Date: Mon 28-June-2010
Speaker: Dr. Ayesha Begum (University of Wisconsin)
Title: "Compact HI clouds from the GALFA-HI survey"
Abstract:The consortium for Galactic studies with the Arecibo L-band Feed Array (ALFA) is conducting a neutral hydrogen survey of the whole Arecibo sky, over a velocity range of -700 to +700 km/s, with high angular (3.5 arcmin) and velocity resolution (~0.2 km/s). The unprecedented resolution and sensitivity of this survey resulted in the detection of numerous isolated, very compact HI clouds at low Galactic velocities, which are distinctly separated from the HI disk emission. In the limited area surveyed so far, we have detected ~100 such compact clouds. The detected clouds have extreme properties; they are very cold with median kinetic temperatures of 380 K. Further, they are quite compact and faint with median properties of 5 arcmin in angular size, 0.7 K in peak brightness temperature, and N_HI of 5x10^18 cm^{-2}. Most of the clouds deviate from Galactic rotation at the 10-50 km/s level, and a significant fraction show evidence for a multiphase medium and velocity gradients. These compact clouds tend to probe ISM mechanisms that act on short time scales and could be related to crucial dynamical processes such as stellar winds, shocks, turbulence and Galactic accretion. In my talk I will discuss various possibilities regarding the origin of these clouds and their significance in the Galactic ISM studies.
