An updated survey of globular clusters in M 31

I. Classification and radial velocity for 76 candidate clusters

¹ Università di Bologna, Dipartimento di Astronomia via Ranzani 1, 40127 Bologna, Italy e-mail: silvia.galleti2@unibo.it
² INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy e-mail: [michele.bellazzini; luciana.federici; alberto.buzzoni; flavio.fusipecci]@oabo.inaf.it

Received: 29 March 2006
Accepted: 15 May 2006

Abstract

Aims.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 () 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 ~ 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 (≳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.