Reigniting the FUSE II: O VI Emission in Massive Elliptical Galaxies

Abstract

This is the second paper in a series where we examine archival far-ultraviolet spectroscopy of 29 massive elliptical galaxies from the Far Ultraviolet Spectroscopic Explorer (FUSE) with modern methods. In the first paper, we performed SED modeling with aperture-matched photometry and analyzed the young and old stellar populations in these galaxies. In this paper, we report extinction-corrected O VI $λλ$1032,1038 $\mathring{\rm A}$ fluxes and upper limits for each galaxy, which we use to infer the rate at which gas is cooling through $10^{5.5}$ K via multiphase condensation of the galaxy's CGM ($\dot{M}_{\rm O\,VI}$) under the assumption of steady radiative cooling. By considering both Galactic and intrinsic extinction, we overwhelmingly find $\dot{M}_{\rm O\,VI}$ to be larger than values found previously in the literature by a median of $\sim 80\%$. Additionally, we quantify correlations between $\dot{M}_{\rm O\,VI}$ and star formation rates, classical luminosity-based X-ray cooling rates, and X-ray spectroscopic cooling rates. The results suggest that the efficiency of cooling from the $\gtrsim 10^7$ K circumgalactic medium evolves with host mass, being suppressed by a factor of $\sim 4$-$5$ more at the cluster scale than it is at the group and elliptical scales. In contrast, under the steady cooling assumption, cooling from $10^{5.5}$ K to the molecular phase appears to be suppressed by an order of magnitude, independent of mass, requiring turbulent mixing layers, thermal conduction, multiphase recycling, a bottom-heavy initial mass function, or some other additional physics to explain.