A nearly complete longitude-velocity map of neutral hydrogen

A longitude-velocity map based on two recent 21-cm neutral hydrogen surveys and covering all but 42 deg of galactic longitude is presented. Latitude information between -2 and +2 deg is included as an integrated quantity by averaging the observed brightness temperatures over latitude at constant longitude and velocity to produce intensity information corresponding to a surface density distribution of neutral hydrogen in the galactic plane. The northern and southern rotation curves of the Galaxy within the solar galactic orbit are derived from the maximum radial velocities by the usual tangent-point method. Five interesting features of the map are discussed: (1) the scale of density variations in the neutral hydrogen; (2) a region of very high brightness centered at 81 deg and 0 km/s which is probably due to the spiral arm with which the sun is associated; (3) a region of very low brightness centered at 242 deg and 39 km/s; (4) negative-velocity features visible in the anticenter direction; and (5) a strong absorption feature at 289 deg having a kinematic distance of about 4 kpc.