A Galaxy-Scale Fountain of Cold Molecular Gas Pumped by a Black Hole (1808.00473v1)

Abstract: We present ALMA and MUSE observations of the Brightest Cluster Galaxy in Abell 2597, a nearby (z=0.0821) cool core cluster of galaxies. The data map the kinematics of a three billion solar mass filamentary nebula that spans the innermost 30 kpc of the galaxy's core. Its warm ionized and cold molecular components are both cospatial and comoving, consistent with the hypothesis that the optical nebula traces the warm envelopes of many cold molecular clouds that drift in the velocity field of the hot X-ray atmosphere. The clouds are not in dynamical equilibrium, and instead show evidence for inflow toward the central supermassive black hole, outflow along the jets it launches, and uplift by the buoyant hot bubbles those jets inflate. The entire scenario is therefore consistent with a galaxy-spanning "fountain", wherein cold gas clouds drain into the black hole accretion reservoir, powering jets and bubbles that uplift a cooling plume of low-entropy multiphase gas, which may stimulate additional cooling and accretion as part of a self-regulating feedback loop. All velocities are below the escape speed from the galaxy, and so these clouds should rain back toward the galaxy center from which they came, keeping the fountain long-lived. The data are consistent with major predictions of chaotic cold accretion, precipitation, and stimulated feedback models, and may trace processes fundamental to galaxy evolution at effectively all mass scales.

Analysis of Cold Molecular Gas Dynamics in Abell 2597

The paper by Tremblay et al. presents a comprehensive examination of cold molecular gas dynamics within the central regions of the Brightest Cluster Galaxy (BCG) in the Abell 2597 cluster. Using ALMA and MUSE observations, the authors describe the kinematics of a large, filamentary nebula consisting of cold molecular gas totaling approximately three billion solar masses. This research provides key insights into the processes of gas dynamics influenced by a central supermassive black hole, contributing significantly to the understanding of galaxy evolution.

Central to the paper is the evidence of dynamical interactions between the central supermassive black hole and the surrounding cold gas. The authors observe that this interaction manifests as a large-scale "fountain" effect: cold gas is observed falling toward the galaxy's center, counterbalanced by the upward motion of gas in the wake of buoyant X-ray cavities inflated by black hole-driven jets. This resultant feedback loop is consistent with theoretical models of chaotic cold accretion, where multiphase gas clouds move in gravitational and pressure-driven flows, periodically cooling and falling back into the black hole's accretion zone.

The paper finds that many observed velocities cannot escape the galaxy, implying that the molecular clouds are eventually recycled back toward the galaxy center. This aligns with theoretical predictions of self-regulating feedback processes that balance inflow and star formation with turbulent uplift, leading to sustained galaxy growth and maintenance.

The authors take a detailed view of the molecular nebula's multiphase components using ALMA CO(2-1) observations, revealing a complex interplay of inflowing, outflowing, and rotating gas features. In particular, extended filaments and clumps exhibit a wide range of velocities that suggest influence by jet-driven mechanical processes. PV diagrams highlight this complex structure and indicate that the largest velocity dispersions occur in regions associated with deflections of the central radio jet. The interaction between these cold gas structures and the radio jet outlines a dynamic environment where mechanical feedback from the AGN heavily influences galaxy-scale gas dynamics.

ALMA observations are supplemented by optical MUSE spectroscopic data, providing additional context in terms of warm ionized gas dynamics. The consistency of Hα emission with cold molecular emission suggests a co-moving system where interaction between warm and cold phases could enhance gas cooling and further drive accretion processes.

From a broader perspective, this work has significant implications for the paper of chaotic cold accretion and galaxy evolution across different mass scales. It suggests that AGN feedback processes are fundamental in shaping the thermodynamic properties and kinematic behavior of galaxy cluster cores. By expanding on models of AGN-driven mechanical feedback, the findings provide a framework for understanding the balance of cooling and heating processes that regulate gas accretion and star formation in galaxy clusters.

Looking ahead, this paper underlines the importance of high-resolution multi-wavelength observations in refining models of galaxy and cluster evolution. Future advances in instrumentation and observational strategies will likely enable even more detailed studies of gas dynamics around supermassive black holes, contributing to our understanding of their role in cosmic structure formation and evolution.