The disruption of the M33 galaxy is evident from its extended gaseous structure .
We present new data from the Galactic Arecibo L-Band Feed Array HI ( GALFA-HI ) Survey that show the full extent and detailed spatial and kinematic structure of M33 ’ s neutral hydrogen .
Over 18 % of the HI mass of M33 ( M _ { HI _ { tot } } = 1.4 \times 10 ^ { 9 } { M } _ { \odot } ) is found beyond the star forming disk as traced in the far-ultraviolet ( FUV ) .
The most distinct features are extended warps , an arc from the northern warp to the disk , diffuse gas surrounding the galaxy , and a southern cloud with a filament back to the galaxy .
The features extend out to 22 kpc from the galaxy center ( 18 kpc from the edge of the FUV disk ) and the gas is directly connected to M33 ’ s disk .
Only five discrete clouds ( i.e. , gas not directly connected to M33 in position-velocity space ) are catalogued in the vicinity of M33 , and these clouds show similar properties to Galactic and M31 halo clouds .
M33 ’ s gaseous features most likely originate from the tidal disruption of M33 by M31 1-3 Gyr ago as shown from an orbit analysis which results in a tidal radius < 15 kpc in the majority of M33 ’ s possible orbits .
M33 is now beyond the disruptive gravitational influence of M31 and the gas appears to be returning to M33 ’ s disk and redistributing its star formation fuel .
M33 ’ s high mean velocity dispersion in the disk ( \sim 18.5 km s ^ { -1 } ) may also be consistent with the previous interaction and high rate of star formation .
M33 will either exhaust its star formation fuel in the next few Gyrs or eventually become star formation fuel for M31 .
The latter represents the accretion of a large gaseous satellite by a spiral galaxy , similar to the Magellanic Clouds ’ relationship to the Galaxy .