A Global Model for Circumgalactic and Cluster-core Precipitation

Abstract

We provide an analytic framework for interpreting observations of multiphase circumgalactic gas that is heavily informed by recent numerical simulations of thermal instability and precipitation in cool-core galaxy clusters. We start by considering the local conditions required for the formation of multiphase gas via two different modes: (1) uplift of ambient gas by galactic outflows, and (2) condensation in a stratified stationary medium in which thermal balance is explicitly maintained. Analytic exploration of these two modes provides insights into the relationships between the local ratio of the cooling and freefall time scales (i.e., t cool /t ff ), the large-scale gradient of specific entropy, and development of precipitation and multiphase media in circumgalactic gas. We then use these analytic findings to interpret recent simulations of circumgalactic gas in which global thermal balance is maintained. We show that long-lasting configurations of gas with 5 min(t cool /t ff ) 20 and radial entropy profiles similar to observations of local cool-core galaxy cluster cores are a natural outcome of precipitation-regulated feedback. We conclude with some observational predictions that follow from these models. This work focuses primarily on precipitation and AGN feedback in galaxy cluster cores, because that is where the observations of multiphase gas around galaxies are most complete. However, many of the physical principles that govern condensation in those environments apply to circumgalactic gas around galaxies of all masses.

COS-burst: Observations of the Impact of Starburst-driven Winds on the Properties of the Circum-galactic Medium

“…Both observations and theoretical models imply that the gas density in the CGM falls with radius roughly like r −1 to r −1.5 (Maller & Bullock 2004;Miller & Bregman 2013Werk et al 2014;Voit et al 2017;Faermon et al 2017). When we take an initial radial density profile for the volume-filling phase of n vf ∝1/r, and following the self-similar solutions for energy-driven bubbles in Dyson (1989), the radius of the expanding bubble is given by ), M hot,10 is the total mass of the volume-filling phase out to a radius of 200 kpc in units of 10 10 M e , and t 8 is the time since the starburst began, given in units of 10 8 years.…”

“…This idea has mostly been proposed and discussed in the context of the effects of AGN-driven outflows (jets) on the observed multiphase gas in the cores of clusters of galaxies (Li & Bryan 2014;Voit et al 2017). In this model, the AGNdriven outflow uplifts diffuse ambient gas.…”

Gentle Heating by Mixing in Cooling Flow Clusters

“…It is thought now that the feedback is closed by the cold feedback mechanism (Pizzolato & Soker 2005), namely, cold dense clumps that feed the AGN (e.g., some papers from the last 2 years, Gaspari 2015; Li et al 2015;Prasad et al 2015;Singh & Sharma 2015;Tremblay et al 2015;Valentini & Brighenti 2015;Choudhury & Sharma 2016;Hamer et al 2016;Loubser et al 2016;Russell et al 2016;McNamara et al 2016;Yang & Reynolds 2016;Barai et al 2016;Prasad et al 2016;Tremblay et al 2016;Donahue et al 2017;Gaspari & Sadowski 2017;Voit et al 2017;Meece et al 2017). The new results of Hogan et al (2017) suggest that the perturbations that feed the AGN should start as non-linear ones, as was suggested in the original paper by Pizzolato & Soker (2005).…”

Alma Observations of Massive Molecular Gas Filaments Encasing Radio Bubbles in the Phoenix Cluster

“…Low entropy X-ray gas should become thermally unstable when lifted to a radius where its cooling time approaches the infall time (Nulsen 1986;Pizzolato & Soker 2005;McNamara et al 2014McNamara et al , 2016. Theoretical models further indicate that lifting low-entropy gas in the updraft of rising radio bubbles stimulates condensation of molecular clouds (Li & Bryan 2014;Brighenti et al 2015;Voit et al 2016). Therefore, an infall time that is significantly longer than the free-fall time will enhance thermal instabilities, and promote the formation of molecular gas clouds in the bubbles' wakes .…”