We present an analysis of 55 central galaxies in clusters and groups with molecular gas masses and star formation rates lying between 10 8 − 10 11 M and 0.5 and 270 M yr −1 , respectively. Using Chandra X-ray observations, we have calculated hydrostatic mass profiles, fully accounting for the central galaxy. We have derived acceleration profiles, atmospheric temperature, density, and other thermodynamic variables. Molecular gas mass is correlated with star formation rate, Hα line luminosity, and central atmospheric gas density. Molecular gas is detected only when the central cooling time or entropy index of the hot atmosphere falls below ∼1 Gyr or ∼35 keV cm 2 , respectively, at a (resolved) radius of 10 kpc. These correlations indicate that the molecular gas condensed from hot atmospheres surrounding the central galaxies. The depletion timescale of molecular gas due to star formation approaches 1 Gyr in most systems. Yet ALMA images of roughly a half dozen systems drawn from this sample suggest the molecular gas formed recently and is in a transient state. We explore the origins of thermally unstable cooling by evaluating whether molecular gas becomes prevalent when the minimum of the cooling to free-fall time ratio (t cool /t ff ) falls below ∼ 10. We find: 1) molecular gas-rich systems instead lie between 10 < min(t cool /t ff ) < 25, where t cool /t ff = 25 corresponds approximately to cooling time and entropy thresholds t cool 1 Gyr and 35 keV cm 2 , respectively, 2) min(t cool /t ff ) is uncorrelated with molecular gas mass and jet power, and 3) the narrow range 10 < min(t cool /t ff ) < 25 can be explained by an observational selection effect. These results and the absence of isentropic cores in cluster atmospheres are in tension with "precipitation" models, particularly those that assume thermal instability ensues from linear density perturbations in hot atmospheres. Some and possibly all of the molecular gas may instead have condensed from atmospheric gas lifted outward either by buoyantly-rising X-ray bubbles or merger-induced gas motions.

We present accurate mass and thermodynamic profiles for 57 galaxy clusters observed with the Chandra X-ray Observatory. We investigate the effects of local gravitational acceleration in central cluster galaxies, and explore the role of the local free-fall time (t ff ) in thermally unstable cooling. We find that the radially averaged cooling time (t cool ) is as effective an indicator of cold gas, traced through its nebular emission, as the ratio t cool /t ff . Therefore, t cool primarily governs the onset of thermally unstable cooling in hot atmospheres. The location of the minimum t cool /t ff , a thermodynamic parameter that many simulations suggest is key in driving thermal instability, is unresolved in most systems. Consequently, selection effects bias the value and reduce the observed range in measured t cool /t ff minima. The entropy profiles of cool-core clusters are characterized by broken power laws down to our resolution limit, with no indication of isentropic cores. We show, for the first time, that mass isothermality and the µ K r 2 3 entropy profile slope imply a floor in t cool /t ff profiles within central galaxies. No significant departures of t cool /t ff below 10 are found. This is inconsistent with models that assume thermally unstable cooling ensues from linear perturbations at or near this threshold. We find that the inner cooling times of cluster atmospheres are resilient to active galactic nucleus (AGN)-driven change, suggesting gentle coupling between radio jets and atmospheric gas. Our analysis is consistent with models in which nonlinear perturbations, perhaps seeded by AGN-driven uplift of partially cooled material, lead to cold gas condensation.

We report on broad multi-wavelength observations of the 2010-2011 periastron passage of the γ-ray loud binary system PSR B1259−63. High resolution interferometric radio observations establish extended radio emission trailing the position of the pulsar. Observations with the Fermi Gamma-ray Space Telescope reveal GeV γ-ray flaring activity of the system, reaching the spin-down luminosity of the pulsar, around 30 days after periastron. There are no clear signatures of variability at radio, X-ray and TeV energies at the time of the GeV flare. Variability around periastron in the Hα emission line, can be interpreted as the gravitational interaction between the pulsar and the circumstellar disk. The equivalent width of the Hα grows from a few days before periastron until a few days later, and decreases again between 18 and 46 days after periastron. In near infrared we observe the similar decrease of the equivalent width of Brγ line between the 40th and 117th day after the periastron. For the idealized disk, the variability of the Hα line represents the variability of the mass and size of the disk. We discuss possible physical relations between the state of the disk and GeV emission under assumption that GeV flare is directly related to the decrease of the disk size.