53 research outputs found
Dissecting the turbulent weather driven by mechanical AGN feedback
Turbulence in the intracluster, intragroup, and circumgalactic medium plays a
crucial role in the self-regulated feeding and feedback loop of central
supermassive black holes. We dissect the three-dimensional turbulent `weather'
in a high-resolution Eulerian simulation of active galactic nucleus (AGN)
feedback, shown to be consistent with multiple multi-wavelength observables of
massive galaxies. We carry out post-processing simulations of Lagrangian
tracers to track the evolution of enstrophy, a proxy of turbulence, and its
related sinks and sources. This allows us to isolate in depth the physical
processes that determine the evolution of turbulence during the recurring
strong and weak AGN feedback events, which repeat self-similarly over the Gyr
evolution. We find that the evolution of enstrophy/turbulence in the gaseous
halo is highly dynamic and variable over small temporal and spatial scales,
similar to the chaotic weather processes on Earth. We observe major
correlations between the enstrophy amplification and recurrent AGN activity,
especially via its kinetic power. While advective and baroclinc motions are
always sub-dominant, stretching motions are the key sources of the
amplification of enstrophy, in particular along the jet/cocoon, while
rarefactions decrease it throughout the bulk of the volume. This natural
self-regulation is able to preserve, as ensemble, the typically-observed
subsonic turbulence during cosmic time, superposed by recurrent spikes via
impulsive anisotropic AGN features (wide outflows, bubbles, cocoon shocks).
This study facilitates the preparation and interpretation of the
thermo-kinematical observations enabled by new revolutionary X-ray IFU
telescopes, such as XRISM and Athena.Comment: 20 pages, 14 figures, published in MNRAS, we updated 4 figures, the
main results remain unaffecte
Simulating the transport of relativistic electrons and magnetic fields injected by radio galaxies in the intracluster medium
Radio galaxies play an important role in the seeding of cosmic rays and
magnetic fields in galaxy clusters. Here, we simulate the evolution of
relativistic electrons injected into the intracluster medium by radio galaxies.
Using passive tracer particles added to magnetohydrodynamical adaptive-mesh
simulations, we calculate the evolution of the spectrum of relativistic
electrons taking into account energy losses and re-acceleration mechanisms
associated with the dynamics of the intracluster medium. Re-acceleration can
occur at shocks via diffusive shock acceleration, and in turbulent flows via
second-order Fermi re-acceleration. This study confirms that relativistic
electrons from radio galaxies can efficiently fill the intracluster medium over
scales of several , and that they create a stable reservoir of
fossil electrons that remains available for further re-acceleration by shock
waves and turbulent gas motions. Our results also show that late evolution of
radio lobes and remnant radio galaxies is significantly affected by the
dynamics of the surrounding intracluster medium. Here the diffusive
re-acceleration couples the evolution of relativistic particles to the gas
perturbations. In the near future, deep radio observations, especially at low
frequencies, can probe such mechanisms in galaxy clusters.Comment: 22 pages, 20 figures, A & A, in pres
Erratum: Dissecting the turbulent weather driven by mechanical AGN feedback
This is an Erratum to the paper entitled ‘Dissecting the turbulent weather driven by mechanical AGN feedback’, which is published in MNRAS, 498(4), 4983–5002 (2020)
Probing the origin of extragalactic magnetic fields with Fast Radio Bursts
The joint analysis of the Dispersion and Faraday Rotation Measure from distant, polarised Fast Radio Bursts may be used to put constraints on the origin and distribution of extragalactic magnetic fields on cosmological scales. While the combination of Dispersion and Faraday Rotation Measure can in principle give the average magnetic fields along the line-of-sight,in practice this method must be used with care because it strongly depends on the assumed magnetisation model on large cosmological scales. Our simulations show that the observation
of Rotation Measures with greater than or equal to 1 − 10 rad/m2 in ∼ 10^2 − 10^3 Fast Radio Bursts will likely
be able to discriminate between extreme scenarios for the origin of cosmic magnetic fields, independent of the exact distribution of sources with redshift. This represent a strong case for incoming (e.g. ALERT, CHIME) and future (e.g. with the Square Kilometer Array) radio
polarisation surveys of the sky
Bent it like frs: Extended radio agn in the cosmos field and their large-scale environment
A fascinating topic in radio astronomy is how to associate the complexity of observed radio structures with their environment in order to understand their interplay and the reason for the plethora of radio structures found in surveys. In this project, we explore the distortion of the radio structure of Fanaroff–Riley (FR)-type radio sources in the VLA-COSMOS Large Project at 3 GHz and relate it to their large-scale environment. We quantify the distortion by using the angle formed between the jets/lobes of two-sided FRs, namely bent angle (BA). Our sample includes 108 objects in the redshift range 0.08 < z < 3, which we cross-correlate to a wide range of large-scale environments (X-ray galaxy groups, density fields, and cosmic web probes) in the COSMOS field. The median BA of FRs in COSMOS at zmed∼0.9 is 167.5 +11.5/−37.5 degrees. We do not find significant correlations between BA and large-scale environments within COSMOS covering scales from a few kpc to several hundred Mpc, nor between BA and host properties. Finally, we compare our observational data to magnetohydrodynamical (MHD) adaptive-mesh simulations ENZO-MHD of two FR sources at z = 0.5 and at z = 1. Although the scatter in BA of the observed data is large, we see an agreement between observations and simulations in the bent angles of FRs, following a mild redshift evolution with BA. We conclude that, for a given object, the dominant mechanism affecting the radio structures of FRs could be the evolution of the ambient medium, where higher densities of the intergalactic medium at lower redshifts as probed by our study allow more space for jet interactions
On the origin of Mega Radiohalos
We present a first attempt to investigate the origin of radio emitting
electrons in the newly discovered class of Mega Radiohalos in clusters of
galaxies. We study the evolution of relativistic electrons accreted by the
external regions of a simulated cluster of galaxy at high resolution, including
the effect of radiative losses and turbulent re-acceleration acting on
relativistic electrons. We conclude that turbulent re-acceleration is enough
prolonged in time to produce a large reservoir of radio emitting electrons in
the large regions illuminated by Mega Radiohalos observed by LOFAR.Comment: 6 pages, 4 figures, submitted to A&A Letter
Life cycle of cosmic-ray electrons in the intracluster medium
We simulate the evolution of relativistic electrons injected into the medium
of a small galaxy cluster by a central radio galaxy, studying how the initial
jet power affects the dispersal and the emission properties of radio plasma. By
coupling passive tracer particles to adaptive-mesh cosmological MHD
simulations, we study how cosmic-ray electrons are dispersed as a function of
the input jet power. We also investigate how the latter affects the thermal and
non-thermal properties of the intracluster medium, with differences discernible
up to Gyr after the start of the jet. We evolved the energy spectra of
cosmic-ray electrons, subject to energy losses that are dominated by
synchrotron and inverse Compton emission as well as energy gains via
re-acceleration by shock waves and turbulence. We find that in the absence of
major mergers the amount of re-acceleration experienced by cosmic-ray electrons
is not enough to produce long-lived detectable radio emissions. However, for
all simulations the role of re-acceleration processes is crucial to maintain a
significant and volume-filling reservoir of fossil electrons () for several Gyrs after the first injection by jets. This is important to
possibly explain recent discoveries of cluster-wide emission and other radio
phenomena in galaxy clusters.Comment: 25 pages, 24 figures. A & A accepted, in pres
Morphology of radio relics-II. Properties of polarized emission
Radio relics are diffuse radio sources in galaxy clusters that are associated with merger shock waves. Detailed observations of radio relics in total intensity and in polarization show complex structures on kiloparsec scales. The relation between the observed features and the underlying morphology of the magnetic field is not clear. Using 3D magneto-hydrodynamical simulations, we study the polarized emission produced by a shock wave that propagates through a turbulent medium that resembles the intracluster medium. We model the polarized synchrotron emission on the basis of diffusive shock acceleration of cosmic ray electrons. We find that the synchrotron emission produced in a shocked turbulent medium can reproduce some of the observed features in radio relics. Shock compression can give rise to a high polarization fraction at the shock front and a partial alignment of the polarization E-vectors with the shock normal. Our work confirms that radio relics can also be formed in an environment with a tangled magnetic field. We also discuss the effect of Faraday rotation intrinsic to the source, and how our results depend on the angular resolution of observations
Constraints on the magnetic field in the inter-cluster bridge A399-A401
Galaxy cluster mergers are natural consequences of the structure formation in
the Universe. Such events involve a large amount of energy ( erg)
dissipated during the process. Part of this energy can be channelled in
particle acceleration and magnetic field amplification, enhancing non-thermal
emission of the intra- and inter-cluster environment. Recently, low-frequency
observations have detected a bridge of diffuse synchrotron emission connecting
two merging galaxy clusters, Abell 399 and Abell 401. Such a result provides
clear observational evidence of relativistic particles and magnetic fields
in-between clusters. In this work, we have used LOw Frequency ARray (LOFAR)
observations at 144 MHz to study for the first time the polarized emission in
the A399-A401 bridge region. No polarized emission was detected from the bridge
region. Assuming a model where polarization is generated by multiple shocks,
depolarization can be due to Faraday dispersion in the foreground medium with
respect to the shocks. We constrained its Faraday dispersion to be greater than
0.10 rad m at 95% confidence level, which corresponds to an average
magnetic field of the bridge region greater than 0.46 nG (or 0.41 nG if we
include regions of the Faraday spectrum that are contaminated by Galactic
emission). This result is largely consistent with the predictions from
numerical simulations for Mpc regions where the gas density is times
larger than the mean gas density.Comment: 12 pages, 13 figures; accepted in A&
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