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Session 10 - Spiral Galaxies.
Display session, Monday, June 10
Great Hall,
HI observations of 23 near face-on galaxies with the NRAO 140 ft telescope detected eight galaxies that show significant evidence of high velocity gas (HVG), most of which have not been previously reported to have such gas. The observed HVG may be a warm component of the ISM, gas accelerated to high velocities, or gas external to the plane of the galaxy.
The chosen galaxies typically have sizes < 20', velocities < 1600 km s^-1, and HI fluxes > 50 Jy km s^-1. About half of the galaxies are irregulars and the rest are spirals. Our observations are well suited to detecting HVG since they have both high sensitivity and good velocity resolution (1 or 2 km s^-1). The work is part of a project to study how the properties of galaxies (e.g., galaxy type, star formation or supernovae rates, and IR emission) and HVG are related.
Since the galaxies were nearly face on, their HI profiles show only slight, if any, rotational broadening. We used multiple Gaussians to model the rotational broadening as well as to identify the existence of HVG. Typically, the detected HVG has a velocity dispersion 2.5 times that of the normal (cold) ISM, regardless of the dispersion of the cold ISM. HVG makes up 10 to 50% of the HI mass in these galaxies.
