Stellar dynamics in the strong-lensing central galaxy of Abell 1201: a low stellar mass-to-light ratio, a large central compact mass and a standard dark matter halo

We analyse the stellar kinematics of the z = 0.169 brightest cluster galaxy in Abell 1201, using integral field observations acquired with the Multi-Unit Spectroscopic Explorer on the Very Large Telescope. This galaxy has a gravitationally lensed arc located at unusually small radius (∼5 kpc), allowing us to constrain the mass distribution using lensing and stellar dynamical information over the same radial range. We measure a velocity dispersion profile which is nearly flat at σ ≈ 285 km s−1 in the inner ∼5 kpc, and then rises steadily to σ ≈ 360 km s−1 at ∼30 kpc. We analyse the kinematics using axisymmetric Jeans models, finding that the data require both a significant dark matter halo (to fit the rising outer profile) and a compact central component, with mass Mcen ≈ 2.5 × 1010 M⊙ (to fit the flat σ in the inner regions). The latter component could represent a supermassive black hole, in which case it would be among the largest known to date. Alternatively Mcen could describe excess mass associated with a gradient in the stellar mass-to-light ratio. Imposing a standard Navarro–Frenk–White (NFW) dark matter density profile, we recover a stellar mass-to-light ratio ϒ, which is consistent with a Milky Way-like initial mass function (IMF). By anchoring the models using the lensing mass constraint, we break the degeneracy between ϒ and the inner slope γ of the dark matter profile, finding γ = 1.0 ± 0.1, consistent with the NFW form. We show that our results are quite sensitive to the treatment of the central mass in the models. Neglecting Mcen biases the results towards both a heavier-than-Salpeter IMF and a shallower-than-NFW dark matter slope (γ ≈ 0.5)

Molecular Flows in Contemporary Active Galaxies and the Efficacy of Radio-Mechanical Feedback

Molecular gas flows are analysed in 14 cluster galaxies (BCGs) centred in cooling hot atmospheres. The BCGs contain 109−1011 M⊙ of molecular gas, much of which is being moved by radio jets and lobes. The molecular flows and radio jet powers are compared to molecular outflows in 45 active galaxies within z < 0.2. We seek to understand the relative efficacy of radio, quasar, and starburst feedback over a range of active galaxy types. Molecular flows powered by radio feedback in BCGs are ∼10–1000 times larger in extent compared to contemporary galaxies hosting quasar nuclei and starbursts. Radio feedback yields lower flow velocities but higher momenta compared to quasar nuclei, as the molecular gas flows in BCGs are usually ∼10–100 times more massive. The product of the molecular gas mass and lifting altitude divided by the AGN or starburst power – a parameter referred to as the lifting factor – exceeds starbursts and quasar nuclei by 2–3 orders of magnitude, respectively. When active, radio feedback is generally more effective at lifting gas in galaxies compared to quasars and starburst winds. The kinetic energy flux of molecular clouds generally lies below and often substantially below a few per cent of the driving power. We find tentatively that star formation is suppressed in BCGs relative to other active galaxies, perhaps because these systems rarely form molecular discs that are more impervious to feedback and are better able to promote star formation

Radio jet–ISM interaction and positive radio-mechanical feedback in Abell 1795

We present XSHOOTER observations with previous ALMA, MUSE, and HST observations to study the nature of radio jet triggered star formation and the interaction of radio jets with the interstellar medium in the brightest cluster galaxy (BCG) in the Abell 1795 cluster. Using HST UV data, we determined an ongoing star formation rate of 9.3 M⊙ yr−1. The star formation follows the global Kennicutt–Schmidt law; however, it has a low efficiency compared to circumnuclear starbursts in nearby galaxies with an average depletion time of ∼1 Gyr. The star formation and molecular gas are offset by ∼1 kpc indicating that stars have decoupled from the gas. We detected an arc of high linewidth in ionized gas where electron densities are elevated by a factor of ∼4 suggesting a shock front driven by radio jets or peculiar motion of the BCG. An analysis of nebular emission line flux ratios suggests that the gas is predominantly ionized by star formation with a small contribution from shocks. We also calculated the velocity structure function (VSF) of the ionized and molecular gases using velocity maps to characterize turbulent motion in the gas. The ionized gas VSF suggests that the radio jets are driving supersonic turbulence in the gas. Thus radio jets cannot only heat the atmosphere on large scales and may quench star formation on longer time-scales while triggering star formation in positive feedback on short time-scales of a few million years

Discovery of a Powerful >1061 erg AGN Outburst in the Distant Galaxy Cluster SPT-CLJ0528-5300

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 × 1033 erg s−1 Hz−1) central active galactic nucleus (AGN) of any cluster in the South Pole Telescope (SPT) Sunyaev–Zeldovich 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 Australia Telescope Compact Array radio data. The combined probability that two such depressions—each at ~1.4–1.8σ significance, oriented ~180° apart and aligned with the jet axis—would occur by chance is 0.1%. At gsim1061 erg, the outburst in SPT0528 is among the most energetic known in the universe, and certainly the most powerful known at z > 0.25. This work demonstrates that such powerful outbursts can be detected even in shallow X-ray exposures out to relatively high redshifts (z ~ 0.8), providing an avenue for studying the evolution of extreme AGN feedback. The ratio of the cavity power (${P}_{\mathrm{cav}}=(9.4\pm 5.8)\times {10}^{45}$ erg s−1) to the cooling luminosity (L cool = (1.5 ± 0.5) × 1044 erg s−1) for SPT0528 is among the highest measured to date. If, in the future, additional systems are discovered at similar redshifts with equally high P cav/L cool ratios, it would imply that the feedback/cooling cycle was not as gentle at high redshifts as in the low-redshift universe

The XMM Cluster Survey: The interplay between the brightest cluster galaxy and the intra-cluster medium via AGN feedback

Using a sample of 123 X-ray clusters and groups drawn from the XMM-Cluster Survey first data release, we investigate the interplay between the brightest cluster galaxy (BCG), its black hole, and the intra-cluster/group medium (ICM). It appears that for groups and clusters with a BCG likely to host significant AGN feedback, gas cooling dominates in those with Tx > 2 keV while AGN feedback dominates below. This may be understood through the sub-unity exponent found in the scaling relation we derive between the BCG mass and cluster mass over the halo mass range 10^13 < M500 < 10^15Msol and the lack of correlation between radio luminosity and cluster mass, such that BCG AGN in groups can have relatively more energetic influence on the ICM. The Lx - Tx relation for systems with the most massive BCGs, or those with BCGs co-located with the peak of the ICM emission, is steeper than that for those with the least massive and most offset, which instead follows self-similarity. This is evidence that a combination of central gas cooling and powerful, well fuelled AGN causes the departure of the ICM from pure gravitational heating, with the steepened relation crossing self-similarity at Tx = 2 keV. Importantly, regardless of their black hole mass, BCGs are more likely to host radio-loud AGN if they are in a massive cluster (Tx > 2 keV) and again co-located with an effective fuel supply of dense, cooling gas. This demonstrates that the most massive black holes appear to know more about their host cluster than they do about their host galaxy. The results lead us to propose a physically motivated, empirical definition of 'cluster' and 'group', delineated at 2 keV.Comment: Accepted for publication in MNRAS - replaced to match corrected proo

Discovery of a Supercluster at z ~ 0.91 and Testing the ΛCDM Cosmological Model

The ΛCDM cosmological model successfully reproduces many aspects of the galaxy and structure formation of the universe. However, the growth of large-scale structures (LSSs) in the early universe is not well tested yet with observational data. Here, we have utilized wide and deep optical–near-infrared data in order to search for distant galaxy clusters and superclusters (0.8 < z < 1.2). From the spectroscopic observation with the Inamori Magellan Areal Camera and Spectrograph (IMACS) on the Magellan telescope, three massive clusters at z ~ 0.91 are confirmed in the SSA22 field. Interestingly, all of them have similar redshifts within Δ z ~ 0.01 with velocity dispersions ranging from 470 to 1300 km s−1. Moreover, as the maximum separation is ~15 Mpc, they compose a supercluster at z ~ 0.91, meaning that this is one of the most massive superclusters at this redshift to date. The galaxy density map implies that the confirmed clusters are embedded in a larger structure stretching over ~100 Mpc. ΛCDM models predict about one supercluster like this in our surveyed volume, consistent with our finding so far. However, there are more supercluster candidates in this field, suggesting that additional studies are required to determine if the ΛCDM cosmological model can successfully reproduce the LSSs at high redshift