An updated survey of globular clusters in M 31 I. Classification and radial velocity for 76 candidate clusters

uAims. We present the first results of a large spectroscopic survey of globular clusters and candidate globular clusters in the nearby M 31 galaxy. The survey is aimed at the classification of known candidate M 31 clusters and at the study of their kinematic properties. Methods. We obtained low-resolution spectroscopy (gimel/Delta gimel similar or equal to 800-1300) for 133 targets, including 76 yet-to-be-confirmed candidate clusters (i.e. with no previous spectroscopic information), 55 already-confirmed genuine M 31 clusters, and 2 uncertain candidates. Our observations allowed a reliable estimate of the target radial velocity, within a typical accuracy of similar to +/- 20 km s(-1). The observed candidates have been robustly classified according to their radial velocity and shape parameters that allowed us to confidently discriminate between point sources and extended objects even from low-spatial-resolution imagery. Results. In our set of 76 candidate clusters we found: 42 newly-confirmed bona-fide M 31 clusters, 12 background galaxies, 17 foreground Galactic stars, 2 HII regions belonging to M 31 and 3 unclassified (possibly M 31 clusters or foreground stars) objects. The classification of a few other candidates not included in our survey has been also reassessed on various observational bases. All the sources of radial velocity estimates for M 31 known globular clusters available in the literature have been compared and checked, and a homogeneous general list has been obtained for 349 confirmed clusters with radial velocity. Conclusions. Our results suggest that a significant number of genuine clusters (greater than or similar to 100) is still hidden among the plethora of known candidates proposed by various authors. Hence our knowledge of the globular cluster system of the M 31 galaxy is still far from complete even in terms of simple membership.