Active Galactic Nucleus Feedback and the Development of Dusty Multiphase Gas in X-Ray Emitting Elliptical Galaxies

This paper investigates the physical and kinematic properties of dust-rich regions in a small sample of group-centered elliptical galaxies, emphasizing their connection with the hot X-ray emitting gas and detailed dust grain characteristics. Comprehensive multiwavelength data—including Hα and CO emission detected by Multi Unit Spectroscopic Explorer and Atacama Large Millimeter/submillimeter Array—demonstrate the presence of dust clouds embedded within complex, hot X-ray atmospheres shaped by active galactic nucleus (AGN) feedback. X-ray images show bubbles and cavities surrounded by bright rims. We find that dust regions containing molecular gas traced by CO are preferentially located at the rims of these X-ray cavities, suggesting that AGN-driven outflows enhance the condensation of cold, dusty gas at these compressive interfaces. Kinematic measurements indicate that molecular and ionized gas phases are dynamically and spatially linked, supporting the framework of a multiphase medium arising from the top-down condensation rain in the hot plasma and related chaotic cold accretion. Crucially, spatial variations in the total-to-selective extinction ratio R V show that regions where dust, CO, and Hα emission coincide exhibit notably smaller R V values, implying steeper extinction curves and the predominance of smaller or less evolved dust grains within these mixed-phase environments. This contrasts with larger R V values found elsewhere in the dust clouds, suggesting grain growth or survival mechanisms within shielded cold gas.