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Cosmological simulations, as well as mounting evidence from observations, have shown that supermassive black holes play a fundamental role in regulating the formation of stars throughout cosmic time. This has been clearly demonstrated in the case of galaxy clusters in which powerful feedback from the central black hole is preventing the hot intracluster gas from cooling catastrophically, thus reducing the expected star formation rates by orders of magnitude. These conclusions, however, have been almost entirely based on nearby clusters. Based on new Chandra X-ray observations, we present the first observational evidence for massive, runaway cooling occurring in the absence of supermassive black hole feedback in the high-redshift galaxy cluster SpARCS104922.6 + 564032.5 (z = 1.709). The hot intracluster gas appears to be fueling a massive burst of star formation (≈900 M o˙ yr-1) that is offset by dozens of kpc from the central galaxy. The burst is co-spatial with the coolest intracluster gas but not associated with any galaxy in the cluster. In less than 100 million years, such runaway cooling can form the same amount of stars as in the Milky Way. Therefore, intracluster stars are not only produced by tidal stripping and the disruption of cluster galaxies, but can also be produced by runaway cooling of hot intracluster gas at early times. Overall, these observations show the dramatic impact when supermassive black hole feedback fails to operate in clusters. They indicate that in the highest overdensities, such as clusters and protoclusters, runaway cooling may be a new and important mechanism for fueling massive bursts of star formation in the early universe.

Using a sample of four galaxy clusters at 1.35 < z < 1.65 and 10 galaxy clusters at 0.85 < z < 1.35, we measure the environmental quenching timescale, t Q, corresponding to the time required after a galaxy is accreted by a cluster for it to fully cease star formation. Cluster members are selected by a photometric-redshift criterion, and categorized as star-forming, quiescent, or intermediate according to their dust-corrected rest-frame colors and magnitudes. We employ a "delayed-then-rapid" quenching model that relates a simulated cluster mass accretion rate to the observed numbers of each type of galaxy in the cluster to constrain t Q. For galaxies of mass M ∗ 1010.5 M o, we find a quenching timescale of t Q = Gyr in the z ∼ 1.5 cluster sample, and Gyr at z ∼ 1. Using values drawn from the literature, we compare the redshift evolution of t Q to timescales predicted for different physical quenching mechanisms. We find t Q to depend on host halo mass such that quenching occurs over faster timescales in clusters relative to groups, suggesting that properties of the host halo are responsible for quenching high-mass galaxies. Between z = 0 and z = 1.5, we find that t Q evolves faster than the molecular gas depletion timescale and slower than an estimated star formation rate-outflow timescale, but is consistent with the evolution of the dynamical time. This suggests that environmental quenching in these galaxies is driven by the motion of satellites relative to the cluster environment, although due to uncertainties in the atomic gas budget at high redshift, we cannot rule out quenching due to simple gas depletion.

Although the study of X-ray binaries has led to major breakthroughs in high-energy astrophysics, their circumbinary environment at scales of ∼100–10,000 au has not been thoroughly investigated. In this paper, we undertake a novel and exploratory study by employing direct and high-contrast imaging techniques on a sample of X-ray binaries, using adaptive optics and the vortex coronagraph on Keck/NIRC2. High-contrast imaging opens up the possibility to search for exoplanets, brown dwarfs, circumbinary companion stars, and protoplanetary disks in these extreme systems. Here we present the first near-infrared high-contrast images of 13 high-mass X-ray binaries located within ∼2–3 kpc. The key results of this campaign involve the discovery of several candidate circumbinary companions ranging from substellar (brown dwarf) to stellar masses. By conducting an analysis based on Galactic population models, we discriminate sources that are likely background/foreground stars and isolate those that have a high probability (≳60%–99%) of being gravitationally bound to the X-ray binary. This paper seeks to establish a preliminary catalog for future analyses of proper motion and subsequent observations. With our preliminary results, we calculate the first estimate of the companion frequency and the multiplicity frequency for X-ray binaries: ≈0.6 and 1.8 ± 0.9, respectively, considering only the sources that are most likely bound to the X-ray binary. In addition to extending our comprehension of how brown dwarfs and stars can form and survive in such extreme systems, our study opens a new window to our understanding of the formation of X-ray binaries. [ABSTRACT FROM AUTHOR]

The cluster of galaxies Abell 2146 is undergoing a major merger and is an ideal cluster to study intracluster medium (ICM) physics, as it has a simple geometry with the merger axis in the plane of the sky, its distance allows us to resolve features across the relevant scales and its temperature lies within Chandra 's sensitivity. Gas from the cool core of the subcluster has been partially stripped into a tail of gas, which gives a unique opportunity to look at the survival of such gas and determine the rate of conduction in the ICM. We use deep 2.4-Ms Chandra observations of Abell 2146 to produce a high spatial resolution map of the temperature structure along a plume in the ram-pressure stripped tail, described by a partial cone, which is distinguishable from the hot ambient gas. Previous studies of conduction in the ICM typically rely on estimates of the survival time for key structures, such as cold fronts. Here we use detailed hydrodynamical simulations of Abell 2146 to determine the flow velocities along the stripped plume and measure the time-scale of the temperature increase along its length. We find that conduction must be highly suppressed by multiple orders of magnitude compared to the Spitzer rate, as the energy used is about 1  per cent of the energy available. We discuss magnetic draping around the core as a possible mechanism for suppressing conduction. [ABSTRACT FROM AUTHOR]

MS 0735.6+7421 (z = 0.216) is a massive cool core galaxy cluster hosting one of the most powerful active galactic nuclei (AGNs) outbursts known. The radio jets of the AGN have carved out an unusually large pair of X-ray cavities, each reaching a diameter of 200 kpc. This makes MS 0735.6+7421 a unique case to investigate active galactic nuclei feedback processes, as well as other cluster astrophysics at radio wavelengths. We present new low radiofrequency observations of MS 0735.6+7421 taken with the Karl G. Jansky Very Large Array (VLA): 5 h of P -band (224–480 MHz) and 5 h of L -band (1–2 GHz) observations, both in C configuration. Our VLA P -band (224–480 MHz) observations reveal the presence of a diffuse radio component reaching a scale of ≈ 900 kpc in the direction of the jets and of ≈ 500 kpc in the direction perpendicular to the jets. This component is centred on the cluster core and has a radio power scaled at 1.4 GHz of P 1.4GHz = (4 ± 2) × 1024 W Hz−1. Its properties are consistent with those expected from a radio minihalo as seen in other massive cool core clusters, although it may also be associated with radio plasma that has diffused out of the X-ray cavities, or to a combination of these two hypotheses. Observations at higher spatial resolution are needed to fully characterize the properties and nature of this component. We also suggest that if radio minihaloes originate from jetted activity, we may be witnessing the early stages of this process. [ABSTRACT FROM AUTHOR]

We present a new |$2\rm \, Ms$| Chandra observation of the cluster merger Abell 2146, which hosts two huge M ∼ 2 shock fronts each |${\sim }500\rm \, kpc$| across. For the first time, we resolve and measure the width of cluster merger shocks. The best-fitting width for the bow shock is |$17\pm 1\rm \, kpc$| and for the upstream shock is |$10.7\pm 0.3\rm \, kpc$|⁠. A narrow collisionless shock will appear broader in projection if its smooth shape is warped by local gas motions. We show that both shock widths are consistent with collisionless shocks blurred by local gas motions of |$290\pm 30{\rm \, km\rm \, s^{-1}}$|⁠. The upstream shock forms later on in the merger than the bow shock and is therefore expected to be significantly narrower. From the electron temperature profile behind the bow shock, we measure the time-scale for the electrons and ions to come back into thermal equilibrium. We rule out rapid thermal equilibration of the electrons with the shock-heated ions at the 6σ level. The observed temperature profile instead favours collisional equilibration. For these cluster merger shocks, which have low sonic Mach numbers and propagate through a high β plasma, we find no evidence for electron heating over that produced by adiabatic compression. Our findings are expected to be valid for collisionless shocks with similar parameters in other environments and support the existing picture from the solar wind and supernova remnants. The upstream shock is consistent with this result but has a more complex structure, including a |${\sim}2\rm \, keV$| increase in temperature |${\sim }50\rm \, kpc$| ahead of the shock. [ABSTRACT FROM AUTHOR]

Expanding from previous work, we present weak-lensing (WL) measurements for a total sample of 30 distant (z median = 0.93) massive galaxy clusters from the South Pole Telescope Sunyaev–Zel'dovich (SPT -SZ) Survey, measuring galaxy shapes in Hubble Space Telescope (HST) Advanced Camera for Surveys images. We remove cluster members and preferentially select z ≳ 1.4 background galaxies via V − I colour, employing deep photometry from VLT/FORS2 and Gemini-South/GMOS. We apply revised calibrations for the WL shape measurements and the source redshift distribution to estimate the cluster masses. In combination with earlier Magellan/Megacam results for lower-redshifts clusters, we infer refined constraints on the scaling relation between the SZ detection significance and the cluster mass, in particular regarding its redshift evolution. The mass scale inferred from the WL data is lower by a factor |$0.76^{+0.10}_{-0.14}$| (at our pivot redshift z = 0.6) compared to what would be needed to reconcile a flat Planck νΛCDM cosmology (in which the sum of the neutrino masses is a free parameter) with the observed SPT-SZ cluster counts. In order to sensitively test the level of (dis-)agreement between SPT clusters and Planck , further expanded WL follow-up samples are needed. [ABSTRACT FROM AUTHOR]

We present new deep, high-resolution, 1.5 GHz observations of the prototypical nearby Perseus galaxy cluster from the Karl G. Jansky Very Large Array. We isolate for the first time the complete tail of radio emission of the bent-jet radio galaxy NGC 1272, which had been previously mistaken to be part of the radio mini-halo. The possibility that diffuse radio galaxy emission contributes to mini-halo emission may be a general phenomenon in relaxed cool-core clusters, and should be explored. The collimated jets of NGC 1272 initially bend to the west, and then transition eastward into faint, 60 kpc long extensions with eddy-like structures and filaments. We suggest interpretations for these structures that involve bulk motions of intracluster gas, the galaxy's orbit in the cluster including projection effects, and the passage of the galaxy through a sloshing cold front. Instabilities and turbulence created at the surface of this cold front and in the turbulent wake of the infalling host galaxy most likely play a role in the formation of the observed structures. We also discover a series of faint rings, southeast of NGC 1272, which are a type of structure that has never been seen before in galaxy clusters. [ABSTRACT FROM AUTHOR]

We present the first high-resolution 230–470 MHz map of the Perseus cluster obtained with the Karl G. Jansky Very Large Array. The high dynamic range and resolution achieved have allowed the identification of previously unknown structures in this nearby galaxy cluster. New hints of sub-structures appear in the inner radio lobes of the brightest cluster galaxy NGC 1275. The spurs of radio emission extending into the outer X-ray cavities, inflated by past nuclear outbursts, are seen for the first time at these frequencies, consistent with spectral aging. Beyond NGC 1275, we also analyse complex radio sources harboured in the cluster. Two new distinct, narrowly collimated jets are visible in IC 310, consistent with a highly projected narrow-angle tail radio galaxy infalling into the cluster. We show how this is in agreement with its blazar-like behaviour, implying that blazars and bent-jet radio galaxies are not mutually exclusive. We report the presence of filamentary structures across the entire tail of NGC 1265, including two new pairs of long filaments in the faintest bent extension of the tail. Such filaments have been seen in other cluster radio sources such as relics and radio lobes, indicating that there may be a fundamental connection between all these radio structures. We resolve the very narrow and straight tail of CR 15 without indication of double jets, so that the interpretation of such head–tail sources is yet unclear. Finally, we note that only the brightest western parts of the mini-halo remain, near NGC 1272 and its bent double jets. [ABSTRACT FROM AUTHOR]

A variety of large-scale diffuse radio structures have been identified in many clusters with the advent of new state-of-the-art facilities in radio astronomy. Among these diffuse radio structures, radio mini-halos are found in the central regions of cool core clusters. Their origin is still unknown and they are challenging to discover; less than 30 have been published to date. Based on new VLA observations, we confirmed the mini-halo in the massive strong cool core cluster PKS 0745−191 (z  = 0.1028) and discovered one in the massive cool core cluster MACS J1447.4+0827 (z  = 0.3755). Furthermore, using a detailed analysis of all known mini-halos, we explore the relation between mini-halos and active galactic nucleus (AGN) feedback processes from the central galaxy. We find evidence of strong, previously unknown correlations between mini-halo radio power and X-ray cavity power, and between mini-halo and the central galaxy radio power related to the relativistic jets when spectrally decomposing the AGN radio emission into a component for past outbursts and one for ongoing accretion. Overall, our study indicates that mini-halos are directly connected to the central AGN in clusters, following previous suppositions. We hypothesize that AGN feedback may be one of the dominant mechanisms giving rise to mini-halos by injecting energy into the intra-cluster medium and reaccelerating an old population of particles, while sloshing motion may drive the overall shape of mini-halos inside cold fronts. AGN feedback may therefore not only play a vital role in offsetting cooling in cool core clusters, but may also play a fundamental role in re-energizing non-thermal particles in clusters. [ABSTRACT FROM AUTHOR]

We present the first results from a galaxy population study in the highest redshift galaxy clusters identified in the 2500 deg2 South Pole Telescope Sunyaev Zel'dovich effect (SPT-SZ) survey, which is sensitive to M500 ≳ 3 × 1014 M⊙ clusters from z ∼ 0.2 out to the highest redshifts where such massive structures exist. The cluster selection is to first order independent of galaxy properties, making the SPT-SZ sample particularly well suited for cluster galaxy population studies. We carried out a four-band imaging campaign with the Hubble and Spitzer Space Telescopes of the five z ≳ 1.4, S/NSZE >  5 clusters, that are among the rarest most massive clusters known at this redshift. All five clusters show clear overdensities of red galaxies whose colors agree with the initial cluster redshift estimates, although one (SPT-CLJ0607–4448) shows a galaxy concentration much less prominent than the others. The highest redshift cluster in this sample, SPT-CLJ0459–4947 at z ∼ 1.72, is the most distant M500 >  1014 M⊙ cluster discovered thus far through its intracluster medium, and is one of only three known clusters in this mass range at z ≳ 1.7, regardless of selection. Based on UVJ-like photometric classification of quiescent and star-forming galaxies, we find that the quiescent fraction in the cluster central regions (r/r500 <  0.7) is higher than in the field at the same redshift, with corresponding environmental quenching efficiencies typically in the range ∼0.5 − 0.8 for stellar masses log(M/M⊙) > 10.85. We have explored the impact of emission from star formation on the selection of this sample, concluding that all five clusters studied here would still have been detected with S/NSZE> 5, even if they had the same quiescent fraction as measured in the field. Our results thus point towards an efficient suppression of star formation in the central regions of the most massive clusters, occurring already earlier than z ∼ 1.5. [ABSTRACT FROM AUTHOR]

The galaxy phase-space distribution in galaxy clusters provides insights into the formation and evolution of cluster galaxies, and it can also be used to measure cluster mass profiles. We present a dynamical study based on ∼3000 passive, non-emission-line cluster galaxies drawn from 110 galaxy clusters. The galaxy clusters were selected using the Sunyaev–Zel'dovich effect (SZE) in the 2500 deg2 South Pole Telescope (SPT)–SZ survey and cover the redshift range 0.2 < |$z$| < 1.3. We model the clusters using the Jeans equation, while adopting NFW mass profiles and a broad range of velocity dispersion anisotropy profiles. The data prefer velocity dispersion anisotropy profiles that are approximately isotropic near the centre and increasingly radial toward the cluster virial radius, and this is true for all redshifts and masses we study. The pseudo-phase-space density profile of the passive galaxies is consistent with expectations for dark matter particles and subhaloes from cosmological N -body simulations. The dynamical mass constraints are in good agreement with external mass estimates of the SPT cluster sample from either weak lensing, velocity dispersions, or X-ray Y X measurements. However, the dynamical masses are lower (at the 2.2σ level) when compared to the mass calibration favoured when fitting the SPT cluster data to a Λcold dark matter model with external cosmological priors, including cosmic microwave background anisotropy data from Planck. The discrepancy grows with redshift, where in the highest redshift bin the ratio of dynamical to SPT + Planck masses is |$\eta = 0.63^{+0.13}_{-0.08}\pm 0.06$| (statistical and systematic), corresponding to a 2.6σ discrepancy. [ABSTRACT FROM AUTHOR]

We have produced for the first time a detailed velocity map of the giant filamentary nebula surrounding NGC 1275, the Perseus cluster's brightest galaxy, and revealed a previously unknown rich velocity structure across the entire nebula. These new observations were obtained with the optical imaging Fourier transform spectrometer SITELLE at CFHT. With its wide field of view ( ∼11 arcmin × 11 arcmin), SITELLE is the only integral field unit spectroscopy instrument able to cover the 80 kpc  ×  55 kpc ( 3.8 arcmin × 2.6 arcmin) large nebula in NGC 1275. Our analysis of these observations shows a smooth radial gradient of the [N  ii ]λ6583/H α line ratio, suggesting a change in the ionization mechanism and source across the nebula. The velocity map shows no visible general trend or rotation, indicating that filaments are not falling uniformly onto the galaxy, nor being uniformly pulled out from it. Comparison between the physical properties of the filaments and Hitomi measurements of the X-ray gas dynamics in Perseus is also explored. [ABSTRACT FROM AUTHOR]

Abell 2146 (z = 0.232) is a massive galaxy cluster currently undergoing a spectacular merger in the plane of the sky with a bullet-like morphology. It was the first system in which both the bow and upstream shock fronts were detected at X-ray wavelengths (Mach ~2), yet deep Giant MetreWave Telescope 325 MHz observations failed to detect extended radio emission associated with the cluster as is typically seen in such systems. We present new, multiconfiguration 1-2 GHz Karl G. Jansky Very Large Array (VLA) observations of Abell 2146 totalling 16 h of observations. These data reveal for the first time the presence of an extended (≈850 kpc), faint radio structure associated with Abell 2146. The structure appears to harbour multiple components, one associated with the upstream shock that we classify as a radio relic and one associated with the subcluster core that is consisted as being a radio halo bounded by the bow shock. The newly detected structures have some of the lowest radio powers detected thus far in any cluster (P1.4 GHz, halo = 2.4± 0.2 × 1023 W Hz-1 and P1.4 GHz, relic = 2.2 ± 0.2 × 1023 W Hz-1). The flux measurement of the halo, as well as its morphology, also suggests that the halo was recently created (≈0.3 Gyr after core passage), consistent with the dynamical state of the cluster. These observations demonstrate the capacity of the upgraded VLA to detect extremely faint and extended radio structures. Based on these observations, we predict that many more radio relics and radio haloes in merging clusters should be detected by future radio facilities such as the Square Kilometre Array. [ABSTRACT FROM AUTHOR]

We perform a detailed study of the location of brightest cluster galaxies (BCGs) on the Fundamental Plane of black hole (BH) accretion, which is an empirical correlation between a BH X-ray and radio luminosity and mass supported by theoretical models of accretion. The sample comprises 72 BCGs out to z ~ 0.3 and with reliable nuclear X-ray and radio luminosities. These are found to correlate as LX ∝ L0.75±0.08 R, favouring an advection-dominated accretion flow as the origin of the X-ray emission. BCGs are found to be on average offset from the Fundamental Plane such that their BH masses seem to be underestimated by the MBH-MK relation a factor ~10. The offset is not explained by jet synchrotron cooling and is independent of emission process or amount of cluster gas cooling. Those core-dominated BCGs are found to be more significantly offset than those with weak core radio emission. For BCGs to on average follow the Fundamental Plane, a large fraction (~40 per cent) should have BH masses >1010M⊙ and thus host ultramassive BHs. The local BH-galaxy scaling relations would not hold for these extreme objects. The possible explanations for their formation, either via a two-phase process (the BH formed first, the galaxy grows later) or as descendants of high-z seed BHs, challenge the current paradigm of a synchronized galaxy-BH growth. [ABSTRACT FROM AUTHOR]

We present a low-frequency view of the Perseus cluster with new observations from the Karl G. Jansky Very Large Array (JVLA) at 230-470 MHz. The data reveal a multitude of new structures associated with the mini-halo. The mini-halo seems to be influenced both by the AGN activity and the sloshing motion of the cool core cluster's gas. In addition, it has a filamentary structure similar to that seen in radio relics found in merging clusters. We present a detailed description of the data reduction and imaging process of the dataset. The depth and resolution of the observations allow us to conduct for the first time a detailed comparison of the mini-halo structure with the X-ray structure as seen in the Chandra X-ray images. The resulting image very clearly shows that the mini-halo emission is mostly contained behind the western cold front, similar to that predicted by simulations of gas sloshing in galaxy clusters, but fainter emission is also seen beyond, as if particles are leaking out. However, due to the proximity of the Perseus cluster, as well as the quality of the data at low radio frequencies and at X-ray wavelengths, we also find evidence of fine structure. This structure includes several radial radio filaments extending in different directions, a concave radio structure associated with the southern X-ray bay and sharp radio edges that correlate with X-ray edges. Minihaloes are therefore not simply diffuse, uniform radio sources, but rather have a rich variety of complex structures. These results illustrate the high-quality images that can be obtained with the new JVLA at low radio frequencies, as well as the necessity to obtain deeper, higher fidelity radio images of mini-haloes in clusters to further understand their origin. [ABSTRACT FROM AUTHOR]

Deep observations of nearby galaxy clusters with Chandra have revealed concave 'bay' structures in a number of systems (Perseus, Centaurus and Abell 1795), which have similar X-ray and radio properties. These bays have all the properties of cold fronts, where the temperature rises and density falls sharply, but are concave rather than convex. By comparing to simulations of gas sloshing, we find that the bay in the Perseus cluster bears a striking resemblance in its size, location and thermal structure, to a giant (≈50 kpc) roll resulting from Kelvin--Helmholtz instabilities. If true, the morphology of this structure can be compared to simulations to put constraints on the initial average ratio of the thermal and magnetic pressure, β = pth/pB, throughout the overall cluster before the sloshing occurs, for which we find β = 200 to best match the observations. Simulations with a stronger magnetic field (β = 100) are disfavoured, as in these the large Kelvin--Helmholtz rolls do not form, while in simulations with a lower magnetic field (β = 500), the level of instabilities is much larger than is observed. We find that the bay structures in Centaurus and Abell 1795 may also be explained by such features of gas sloshing. [ABSTRACT FROM AUTHOR]

Hyper-luminous infrared galaxies (HyLIRGs) lie at the extreme luminosity end of the IR galaxy population with LIR > 1013 L⊙. They are thought to be closer counterparts of the more distant sub-millimeter galaxies, and should therefore be optimal targets to study the most massive systems in formation. We present deep Chandra observations of IRAS F15307+3252 (100 ks), a classical HyLIRG located at z=0.93 and hosting a radio-loudAGN(L1.4 GHz ~3.5× 1025WHz-1). The Chandra images reveal the presence of extended (r=160 kpc), asymmetric X-ray emission in the soft 0.3-2.0 keV band that has no radio counterpart. We therefore argue that the emission is of thermal origin originating from a hot intragroup or intracluster medium virializing in the potential. We find that the temperature (~2 keV) and bolometric X-ray luminosity (~3 × 1043 erg s-1) of the gas follow the expected LX-ray-T correlation for groups and clusters, and that the gas has a remarkably short cooling time of 1.2 Gyr. In addition, VLA radio observations reveal that the galaxy hosts an unresolved compact steep-spectrum (CSS) source, most likely indicating the presence of a young radio source similar to 3C186. We also confirm that the nucleus is dominated by a redshifted 6.4 keV Fe Ka line, strongly suggesting that the AGN is Compton-thick. Finally, Hubble images reveal an overdensity of galaxies and sub-structure in the galaxy that correlates with soft X-ray emission. This could be a snapshot view of on-going groupings expected in a growing cluster environment. IRAS F15307+3252 might therefore be a rare example of a group in the process of transforming into a cluster. [ABSTRACT FROM AUTHOR]

We present a study of the optical properties of the 26 most massive galaxy clusters within the South Pole Telescope Sunyaev-Zel'dovich (SPT-SZ) 2500 deg² survey spanning the redshift range 0.10 < z < 1.13. We measure the radial profiles, the luminosity functions (LFs), and the halo occupation numbers (HONs) using optical data of typical depth m* + 2. The stacked radial profiles are consistent with a Navarro-Frenk-White profile of concentration 2.84+0.40−0.37 for the red sequence (RS) and 2.36+0.38−0.35 for the total population. Stacking the data in multiple redshift bins shows slight redshift evolution in the concentration when both the total population is used, and when only RS galaxies are used (at 2.1σ and 2.8σ, respectively). The stacked LF shows a faint end slope α=−1.06+0.04−0.03 for the total and α=−0.80+0.04−0.03 for the RS population. The redshift evolution of m* is consistent with a passively evolving composite stellar population (CSP) model. Adopting the CSP model predictions, we explore the redshift evolution of the Schechter parameters α and ϕ*. We find α for the total population to be consistent with no evolution (0.3σ), and mildly significant evidence of evolution for the red galaxies (1.1-2.1σ). The data show that the density ϕ*/E²(z) decreases with redshift, in tension with the self-similar expectation at a 2.4σ level for the total population. The measured HON-mass relation has a lower normalization than previous low redshift studies. Finally, our data support HON redshift evolution at a 2.1σ level, with clusters at higher redshift containing fewer galaxies than their low-z counterparts. [ABSTRACT FROM AUTHOR]

We present an Integral Field Unit survey of 73 galaxy clusters and groups with the VIsible Multi Object Spectrograph on the Very Large Telescope. We exploit the data to determine the H α gas dynamics on kpc scales to study the feedback processes occurring within the dense cluster cores. We determine the kinematic state of the ionized gas and show that the majority of systems (~2/3) have relatively ordered velocity fields on kpc scales that are similar to the kinematics of rotating discs and are decoupled from the stellar kinematics of the brightest cluster galaxy. The majority of the H α flux (>50 per cent) is typically associated with these ordered kinematics and most systems show relatively simple morphologies suggesting they have not been disturbed by a recent merger or interaction. Approximately 20 per cent of the sample (13/73) have disturbed morphologies which can typically be attributed to active galactic nuclei activity disrupting the gas. Only one system shows any evidence of an interaction with another cluster member. A spectral analysis of the gas suggests that the ionization of the gas within cluster cores is dominated by non-stellar processes, possibly originating from the intracluster medium itself. [ABSTRACT FROM AUTHOR]

We examine deep Chandra X-ray observations of the Centaurus cluster of galaxies, Abell 3526. Applying a gradient magnitude filter reveals a wealth of structure, from filamentary soft emission on 100 pc (0.5 arcsec) scales close to the nucleus tofeatures 10 s of kpc in size at larger radii. The cluster contains multiple high-metallicity regions with sharp edges. Relative to an azimuthal average, the deviations of metallicity and surface brightness are correlated, and the temperature is inversely correlated, as expected if the larger scale asymmetries in the cluster are dominated by sloshing motions. Around the western cold front are a series of ∼7 kpc 'notches', suggestive of Kelvin-Helmholtz instabilities. The cold front width varies from 4 kpc down to close to the electron mean free path. Inside the front are multiple metallicity blobs on scales of 5-10 kpc, which could have been uplifted by AGN activity, also explaining the central metallicity drop and flat inner metallicity profile. Close to the nucleus are multiple shocks, including a 1.9-kpc-radius inner shell-like structure and a weak 1.1-1.4 Mach number shock around the central cavities. Within a 10 kpc radius are nine depressions in surface brightness, several of which appear to be associated with radio emission. The shocks and cavities imply that the nucleus has been repeatedly active on 5-10 Myr time-scales, indicating a tight balance between heating and cooling. We confirm the presence of a series of linear quasi-periodic structures. If they are sound waves, the ∼5 kpc spacing implies a period of 6 Myr, similar to the ages of the shocks and cavities. Alternatively, these structures may be Kelvin-Helmholtz instabilities, their associated turbulence or amplified magnetic field layers. [ABSTRACT FROM AUTHOR]

We consider the high radio-frequency (15-353 GHz) properties and variability of 35 brightest cluster galaxies (BCGs). These are the most core-dominated sources drawn from a parent sample of more than 700 X-ray selected clusters, thus allowing us to relate our results to the general population. We find that =6.0 per cent of our parent sample (=15.1 per cent if only cool-core clusters are considered) contain a radio source at 150 GHz of at least 3 mJy (1×1023 W Hz-1 at our median redshift of z 0.13). Furthermore, =3.4 per cent of the BCGs in our parent sample contain a peaked component (Gigahertz Peaked Spectrum, GPS) in their spectra that peaks above 2 GHz, increasing to =8.5 per cent if only cool-core clusters are considered. We see little evidence for strong variability at 15 GHz on short (week-month) time-scales although we see variations greater than 20 per cent at 150 GHz over six-month time frames for 4 of the 23 sources with multi-epoch observations. Much more prevalent is long-term (year-decade time-scale) variability, with average annual amplitude variations greater than 1 per cent at 15 GHz being commonplace. There is a weak trend towards higher variability as the peak of the GPS-like component occurs at higher frequency. We demonstrate the complexity that is seen in the radio spectra of BCGs and discuss the potentially significant implications of these high-peaking components for Sunyaev-Zel'dovich cluster searches. [ABSTRACT FROM AUTHOR]

We examine the radio properties of the brightest cluster galaxies (BCGs) in a large sample of X-ray selected galaxy clusters comprising the Brightest Cluster Sample (BCS), the extended BCS and ROSAT-ESO Flux Limited X-ray cluster catalogues. We have multifrequency radio observations of the BCG using a variety of data from the Australia Telescope Compact Array, Jansky Very Large Array and Very Long Baseline Array telescopes. The radio spectral energy distributions of these objects are decomposed into a component attributed to on-going accretion by the active galactic nuclei (AGN) that we refer to as 'the core', and a more diffuse, ageing component we refer to as the 'non-core'. These BCGs are matched to previous studies to determine whether they exhibit emission lines (principally Hα), indicative of the presence of a strong cooling cluster core. We consider how the radio properties of the BCGs vary with cluster environmental factors. Line emitting BCGs are shown to generally host more powerful radio sources, exhibiting the presence of a strong, distinguishable core component in about 60 per cent of cases. This core component more strongly correlates with the BCG's [O III] 5007 Å line emission. For BCGs in line emitting clusters, the X-ray cavity power correlates with both the extended and core radio emission, suggestive of steady fuelling of the AGN over bubble-rise time-scales in these clusters. [ABSTRACT FROM AUTHOR]

We present Chandra X-ray Observatory observations of the core of the galaxy cluster PKS 0745−191. Its centre shows X-ray cavities caused by AGN feedback and cold fronts with an associated spiral structure. The cavity energetics imply they are powerful enough to compensate for cooling. Despite the evidence for AGN feedback, the Chandra and XMM-RGS X-ray spectra are consistent with a few hundred solar masses per year cooling out of the X-ray phase, sufficient to power the emission line nebula. The coolest X-ray emitting gas and brightest nebula emission is offset by around 5 kpc from the radio and X-ray nucleus. Although the cluster has a regular appearance, its core shows density, temperature and pressure deviations over the inner 100 kpc, likely associated with the cold fronts. After correcting for ellipticity and projection effects, we estimate density fluctuations of ∼4 per cent, while temperature, pressure and entropy have variations of 10–12 per cent. We describe a new code, mbproj, able to accurately obtain thermodynamical cluster profiles, under the assumptions of hydrostatic equilibrium and spherical symmetry. The forward-fitting code compares model to observed profiles using Markov Chain Monte Carlo and is applicable to surveys, operating on 1000 or fewer counts. In PKS 0745, a very low gravitational acceleration is preferred within 40 kpc radius from the core, indicating a lack of hydrostatic equilibrium, deviations from spherical symmetry or non-thermal sources of pressure. [ABSTRACT FROM PUBLISHER]

We present the results of our study of a volume-limited sample (z ≤ 0.071) of 101 X-ray galaxy groups and clusters, in which we explore the X-ray cavity energetics. Out of the 101 sources in our parent sample, X-ray cavities are found in 30 of them, all of which have a central cooling time of ≤3 Gyr. New X-ray cavities are detected in three sources. We focus on the subset of sources that have a central cooling time of ≤3 Gyr, whose active galactic nucleus (AGN) duty cycle is ≃61 per cent (30/49). This rises to >80 per cent for a central cooling time of ≤0.5 Gyr. When projection effects and central radio source detection rates are considered, the actual duty cycle is probably much higher. In addition, we show that data quality strongly affects the detection rates of X-ray cavities. After calculating the cooling luminosity and cavity powers of each source with cavities, it is evident that the bubbling process induced by the central AGN has to be, on average, continuous, to offset cooling. We find that the radius of the cavities, r, loosely depends on the ambient gas temperature as r ∝ T0.5, above about 1.5 keV, with much more scatter below that temperature. Finally, we show that, at a given location in a group or cluster, larger bubbles travel faster than smaller ones. This means that the bubbles seen at larger distances from cluster cores could be the result of the merging of several smaller bubbles, produced in separate AGN cycles. [ABSTRACT FROM PUBLISHER]

We present a detailed Chandra, XMM-Newton, Very Large Array (VLA) and Hubble Space Telescope analysis of one of the strongest cool core clusters known, RX J1532.9+3021 (z = 0.3613). Using new, deep 90 ks Chandra observations, we confirm the presence of a western X-ray cavity or bubble, and report on a newly discovered eastern X-ray cavity. The total mechanical power associated with these active galactic nucleus (AGN) driven outflows is (22 ± 9) × 1044 erg s–1, and is sufficient to offset the cooling, indicating that AGN feedback still provides a viable solution to the cooling flow problem even in the strongest cool core clusters. Based on the distribution of the optical filaments, as well as a jet-like structure seen in the 325 MHz VLA radio map, we suggest that the cluster harbors older outflows along the north to south direction. The jet of the central AGN is therefore either precessing or sloshing-induced motions have caused the outflows to change directions. There are also hints of an X-ray depression to the north aligned with the 325 MHz jet-like structure, which might represent the highest redshift ghost cavity discovered to date. We further find evidence of a cold front (r ≈ 65 kpc) that coincides with the outermost edge of the western X-ray cavity and the edge of the radio mini-halo. The common location of the cold front with the edge of the radio mini-halo supports the idea that the latter originates from electrons being reaccelerated due to sloshing-induced turbulence. Alternatively, its coexistence with the edge of the X-ray cavity may be due to cool gas being dragged out by the outburst. We confirm that the central AGN is highly sub-Eddington and conclude that a >1010M☼ or a rapidly spinning black hole is favored to explain both the radiative-inefficiency of the AGN and the powerful X-ray cavities. [ABSTRACT FROM AUTHOR]

We present an analysis of the 2–10 keV X-ray emission associated with the active galactic nuclei (AGN) in brightest cluster galaxies (BCGs). Our sample consists of 32 BCGs that lie in highly X-ray luminous cluster of galaxies ($L_{\rm X{-}ray }{\rm (0.1{-}2.4\,{\rm keV})}>3\times 10^{44}\,{\rm erg}\,{\rm s}^{-1}\,$) in which AGN-jetted outflows are creating and sustaining clear X-ray cavities. Our sample covers the redshift range 0 < z < 0.6 and reveals strong evolution in the nuclear X-ray luminosities, such that the black holes in these systems have become on average at least 10 times fainter over the last 5 Gyr. Mindful of potential selection effects, we propose two possible scenarios to explain our results: (1) either that the AGN in BCGs with X-ray cavities are steadily becoming fainter, or more likely, (2) that the fraction of these BCGs with radiatively efficient nuclei is decreasing with time from roughly 60 per cent at z ≈ 0.6 to 30 per cent at z ≈ 0.1. Based on this strong evolution, we predict that a significant fraction of BCGs in z ≈ 1 clusters may host quasars at their centres, potentially complicating the search for such clusters at high redshift. In analogy with black hole binaries and based on the observed Eddington ratios of our sources, we further propose that the evolving AGN population in BCGs with X-ray cavities may be transiting from a canonical low/hard state, analogous to that of X-ray binaries, to a quiescent state over the last 5 Gyr. [ABSTRACT FROM AUTHOR]

ABSTRACT We investigate where brightest cluster galaxies (BCGs) sit on the Fundamental Plane of black hole (BH) activity, an established relation between the X-ray luminosity, the radio luminosity and the mass of a BH. Our sample mostly consists of BCGs that lie at the centres of massive, strong cooling flow clusters, therefore requiring extreme mechanical feedback from their central active galactic nucleus (AGN) to offset cooling of the intracluster plasma ( Lmech>1044 -1045 erg s−1). Based on the BH masses derived from the and MBH - MK correlations, we find that all of our objects are offset from the plane such that they appear to be less massive than predicted from their X-ray and radio luminosities (to more than a 99 per cent confidence level). For these objects to be consistent with the Fundamental Plane, the and MBH - MK correlations therefore seem to underestimate the BH masses of BCGs, on average by a factor of 10. Our results suggest that the standard relationships between BH mass and host galaxy properties no longer hold for these extreme galaxies. Furthermore, our results imply that if these BHs follow the Fundamental Plane, then many of those that lie in massive, strong cool core clusters must be ultramassive with MBH > 1010 M⊙. This rivals the largest BH masses known and has important ramifications for our understanding of the formation and evolution of BHs. [ABSTRACT FROM AUTHOR]

ABSTRACT We present the first statistical study of X-ray cavities in distant clusters of galaxies ( z > 0.3). With the aim of providing further insight into how active galactic nucleus (AGN) feedback operates at higher redshift, we have analysed the Chandra X-ray observations of the MAssive Cluster Survey (MACS) and searched for surface brightness depressions associated with the brightest cluster galaxy (BCG). The MACS sample consists of the most X-ray luminous clusters within 0.3 ≤ z≤ 0.7 (median LX, RASS= 7 × 1044 erg s−1), and out of 76 clusters, we find 13 with 'clear' cavities and seven with 'potential' cavities (detection rate ∼25 per cent). Most of the clusters in which we find cavities have a short central cooling time below 3-5 Gyr, consistent with the idea that cavities sit predominantly in cool core clusters. We also find no evidence for evolution in any of the cavity properties with redshift, up to z∼ 0.6. The cavities of powerful outbursts are not larger (or smaller) at higher redshift, and are not able to rise to further (or lesser) distances from the nucleus. The energetics of these outbursts also remain the same. This suggests that extreme 'radio mode' feedback ( Lmech > 1044 erg s−1) starts to operate as early as 7-8 Gyr after the big bang and shows no sign of evolution since then. In other words, AGNs lying at the centre of clusters are able to operate at early times with extreme mechanical powers, and have been operating in such a way for at least the past 5 Gyr. [ABSTRACT FROM AUTHOR]

ABSTRACT We present new Chandra images of the X-ray emission from the core of the Perseus cluster of galaxies. The total observation time is now 1.4 Ms. New depressions in X-ray surface brightness are discovered to the north of NGC 1275, which we interpret as old rising bubbles. They imply that bubbles are long-lived and do not readily breakup when rising in the hot cluster atmosphere. The existence of a 300 kpc long NNW-SSW bubble axis means there cannot be significant transverse large-scale flows exceeding 100 km s−1. Interesting spatial correlations are seen along that axis in early deep radio maps. A semicircular cold front about 100 kpc west of the nucleus is seen. It separates an inner disturbed region dominated by the activity of the active nucleus of NGC 1275 from the outer region where a subcluster merger dominates. [ABSTRACT FROM AUTHOR]

ABSTRACT It has been suggested that diffuse ionized gas can extend all the way to the end of the H i disc, and even beyond, such as in the case of the warped galaxy NGC 253 (Bland-Hawthorn et al.). Detecting ionized gas at these radii could carry significant implications as to the distribution of dark matter in galaxies. With the aim of detecting this gas, we carried out a deep Hα kinematical analysis of two Sculptor group galaxies, NGC 247 and 300. The Fabry-Perot data were taken at the 36-cm Marseille Telescope in La Silla, Chile, offering a large field of view. With almost 20 hours of observations for each galaxy, very faint diffuse emission is detected. Typical emission measures of 0.1 cm−6 pc are reached. For NGC 247, emission extending up to a radius comparable with that of the H i disc ( r∼ 13 arcmin) is found, but no emission is seen beyond the H i disc. For NGC 300, we detect ionized gas on the entirety of our field of view ( rmax∼ 14 arcmin), and find that the bright H ii regions are embedded in a diffuse background. Using the deep data, extended optical rotation curves are obtained, as well as mass models. These are the most extended optical rotation curves thus far for these galaxies. We find no evidence suggesting that NGC 247 has a warped disc, and to account for our non-detection of Hα emission beyond its H i disc, as opposed to the warped galaxy NGC 253, our results favour the model in which, only through a warp, ionization by hot young stars in the central region of a galaxy can let photons escape and ionize the interstellar medium in the outer parts. [ABSTRACT FROM AUTHOR]

ABSTRACT We present a detailed X-ray analysis of 4C+55.16, an unusual and interesting radio galaxy, located at the centre of a cool core cluster of galaxies. 4C+55.16 is X-ray bright ( LX(cluster)∼ 1045 erg s−1), radio powerful, and shows clear signs of interaction with the surrounding intracluster medium (ICM). By combining deep Chandra (100 ks) with 1.4 GHz Very Large Array observations, we find evidence of multiple outbursts from the central active galactic nucleus (AGN), providing enough energy to offset cooling of the ICM ( Pbubbles= 6.7 × 1044 erg s−1). Furthermore, 4C+55.16 has an unusual intracluster iron distribution showing a plume-like feature rich in Fe L emission that runs along one of the X-ray cavities. The excess of iron associated with the plume is around 107 M⊙. The metal abundances are consistent with being solar-like, indicating that both Type Ia supernova and Type II supernova contribute to the enrichment. The plume and southern cavity form a region of cool metal-rich gas, and at the edge of this region, there is a clear discontinuity in temperature (from kT∼ 2.5 to ∼5.0 keV), metallicity (from ∼0.4 to ∼0.8 Z⊙), and surface brightness distribution, consistent with it being caused by a cold front. However, we also suggest that this discontinuity could be caused by cool metal-rich gas being uplifted from the central AGN along one of its X-ray cavities. [ABSTRACT FROM AUTHOR]

ABSTRACT We present a study of strong cool core, highly luminous (most with LX≥ 1045 erg s−1) clusters of galaxies in which the mean jet power of the central active galactic nucleus 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, RXCJ 1504.1−0248. All of the central galaxies host a radio source, indicating an active nucleus, and no obvious X-ray point source. For all clusters in the sample, the nucleus has an X-ray bolometric luminosity below 2 per cent of that of the entire cluster. Most have a nucleus 2-10 keV X-ray luminosity less than about 1042 erg s−1. We investigate how these clusters can have such strong X-ray luminosities, short radiative cooling times of the inner intracluster gas requiring strong energy feedback to counterbalance that cooling and yet have such radiatively inefficient cores. If the central black holes have masses ∼109 M⊙ then the power exceeds 1 per cent of the Eddington luminosity, and they are expected to be radiatively efficient. Only if they are ultramassive ( MBH > 1010 M⊙), would their behaviour resemble that of lower mass accreting black holes. Our study focuses on deriving the nucleus X-ray properties of the clusters as defined in the above question, while briefly addressing possible solutions. [ABSTRACT FROM AUTHOR]

This study presents a deep Hα kinematical analysis of the Sculptor Group galaxy NGC 253. The Fabry-Perot data were taken with the 36-cm Marseille Telescope in La Silla, Chile, using an EMCCD detector. Typical emission measures of ∼0.1 cm pc are reached. The observations allow the detection of the diffuse ionized gas component through [N ] emission at very large radii of 11.5, 12.8 and 19.0 arcmin, on the receding side of the galaxy. No Hα emission is observed at radii larger than the neutral component (11.5 arcmin). The very extended rotation curve confirms previous results and shows signs of a significant decline, on the order of 30 per cent v. Using the rotation data, mass models are constructed with and without the outer [N ] data points, and similar results are found. The declining part of the rotation curve is very well modelled, and seems to be truly declining. [ABSTRACT FROM AUTHOR]

Background: The aim of this study was to determine the incidence of swallowing dysfunction in nonneurologic critically ill patients who require percutaneous dilatational tracheostomy (PDT) for prolonged mechanical ventilation (MV) and to compare the duration of the cannulation period and length of stay in the critical care unit (CCU) in patients with and without swallowing dysfunction.Methods: A total of 40 consecutive patients without neurologic disorders who require PDT for prolonged MV were included. Previous to the tracheostomy decannulation process, an otolaryngologist performed a fiberoptic endoscopic evaluation of swallowing (FEES). We used analysis of variance for the analysis; the results are presented as mean values +/- SD.Results: Mean age was 62 +/- 15 years. Acute Physiology and Chronic Health Evaluation II and Sequential Organ Failure Assessment scores were 21 +/- 2 and 9 +/- 1, respectively. Time of MV previous to PDT was 20 +/- 11 days, total MV duration was 38 +/- 16 days, and CCU stay was 63 +/- 27 days. The incidence of swallowing dysfunction in this group of patients was 38% (15/40). No difference was found in the age or time period of MV previous to PDT between groups. The time period between FEES to tracheostomy decannulation process was 19 +/- 11 days in patients with swallowing dysfunction vs 2 +/- 4 days in those patients without dysfunction (P < .001). Patients who developed swallowing dysfunction stayed longer in the CCU (69 +/- 23 vs 47 +/- 19 days, P < .01).Conclusions: Nearly 40% of nonneurologic critically ill patients requiring PDT for prolonged MV presented swallowing dysfunction and experienced a significant delay in their tracheostomy decannulation process. [ABSTRACT FROM AUTHOR]