3 research outputs found
The outermost cluster of M31
We report on the identification of a new cluster in the far halo of the M31
galaxy. The cluster, named Bologna 514 (B514) has an integrated magnitude
M_V=-8.5 +- 0.6, and a radial velocity, as estimated from two independent
low-resolution spectra, V_r=-456 +- 23 km/s, which fully confirms its
membership to the M31 system. The observed integrated spectrum is very similar
to those of classical globular clusters. Being located at ~ 4^o (~55 kpc in
projected distance) from the center of the parent galaxy, B514 is by far the
most remote M31 cluster ever discovered. Its projected position, near the
galaxy major axis, and M31-centric velocity, similar to that observed in the
outermost regions of the HI rotation curve, may indicate that it belongs to the
subsystem of M31 clusters that has been recently proposed (Morrison et al.
2004) to be part of the dynamically-cold thin disc of the galaxy.Comment: 6 pages, 4 figures, accepted for publication in A &
Globular cluster luminosity function as distance indicator
Globular clusters are among the first objects used to establish the distance
scale of the Universe. In the 1970-ies it has been recognized that the
differential magnitude distribution of old globular clusters is very similar in
different galaxies presenting a peak at M_V ~ -7.5. This peak magnitude of the
so-called Globular Cluster Luminosity Function has been then established as a
secondary distance indicator. The intrinsic accuracy of the method has been
estimated to be of the order of ~0.2 mag, competitive with other distance
determination methods. Lately the study of the Globular Cluster Systems has
been used more as a tool for galaxy formation and evolution, and less so for
distance determinations. Nevertheless, the collection of homogeneous and large
datasets with the ACS on board HST presented new insights on the usefulness of
the Globular Cluster Luminosity Function as distance indicator. I discuss here
recent results based on observational and theoretical studies, which show that
this distance indicator depends on complex physics of the cluster formation and
dynamical evolution, and thus can have dependencies on Hubble type, environment
and dynamical history of the host galaxy. While the corrections are often
relatively small, they can amount to important systematic differences that make
the Globular Cluster Luminosity Function a less accurate distance indicator
with respect to some other standard candles.Comment: Accepted for publication in Astrophysics and Space Science. Review
paper based on the invited talk at the conference "The Fundamental Cosmic
Distance Scale: State of the Art and Gaia Perspective", Naples, May 2011. (13
pages, 8 figures