The Disruption and Fueling of M33

Abstract

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 HItot = 1.4 × 10 9 M ⊙ ) 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 (∼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.

The elusive stellar halo of the Triangulum galaxy

“…M33 has also been found to possess extensive stellar substructure, in the form of a highly distorted outer disk, thought to have been formed in an interaction with the larger M31 (McConnachie et al 2009;McConnachie et al 2010); this substructure is roughly aligned with the previously detected distorted HI disk (Putman et al 2009;Lewis et al 2013). Being about a tenth the size of the two other large galaxies within the Local Group, the properties of any stellar halo of M33 would provide clues to galaxy evolution on a different mass scale than for the Milky Way and M31.…”

Neutral Gas Accretion onto Nearby Galaxies

“…There are also HVCs around M33, though here confusion with that galaxy's disk and possibly unrelated extraplanar gas makes it difficult to separate the populations cleanly (Grossi et al, 2008;Putman et al, 2009;Keenan et al, 2016). The total H I mass in the M33 HVCs is 3.5 × 10 7 M using only the data from the most recent study (Keenan et al, 2016).…”

“…The total H I mass in the M33 HVCs is 3.5 × 10 7 M using only the data from the most recent study (Keenan et al, 2016). If we include clouds that may be located in the diskhalo region (Grossi et al, 2008;Putman et al, 2009) the total M33 HVC H I mass increases to ∼ 5 × 10 7 M . Figure 4 shows the velocity and location of the HVCs of M31 and M33 with respect to M31.…”

“…4 The HVC systems of M31 and M33 (red circles), where the velocity with respect to the Local Group Standard of rest, V LGSR , is plotted against the angular distance from M31 in the direction of M33. To the samples of M31 and M33 HVCs (Westmeier et al, 2008;Keenan et al, 2016) are added clouds that may be in the halo of M33 (blue circles) (Grossi et al, 2008;Putman et al, 2009). It can be difficult to distinguish between the two groups, which may actually blend together.…”

Accretion Onto the Milky Way: The Smith Cloud

“…HVCs are now known to exist around nearby galaxies in a population that exends at least 50 kpc from the host system (Thilker et al(2004), Grossi et al(2008), Westmeier et al(2008), Putman et al(2009).) The possibility that some HVCs may be intra-group or even intergalactic, or associated with dark matter halos, or tracers of faint dwarf galaxies, cannot be excluded (e.g., Blitz et al(1999), Braun & Burton(1999), Adams et al(2013)).…”