The Anisotropic Circumgalactic Medium of Massive Early-type Galaxies

Abstract

Using measurements of the [O iii ], H α , and [N ii ] emission line fluxes originating in the cool ( T ∼10 4 K) gas that populates the halos of massive early-type galaxies with stellar masses greater than 10 10.4 M ⊙ , we explore the recent conjecture that active galactic nucleus (AGN) activity preferentially removes the circumgalactic medium (CGM) along the polar (minor-axis) direction. We find deficits in the mean emission line flux of [O iii ] and H α (65% and 43%, respectively) along the polar versus planar directions, although due to the large uncertainties in these difficult measurements the results are of marginal statistical significance (1.5 σ ). More robustly (97%–99.9% confidence depending on the statistical test), diagnostic line ratios show stronger AGN ionization signatures along the polar direction at small radii than at other angles or radii. Our results are consistent with the conjecture of an anisotropic CGM in massive early-type galaxies, suggested on independent grounds, that is tied to AGN activity and begin to show the potential of CGM mapping using emission lines.