Extragalactic Nebulae Close to the Galactic Plane
Publications of the Astronomical Society of the Pacific
In 1954 Shane and Wirtanen described the density distribution for extragalactic nebulae counted in their Area III, extending from Ô = -20° to -f-20° and from a = 12 h to 18 11 . 1 The results were given in their Figure 2 . In this figure are also plotted a number of objects which, on the plates of the 20-inch Carnegie astrograph of the Lick Observatory, appeared very much like extragalactic nebulae, but which were found close to the galactic plane in the so-called zone of avoidance. Similar
... cts have been picked out by Shane in his Area V, which extends from ô = +20° to -j-60° and from a = 0* to 6\ An investigation of these nebulae was recently undertaken while I was at the Lick Observatory, since a confirmation of the extragalactic nature of these objects might afford information about the density distribution of the obscuring matter in the Milky Way. Dr. Shane kindly placed at my disposal his list of suspected nebulae in the zone of avoidance. In Area V near galactic longitude 120°, and including the direction of the galactic anticenter, only nebulae with galactic latitudes between ±5° were picked out for investigation. There were 72 of these nebulae.* In Area III, near galactic longitude 345°, where there were no nebulae in the ±5° zone, 66 suspected extragalactic nebulae between galactic latitudes ±15° were selected,f omitting those which were known to be planetaries or red stars (cf. Shane and Wirtanen, 1 p. 295). Because of limited observing time not all of the objects could be observed, so a selection was made from the brightest ones and from those whose positions fitted best with the observing program. Direct photographs of 22 nebulae in each of the Areas III and V were taken with Crossley reflector of the Lick Observatory.