EDP Sciences
Free access
Volume 436, Number 2, June III 2005
Page(s) 535 - 540
Section Galactic structure, stellar clusters and populations
DOI http://dx.doi.org/10.1051/0004-6361:20052861

A&A 436, 535-540 (2005)
DOI: 10.1051/0004-6361:20052861

The outermost cluster of M 31

S. Galleti1, 2, M. Bellazzini2, L. Federici2 and F. Fusi Pecci2

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)

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 $M_{V}=-8.5 \pm 0.6$, and a radial velocity, as estimated from two independent low-resolution spectra, $V_{\rm r}=-456 \pm 23$ 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 ${\simeq} 4^\circ$ ( ${\simeq} 55$ 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.

Key words: galaxies: Local Group -- galaxies: star clusters -- galaxies: kinematics and dynamics -- galaxies: spiral

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