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ABSTRACT We present new Chandra X-ray observations of the brightest cluster galaxy (BCG) in the cool-core cluster Abell 2597 ( z= 0.0821). The data reveal an extensive kpc-scale X-ray cavity network as well as a 15-kpc filament of soft-excess gas exhibiting strong spatial correlation with archival Very Large Array radio data. In addition to several possible scenarios, multiwavelength evidence may suggest that the filament is associated with multiphase (103-107 K) gas that has been entrained and dredged-up by the propagating radio source. Stemming from a full spectral analysis, we also present profiles and 2D spectral maps of modelled X-ray temperature, entropy, pressure and metal abundance. The maps reveal an arc of hot gas which in projection borders the inner edge of a large X-ray cavity. Although limited by strong caveats, we suggest that the hot arc may be (a) due to a compressed rim of cold gas pushed outwards by the radio bubble or (b) morphologically and energetically consistent with cavity-driven active galactic nucleus heating models invoked to quench cooling flows, in which the enthalpy of a buoyant X-ray cavity is locally thermalized as ambient gas rushes to refill its wake. If confirmed, this would be the first observational evidence for this model. [ABSTRACT FROM AUTHOR]

ABSTRACT New Chandra X-ray and Herschel Far-Infrared (FIR) observations enable a multiwavelength study of active galactic nucleus (AGN) heating and intracluster medium (ICM) cooling in the brightest cluster galaxy (BCG) of Abell 2597 ( z= 0.0821). The new Chandra observations reveal the central ≲30 kpc X-ray cavity network to be more extensive than previously thought, and associated with enough enthalpy to theoretically inhibit the inferred classical cooling flow. Nevertheless, we present new evidence, consistent with previous results, that a moderately strong residual cooling flow is persisting at 4-8 per cent of the classically predicted rates in a spatially structured manner amid the feedback-driven excavation of the X-ray cavity network. New Herschel observations are used to estimate warm and cold dust masses, a lower limit gas-to-dust ratio and a star formation rate consistent with previous measurements. [O i] and CO(2−1) line profiles are used to constrain the kinematics of the ∼109 M⊙ reservoir of cold molecular gas. The cooling time profile of the ambient X-ray atmosphere is used to map the locations of the observational star formation entropy threshold as well as the theoretical thermal instability threshold. Both lie just outside the ≲30-kpc central region permeated by X-ray cavities, and star formation as well as ionized and molecular gas lie interior to both. The young stars are distributed in an elongated region that is aligned with the radio lobes, and their estimated ages are both younger and older than the X-ray cavity network, suggesting both jet-triggered as well as persistent star formation over the current AGN feedback episode. Bright X-ray knots that are coincident with extended Lyα and far-ultraviolet continuum filaments motivate a discussion of structured cooling from the ambient hot atmosphere along a projected axis that is perpendicular to X-ray cavity and radio axis. We conclude that the cooling ICM is the dominant contributor of the cold gas reservoir fuelling star formation and AGN activity in the Abell 2597 BCG. [ABSTRACT FROM AUTHOR]

Abstract We present a large sample of H - and K -band spectra of 32 optically line-luminous central cluster galaxies. We find significant rovibrational H 2 emission in 23 of these galaxies as well as H recombination and/or [Fe ii] emission in another five. This represents a fourfold increase in the number of molecular line detections known. A number of the detections are of extended emission (5–20 kpc). In several objects we find significant [Si vi] emission that appears to correlate with the strength of high ionization lines in the optical (e.g. [O iii]). This comprehensive sample builds on previous work and confirms that warm (1000–2500 K) molecular hydrogen is present wherever there is ionized material in the cores of cooling flows and in most cases it also coincides with CO molecular line emission. [ABSTRACT FROM AUTHOR]

The origin of rovibrational H[sub 2] emission in the central galaxies of cooling flow clusters is poorly understood. Here we address this issue using data from our near-infrared spectroscopic survey of 32 of the most line-luminous such systems, presented in the companion paper by Edge et al. We consider excitation by X-rays from the surrounding intracluster medium (ICM), ultraviolet (UV) radiation from young stars, and shocks. The v = 1-0 K-band lines with upper levels within 10[sup 4] K of the ground state appear to be mostly thermalized (implying gas densities ... 10[sup 5] cm[sup -3]), with the excitation temperature typically exceeding 2000 K, as found earlier by Jaffe, Bremer & van der Werf. Together with the lack of strong v = 2-0 lines in the H-band, this rules out UV radiative fluorescence. Using the CLOUDY photoionization code, we deduce that the H[sub 2] lines can originate in a population of dense clouds, exposed to the same hot (T ∼ 50000 K) stellar continuum as the lower density gas which produces the bulk of the forbidden optical line emission in the Hα-luminous systems. This dense gas may be in the form of self-gravitating clouds deposited directly by the cooling flow, or may instead be produced in the high-pressure zones behind strong shocks. Furthermore, the shocked gas is likely to be gravitationally unstable, so collisions between the larger clouds may lead to the formation of globular clusters. [ABSTRACT FROM AUTHOR]