Velocity dispersion (moment-2) map of the 21 cm line emission in M 33 at 10 arcsec resolution (left panel). The black contours underline the location of the bright HI filaments or arms, they are drawn at 0.2 Jy beam⁻¹ km s⁻¹ and overlaid also on the moment-0 map in the right panel. The two areas that have been masked out for the likely presence of gas infall/outflow (the stream toward the central region in the southern half and a smaller region above the northern arm) have anomalously large velocity dispersions and have yellow-red colors in the velocity dispersion map. The color legend for the velocity dispersion map (left panel) is in units of km s⁻¹, and for the intensity map (right panel), it is in Jy beam⁻¹ km s⁻¹. Maps are centered on RA = 23.4620417 and Dec = 30.6602222, (M33 coordinates).