We present a new implementation of the tracer particles algorithm based on a Monte Carlo approach for the Eulerian adaptive mesh refinement code RAMSES. The purpose of tracer particles is to keep ...track of where fluid elements originate in Eulerian mesh codes, so as to follow their Lagrangian trajectories and re-processing history. We provide a comparison to the more commonly used velocity-based tracer particles, and show that the Monte Carlo approach reproduces the gas distribution much more accurately. We present a detailed statistical analysis of the properties of the distribution of tracer particles in the gas and report that it follows a Poisson law. We extend these Monte Carlo gas tracer particles to tracer particles for the stars and black holes, so that they can exchange mass back and forth between themselves. With such a scheme, we can follow the full cycle of baryons, that is, from gas-forming stars to the release of mass back to the surrounding gas multiple times, or accretion of gas onto black holes. The overall impact on computation time is ∼3% per tracer per initial cell. As a proof of concept, we study an astrophysical science case – the dual accretion modes of galaxies at high redshifts –, which highlights how the scheme yields information hitherto unavailable. These tracer particles will allow us to study complex astrophysical systems where both efficiency of shock-capturing Godunov schemes and a Lagrangian follow-up of the fluid are required simultaneously.
The growth of a supermassive black hole (BH) is determined by how much gas the host galaxy is able to feed it, which in turn is controlled by the cosmic environment, through galaxy mergers and ...accretion of cosmic flows that time how galaxies obtain their gas, and also by internal processes in the galaxy, such as star formation and feedback from stars and the BH itself. In this paper, we study the growth of a 1012 M⊙ halo at z = 2, which is the progenitor of a group of galaxies at z = 0, and of its central BH by means of a high-resolution zoomed cosmological simulation, the Seth simulation. We study the evolution of the BH driven by the accretion of cold gas in the galaxy, and explore the efficiency of the feedback from supernovae (SNe). For a relatively inefficient energy input from SNe, the BH grows at the Eddington rate from early times, and reaches self-regulation once it is massive enough. We find that at early cosmic times z > 3.5, efficient feedback from SNe forbids the formation of a settled disc as well as the accumulation of dense cold gas in the vicinity of the BH and starves the central compact object. As the galaxy and its halo accumulate mass, they become able to confine the nuclear inflows provided by major mergers and the BH grows at a sustained near-to-Eddington accretion rate. We argue that this mechanism should be ubiquitous amongst low-mass galaxies, corresponding to galaxies with a stellar mass below ≲ 109 M⊙ in our simulations.
Super-Eddington accretion is one scenario that may explain the rapid assembly of ∼10
9
M
⊙
supermassive black holes (BHs) within the first billion year of the Universe. This critical regime is ...associated with radiatively inefficient accretion and accompanied by powerful outflows in the form of winds and jets. By means of hydrodynamical simulations of BH evolution in an isolated galaxy and its host halo with 12 pc resolution, we investigate how super-Eddington feedback affects the mass growth of the BH. It is shown that super-Eddington feedback efficiently prevents BH growth within a few Myr. The super-Eddington accretion events remain relatively mild with typical rates of about 2−3 times the Eddington limit, because of the efficient regulation by jets in that regime. We find that these jets are powerful enough to eject gas from the centre of the host galaxy all the way up to galactic scales at a few kpc, but do not significantly impact gas inflows at those large scales. By varying the jet feedback efficiency, we find that weaker super-Eddington jets allow for more significant BH growth through more frequent episodes of super-Eddington accretion. We conclude that effective super-Eddington growth is possible, as we find that simulations with weak jet feedback efficiencies provide a slightly larger BH mass evolution over long periods of time (∼80 Myr) than that for a BH accreting at the Eddington limit.
Cosmic rays (CRs) are thought to play a dynamically important role in several key aspects of galaxy evolution, including the structure of the interstellar medium, the formation of galactic winds, and ...the non-thermal pressure support of halos. We introduce a numerical model solving for the CR streaming instability and acceleration of CRs at shocks with a fluid approach in the adaptive mesh refinement code RAMSES. CR streaming is solved with a diffusion approach and its anisotropic nature is naturally captured. We introduce a shock finder for the RAMSES code that automatically detects shock discontinuities in the flow. Shocks are the loci for CR injection, and their efficiency of CR acceleration is made dependent on the upstream magnetic obliquity according to the diffuse shock acceleration mechanism. We show that the shock finder accurately captures shock locations and estimates the shock Mach number for several problems. The obliquity-dependent injection of CRs in the Sedov solution leads to situations where the supernova bubble exhibits large polar caps (homogeneous background magnetic field), or a patchy structure of the CR distribution (inhomogeneous background magnetic field). Finally, we combine both accelerated CRs with streaming in a simple turbulent interstellar medium box, and show that the presence of CRs significantly modifies the structure of the gas.
Context.
Cosmic rays propagate through the galactic scales down to the smaller scales at which stars form. Cosmic rays are close to energy equipartition with the other components of the interstellar ...medium and can provide a support against gravity if pressure gradients develop.
Aims.
We study the propagation of cosmic rays within the turbulent and magnetised bi-stable interstellar gas. The conditions necessary for cosmic-ray trapping and cosmic-ray pressure gradient development are investigated.
Methods.
We derived an analytical value of the critical diffusion coefficient for cosmic-ray trapping within a turbulent medium, which follows the observed scaling relations. We then presented a numerical study using 3D simulations of the evolution of a mixture of interstellar gas and cosmic rays, in which turbulence is driven at varying scales by stochastic forcing within a box of 40 pc. We explored a large parameter space in which the cosmic-ray diffusion coefficient, the magnetisation, the driving scale, and the amplitude of the turbulence forcing, as well as the initial cosmic-ray energy density, vary.
Results.
We identify a clear transition in the interstellar dynamics for cosmic-ray diffusion coefficients below a critical value deduced from observed scaling relations. This critical diffusion depends on the characteristic length scale
L
of
D
crit
≃ 3.1 × 10
23
cm
2
s
−1
(
L
/1 pc)
q+1
, where the exponent
q
relates the turbulent velocity dispersion
σ
to the length scale as
σ
~
L
q
. Hence, in our simulations this transition occurs around
D
crit
≃ 10
24
–
10
25
cm
2
s
−1
. The transition is recovered in all cases of our parameter study and is in very good agreement with our simple analytical estimate. In the trapped cosmic-ray regime, the induced cosmic-ray pressure gradients can modify the gas flow and provide a support against the thermal instability development. We discuss possible mechanisms that can significantly reduce the cosmic-ray diffusion coefficients within the interstellar medium.
Conclusions.
Cosmic-ray pressure gradients can develop and modify the evolution of thermally bi-stable gas for diffusion coefficients
D
0
≤ 10
25
cm
2
s
−1
or in regions where the cosmic-ray pressure exceeds the thermal one by more than a factor of ten. This study provides the basis for further works including more realistic cosmic-ray diffusion coefficients, as well as local cosmic-ray sources.
Jet-regulated cooling catastrophe Dubois, Yohan; Devriendt, Julien; Slyz, Adrianne ...
Monthly notices of the Royal Astronomical Society,
12/2010, Letnik:
409, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We present the first implementation of active galactic nuclei (AGN) feedback in the form of momentum-driven jets in an adaptive mesh refinement (AMR) cosmological resimulation of a galaxy cluster. ...The jets are powered by gas accretion on to supermassive black holes (SMBHs) which also grow by mergers. Throughout its formation, the cluster experiences different dynamical states: both a morphologically perturbed epoch at early times and a relaxed state at late times allowing us to study the different modes of black hole (BH) growth and associated AGN jet feedback. BHs accrete gas efficiently at high redshift (z > 2), significantly pre-heating proto-cluster haloes. Gas-rich mergers at high redshift also fuel strong, episodic jet activity, which transports gas from the proto-cluster core to its outer regions. At later times, while the cluster relaxes, the supply of cold gas on to the BHs is reduced leading to lower jet activity. Although the cluster is still heated by this activity as sound waves propagate from the core to the virial radius, the jets inefficiently redistribute gas outwards and a small cooling flow develops, along with low-pressure cavities similar to those detected in X-ray observations. Overall, our jet implementation of AGN feedback quenches star formation quite efficiently, reducing the stellar content of the central cluster galaxy by a factor of 3 compared to the no-AGN case. It also dramatically alters the shape of the gas density profile, bringing it in close agreement with the β model favoured by observations, producing quite an isothermal galaxy cluster for gigayears in the process. However, it still falls short in matching the lower than universal baryon fractions which seem to be commonplace in observed galaxy clusters.
AGN feedback in dwarf galaxies? Dashyan, Gohar; Silk, Joseph; Mamon, Gary A. ...
Monthly notices of the Royal Astronomical Society,
02/2018, Letnik:
473, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Dwarf galaxy anomalies, such as their abundance and cusp-core problems, remain a prime challenge in our understanding of galaxy formation. The inclusion of baryonic physics could potentially solve ...these issues, but the efficiency of stellar feedback is still controversial. We analytically explore the possibility of feedback from active galactic nuclei (AGNs) in dwarf galaxies and compare AGN and supernova (SN) feedback. We assume the presence of an intermediate-mass black hole within low-mass galaxies and standard scaling relations between the relevant physical quantities. We model the propagation and properties of the outflow and explore the critical condition for global gas ejection. Performing the same calculation for SNe, we compare the ability of AGNs and SNe to drive gas out of galaxies. We find that a critical halo mass exists below which AGN feedback can remove gas from the host halo and that the critical halo mass for an AGN is greater than the equivalent for SNe in a significant part of the parameter space, suggesting that an AGN could provide an alternative and more successful source of negative feedback than SNe, even in the most massive dwarf galaxies.
By performing three-dimensional hydrodynamical (3D MHD) simulations of a galaxy in an isolated dark matter halo, we are able to trace the evolution of the spin parameter
a
of a black hole (BH) ...undergoing super-Eddington phases throughout its growth. This regime, suspected to be accompanied by powerful jet outflows, is expected to decrease the BH spin magnitude. We combined super-Eddington accretion with sub-Eddington phases (quasar and radio modes) and followed the BH spin evolution. Due to the low frequency of the super-Eddington episodes, relativistic jets in this regime are not able to decrease the magnitude of the spin effectively, as thin-disc accretion in the quasar mode inevitably increases the BH spin. The combination of super- and sub-Eddington accretion does not lead to a simple explicit expression for the spin evolution because of feedback from super-Eddington events. An analytical expression can be used to calculate the evolution for
a
≲ 0.3, assuming the super-Eddington feedback is consistently weak. Finally, BHs starting with a low spin magnitude are able to grow to the highest mass and if they initially start out as being misaligned with the galactic disc, they get a small boost of accretion via retrograde accretion.
ABSTRACT
Cosmic rays (CRs) are thought to play an important role in galaxy evolution. We study their effect when coupled to other important sources of feedback, namely supernovae (SNe) and stellar ...radiation, by including CR anisotropic diffusion and radiative losses but neglecting CR streaming. Using the ramses-rt code, we perform the first radiation-magnetohydrodynamics simulations of isolated disc galaxies with and without CRs. We study galaxies embedded in dark matter haloes of 1010, 1011, and $10^{12}\, \rm M_{\odot }$ with a maximum resolution of $9 \, \rm pc$. We find that CRs reduce the star formation (SF) rate in our two dwarf galaxies by a factor of 2, with decreasing efficiency with increasing galaxy mass. They increase significantly the outflow mass loading factor in all our galaxies and make the outflows colder. We study the impact of the CR diffusion coefficient, exploring values from κ = 1027 to $\rm 3\times 10^{29}\, cm^2\, s^{-1}$. With a lower κ, CRs remain confined for longer on small scales and are consequently efficient in suppressing SF, whereas a higher diffusion coefficient reduces the effect on SF and increases the generation of cold outflows. Finally, we compare CR feedback to a calibrated ’strong’ SN feedback model known to sufficiently regulate SF in high-redshift cosmological simulations. We find that CR feedback is not sufficiently strong to replace this strong SN feedback. As they tend to smooth out the ISM and fill it with denser gas, CRs also lower the escape fraction of Lyman continuum photons from galaxies.
ABSTRACT
The occurrence of dual active galactic nuclei (AGN) on scales of a few tens of kpc can be used to study merger-induced accretion on massive black holes (MBHs) and to derive clues on MBH ...mergers, using dual AGN as a parent population of precursors. We investigate the properties of dual AGN in the cosmological simulation Horizon-AGN. We create catalogs of dual AGN selected with distance and luminosity criteria, plus sub-catalogs where further mass cuts are applied. We divide the sample into dual AGN hosted in different galaxies, on the way to a merger, and into those hosted in one galaxy, after the galaxy merger has happened. We find that the relation between MBH and galaxy mass is similar to that of general AGN population and we compare the properties of dual AGN also with a control sample, discussing differences and similarities in masses and Eddington ratios. The typical mass ratio of galaxy mergers associated to dual AGN is 0.2, with mass loss in the smaller galaxy decreasing the mass ratio as the merger progresses. Between 30 and 80 per cent of dual AGN with separations between 4 and 30 kpc can be matched to an ensuing MBH merger. The dual AGN fraction increases with redshift and with separation threshold, although above 50 kpc the increase of multiple AGN limits that of duals. Multiple AGN are generally associated with massive haloes, and mass loss of satellites shapes the galaxy–halo relation.
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