Mass Ratio ◽  
Intermediate Mass ◽  
Laser Interferometer Space Antenna ◽  
Total Phase ◽  
Accretion Rates ◽  
Hydrodynamical Simulations ◽  
And Migration

Abstract The coalescence of a compact object with a $10^{4}\hbox{--}10^{7}\, {\rm M_\odot }$ supermassive black hole (SMBH) produces mHz gravitational waves (GWs) detectable by the future Laser Interferometer Space Antenna (LISA). If such an inspiral occurs in the accretion disc of an active galactic nucleus (AGN), the gas torques imprint a small deviation in the GW waveform. Here, we present two-dimensional hydrodynamical simulations with the moving-mesh code disco of a BH inspiraling at the GW rate in a binary system with a mass ratio q = M2/M1 = 10−3, embedded in an accretion disc. We assume a locally isothermal equation of state for the gas (with Mach number $\mathcal {M}=20$) and implement a standard α-prescription for its viscosity (with α = 0.03). We find disc torques on the binary that are weaker than in previous semi-analytic toy models, and are in the opposite direction: the gas disc slows down, rather than speeds up the inspiral. We compute the resulting deviations in the GW waveform, which scale linearly with the mass of the disc. The SNR of these deviations accumulates mostly at high frequencies, and becomes detectable in a 5 yr LISA observation if the total phase shift exceeds a few radians. We find that this occurs if the disc surface density exceeds $\Sigma _0 \gtrsim 10^{2-3}\rm g\, cm^{-2}$, as may be the case in thin discs with near-Eddington accretion rates. Since the characteristic imprint on the GW signal is strongly dependent on disc parameters, a LISA detection of an intermediate mass ratio inspiral would probe the physics of AGN discs and migration.

scholarly journals Structure Formation in Anisotropic Disks

2006 ◽  
Vol 2 (S235) ◽  
pp. 143-143
Author(s):  
Eduard Vorobyov ◽  
Christian Theis
Keyword(s):  
Stability Analysis ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Disk Galaxies ◽  
Structural Elements ◽  
Small Perturbations ◽  
Gravitational Instabilities ◽  
Hydrodynamical Simulations ◽  
Axisymmetric Structures ◽  
Insight Into

The majority of normal disk galaxies are characterized by non-axisymmetric structures like spirals or bars. These structural elements have been widely discussed in the literature as a result of gravitational instabilities which are connected to growing density waves or global instabilities of disks. A first insight into the properties of galactic discs was provided by linear stability analysis. However, a disadvantage of linear stability analysis remained its restriction to small perturbations, both in amplitude and wavelength. Thus, numerical simulations, especially hydrodynamical and stellar-hydrodynamical simulations became a primary tool for the analysis of galactic evolution.

scholarly journals Physical properties of galaxies: towards a consistent comparison between hydrodynamical simulations and SDSS

2016 ◽  
Vol 462 (2) ◽  
pp. 2046-2062 ◽  
Author(s):  
Giovanni Guidi ◽  
Cecilia Scannapieco ◽  
Jakob Walcher ◽  
Anna Gallazzi
Keyword(s):  
Physical Properties ◽  
Hydrodynamical Simulations

scholarly journals The dynamic ejecta of compact object mergers and eccentric collisions

2013 ◽  
Vol 371 (1992) ◽  
pp. 20120272 ◽  
Author(s):  
Stephan Rosswog
Keyword(s):  
Globular Clusters ◽  
Gamma Ray ◽  
Ambient Medium ◽  
Compact Object ◽  
Solar Mass ◽  
Abundance Pattern ◽  
Compact Binary ◽  
Hydrodynamical Simulations ◽  
Rich Material ◽  
R Process

Compact object mergers eject neutron-rich matter in a number of ways: by the dynamical ejection mediated by gravitational torques, as neutrino-driven winds, and probably also a good fraction of the resulting accretion disc finally becomes unbound by a combination of viscous and nuclear processes. If compact binary mergers indeed produce gamma-ray bursts, there should also be an interaction region where an ultra-relativistic outflow interacts with the neutrino-driven wind and produces moderately relativistic ejecta. Each type of ejecta has different physical properties, and therefore plays a different role for nucleosynthesis and for the electromagnetic (EM) transients that go along with compact object encounters. Here, we focus on the dynamic ejecta and present results for over 30 hydrodynamical simulations of both gravitational wave-driven mergers and parabolic encounters as they may occur in globular clusters. We find that mergers eject approximately 1 per cent of a Solar mass of extremely neutron-rich material. The exact amount, as well as the ejection velocity, depends on the involved masses with asymmetric systems ejecting more material at higher velocities. This material undergoes a robust r-process and both ejecta amount and abundance pattern are consistent with neutron star mergers being a major source of the ‘heavy’ ( A >130) r-process isotopes. Parabolic collisions, especially those between neutron stars and black holes, eject substantially larger amounts of mass, and therefore cannot occur frequently without overproducing gala- ctic r-process matter. We also discuss the EM transients that are powered by radioactive decays within the ejecta (‘macronovae’), and the radio flares that emerge when the ejecta dissipate their large kinetic energies in the ambient medium.

scholarly journals Physics and modes of star cluster formation

2009 ◽  
Vol 5 (S266) ◽  
pp. 29-34
Author(s):  
Matthew R. Bate
Keyword(s):  
Radiative Transfer ◽  
Magnetic Fields ◽  
Cluster Formation ◽  
Star Cluster ◽  
Hydrodynamical Simulations ◽  
Made In

AbstractI review the progress made in understanding the physics and modes of star cluster formation through the use of direct self-gravitating hydrodynamical simulations, including those that have recently been performed incorporating radiative transfer and magnetic fields.

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