W. W. Morgan

CD galaxies in poor clusters

An investigation has been made to determine whether the supergiant cD galaxies, which are at present only known in rich galaxy clusters, are also present in galaxy clusterings poorer than those of the Abell catalog. A search was carried out over 73 fields of the National Geographic Society-Palomar Observatory Sky Survey; the fields were located in galactic latitudes greater than +30degree. Eight clusters were found which probably contain galaxies of the cD type. While it will be necessary to obtain redshifts before cluster membership is definitely established, it seems likely that cD galaxies do occur in some poor clusters.

On the distribution of interstellar gas in the galactic halo

New and existing observations of 21-cm emission lines toward 10 distant, high-latitude OB stars are combined with existing observations of interstellar Ly..cap alpha.. absorption lines, in order to determine the ratio, N/sub 21//N/sub ..cap alpha../, of the two different column densities of H i. This ratio, which is related to the fraction of the cool, neutral gas in the halo that lies beyond each star, decreases smoothly to about unity with increasing distance from the galactic plane. The column density of neutral gas beyond about 1 kpc can be as much as one-third of the total above the plane, but only relatively small amounts of such gas lie more than 2 kpc from the plane. The distances to, and the possible birthplaces of, these Population I stars in the halo are discussed.