We propose a novel method to constrain turbulence and bulk motions in massive galaxies, galaxy groups and clusters, exploring both simulations and observations. As emerged in the recent picture of the top-down multiphase condensation, the hot gaseous halos are tightly linked to all other phases in terms of cospatiality and thermodynamics. While hot halos (∼ 10 7 K) are perturbed by subsonic turbulence, warm (∼ 10 4 K) ionized and neutral filaments condense out of the turbulent eddies. The peaks condense into cold molecular clouds (< 100 K) raining in the core via chaotic cold accretion (CCA). We show all phases are tightly linked in terms of the ensemble (wide-aperture) velocity dispersion along the line of sight. The correlation arises in complementary long-term AGN feedback simulations and high-resolution CCA runs, and is corroborated by the combined Hitomi and new Integral Field Unit measurements in Perseus cluster. The ensemble multiphase gas distributions (from UV to radio band) are characterized by substantial spectral line broadening (σ v,los ≈ 100 -200 km s −1 ) with mild line shift. On the other hand, pencil-beam detections (as HI absorption against the AGN backlight) sample the small-scale clouds displaying smaller broadening and significant line shift up to several 100 km s −1 (for those falling toward the AGN), with increased scatter due to the turbulence intermittency. We present new ensemble σ v,los of the warm Hα+[NII] gas in 72 observed cluster/group cores: the constraints are consistent with the simulations and can be used as robust proxies for the turbulent velocities, in particular for the challenging hot plasma (otherwise requiring extremely long X-ray exposures). Finally, we show the physically motivated criterion C ≡ t cool /t eddy ≈ 1 best traces the condensation extent region and presence of multiphase gas in observed clusters and groups. The ensemble method can be applied to many available spectroscopic datasets and can substantially advance our understanding of multiphase halos in light of the next-generation multiwavelength missions.

An ALMA observation of the early-type galaxy NGC 5044, which resides at the center of an X-ray bright group with a moderate cooling flow, detected 24 molecular structures within the central 2.5 kpc. The masses of the molecular structures vary from 3 × 10 5 M to 10 7 M and the CO(2-1) linewidths vary from 15 to 65 km s −1 . Given the large CO(2-1) linewidths, the observed structures are likely giant molecular associations (GMAs) and not individual molecular clouds (GMCs). Only a few of the GMAs are spatially resolved and the average density of these GMAs yields a GMC volume filling factor of about 15%. The masses of the resolved GMAs are insufficient for them to be gravitationally bound, however, the most massive GMA does contain a less massive component with a linewidth of 5.5 km s −1 (typical of an individual virialized GMC). We also show that the GMAs cannot be pressure confined by the hot gas. Given the CO(2-1) linewidths of the GMAs (i.e., the velocity dispersion of the embedded GMCs) they should disperse on a timescale of about 12 Myr. No disk-like molecular structures are detected and all indications suggest that the molecular gas follows ballistic trajectories after condensing out of the thermally unstable hot gas. The 230 GHz luminosity of the central continuum source is 500 times greater than its low frequency radio luminosity and probably reflects a recent accretion event. The spectrum of the central continuum source also exhibits an absorption feature with a linewidth typical of an individual GMC and an infalling velocity of 250 km s −1 .

Supermassive black holes in galaxy centres can grow by the accretion of gas, liberating energy that might regulate star formation on galaxy-wide scales 1-3 . The nature of the gaseous fuel reservoirs that power black hole growth is nevertheless largely unconstrained by observations, and is instead routinely simplified as a smooth, spherical inflow of very hot gas 4 . Recent theory 5-7 and simulations 8-10 instead predict that accretion can be dominated by a stochastic, clumpy distribution of very cold molecular clouds -a departure from the 'hot mode' accretion model -although unambiguous observational support for this prediction remains elusive. Here we report observations that reveal a cold, clumpy accretion flow towards a supermassive black hole fuel reservoir in the nucleus of the Abell 2597 Brightest Cluster Galaxy (BCG), a nearby (redshift z = 0.0821) giant elliptical galaxy surrounded by a dense halo of hot plasma [11][12][13] . Under the right conditions, thermal instabilities can precipitate from this hot gas, producing a rain of cold clouds that fall toward the galaxy's centre 14 , sustaining star formation amid a kiloparsec-scale molecular nebula that inhabits its core 15 . The observations show that these cold clouds also fuel black hole accretion, revealing 'shadows' cast by the molecular clouds as they move inward at about 300 kilometres per second towards the active supermassive black hole in the galaxy centre, which serves as a bright backlight. Corroborating evidence from prior observations 16 of warmer atomic gas at extremely high spatial resolution 17 , along with simple arguments based on geometry and probability, indicate that these clouds are within the innermost hundred parsecs of the black hole, and falling closer towards it. We observed the Abell 2597 Brightest Cluster Galaxy (Fig. 1) with the Atacama Large Millimeter/submillimeter Array (ALMA), enabling us to create a three-dimensional map of both the location and motions of cold gas at uniquely high sensitivity and spatial resolution. The ALMA receivers were sensitive to emission from the J = 2 − 1 rotational line of the carbon monoxide (CO) molecule. CO(2-1) emission is used as a tracer of cold (∼ 10 − 30 K) molecular hydrogen, which is vastly more abundant, but not directly observable at these low temperatures.The continuum-subtracted CO(2-1) images (Fig. 2) reveal that the filamentary emission line nebula that spans the galaxy's innermost ∼ 30 kpc (Fig. 1b) consists not only of warm ionised gas [18][19][20] , but cold molecular gas as well. In projection, the optical emission line nebula is cospatial and morphologically matched with CO(2-1) emission detected at a significance between > ∼ 3σ (in the outer filaments) and > ∼ 20σ (in the nuclear region) above the background noise level. The warm ionised nebula is therefore likely to have a substantial molecular component, consistent with results for other similar galaxies 21 . The total measured CO(2-1) line flux corresponds to a molecular hydrogen gas mass of M H 2 = (1.8 ± 0.2) × 10 9...

Multi-phase filamentary structures around Brightest Cluster Galaxies (BCG) are likely a key step of AGN-feedback. We observed molecular gas in 3 cool cluster cores: Centaurus, Abell S1101, and RXJ1539.5 and gathered ALMA (Atacama Large Millimeter/submillimeter Array) and MUSE (Multi Unit Spectroscopic Explorer) data for 12 other clusters. Those observations show clumpy, massive and long, 3-25 kpc, molecular filaments, preferentially located around the radio bubbles inflated by the AGN (Active Galactic Nucleus). Two objects show nuclear molecular disks. The optical nebula is certainly tracing the warm envelopes of cold molecular filaments. Surprisingly, the radial profile of the Hα/CO flux ratio is roughly constant for most of the objects, suggesting that (i) between 1.2 to 7 times more cold gas could be present and (ii) local processes must be responsible for the excitation. Projected velocities are between 100-400 km s −1 , with disturbed kinematics and sometimes coherent gradients. This is likely due to the mixing in projection of several thin (as yet) unresolved filaments. The velocity fields may be stirred by turbulence induced by bubbles, jets or merger-induced sloshing. Velocity and dispersions are low, below the escape velocity. Cold clouds should eventually fall back and fuel the AGN. We compare the filament's radial extent, r fil , with the region where the X-ray gas can become thermally unstable. The filaments are always inside the low-entropy and short cooling time region, where t cool /t ff <20 (9 of 13 sources). The range t cool /t ff , 8-23 at r fil , is likely due to (i) a more complex gravitational potential affecting the free-fall time t ff (sloshing, mergers. . . ); (ii) the presence of inhomogeneities or uplifted gas in the ICM, affecting the cooling time t cool . For some of the sources, r fil lies where the ratio of the cooling time to the eddy-turnover time, t cool /t eddy , is approximately unity.

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 (eBCS) and ROSAT-ESO Flux Limited X-ray (REFLEX) cluster catalogues. We have multi-frequency radio observations of the BCG using a variety of data from the Australia Telescope Compact Array (ATCA), Jansky Very Large Array (VLA) and Very Long Baseline Array (VLBA) telescopes. The radio spectral energy distributions (SEDs) 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 H-α), 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% of cases. This core component more strongly correlates with the BCG's [OIII]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 fueling of the AGN over bubble-rise timescales in these clusters.

We have conducted a two-layered spectroscopic survey (1 × 1 ultra deep and 3 × 3 deep regions) in the Hubble Ultra Deep Field (HUDF) with the Multi Unit Spectroscopic Explorer (MUSE). The combination of a large field of view, high sensitivity, and wide wavelength coverage provides an order of magnitude improvement in spectroscopically confirmed redshifts in the HUDF; i.e., 1206 secure spectroscopic redshifts for HST continuum selected objects, which corresponds to 15% of the total (7904). The redshift distribution extends well beyond z > 3 and to HST/F775W magnitudes as faint as ≈ 30 mag (AB, 1σ). In addition, 132 secure redshifts were obtained for sources with no Hubble Space Telescope (HST) counterparts that were discovered in the MUSE data cubes by a blind search for emission-line features. In total, we present 1338 high quality redshifts, which is a factor of eight increase compared with the previously known spectroscopic redshifts in the same field. We assessed redshifts mainly with the spectral features [O ii] at z < 1.5 (473 objects) and Lyα at 2.9 < z < 6.7 (692 objects). With respect to F775W magnitude, a 50% completeness is reached at 26.5 mag for ultra deep and 25.5 mag for deep fields, and the completeness remains 20% up to 28 − 29 mag and ≈ 27 mag, respectively. We used the determined redshifts to test continuum color selection (dropout) diagrams of high-z galaxies. The selection condition for F336W dropouts successfully captures ≈ 80% of the targeted z ∼ 2.7 galaxies. However, for higher redshift selections (F435W, F606W, and F775W dropouts), the success rates decrease to ≈ 20 − 40%. We empirically redefine the selection boundaries to make an attempt to improve them to ≈ 60%. The revised boundaries allow bluer colors that capture Lyα emitters with high Lyα equivalent widths falling in the broadbands used for the color-color selection. Along with this paper, we release the redshift and line flux catalog.

We report ALMA Early Science observations of the Abell 1835 brightest cluster galaxy (BCG) in the CO (3-2) and CO (1-0) emission lines. We detect 5 × 10 10 M of molecular gas within 10 kpc of the BCG. Its ensemble velocity profile width of ∼ 130 km s −1 FWHM is too narrow for the molecular clouds to be supported in the galaxy by dynamic pressure. The gas may instead be supported in a rotating, turbulent disk oriented nearly face-on. Roughly 10 10 M of molecular gas is projected 3 − 10 kpc to the north-west and to the east of the nucleus with line of sight velocities lying between −250 km s −1 to +480 km s −1 with respect to the systemic velocity. The high velocity gas may be either inflowing or outflowing. However, the absence of high velocity gas toward the nucleus that would be expected in a steady inflow, and its bipolar distribution on either side of the nucleus, are more naturally explained as outflow. Star formation and radiation from the AGN are both incapable of driving an outflow of this magnitude. The location of the high velocity gas projected behind buoyantly rising X-ray cavities and favorable energetics suggest an outflow driven by the radio AGN. If so, the molecular outflow may be associated a hot outflow on larger scales reported by Kirkpatrick and colleagues. The molecular gas flow rate of approximately 200 M yr −1 is comparable to the star formation rate of 100 − 180 M yr −1 in the central disk. How radio bubbles would lift dense molecular gas in their updrafts, how much gas will be lost to the BCG, and how much will return to fuel future star formation and AGN activity are poorly understood. Our results imply that radio-mechanical (radio mode) feedback not only heats hot atmospheres surrounding elliptical galaxies and BCGs, it is able to sweep higher density molecular gas away from their centers.

We present an Integral Field Unit survey of 73 galaxy clusters and groups with the VIsible Multi Object Spectrograph (VIMOS) on VLT. We exploit the data to determine the Hα gas dynamics on kpc-scales to study the feedback processes occurring within the dense cluster cores. We determine the kinematic state of the ionised 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 Hα flux (> 50 %) 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 % of the sample (13/73) have disturbed morphologies which can typically be attributed to AGN 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 ionisation of the gas within cluster cores is dominated by non stellar processes, possibly originating from the intracluster medium itself.