Cold Filaments Formed in Hot Wake Flows Uplifted by Active Galactic Nucleus Bubbles in Galaxy Clusters

Abstract

Multi-wavelength observations indicate that the intracluster medium in some galaxy clusters contains cold filaments, while their formation mechanism remains debated. Using hydrodynamic simulations, we show that cold filaments could naturally condense out of hot gaseous wake flows uplifted by the jet-inflated active galactic nucleus (AGN) bubbles. Consistent with observations, the simulated filaments extend to tens of kiloparsecs from the cluster center, with a representative mass of $\rm 10^{8}- 10^{9}\ M_{\odot}$ for a typical AGN outburst energy of $10^{60}~ \rm erg$. They show smooth velocity gradients, stretching typically from inner inflows to outer outflows with velocity dispersions of several hundred kilometers per second. The properties of cold filaments are affected substantially by jet properties. Compared to kinetic-energy-dominated jets, thermal-energy-dominated jets are easier to produce long cold filaments with large masses as observed. AGN jets with an early turn-on time, a low jet base, or a very high power tend to overheat the cluster center, and produce short cold filaments that take a relatively long time to condense out.