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Register a new userUsing H$alpha$ Filaments to Probe AGN Feedback in Galaxy Clusters
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Yu Qiu
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Recent observations of giant ellipticals and brightest cluster galaxies (BCGs) provide tentative evidence for a correlation between the luminosity of the H$alpha$ emitting gas filaments and the strength of feedback associated with the active galactic nucleus (AGN). Motivated by this, we use 3D radiation-hydrodynamic simulations with the code Enzo to examine and quantify the relationship between the observable properties of the H$alpha$ filaments and the kinetic and radiative feedback from supermassive black holes in BCGs. We find that the spatial extent and total mass of the filaments show positive correlations with AGN feedback power and can therefore be used as probes of the AGN activity. We also examine the relationship between the AGN feedback power and velocity dispersion of the H$alpha$ filaments and find that the kinetic luminosity shows statistically significant correlation with the component of the velocity dispersion along the jet axis but not the components perpendicular to it.
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The central regions of cool-core galaxy clusters harbour multiphase gas with temperatures ranging from $10 mathrm{K}$--$10^7 mathrm{K}$. Feedback from AGN jets prevents the gas from undergoing a catastrophic cooling flow. However, the exact mechanism of this feedback energy input is unknown, mainly due to the lack of velocity measurements of the hot phase gas, which has large thermal velocities. However, recent observations have measured the velocity structure functions ($mathrm{VSF}$s) of the cooler phases (at $10 mathrm{K}$ and $10^4 mathrm{K}$) and used them to indirectly estimate the motions of the hot phase. In the first part of this study, we conduct high-resolution ($384^3$--$1536^3$ resolution elements) simulations of homogeneous isotropic subsonic turbulence, without radiative cooling. We analyse the second-order velocity structure functions ($mathrm{VSF}_2$) in these simulations and study the effects of varying spatial resolution, the introduction of magnetic fields and the effect of line of sight (LOS) projection on the $mathrm{VSF}_2$. In the second part of the study, we analyse high-resolution ($768^3$ resolution elements) idealised simulations of multiphase turbulence in the intracluster medium (ICM) from Mohapatra et al 2021. We compare $mathrm{VSF}_2$ for both the hot ($Tsim10^7 mathrm{K}$) and cold ($Tsim10^4 mathrm{K}$) phases. We also look for the effect of LOS projection. For turbulence without radiative cooling, we observe a steepening in the slopes of the $mathrm{VSF}_2$ upon projection. In our runs with radiative cooling and multiphase gas, we find that the $mathrm{VSF}_2$ of the hot and cold phases have similar scaling, but introducing magnetic fields steepens the $mathrm{VSF}_2$ of the cold phase only. We also find that projection along the LOS steepens the $mathrm{VSF}_2$ for the hot phase and mostly flattens it for the cold phase.
The orientations of the red galaxies in a filament are aligned with the orientation of the filament. We thus develop a location-alignment-method (LAM) of detecting filaments around clusters of galaxies, which uses both the alignments of red galaxies and their distributions in two-dimensional images. For the first time, the orientations of red galaxies are used as probes of filaments. We apply LAM to the environment of Coma cluster, and find four filaments (two filaments are located in sheets) in two selected regions, which are compared with the filaments detected with the method of cite{Falco14}. We find that LAM can effectively detect the filaments around a cluster, even with $3sigma$ confidence level, and clearly reveal the number and overall orientations of the detected filaments. LAM is independent of the redshifts of galaxies, and thus can be applied at relatively high redshifts and to the samples of red galaxies without the information of redshifts. We also find that the images of background galaxies (interlopers) which are lensed by the gravity of foreground filaments are amplifiers to probe the filaments.
We investigate the kinematic properties of a large (N=998) sample of COSMOS spectroscopic galaxy members distributed among 79 groups. We identify the Brightest Group Galaxies (BGGs) and cross-match our data with the VLA-COSMOS Deep survey at 1.4 GHz, classifying our parent sample into radio/non-radio BGGs and radio/non-radio satellites. The radio luminosity distribution spans from $L_Rsim2times10^{21}$ W Hz$^{-1}$ to $L_Rsim3times$10$^{25}$ W Hz$^{-1}$. A phase-space analysis, performed by comparing the velocity ratio (line-of-sight velocity divided by the group velocity dispersion) with the galaxy-group centre offset, reveals that BGGs (radio and non-radio) are mostly ($sim$80%) ancient infallers. Furthermore, the strongest ($L_R>10^{23}$ W Hz$^{-1}$) radio galaxies are always found within 0.2$R_{rm vir}$ from the group centre. Comparing our samples with HORIZON-AGN, we find that the velocities and offsets of simulated galaxies are more similar to radio BGGs than to non-radio BGGs, albeit statistical tests still highlight significant differences between simulated and real objects. We find that radio BGGs are more likely to be hosted in high-mass groups. Finally, we observe correlations between the powers of BGG radio galaxies and the X-ray temperatures, $T_{rm x}$, and X-ray luminosities, $L_{rm x}$, of the host groups. This supports the existence of a link between the intragroup medium and the central radio source. The occurrence of powerful radio galaxies at group centres can be explained by Chaotic Cold Accretion, as the AGN can feed from both the galactic and intragroup condensation, leading to the observed positive $L_{rm R}-T_{rm x}$ correlation.
Recent observations provide evidence that some cool-core clusters (CCCs) host quasars in their brightest cluster galaxies (BCGs). Motivated by these findings we use 3D radiation-hydrodynamic simulations with the code Enzo to explore the joint role of the kinetic and radiative feedback from supermassive black holes (SMBHs) in BCGs. We implement kinetic feedback as sub-relativistic plasma outflows and model radiative feedback using the ray-tracing radiative transfer or thermal energy injection. In our simulations the central SMBH transitions between the radiatively efficient and radiatively inefficient states on timescales of a few Gyr, as a function of its accretion rate. The timescale for this transition depends primarily on the fraction of power allocated to each feedback mode, and to a lesser degree on the overall feedback luminosity of the active galactic nucleus (AGN). Specifically, we find that (a) kinetic feedback must be present at both low and high accretion rates in order to prevent the cooling catastrophe, and (b) its contribution likely accounts for > 10% of the total AGN feedback power, since below this threshold simulated BCGs tend to host radio-loud quasars most of the time, in apparent contrast with observations. We also find a positive correlation between the AGN feedback power and the mass of the cold gas filaments in the cluster core, indicating that observations of H$alpha$ filaments can be used as a measure of AGN feedback.
The Lyman-$alpha$ forest is a powerful probe for cosmology, but it is also strongly impacted by galaxy evolution and baryonic processes such as Active Galactic Nuclei (AGN) feedback, which can redistribute mass and energy on large scales. We constrain the signatures of AGN feedback on the 1D power spectrum of the Lyman-$alpha$ forest using a series of eight hydro-cosmological simulations performed with the Adaptative Mesh Refinement code RAMSES. This series starts from the Horizon-AGN simulation and varies the sub-grid parameters for AGN feeding, feedback and stochasticity. These simulations cover the whole plausible range of feedback and feeding parameters according to the resulting galaxy properties. AGNs globally suppress the Lyman-$alpha$ power at all scales. On large scales, the energy injection and ionization dominate over the supply of gas mass from AGN-driven galactic winds, thus suppressing power. On small scales, faster cooling of denser gas mitigates the suppression. This effect increases with decreasing redshift. We provide lower and upper limits of this signature at nine redshifts between $z=4.25$ and $z=2.0$, making it possible to account for it at post-processing stage in future work given that running simulations without AGN feedback can save considerable amounts of computing resources. Ignoring AGN feedback in cosmological inference analyses leads to strong biases with 2% shift on $sigma_8$ and 1% shift on $n_s$, which represents twice the standards deviation of the current constraints on $n_s$.
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