Bibcode
Monelli, M.; Gallart, C.; Hidalgo, S. L.; Aparicio, A.; Skillman, E. D.; Cole, A. A.; Weisz, D. R.; Mayer, L.; Bernard, E. J.; Cassisi, S.; Dolphin, A. E.; Drozdovsky, I.; Stetson, P. B.
Referencia bibliográfica
The Astrophysical Journal, Volume 722, Issue 2, pp. 1864-1878 (2010).
Advertised on:
10
2010
Revista
Número de citas
98
Número de citas referidas
87
Descripción
We present a detailed study of the star formation history (SFH) of the
Tucana dwarf spheroidal galaxy. High-quality, deep HST/ACS data,
collected in the framework of the LCID project, allowed us to obtain the
deepest color-magnitude diagram to date, reaching the old main-sequence
turnoff (F814 ~ 29) with good photometric accuracy. Our analysis, based
on three different SFH codes, shows that Tucana is an old and metal-poor
stellar system, which experienced a strong initial burst of star
formation at a very early epoch (sime13 Gyr ago) which lasted a maximum
of 1 Gyr (sigma value). We are not able to unambiguously answer the
question of whether most star formation in Tucana occurred before or
after the end of the reionization era, and we analyze alternative
scenarios that may explain the transformation of Tucana from a gas-rich
galaxy into a dSph. Current measurements of its radial velocity do not
preclude that Tucana may have crossed the inner regions of the Local
Group (LG) once, and so gas stripping by ram pressure and tides due to a
close interaction cannot be ruled out. A single pericenter passage would
generate insufficient tidal heating to turn an originally disky dwarf
into a true dSph; however, this possibility would be consistent with the
observed residual rotation in Tucana. On the other hand, the high star
formation rate measured at early times may have injected enough energy
into the interstellar medium to blow out a significant fraction of the
initial gas content. Gas that is heated but not blown out would also be
more easily stripped via ram pressure. We compare the SFH inferred for
Tucana with that of Cetus, the other isolated LG dSph galaxy in the LCID
sample. We show that the formation time of the bulk of star formation in
Cetus is clearly delayed with respect to that of Tucana. This reinforces
the conclusion of Monelli et al. that Cetus formed the vast majority of
its stars after the end of the reionization era implying, therefore,
that small dwarf galaxies are not necessarily strongly affected by
reionization, in agreement with many state-of-the-art cosmological
models.
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 NAS5-26555. These observations are associated with program
10505.
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