An H I survey of high-velocity clouds in nearby disk galaxies

Abstract

We observed 14 nearly face-on disk galaxies with the Arecibo 305 m telescope and found the double-horned H I profiles to have high-velocity wings in 10 of these galaxies. Such wings can be caused by high-velocity clouds, similar to those observed in our own Galaxy. Disk galaxy models were constructed that include both high-velocity clouds (modeled as a component of galactic gas with a velocity dispersion of either 30 or 50 km s^-1^) and warped H I disks. We find that the high-velocity wings can be reproduced by models with high-velocity clouds but not by models with warps that are similar to those observed in other galaxies. If these wings are due to high-velocity clouds, then the mass of neutral hydrogen in high-velocity clouds for the 10 galaxies ranges from 6 x 10^7^ M_sun_ to 4 x 10^9^ M_sun_, which corresponds to 4%-14% of the total H I in these galaxies. The galaxies with no detected high-velocity wings are also those with the lowest far-infrared fluxes as measured by IRAS, which is consistent with the galactic fountain model in which the young stellar population (responsible for most of the far-infrared emission) produces supernovae which then provide the kinetic energy of the high-velocity clouds.