The Discovery and Origin of a Very High-velocity Cloud Toward M33

Abstract

Abstract We report the detection of a largely ionized very high-velocity cloud (VHVC; km ) toward M33 with the Hubble Space Telescope/Cosmic Origin Spectrograph. The VHVC is detected in O i, C ii, Si ii, and Si iii absorption along five sightlines separated by . On sub-degree scales, the velocities and ionic column densities of the VHVC remain relatively smooth with standard deviations of ±14 km and ±0.15 dex between the sightlines, respectively. The VHVC has a metallicity of [O i/H i] = −0.56 ± 0.17 dex (Z = 0.28 ± 0.11 ). Despite the position–velocity proximity of the VHVC to the ionized Magellanic Stream, the VHVC’s higher metallicity makes it unlikely to be associated with the Stream, highlighting the complex velocity structure of this region of sky. We investigate the VHVC’s possible origin by revisiting its surrounding H i environment. We find that the VHVC may be (1) a MW CGM cloud, (2) related to a nearby H i VHVC—Wright’s Cloud, or (3) connected to M33's northern warp. Furthermore, the VHVC could be a bridge connecting Wright’s Cloud and M33's northern warp, which would make it a Magellanic-like structure in the halo of M33.