The Fate of AGB Wind in Massive Galaxies and the ICM

Abstract

Asymptotic Giant Branch (AGB) winds from evolved stars not only provide a non-trivial amount of mass and energy return, but also produce dust grains in massive elliptical galaxies. Due to the fast stellar velocity and the high ambient temperature, the wind is thought to form a comet-like tail, similar to Mira in the Local Bubble. Many massive elliptical galaxies and cluster central galaxies host extended dusty cold filaments. The fate of the cold dusty stellar wind and its relation to cold filaments are not well understood. In this work, we carry out both analytical and numerical studies of the interaction between an AGB wind and the surrounding hot gas. We find that the cooling time of the tail is inversely proportional to the ambient pressure. In the absence of cooling, or in low pressure environments (e.g., the outskirts of elliptical galaxies), AGB winds are quickly mixed into the hot gas, and all the AGB winds have similar appearance and head-to-tail ratio. In high pressure environments, such as the Local Bubble and the central regions of massive elliptical galaxies, some of the gas in the mixing layer between the stellar wind and the surrounding hot gas can cool efficiently and cause the tail to become longer. Our simulated tail of Mira itself has similar length and velocity to that observed, and appears similar to the simulated AGB tail in the central regions of massive galaxies. We speculate that instead of thermal instability, the induced condensation at the mixing layer of AGB winds may be the origin of cold filaments in massive galaxies and galaxy clusters. This naturally explains the existence of dust and PAH in the filaments.

Direct Detection of Black Hole-driven Turbulence in the Centers of Galaxy Clusters

“…Our results suggest that the motion of cold filaments is well-coupled with the hot ICM. The origin of the Hα fila-ments and their fate are still uncertain, but two scenarios would allow the filaments to share the same turbulent motion of the hot ICM: (1) if they originate from the hot gas, either due to thermal instabilities or induced cooling (McCourt et al 2012;Li & Bryan 2014;Li et al 2019), but are very short-lived (dissolve quickly) such that they keep the memory of the turbulent motion of the hot gas, and/or (2) if they are very "misty" and quickly become co-moving with the hot gas (McCourt et al 2018) even if they are created independently of it (Qiu et al 2019). On the other hand, if the cold gas is poorly coupled to the hot gas and follows ballistic trajectories, neighboring cold filaments would move independently and show little kinematic correlation.…”

The Dust and Molecular Gas in the Brightest Cluster Galaxy in MACS 1931.8-2635

“…Dust in the BCG either forms in situ, is launched out of the BCG core by jets, or is the result of a combination of processes. In situ cooling requires that dusty winds from AGB stars are preserved long enough to end up in the surrounding dusty nebular structure (Li et al 2019). This source of dust may be supplemented by supernova production boosted by the starburst (Dunne et al 2003).…”

Instability of supersonic cold streams feeding galaxies – IV. Survival of radiatively cooling streams

“…Cooling can have a strong influence on KHI in both the linear and non-linear regimes (Massaglia et al 1992(Massaglia et al , 1996Bodo et al 1993;Vietri, Ferrara & Miniati 1997;Rossi et al 1997;Stone, Xu & Hardee 1997;Xu, Hardee & Stone 2000;Micono et al 2000), and can either enhance or inhibit the growth rates depending on the cooling function. Additionally, studies of turbulent mixing layers, such as those formed as the result of KHI, show that cooling can qualitatively alter their evolution (Gronke & Oh 2018Ji, Oh & Masterson 2019, hereafter G18;G19;and J19 respectively;Li, Bryan & Quataert 2019). This has been shown to significantly extend the lifetime of cool clouds traveling through a hot background due to condensation of hot gas onto the cloud tail.…”