The origin of the bimodality in cluster core entropy is still unknown. At the same time, recent work has shown that thermal conduction in clusters is likely a time-variable phenomenon. We consider if time-variable conduction and AGN outbursts could be responsible for the cool-core (CC), non cool-core (NCC) dichotomy. We show that strong AGN heating can bring a CC cluster to a NCC state, which can be stably maintained by conductive heating from the cluster outskirts. On the other hand, if conduction is shut off by the heat-flux driven buoyancy instability, then the cluster will cool to the CC state again, where it is stabilized by low-level AGN heating. Thus, the cluster cycles between CC and NCC states. In contrast with massive clusters, we predict the CC/NCC bimodality should vanish in groups, due to the lesser role of conductive heating there. We find tentative support from the distribution of central entropy in groups, though firm conclusions require a larger sample carefully controlled for selection effects.
Recent X-ray observations of galaxy clusters suggest that cluster populations are bimodally distributed according to central gas entropy and are separated into two distinct classes: cool core (CC) and non-cool core (NCC) clusters. While it is widely accepted that AGN feedback plays a key role in offsetting radiative losses and maintaining many clusters in the CC state, the origin of NCC clusters is much less clear. At the same time, a handful of extremely powerful AGN outbursts have recently been detected in clusters, with a total energy ~10^{61}-10^{62} erg. Using two dimensional hydrodynamic…
Although the energetic feedback from active galactic nuclei (AGN) is believed to have a profound effect on the evolution of galaxies and clusters of galaxies, details of the AGN heating remain elusive. Here, we study NGC 193 - a nearby lenticular galaxy - based on X-ray (Chandra) and radio (VLA and GMRT) observations. These data reveal the complex AGN outburst history of the galaxy: we detect a pair of inner X-ray cavities, an outer X-ray cavity, a shock front, and radio lobes extending beyond the inner cavities. We suggest that the inner cavities were produced ~78 Myr ago by a weaker AGN outb…
We present results from a very deep (650 ks) Chandra X-ray observation of the galaxy group NGC~5813, the deepest Chandra observation of a galaxy group to date. Earlier observations showed two pairs of cavities distributed roughly collinearly, with each pair associated with an elliptical shock front. The new observations confirm a third pair of outer cavities, collinear with the other pairs, and reveal an associated outer outburst shock at ~30 kpc. This system is therefore unique in exhibiting three cavity pairs, each associated with an unambiguous AGN outburst shock front. The implied mean kin…
By conducting axisymmetrical hydrodynamical numerical simulations (2.5 dimensional code) we show that slow, massive, wide jets can reproduce the morphology of the huge X-ray deficient bubble pair in the cluster of galaxies MS0735+7421. The total energy of the jets, composed of the energy in the bubble pair and in the shock wave, is constraint by observations conducted by McNamara et al. (2009) to be ~10^{62}erg. We show that two opposite jets that are active for ~100Myr, each with a launching half opening angle of ~70 degrees, an initial velocity of ~0.1c, and a total mass loss rate of the two…
We present results from new Chandra, GMRT, and SOAR observations of NGC 5813, the dominant central galaxy in a nearby galaxy group. The system shows three pairs of collinear cavities at 1 kpc, 8 kpc, and 20 kpc from the central source, from three distinct outbursts of the central AGN, which occurred 3x10^6, 2x10^7, and 9x10^7 yr ago. The H-alpha and X-ray observations reveal filaments of cool gas that has been uplifted by the X-ray cavities. The inner two cavity pairs are filled with radio emitting plasma, and each pair is associated with an elliptical surface brightness edge, which we unambig…
Both radiative and mechanical feedback from Active Galactic Nuclei have been found to be important for the evolution of elliptical galaxies. We compute how a shock may be driven from a central black hole into the gaseous envelope of an elliptical galaxy by mechanical as well as radiative feedback (in the form of nuclear winds) using high resolution 1-D hydrodynamical simulations. We calculate the synchrotron emission from the electron cosmic rays accelerated by the shocks (not the jets) in the central part of elliptical galaxies, and we also study the synchrotron spectrum's evolution using the…
We present results from a 42 ks Chandra/ACIS-S observation of the transitional FRI/FRII radio galaxy 3C288 at z = 0.246. We detect $\sim$3 keV gas extending to a radius of $\sim$0.5 Mpc with a 0.5-2.0 keV luminosity of 6.6 $\times$ 10$^{43}$ ergs s$^{-1}$, implying that 3C288 lies at the center of a poor cluster. We find multiple surface brightness discontinuities in the gas indicative of either a shock driven by the inflation of the radio lobes or a recent merger event. The temperature across the discontinuities is roughly constant with no signature of a cool core, thus disfavoring either the…
We present results from Chandra observations of NGC 5813, the dominant central galaxy in a nearby galaxy group. We focus on three main results. 1) The diffuse gas shows clear signatures from three distinct outbursts of the central AGN, with three pairs of roughly collinear cavities. The inner two cavity pairs are associated with unambiguous elliptical shock fronts, with Mach numbers M~1.7 and M~1.5 for the inner and outer shocks, respectively. 2) The mean power of the two most recent outbursts differs by a factor of six, indicating that the mean jet power varies over long (~10^7 yr) time scale…
We present ~103 ks of Chandra observations of the galaxy cluster SPT-CLJ0528-5300 (SPT0528, z=0.768). This cluster harbors the most radio-loud (L_1.4GHz = 1.01 x 10^33 erg/s/Hz) central AGN of any cluster in the South Pole Telescope (SPT) SZ survey with available X-ray data. We find evidence of AGN-inflated cavities in the X-ray emission, which are consistent with the orientation of the jet direction revealed by ATCA radio data. The combined probability that two such depressions -- each at ~1.4-1.8sigma significance, oriented ~180 degrees apart and aligned with the jet axis -- would occur by c…
Utilizing $\sim 50$ ks of Chandra X-ray Observatory imaging, we present an analysis of the intracluster medium (ICM) and cavity system in the galaxy cluster RBS 797. In addition to the two previously known cavities in the cluster core, the new and deeper X-ray image has revealed additional structure associated with the active galactic nucleus (AGN). The surface brightness decrements of the two cavities are unusually large, and are consistent with elongated cavities lying close to our line-of-sight. We estimate a total AGN outburst energy and mean jet power of $\approx 3 - 6 \times 10^{60}$ erg…
We present Chandra ACIS-I and ACIS-S observations ($\sim$200 ks in total) of the X-ray luminous elliptical galaxy NGC 4636, located in the outskirts of the Virgo cluster. A soft band (0.5-2 keV) image shows the presence of a bright core in the center surrounded by an extended X-ray corona and two pronounced quasi-symmetric, 8 kpc long, arm-like features. Each of this features defines the rimof an ellipsoidal bubble. An additional bubble-like feature, whose northern rim is located $\sim2$ kpc south of the north-eastern arm, is detected as well. We present surface brightness and temperature prof…
We report on an analysis of new Chandra data of the galaxy group HCG 62, well known for possessing cavities in its intragroup medium (IGM) that were inflated by the radio lobes of its central active galactic nucleus (AGN). With the new data, a factor of three deeper than previous Chandra data, we re-examine the energetics of the cavities and determine new constraints on their contents. We confirm that the ratio of radiative to mechanical power of the AGN outburst that created the cavities is less than 10^-4, among the lowest of any known cavity system, implying that the relativistic electrons …
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…
Radio AGN feedback in X-ray cool cores has been proposed as a crucial ingredient in the evolution of baryonic structures. However, it has long been known that strong radio AGN also exist in "noncool core" clusters, which brings up the question whether an X-ray cool core is always required for radio feedback. In this work, we present a systematic analysis of BCGs and strong radio AGN in 152 groups and clusters from the Chandra archive. All 69 BCGs with radio AGN more luminous than 2x10^23 W Hz^-1 at 1.4 GHz are found to have X-ray cool cores. The BCG cool cores can be divided into two classes, …
Outbursts from active galactic nuclei (AGN) affect the hot atmospheres of isolated giant elliptical galaxies (gE's), as well as those in groups and clusters of galaxies. Chandra observations of a sample of nearby gE's show that the average power of AGN outbursts is sufficient to stop their hot atmospheres from cooling and forming stars, consistent with radio mode feedback models. The outbursts are intermittent, with duty cycles that increases with size.
Cool core clusters of galaxies require strong feedback from their central AGN to offset cooling. We present a study of strong cool core, highly-luminous (most with L_x > 10^(45) erg/s), clusters of galaxies in which the mean central AGN jet power must be very high yet no central point X-ray source is detected. Using the unique spatial resolution of Chandra, a sample of 13 clusters is analysed, including A1835, A2204, and one of the most massive cool core clusters, RXCJ1504.1-0248. All of the central galaxies host a radio source, indicating an active nucleus, and no obvious X-ray point source. …
After the All-Sky Automated Survey for SuperNovae (ASAS-SN) discovered a significant brightening of the inner region of NGC 2617, we began a ~70 day photometric and spectroscopic monitoring campaign from the X-ray through near-infrared (NIR) wavelengths. We report that NGC 2617 went through a dramatic outburst, during which its X-ray flux increased by over an order of magnitude followed by an increase of its optical/ultraviolet (UV) continuum flux by almost an order of magnitude. NGC 2617, classified as a Seyfert 1.8 galaxy in 2003, is now a Seyfert 1 due to the appearance of broad optical emi…
It is commonly thought that AGN feedback can break the self-similar scaling relations of galaxies, groups, and clusters. Using high-resolution 3D hydrodynamic simulations, we isolate the impact of AGN feedback on the $L_{\rm x}-T_{\rm x} $ relation, testing the two archetypal and common regimes, self-regulated mechanical feedback and a quasar thermal blast. We find that AGN feedback has severe difficulty in breaking the relation in a consistent way. The similarity breaking is directly linked to the gas evacuation within $R_{500}$, while the central cooling times are inversely proportional to t…
We present the results of a Chandra study of the Hydra A galaxy cluster, where a powerful AGN outburst created a large-scale cocoon shock. We investigated possible azimuthal variations in shock strength and shape, finding indications for a weak shock with a Mach number in the range ~1.2-1.3. We measured the temperature change across the shock front. However, the detection of a temperature rise in the regions immediately inside of the front is complicated by the underlying temperature profile of the cluster atmosphere. We measured the global temperature profile of the cluster up to 700 kpc, whi…
Radio AGN feedback in X-ray cool cores has been proposed as a crucial ingredient in the evolution of baryonic structures. However, it has long been known that strong radio AGNs also exist in "noncool core" clusters, which brings up the question whether an X-ray cool core is always required for radio feedback. We present a systematic analysis of 152 groups and clusters to show that every BCG with a strong radio AGN has an X-ray cool core. Those strong radio AGNs in the center of the "noncool core" systems identified before are in fact associated with small X-ray cool cores with typical radii of…
Simulating cosmic ray electron spectra and radio emission from an AGN jet outburst in a cool-core cluster
Leibniz-Institut für Astrophysik Potsdam (AIP)（波茨坦阿斯特拉物理学会）；Institut für Physik und Astronomie, Universität Potsdam（波茨坦大学物理与天文学研究所）；Max-Planck-Institut für Astrophysik（马克斯·普朗克天体物理学研究所）；Universität Heidelberg, Zentrum für Astronomie, Institut für Theoretische Astrophysik（海德堡大学天文学中心理论天体物理研究所）
A deep Chandra observation of the X-ray bright group, NGC 5044, shows that the central region of this group has been strongly perturbed by repeated AGN outbursts. These recent AGN outbursts have produced many small X-ray cavities, cool filaments and cold fronts. We find a correlation between the coolest X-ray emitting gas and the morphology of the Ha filaments. The Ha filaments are oriented in the direction of the X-ray cavities, suggesting that the warm gas responsible for the Halpha emission originated near the center of NGC 5044 and was dredged up behind the buoyant, AGN-inflated X-ray cavi…
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 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…
We present new Chandra observations of Abell 2199 that show evidence of gas sloshing due to a minor merger, as well as impacts of the radio source, 3C 338, hosted by the central galaxy, NGC 6166, on the intracluster gas. The new data are consistent with previous evidence of a Mach 1.46 shock 100" from the cluster center, although there is still no convincing evidence for the expected temperature jump. Other interpretations of this feature are possible, but none is fully satisfactory. Large scale asymmetries, including enhanced X-ray emission 200" southwest of the cluster center and a plume of …
Recent observations show that the star formation rate (SFR) in the {\it Phoenix} cluster's central galaxy is $\sim 500$ M$_\odot$ yr$^{-1}$. Even though {\it Phoenix} is a massive cluster ($M_{200} \approx 2.0\times 10^{15}$ M$_\odot$; $z\approx 0.6$) such a high central SFR is not expected in a scenario in which feedback from an active galactic nucleus (AGN) maintains the intracluster medium (ICM) in a state of rough thermal balance. It has been argued that either AGN feedback saturates in very massive clusters or the central supermassive black hole (SMBH) is too small to produce enough kinet…
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). Mor…
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）
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 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 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 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 report the results of a multi-wavelength study of the nearby galaxy group, Abell 3581 (z=0.0218). This system hosts the most luminous cool core of any nearby group and exhibits active radio mode feedback from the super-massive black hole in its brightest group galaxy, IC 4374. The brightest galaxy has suffered multiple active galactic nucleus outbursts, blowing bubbles into the surrounding hot gas, which have resulted in the uplift of cool ionised gas into the surrounding hot intragroup medium. High velocities, indicative of an outflow, are observed close to the nucleus and coincident with …
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…
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…
We report on a deep, multiwavelength study of the galaxy cluster MACS J1931.8-2634 using Chandra X-ray, Subaru optical, and VLA 1.4 GHz radio data. This cluster (z=0.352) harbors one of the most X-ray luminous cool cores yet discovered, with an equivalent mass cooling rate within the central 50 kpc is approximately 700 solar masses/yr. Unique features observed in the central core of MACSJ1931.8-2634 hint to a wealth of past activity that has greatly disrupted the original cool core. We observe a spiral of relatively cool, dense, X-ray emitting gas connected to the cool core, as well as highly …
The brightest cluster galaxy (BCG) in the majority of relaxed, cool core galaxy clusters is radio loud, showing non-thermal radio jets and lobes ejected by the central active galactic nucleus (AGN). Such relativistic plasma has been unambiguously shown to interact with the surrounding thermal intra-cluster medium (ICM) thanks to spectacular images where the lobe radio emission is observed to fill the cavities in the X-ray-emitting gas. This `radio-mode AGN feedback' phenomenon, which is thought to quench cooling flows, is widespread and is critical to understand the physics of the inner region…
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…
The intracluster medium (ICM) is a multi-phase environment, dynamically regulated by Active Galactic Nuclei (AGN), the motions of galaxies through it, and mergers with other clusters. AGN as a central heating source are key to preventing runaway cooling flows, but their role in heating cores in a cosmological context is still poorly understood. The activity of the AGN is strongly linked to star formation, especially in the Brightest Cluster Galaxy (BCG), likely because both rely on cold phase gas. A self-consistent model for AGN and star formation in galaxy clusters thus requires cosmological …
