Bibcode
Hidalgo, S. L.; Monelli, M.; Aparicio, A.; Gallart, C.; Skillman, Evan D.; Cassisi, Santi; Bernard, Edouard J.; Mayer, Lucio; Stetson, Peter; Cole, Andrew; Dolphin, Andrew
Bibliographical reference
The Astrophysical Journal, Volume 778, Issue 2, article id. 103, 11 pp. (2013).
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12
2013
Journal
Citations
64
Refereed citations
62
Description
Based on Hubble Space Telescope observations from the Local Cosmology
from Isolated Dwarfs project, we present the star formation histories,
as a function of galactocentric radius, of four isolated Local Group
dwarf galaxies: two dSph galaxies, Cetus and Tucana, and two transition
galaxies (dTrs), LGS-3 and Phoenix. The oldest stellar populations of
the dSphs and dTrs are, within the uncertainties, coeval (~13 Gyr) at
all galactocentric radii. We find that there are no significative
differences between the four galaxies in the fundamental properties
(such as the normalized star formation rate or age-metallicity relation)
of their outer regions (radii greater than four exponential scale
lengths); at large radii, these galaxies consist exclusively of old
(gsim 10.5 Gyr) metal-poor stars. The duration of star formation in the
inner regions varies from galaxy to galaxy, and the extended central
star formation in the dTrs produces the dichotomy between dSph and dTr
galaxy types. The dTr galaxies show prominent radial stellar population
gradients: The centers of these galaxies host young (lsim 1 Gyr)
populations, while the age of the last formation event increases
smoothly with increasing radius. This contrasts with the two dSph
galaxies. Tucana shows a similar, but milder, gradient, but no gradient
in age is detected Cetus. For the three galaxies with significant
stellar population gradients, the exponential scale length decreases
with time. These results are in agreement with outside-in scenarios of
dwarf galaxy evolution, in which a quenching of the star formation
toward the center occurs as the galaxy runs out of gas in the outskirts.
Based on observations made with the NASA/ESA Hubble Space Telescope,
obtained at the Space Telescope Science Institute, which is operated by
the Association of Universities for Research in Astronomy, Inc., under
NASA contract NAS 5-26555. These observations are associated with
program 10505.
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