An updated survey of globular clusters in M 31. II. Newly discovered bright and remote clusters

Aims. We present the first results of a large spectroscopic survey of candidate globular clusters located in the extreme outskirts of the nearby M 31 galaxy. The survey is aimed at ascertaining the nature of the selected candidates to increase the sample of confirmed M 31 clusters lying more that 2 ◦ away from the center of the galaxy. Methods. We obtained low resolution spectra (λ/∆λ � 800–1300) of 48 targets selected from the Extended Source Catalogue of 2MASS, as in Galleti et al. (2005, AA the other four are completely new discoveries: B516, B517, B518, B519. The newly discovered clusters lie at projected distance 40 kpc Rp 100 kpc from the center of M 31, and have absolute integrated magnitude −9.5 MV −7.5. For all the observed clusters we have measured the strongest Lick indices and we have obtained spectroscopic metallicity estimates. Mackey-GC1, Martin-GC1, B517 and B518 have spectra typical of old and metal poor globular clusters ([Fe/H] −1.3); B519 appears old but quite metal-rich ([Fe/H] �− 0.5); B516 presents very strong Balmer absorption lines: if this is indeed a cluster it should have a relatively young age (likely < 2 Gyr). Conclusions. The present analysis nearly doubles the number of M 31 globulars at Rp ≥ 40 kpc. At odds with the Milky Way, M 31 appears to have a significant population of very bright globular clusters in its extreme outskirts.

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