13,740 research outputs found
The Self-Enrichment of Galactic Halo Globular Clusters: the mass-metallicity relation
We discuss the existence of a mass-metallicity relation among galactic halo
globular clusters. The lack of any luminosity-metallicity correlation in
globular cluster systems has been used as an argument against self-enrichment
models of cluster formation. We show that such a relation is statistically
present among the galactic Old Halo globulars. This observational correlation
implies that the least massive old clusters are the most metal-rich. This is in
contradiction with the idea that, if globular clusters were self-enriched
systems, the most metal-rich clusters would also be the most massive ones. We
further show that this anti-correlation is as predicted by self-enrichment
models.Comment: 5 pages, accepted for publication in A&
Chemical evolution of the M82 B fossil starburst
M82 B is an old starburst site located in the eastern part of the M82 disc.
We derive the distributions of age and metallicity of the star clusters located
in this region of M82 by using theoretical evolutionary population synthesis
models. Our analysis is based on the comparison of the photometry
obtained by de Grijs et al. (2001) with the colours of single-generation
stellar populations. We show that M82 B went through a chemical enrichment
phase up to super-solar metallicities around the time of the last close
encounter between M82 and its large neighbour galaxy M81. We date and confirm
the event triggering the enhanced cluster formation at about 1 Gyr ago. At
almost the same time an additional, distinct subpopulation of metal-poor
clusters formed in the part of M82 B nearest to the galactic centre. The
formation of these peculiar clusters may be related to infall of circumgalactic
gas onto M82 B.Comment: 14 pages, accepted for publication in MNRA
A near-infrared and optical photometric study of the Sculptor dwarf spheroidal galaxy: implications for the metallicity spread
We present here a detailed study of the Sculptor dSph galaxy red giant branch
(RGB) and horizontal branch (HB) morphology, combining new near-infrared
photometry from CIRSI, with optical data from the ESO WFI. For a Sculptor-like
old and generally metal-poor system, the position of RGB stars on the
colour-magnitude diagram is mainly metallicity dependent. The advantage of
using optical-NIR colours is that the position of the RGB locus is much more
sensitive to metallicity than with optical colours alone. In contrast the
horizontal branch (HB) morphology is strongly dependent on both metallicity and
age. Therefore a detailed study of both the RGB in optical-NIR colours and the
HB can help break the age-metallicity degeneracy. Our measured photometric
width of the Sculptor giant branch corresponds to a range in metallicity of
0.75 dex. We detect the RGB and AGB bumps in both the NIR and optical
luminosity functions, and derive from them a mean metallicity of [M/H] = -1.3
+/- 0.1. From isochrone fitting we derive a mean metallicity of [Fe/H] = -1.42
with a dispersion of 0.2 dex. These photometric estimators are for the first
time consistent with individual metallicity measurements derived from
spectroscopic observations. No spatial gradient is detected in the RGB
morphology within a radius of 13 arcmin, twice the core radius. On the other
hand, a significant gradient is observed in the HB morphology index, confirming
the `second parameter problem' present in this galaxy. These observations are
consistent with an early extended period of star formation continuing in time
for a few Gyr. (Abridged)Comment: 9 pages, 10 figures. Accepted for publication in MNRA
Stellar Populations with ELTs
The star formation, mass assembly and chemical enrichment histories of
galaxies, and their present distributions of dark matter, remain encoded in
their stellar populations. Distinguishing the actual distribution functions of
stellar age, metallicity and kinematics at several locations in a range of
galaxies, sampling across Hubble types and representative environments, is the
information required for a robust description of galaxy histories. Achieving
this requires large aperture, to provide the sensitivity to reach a range of
environs and Hubble types beyond the Local Group, to provide high spatial
resolution, since the fields are crowded, and preferably with optical
performance since age-sensitivity is greatest near the main-sequence turn-off,
and metallicity-sensitivity for these warm stars is greatest in the optical.Comment: IAU Symposium No. 232, eds P. Whitelock, B. Leidundgeit & M.
Dennefel
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