We have studied the effects of electron-ion non-equipartition in the outer regions of relaxed clusters for a wide range of masses in the ΛCDM cosmology using one-dimensional hydrodynamic simulations. The effects of the non-adiabatic electron heating efficiency, β, on the degree of non-equipartition are also studied. Using the gas fraction f gas = 0.17 (which is the upper limit for a cluster), we give a conservative lower limit of the non-equipartition effect on clusters. We have shown that for a cluster with a mass of M vir ∼ 1.2 × 10 15 M ⊙ , electron and ion temperatures differ by less than a percent within the virial radius R vir . The difference is ≈ 20% for a non-adiabatic electron heating efficiency of β ∼ 1/1800 to 0.5 at ∼ 1.4R vir . Beyond that radius, the non-equipartition effect depends rather strongly on β, and such a strong dependence at the shock radius can be used to distinguish shock heating models or constrain the shock heating efficiency of electrons. With our simulations, we have also studied systematically the signatures of non-equipartition on X-ray and Sunyaev-Zel'dovich (SZ) observables. We have calculated the effect of non-equipartition on the projected temperature and X-ray surface brightness profiles using the MEKAL emission model. We found that the effect on the projected temperature profiles is larger than that on the deprojected (or physical) temperature profiles. The non-equipartition effect can introduce a ∼ 10% bias in the projected temperature at R vir for a wide range of β. We also found that the effect of non-equipartition on the projected temperature profiles can be enhanced by increasing metallicity. In the low-energy band 1 keV, the non-equipartition model surface brightness can be higher than that of the equipartition model in the cluster outer regions. Future X-ray observations extending to ∼ R vir or even close to the shock radius should be able to detect these non-equipartition signatures. For a given cluster, the difference between the SZ temperature decrements for the equipartition and the non-equipartition models, δ∆T SZE , is larger at a higher redshift. For the most massive clusters at z ≈ 2, the differences can be δ∆T SZE ≈ 4-5 µK near the shock radius. We also found that for our model in the ΛCDM universe, the integrated SZ bias, Y non-eq /Y eq , evolves slightly (at a percentage level) with redshift, which is in contrast to the self-similar model in the Einstein-de Sitter universe. This may introduce biases in cosmological studies using the f gas technique. We discussed briefly whether the equipartition and non-equipartition models near the shock region can be distinguished by future radio observations with, for example, the Atacama Large Millimeter Array. Subject headings: cosmic microwave background -galaxies: clusters: general -hydrodynamicsintergalactic medium -shock waves -X-rays: galaxies: clusters 1 R ∆ is the radius within which the mean total mass density of the cluster is ∆ times the critical density. The virial radius R vir is defined as a radius within...

Observational confirmation of hot accretion model predictions has been hindered by the challenge to resolve spatially the Bondi radii of black holes with X-ray telescopes. Here, we use the Megasecond Chandra X-ray Visionary Project (XVP) observation of the NGC 3115 supermassive black hole to place the first direct observational constraints on the spatially and spectroscopically resolved structures of the X-ray emitting gas inside the Bondi radius of a black hole. We measured temperature and density profiles of the hot gas from a fraction out to tens of the Bondi radius (R B = 2. ′′ 4-4. ′′ 8 = 112-224 pc). The projected temperature jumps significantly from ∼ 0.3 keV beyond 5 ′′ to ∼ 0.7 keV within ∼ 4 ′′ -5 ′′ , but then abruptly drops back to ∼ 0.3 keV within ∼ 3 ′′ . This is contrary to the expectation that the temperature should rise toward the center for a radiatively inefficient accretion flow. A hotter thermal component of ∼ 1 keV inside 3 ′′ (∼ 150 pc) is revealed using a two component thermal model, with the cooler ∼0.3 keV thermal component dominating the spectra. We argue that the softer emission comes from diffuse gas physically located within ∼ 150 pc from the black hole. The density profile is broadly consistent with ρ ∝ r −1 within the Bondi radius for either the single temperature or the two-temperature model. The X-ray data alone with physical reasoning argue against the absence of a black hole, supporting that we are witnessing the onset of the gravitational influence of the supermassive black hole.

Gas undergoing Bondi accretion onto a supermassive black hole (SMBH) becomes hotter toward smaller radii. We searched for this signature with a Chandra observation of the hot gas in NGC 3115, which optical observations show has a very massive SMBH. Our analysis suggests that we are resolving, for the first time, the accretion flow within the Bondi radius of an SMBH. We show that the temperature is rising toward the galaxy center as expected in all accretion models in which the black hole is gravitationally capturing the ambient gas. There is no hard central point source that could cause such an apparent rise in temperature. The data support that the Bondi radius is at about 4 ′′ -5 ′′ (188-235 pc), suggesting an SMBH of 2 × 10 9 M ⊙ that is consistent with the upper end of the optical results. The density profile within the Bondi radius has a power-law index of 1.03 +0.23 −0.21 which is consistent with gas in transition from the ambient medium and the accretion flow. The accretion rate at the Bondi radius is determined to beṀ B = 2.2 × 10 −2 M ⊙ yr −1 . Thus, the accretion luminosity with 10% radiative efficiency at the Bondi radius (10 44 erg s −1 ) is about six orders of magnitude higher than the upper limit of the X-ray luminosity of the nucleus.

We present a detailed analysis of the XMM-Newton and Chandra observations of Abell 2626 focused on the X-ray and radio interactions. Within the region of the radio mini-halo (∼ 70 kpc), there are substructures which are probably produced by the central radio source and the cooling core. We find that there is no obvious correlation between the radio bars and the X-ray image. The morphology of Abell 2626 is more complex than that of the standard X-ray radio bubbles seen in other cool core clusters. Thus, Abell 2626 provides a challenge to models for the cooling flow -radio source interaction. We identified two soft X-ray (0.3-2 keV) peaks with the two central cD nuclei; one of them has an associated hard X-ray (2-10 keV) point source. We suggest that the two symmetric radio bars can be explained by two precessing jets ejected from an AGN. Beyond the central regions, we find two extended X-ray sources to the southwest and northeast of the cluster center which are apparently associated with merging subclusters. The main Abell 2626 cluster and these two subclusters are extended along the direction of the Perseus-Pegasus supercluster, and we suggest that Abell 2626 is preferentially accreting subclusters and groups from this large-scale structure filament. We also find an extended X-ray source associated with the cluster S0 galaxy IC 5337; the morphology of this source suggests that it is infalling from the west, and is not associated with the southwest subcluster, as had been previously suggested.

We present Hubble Space Telescope/Advanced Camera for Surveys (HST/ACS) g and z photometry and half-light radii R h measurements of 360 globular cluster (GC) candidates around the nearby S0 galaxy NGC 3115. We also include Subaru/Suprime-Cam g, r, and i photometry of 421 additional candidates. The well-established color bimodality of the GC system is obvious in the HST/ACS photometry. We find evidence for a "blue tilt" in the blue GC subpopulation, wherein the GCs in the blue subpopulation get redder as luminosity increases, indicative of a mass-metallicity relationship. We find a color gradient in both the red and blue subpopulations, with each group of clusters becoming bluer at larger distances from NGC 3115. The gradient is of similar strength in both subpopulations, but is monotonic and more significant for the blue clusters. On average, the blue clusters have ∼10% larger R h than the red clusters. This average difference is less than is typically observed for early-type galaxies but does match that measured in the literature for the Sombrero Galaxy (M104), suggesting that morphology and inclination may affect the measured size difference between the red and blue clusters. However, the scatter on the R h measurements is large. We also identify 31 clusters more extended than typical GCs, which we term ultra-compact dwarf (UCD) candidates. Many of these objects are actually considerably fainter than typical UCDs. While it is likely that a significant number will be background contaminants, six of these UCD candidates are spectroscopically confirmed as NGC 3115 members. To explore the prevalence of low-mass X-ray binaries in the GC system, we match our ACS and Suprime-Cam detections to corresponding Chandra X-ray sources. We identify 45 X-ray-GC matches: 16 among the blue subpopulation and 29 among the red subpopulation. These X-ray/GC coincidence fractions are larger than is typical for most GC systems, probably due to the increased depth of the X-ray data compared to previous studies of GC systems.

Context. We present the results of a new Chandra study of the galaxy cluster Abell 2626. The radio emission of the cluster shows a complex system of four symmetric arcs without known correlations with the thermal X-ray emission. The mirror symmetry of the radio arcs toward the center and the presence of two optical cores in the central galaxy suggested that they may be created by pairs of precessing radio jets powered by dual AGNs inside the core dominant galaxy. However, previous observations failed to observe the second jetted AGN and the spectral trend due to radiative age along the radio arcs, thus challenging this interpretation. Aims. The new Chandra observation had several scientific objectives, including the search for the second AGN that would support the jet precession model. We focus here on the detailed study of the local properties of the thermal and non-thermal emission in the proximity of the radio arcs, in order to get more insights into their origin. Methods. We performed a standard data reduction of the Chandra dataset deriving the radial profiles of temperature, density, pressure and cooling time of the intra-cluster medium. We further analyzed the 2-D distribution of the gas temperature, discovering that the south-western junction of the radio arcs surrounds the cool core of the cluster. Results. We studied the X-ray surface brightness and spectral profiles across the junction, finding a cold front spatially coincident with the radio arcs. This may suggest a connection between the sloshing of the thermal gas and the nature of the radio filaments, raising new scenarios for their origin. A tantalizing possibility is that the radio arcs trace the projection of a complex surface connecting the sites where electrons are most efficiently reaccelerated by the turbulence that is generated by the gas sloshing. In this case, diffuse emission embedded by the arcs and with extremely steep spectrum should be most visible at very low radio frequencies.

Based on the dynamical black hole (BH) mass estimates, NGC 3115 hosts the closest billion solar mass BH. Deep studies of the center revealed a very underluminous active galactic nucleus (AGN) immersed in an old massive nuclear star cluster. Recent 1 Ms Chandra X-ray visionary project observations of the NGC 3115 nucleus resolved hot tenuous gas, which fuels the AGN. In this paper we connect the processes in the nuclear star cluster with the feeding of the supermassive BH. We model the hot gas flow sustained by the injection of matter and energy from the stars and supernova explosions. We incorporate electron heat conduction as the small-scale feedback mechanism, the gravitational pull of the stellar mass, cooling, and Coulomb collisions. Fitting simulated X-ray emission to the spatially and spectrally resolved observed data, we find the best-fitting solutions with χ 2 /dof = 1.00 for dof = 236 both with and without conduction. The radial modeling favors a low BH mass <1.3 × 10 9 M . The best-fitting supernova rate and the best-fitting mass injection rate are consistent with their expected values. The stagnation point is at r st 1 , so that most of the gas, including the gas at a Bondi radius r B = 2 -4 , outflows from the region. We put an upper limit on the accretion rate at 2 × 10 −3 M yr −1 . We find a shallow density profile n ∝ r −β with β ≈ 1 over a large dynamic range. This density profile is determined in the feeding region 0. 5-10 as an interplay of four processes and effects: (1) the radius-dependent mass injection, (2) the effect of the galactic gravitational potential, (3) the accretion flow onset at r 1 , and (4) the outflow at r 1 . The gas temperature is close to the virial temperature T v at any radius.

We propose a new method to probe the Warm Hot Intergalactic Medium (WHIM) beyond the virial radius (R 200 ) of a cluster of galaxies, where X-ray observations are not easily achievable. In this method, we use dispersion measures (DMs) of Fast Radio Bursts (FRBs) that appear behind the cluster and the Sunyaev-Zel'dovich (SZ) effect towards the cluster. The DMs reflect the density of the intracluster medium (ICM) including the WHIM. If we observe a sufficient number of FRBs in the direction of the cluster, we can derive the density profile from the DMs. Similarly, we can derive the pressure profile from the SZ effect. By combining the density and the pressure profiles, the temperature profile can be obtained. Based on mock observations of nearby clusters, we find that the density of the WHIM can be determined even at > 2 R 200 from the cluster center when FRB observations with the Square Kilometre Array (SKA) become available. The temperature can be derived out to r ∼ 1.5 R 200 , and the radius is limited by the current sensitivity of SZ observations.