The outermost cluster of M 31

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;flavio.fusipecci]@bo.astro.it

Received: 10 February 2005
Accepted: 1 March 2005

Abstract

We report on the identification of a new cluster in the far halo of the M 31 galaxy. The cluster, named Bologna 514 (B514) has an integrated magnitude , and a radial velocity, as estimated from two independent low-resolution spectra,  km s^-1, which fully confirms its membership to the M 31 system. The observed integrated spectrum is very similar to those of classical globular clusters. Being located at ( kpc in projected distance) from the center of the parent galaxy, B514 is by far the most remote M 31 cluster ever discovered. Its projected position, near the galaxy major axis, and M 31-centric velocity, similar to that observed in the outermost regions of the HI rotation curve, may indicate that it belongs to the subsystem of M 31 clusters that has been recently proposed (Morrison et al. 2004 ) to be part of the dynamically-cold thin disc of the galaxy.