Abstract
We present high resolution (15'' and 2.5 km/s) HI observations of the S0 gal axy NGC 404. We derive an HI mass of MHI = 6.7 × 107 Msolar, in good agreement with previous measurements. The HI is distributed in a broad annulus and extends out to a diameter of 9', well beyond the optical diameter of 6'. The velocity field is regular and shows, surprisingly, a declining rotation curve. This decline is purely Keplerian, strongly suggesting that all the mass is contained within the inner 200''.
