Observed clusters of galaxies essentially come in two flavors: non cool core clusters characterized by an isothermal temperature profile and a central entropy floor, and cool-core clusters where temperature and entropy in the central region are increasing with radius. Using cosmological resimulations of a galaxy cluster, we study the evolution of its intracluster medium (ICM) gas properties, and through them we assess the effect of different (sub-grid) modelling of the physical processes at play, namely gas cooling, star formation, feedback from supernovae and active galactic nuclei (AGN). More specifically we show that AGN feedback plays a major role in the pre-heating of the proto-cluster as it prevents a high concentration of mass from collecting in the center of the future galaxy cluster at early times. However, AGN activity during the cluster's later evolution is also required to regulate the mass flow into its core and prevent runaway star formation in the central galaxy. Whereas the energy deposited by supernovae alone is insufficient to prevent an overcooling catastrophe, supernovae are responsible for spreading a large amount of metals at high redshift, enhancing the cooling efficiency of the ICM gas. As the AGN energy release depends on the accretion rate of gas onto its central black hole engine, the AGN responds to this supernova enhanced gas accretion by injecting more energy into the surrounding gas, and as a result increases the amount of early pre-heating. We demonstrate that the interaction between an AGN jet and the ICM gas that regulates the growth of the AGN's BH, can naturally produce cool core clusters if we neglect metals. However, as soon as metals are allowed to contribute to the radiative cooling, only the non cool core solution is produced.
Chandra X-ray Observatory has revealed X-ray cavities in many nearby cooling flow clusters. The cavities trace feedback from the central active galactic nulceus (AGN) on the intracluster medium (ICM), an important ingredient in stabilizing cooling flows and in the process of galaxy formation and evolution. But, the prevalence and duty cycle of such AGN outbursts is not well understood. To this end, we study how the cooling is balanced by the cavity heating for a complete sample of clusters (the Brightest 55 clusters of galaxies, hereafter B55). In the B55, we found 33 cooling flow clusters, 20…
We find that the power of jets that inflate bubble pairs in cooling flow clusters of galaxies correlates with the size of the inner region where the entropy profile is flat, as well as with the gas mass in that region and the entropy floor (the entropy value at the center of the cluster). These correlations strengthen the cold feedback mechanism that is thought to operate in cooling flow clusters and during galaxy formation. In the cold feedback mechanism the central super-massive black hole (SMBH) is fed with cold clumps that originate in an extended region of the cooling flow volume, in part…
We show that cold clumps in the intra--cluster medium (ICM) efficiently lose their angular momentum as they fall in, such that they can rapidly feed the central AGN and maintain a heating feedback process. Such cold clumps are predicted by the cold feedback model, a model for maintaining the ICM in cooling flows hot by a feedback process. The clumps very effectively lose their angular momentum in two channels: the drag force exerted by the ICM and the random collisions between clumps when they are close to the central black hole. We conclude that the angular momentum cannot prevent the accreti…
We investigate the impact of AGN feedback on the gravitational lensing properties of a sample of galaxy clusters with masses in the range 10^14 - 10^15 Msol, using state-of-the-art simulations. Adopting a ray-tracing algorithm, we compute the cross-section of giant arcs from clusters simulated with dark-matter only physics (DM), dark matter plus gas with cooling and star formation (CSF), and dark matter plus gas with cooling, star formation and AGN feedback (CSFBH). Once AGN feedback is included, baryonic physics boosts the strong lensing cross-section by much less than previously estimated us…
We present a detailed investigation of the X-ray luminosity (Lx)-gas temperature (Tvir) relation of the complete X-ray flux-limited sample of the 64 brightest galaxy clusters in the sky (HIFLUGCS). We study the influence of two astrophysical processes, active galactic nuclei (AGN) heating and intracluster medium (ICM) cooling, on the Lx-Tvir relation, simultaneously for the first time. We determine best-fit relations for different subsamples using the cool-core strength and the presence of central radio activity as selection criteria. We find the strong cool-core clusters (SCCs) with short coo…
We present a study of an extended Lyman-alpha (Lya) nebula located in a known overdensity at z~2.38. The data include multiwavelength photometry covering the rest-frame spectral range from 0.1 to 250um, and deep optical spectra of the sources associated with the extended emission. Two galaxies are associated with the Lya nebula. One of them is a dust enshrouded AGN, while the other is a powerful starburst, forming stars at >~600 Msol/yr. We detect the HeII emission line at 1640A in the spectrum of the obscured AGN, but detect no emission from other highly ionized metals (CIV or NV) as is expec…
Galaxy clusters are the largest structures for which there is observational evidence of a magnetised medium. Central cores seem to host strong magnetic fields ranging from a few 0.1 microG up to several 10 microG in cooling flow clusters. Numerous clusters harbor central powerful AGN which are thought to prevent cooling flows in some clusters. The influence of such feedback on the magnetic field remains unclear: does the AGN-induced turbulence compensate the loss of magnetic amplification within a cool core? And how is this turbulence sustained over several Gyr? Using high resolution magneto-h…
Simulations of galaxy growth need to invoke strong negative feedback from active galactic nuclei (AGN) to suppress the formation of stars and thus prevent the over-production of very massive systems. While some observations provide evidence for such negative feedback, other studies find either no feedback, or even positive feedback, with increased star formation associated with higher AGN luminosities. Here we report an analysis of several hundred AGN and their host galaxies in the Chandra Deep Field South using X-ray and radio data for sample selection. Combined with archival far infrared dat…
Galaxy clusters are valuable cosmological probes. However, cluster mass estimates rely on observable quantities that are affected by complicated baryonic physics in the intracluster medium (ICM), including feedback from active galactic nuclei (AGN). Cosmological simulations have started to include AGN feedback using subgrid models. In order to make robust predictions, the systematics of different implementations and parametrizations need to be understood. We have developed an AGN subgrid model in FLASH that supports a few different black hole accretion models and feedback models. We use this m…
Unopposed radiative cooling of plasma would lead to the cooling catastrophe, a massive inflow of condensing gas, manifest in the core of galaxies, groups and clusters. The last generation X-ray telescopes, Chandra and XMM, have radically changed our view on baryons, indicating AGN heating as the balancing counterpart of cooling. This work reviews our extensive investigation on self-regulated heating. We argue that the mechanical feedback, based on massive subrelativistic outflows, is the key to solving the cooling flow problem, i.e. dramatically quenching the cooling rates for several Gyr with…
Flux limited X-ray surveys of galaxy clusters show that clusters come in two roughly equally proportioned varieties: "cool core" clusters (CCs) and non-"cool core" clusters (NCCs). In previous work, we have demonstrated using cosmological $N$-body + Eulerian hydrodynamic simulations that NCCs are often consistent with early major mergers events that destroy embryonic CCs. In this paper we extend those results and conduct a series of simulationsusing different methods of gas cooling, and of energy and metal feedback from supernovae, where we attempt to produce a population of clusters with real…
Observations support the view that feedback, in the form of radio outbursts from active nuclei in central galaxies, prevents catastrophic cooling of gas and rapid star formation in many groups and clusters of galaxies. Variations in jet power drive a succession of weak shocks that can heat regions close to the active galactic nuclei (AGN). On larger scales, shocks fade into sound waves. The Braginskii viscosity determines a well-defined sound damping rate in the weakly magnetized intracluster medium (ICM) that can provide sufficient heating on larger scales. It is argued that weak shocks and s…
We study the X-ray properties of 393 optically selected early-type galaxies (ETGs) over the redshift range of z~0.0-1.2 in the Chandra Deep Fields. To measure the average X-ray properties of the ETG population, we use X-ray stacking analyses with a subset of 158 passive ETGs (148 of which were individually undetected in X-ray). This ETG subset was constructed to span the redshift ranges of z = 0.1-1.2 in the ~4 Ms CDF-S and ~2 Ms CDF-N and z = 0.1-0.6 in the ~250 ks E-CDF-S where the contribution from individually undetected AGNs is expected to be negligible in our stacking. We find that 55 of…
Cool-Core Destruction in Merging Clusters with AGN Feedback and Radiative Cooling
National Taiwan University（台湾大学）；California Institute of Technology（加州理工学院）；National Tsing Hua University（清华大学）；National Center for Theoretical Sciences（国家理论科学中心）；Harvard-Smithsonian Center for Astrophysics（哈佛-史密松天体物理中心）；University of Modena and Reggio Emilia（摩德纳和雷焦艾米利亚大学）
We study the effect of AGN mechanical and radiation feedback on the formation of bulge dominated galaxies via mergers of disc galaxies. The merging galaxies have mass-ratios of 1:1 to 6:1 and include pre-existing hot gaseous halos to properly account for the global impact of AGN feedback. Using smoothed particle hydrodynamics simulation code (GADGET-3) we compare three models with different AGN feedback models: (1) no black hole and no AGN feedback; (2) thermal AGN feedback; and (3) mechanical and radiative AGN feedback. The last model is motivated by observations of broad line quasars which s…
We use hydrodynamical simulations from the OWLS project to investigate the dependence of the physical properties of galaxy populations at redshift 2 on metal-line cooling and feedback from star formation and active galactic nuclei (AGN). We find that if the sub-grid feedback from star formation is implemented kinetically, the feedback is only efficient if the initial wind velocity exceeds a critical value. This critical velocity increases with galaxy mass and also if metal-line cooling is included. This suggests that radiative losses quench the winds if their initial velocity is too low. If th…
Radiative cooling may plausibly cause hot gas in the centre of a massive galaxy, or galaxy cluster, to become gravitationally unstable. The subsequent collapse of this gas on a dynamical timescale can provide an abundant source of fuel for AGN heating and star formation. Thus, this mechanism provides a way to link the AGN accretion rate to the global properties of an ambient cooling flow, but without the implicit assumption that the accreted material must have flowed onto the black hole from 10s of kiloparsecs away. It is shown that a fuelling mechanism of this sort naturally leads to a close …
We study the long-term evolution of an idealized cool-core galaxy cluster under the influence of momentum-driven AGN feedback using three-dimensional high-resolution (60 pc) adaptive mesh refinement (AMR) simulations. The momentum-driven AGN feedback is modeled with a pair of (small-angle) precessing jets, and the jet power is calculated based on the accretion rate of the cold gas in the vicinity of the Supermassive Black Hole (SMBH). The ICM first cools into clumps along the propagation direction of the AGN jets. As the jet power increases, gas condensation occurs isotropically, forming spati…
We are looking for radio `relics' and `halos' in an X-ray selected sample of clusters of galaxies. These radio features are not a product of the Active Galactic Nuclei (AGN)-mechanism, but more likely are associated with past cluster merger events. AGN hosts of cooling flow clusters contain particle bubbles that show non-thermal radio emission. These bubbles could explain the presence of radio relics and halos if they can restrict cosmic rays efficiently. Intracluster magnetic fields and cluster environments can reveal the acceleration mechanisms of cosmic rays. Using radio/X-ray data and anal…
Detection of the copious amount of X-ray emission from the dilute hot plasma in galaxy clusters suggests that a substantial fraction of the central intracluster medium (ICM) is cooling radiatively on a time scale much faster than the Hubble time. Theoretical models predict the cooling rate as high as about few hundred to few thousand solar mass per year, which would be then made available for the formation of new stars in the core of these clusters. However, systematic studies of the cores of such clusters failed to detect the expected reservoirs of cooled gas. Thus, the gas in the cores of ga…
The Lyman-$α$ 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-$α$ 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…
We perform high resolution N-body+SPH simulations of isolated Milky-Way-like galaxies and major mergers between them, to investigate the effect of feedback from both an active galactic nucleus (AGN) and supernovae on the galaxy's evolution. Several AGN methods from the literature are used independently and in conjunction with supernova feedback to isolate the most important factors of these feedback processes. We find that in isolated galaxies, supernovae dominate the suppression of star formation but the star formation rate is unaffected by the presence of an AGN. In mergers the converse is t…
One of the legacies of the {\rm Chandra} era is the discovery of AGN-inflated X-ray cavities in virtually all cool-core clusters, with mechanical luminosities comparable to or larger than the cluster cooling rate, suggesting that AGN might be responsible for heating clusters. This discovery poses a new set of questions that cannot be addressed by X-ray imaging or modeling alone: Are AGN actually responsible for halting cooling flows? How is the AGN energy transferred to heat? How tight is the observed balance between heating and cooling? Using numerical simulations and a new virtual X-ray obse…
Recent observations of giant ellipticals and brightest cluster galaxies (BCGs) provide tentative evidence for a correlation between the luminosity of the H$α$ 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$α$ 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 co…
In several models of galaxy formation feedback occurs in cycles or mainly at high redshift. At times and in regions where feedback heating is ineffective, hot gas in the galaxy halo is expected to form a cooling flow, where the gas advects inward on a cooling timescale. Cooling flow solutions can thus be used as a benchmark for observations and simulations to constrain the timing and extent of feedback heating. Using analytic calculations and idealized 3D hydrodynamic simulations, we show that for a given halo mass and cooling function, steady-state cooling flows form a single-parameter family…
We show that feedback from active galactic nuclei (AGN) plays an essential role in reproducing the down-sizing phenomena, namely: the colour-magnitude relation; specific star formation rates; and the $α$ enhancement of early type galaxies. In our AGN model, black holes originate from Population III stars, in contrast to the merging scenario of previous works. In this paper, we show how the properties of present-day galaxies in cosmological chemo-hydrodynamical simulations change when we include our model for AGN feedback. Massive galaxies become redder, older, less massive, less compact, and s…
Radio AGN feedback is often assumed to work, but detailed physical models of this process are not well developed. This paper examines a possible path for radio AGN feedback to heat the gas in and around galaxies and perhaps suppress star formation. Nearby radio AGN are almost all FR-I radio galaxies, and it is argued that such outflows become decelerated and fully turbulent in their early stages. A 3D non-linear MHD turbulence calculation is made to determine the time required for this outflowing turbulent energy to be converted into heat. Using radio and x-ray observations of nearby FR-I AGN …
We present a multi-wavelength analysis of the galaxy cluster A1668, performed by means of new EVLA and Chandra observations and archival H$α$ data. The radio images exhibit a small central source ($\sim$14 kpc at 1.4 GHz) with L$_{\text{1.4 GHz}}$ $\sim$6 $\cdot$ 10$^{23}$ W Hz$^{-1}$. The mean spectral index between 1.4 GHz and 5 GHz is $\sim$ -1, consistent with the usual indices found in BCGs. The cooling region extends for 40 kpc, with bolometric X-ray luminosity L$_{\text{cool}} = 1.9\pm 0.1 \cdot$ 10$^{43}$ erg s$^{-1}$. We detect an offset of $\sim$ 6 kpc between the cluster BCG and the…
Hydrodynamic simulations of galaxies with active galactic nuclei (AGN) have typically employed feedback that is purely local: i.e., an injection of energy to the immediate neighborhood of the black hole. We perform GADGET-2 simulations of massive elliptical galaxies with an additional feedback component: an observationally calibrated X-ray radiation field which emanates from the black hole and heats gas out to large radii from the galaxy center. We find that including the heating and radiation pressure associated with this X-ray flux in our simulations enhances the effects which are commonly r…
We present a multi-wavelength analysis of the galaxy cluster SPT-CL J0607-4448 (SPT0607), which is one of the most distant clusters discovered by the South Pole Telescope (SPT) at $z=1.4010\pm0.0028$. The high-redshift cluster shows clear signs of being relaxed with well-regulated feedback from the active galactic nucleus (AGN) in the brightest cluster galaxy (BCG). Using Chandra X-ray data, we construct thermodynamic profiles and determine the properties of the intracluster medium. The cool core nature of the cluster is supported by a centrally-peaked density profile and low central entropy (…
We study the interaction of feedback from active galactic nuclei (AGN) and a multi-phase interstellar medium (ISM), in simulations including explicit stellar feedback, multi-phase cooling, accretion-disk winds, and Compton heating. We examine radii ~0.1-100 pc around a black hole (BH), where the accretion rate onto the BH is determined and where AGN-powered winds and radiation couple to the ISM. We conclude: (1) The BH accretion rate is determined by exchange of angular momentum between gas and stars in gravitational instabilities. This produces accretion rates ~0.03-1 Msun/yr, sufficient to p…
New Chandra X-ray and Herschel FIR observations enable a multiwavelength study of active galactic nucleus (AGN) heating and intracluster medium (ICM) cooling in the brightest cluster galaxy of Abell 2597. The new Chandra observations reveal the central < 30 kiloparsec X-ray cavity network to be more extensive than previously thought, and associated with enough enthalpy to theoretically inhibit the inferred classical cooling flow. Nevertheless, we present new evidence, consistent with previous results, that a moderately strong residual cooling flow is persisting at 4%-8% of the classically pred…
A fundamental gap in the current understanding of galaxies concerns the thermodynamical evolution of the ordinary, baryonic matter. On one hand, radiative emission drastically decreases the thermal energy content of the interstellar plasma (ISM), inducing a slow cooling flow toward the centre. On the other hand, the active galactic nucleus (AGN) struggles to prevent the runaway cooling catastrophe, injecting huge amount of energy in the ISM. The present study intends to deeply investigate the role of mechanical AGN feedback in (isolated or massive) elliptical galaxies, extending and completing…
