H-I IN THE GIANT ELLIPTIC GALAXY NGC-4406

The Arecibo 305 m radio telescope was used to make 21 cm measurements of NGC 4406, an elliptical galaxy containing 1010 M⊙ of hot diffuse gas. The H I decreases by a factor of 3 one beamwidth from the center (3′.5; 20.4 kpc for d = 20 Mpc) and by an order of magnitude two beamwidths from the center. Excess H I emission is seen in the X-ray tail, but not in dust-rich regions. The H I measurements do not support the suggestion that the X-ray tail is hot gas being stripped from the galaxy. The velocities of the peaks of the emission differ by less than 20 km s-1 for observations separated by more than 40 kpc, indicating that the H I has little rotation. Infall is also inconsistent with the line profiles, and we argue that random motion of H I clouds is the probable origin of the H I profile shapes. The properties of the H I gas agree with expectations of the cooling flow model in which cold gas is produced in situ as the hot gas radiatively cools.