X-Ray Constraints on the Hot Gas Content of Early-type Galaxies in Virgo

Abstract

Abstract We present a systematic study of the diffuse hot gas around early-type galaxies (ETGs) residing in the Virgo cluster, based on archival Chandra observations. Our representative sample consists of 79 galaxies with low-to-intermediate stellar masses (M * ≈ 109−11 M ⊙), a mass range that has not been extensively explored with X-ray observations thus far. We detect diffuse X-ray emission in only eight galaxies and find that in five cases a substantial fraction of the detected emission can be unambiguously attributed to truly diffuse hot gas, based on their spatial distribution and spectral properties. For the individually nondetected galaxies, we constrain their average X-ray emission by performing a stacking analysis, finding a specific X-ray luminosity of L X / M * ∼ 10 28 erg s − 1 M ⊙ − 1 , which is consistent with unresolved stellar populations. The apparent paucity of truly diffuse hot gas in these low- and intermediate-mass ETGs may be the result of efficient ram pressure stripping by the hot intracluster medium. However, we also find no significant diffuse hot gas in a comparison sample of 57 field ETGs of similar stellar masses, for which archival Chandra observations with similar sensitivity are available. This points to the alternative possibility that galactic winds evacuate the hot gas from the inner region of low- and intermediate-mass ETGs, regardless of the galactic environment. Nevertheless, we do find strong morphological evidence for ongoing ram pressure stripping in two galaxies (NGC 4417 and NGC 4459). A better understanding of the roles of ram pressure stripping and galactic winds in regulating the hot gas content of ETGs invites sensitive X-ray observations for a large galaxy sample.