Bibcode
Carrera, R.; Gallart, C.; Aparicio, A.; Hardy, E.
Referencia bibliográfica
The Astronomical Journal, Volume 142, Issue 2, article id. 61 (2011).
Fecha de publicación:
8
2011
Número de citas
55
Número de citas referidas
49
Descripción
The outer disk of the Large Magellanic Cloud (LMC) is studied in order
to unveil clues about its formation and evolution. Complementing our
previous studies in innermost fields (3 kpc lsim R <~ 7 kpc), we
obtained deep color-magnitude diagrams in six fields with galactocentric
distances from 5.2 kpc to 9.2 kpc and different azimuths. The comparison
with isochrones shows that while the oldest population is approximately
coeval in all fields, the age of the youngest populations increases with
increasing radius. This agrees with the results obtained in the
innermost fields. Low-resolution spectroscopy in the infrared Ca II
triplet region has been obtained for about 150 stars near the tip of the
red giant branch in the same fields. Radial velocities and stellar
metallicities have been obtained from these spectra. The metallicity
distribution of each field has been analyzed together with those
previously studied. The metal content of the most metal-poor objects,
which are also the oldest according to the derived age-metallicity
relationships, is similar in all fields independently of the
galactocentric distance. However, while the metallicity of the most
metal-rich objects measured, which are the youngest ones, remains
constant in the inner 6 kpc, it decreases with increasing radius from
there on. The same is true for the mean metallicity. According to the
derived age-metallicity relationships, which are consistent with being
the same in all fields, this result may be interpreted as an outside-in
formation scheme in opposition with the inside-out scenario predicted by
ΛCDM cosmology for a galaxy like the LMC. The analysis of the
radial velocities of our sample of giants shows that they follow a
rotational cold disk kinematics. The velocity dispersion increases as
metallicity decreases indicating that the most metal-poor/oldest objects
are distributed in a thicker disk than the most metal-rich/youngest ones
in agreement with the findings in other disks such as that of the Milky
Way. They do not seem to be part of a hot halo, if one exists in the
LMC.
Based on observations collected at the European Southern Observatory,
Chile, within the observing programs 074.B-0474 and 082.B-0900.
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