On the systematic optical identification of the remaining 3C radio sources. I. A search in 47 fields.

Abstract

Forty-seven 3CR radio sources that were either unidentified or identified only provisionally are investigated, mostly to fainter limits than the Palomar Sky Survey. New plates, taken with the Palomar 48-inch (1 .2-m) Schmidt or the 200-inch (5-m) Hale reflector, were measured for positions of objects near each radio position. Optical identifications are made on the basis of positional coincidence alone to within 3 a of the combined radio and optical errors, which is of order + 4" for most fields. Of the 47 fields, positive identifications are made for 19 objects; possible or probable identifications for 7; and 21 are still empty to the limit of our best optical material. Most of the 26 positive or probable identifications are galaxies. Of these, 10 are in groups or clusters: the best cases are 3C 268.3, 299, 324, 330, and 337. Only four probable quasar candidates (3C 36, 272, 321, and 418) are among the 26 cases. Previously suggested identifications for 3C 36, 68.2, 99, 114, 124, 175.1, 210, 228, 263.1, 289, and 356 are shown to be unlikely on the basis of positional disagreement. Optical positions of the 26 new candidates and other stars in the fields are given. No spectroscopy or photometry is given for any of the candidates except 3C 460, where a low-spectral-resolution scan gave z = 0.27 + 0.02 for the identified ES galaxy. Subject headings: galaxies - quasi-stellar sources or objects - radio sources