Atomic gas far away from the Virgo cluster core galaxy NGC 4388

Abstract

We have discovered of atomic gas at a projected distance greater than 4' (20 kpc) from the highly inclined Virgo spiral galaxy NGC 4388. This gas is most probably connected to the very extended Hα plume detected by Yoshida et al. ([CITE]). Its mass makes a nuclear outflow and its radial velocity a minor merger as the origin of the atomic and ionized gas very unlikely. A numerical ram pressure simulation can account for the observed Hi spectrum and the morphology of the Hα plume. An additional outflow mechanism is still needed to reproduce the velocity field of the inner Hα plume. The extraplanar compact Hii region recently found by Gerhard et al. ([CITE]) can be explained as a stripped gas cloud that collapsed and decoupled from the ram pressure wind due to its increased surface density. The star-forming cloud is now falling back onto the galaxy.