Bibcode
Hidalgo, S. L.; Aparicio, A.; Skillman, Evan; Monelli, M.; Gallart, C.; Cole, Andrew; Dolphin, Andrew; Weisz, Daniel; Bernard, Edouard J.; Cassisi, Santi; Mayer, Lucio; Stetson, Peter; Tolstoy, Eline; Ferguson, Henry
Bibliographical reference
The Astrophysical Journal, Volume 730, Issue 1, article id. 14 (2011).
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3
2011
Journal
Citations
112
Refereed citations
98
Description
We present an analysis of the star formation history (SFH) of the
transition-type (dIrr/dSph) Local Group galaxy LGS-3 (Pisces) based on
deep photometry obtained with the Advanced Camera for Surveys onboard
the Hubble Space Telescope. Our observations reach the oldest
main-sequence turnoffs at high signal to noise, allowing a time
resolution at the oldest ages of σ ~ 1.1 Gyr. Our analysis, based
on three different SFH codes, shows that the SFH of LGS-3 is dominated
by a main episode ~11.7 Gyr ago with a duration of ~1.4 Gyr.
Subsequently, LGS-3 continued forming stars until the present, although
at a much lower rate. Roughly 90% of the stars in LGS-3 were formed in
the initial episode of star formation. Extensive tests of
self-consistency, uniqueness, and stability of the solution have been
performed together with the IAC-star/IAC-pop/MinnIAC codes, and these
results are found to be independent of the photometric reduction
package, the stellar evolution library, and the SFH recovery method.
There is little evidence of chemical enrichment during the initial
episode of star formation, after which the metallicity increased more
steeply reaching a present-day value of Z ~ 0.0025. This suggests a
scenario in which LGS-3 first formed stars mainly from infalling fresh
gas, and after about 9 Gyr ago, from a larger fraction of recycled gas.
The lack of early chemical enrichment is in contrast to that observed in
the isolated dSph galaxies of comparable luminosity, implying that the
dSphs were more massive and subjected to more tidal stripping. We
compare the SFH of LGS-3 with expectations from cosmological models.
Most or all the star formation was produced in LGS-3 after the
reionization epoch, assumed to be completed at z ~ 6 or ~12.7 Gyr ago.
The total mass of the galaxy is estimated to be between 2 and 4 ×
108 M sun corresponding to circular velocities
between 28 km s-1 and 36 km s-1. These values are
close to but somewhat above the limit of 30 km s-1 below
which the UV background is expected to prevent any star formation after
reionization. Feedback from supernovae (SNe) associated with the initial
episode of star formation (mechanical luminosity from SNe Lw
= 5.3 × 1038 erg s-1) is probably inadequate
to completely blow away the gas. However, the combined effects of SN
feedback and UV background heating might be expected to completely halt
star formation at the reionization epoch for the low mass of LGS-3; this
suggests that self-shielding is important to the early evolution of
galaxies in this mass range.
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.
Related projects
Milky Way and Nearby Galaxies
The general aim of the project is to research the structure, evolutionary history and formation of galaxies through the study of their resolved stellar populations, both from photometry and spectroscopy. The group research concentrates in the most nearby objects, namely the Local Group galaxies including the Milky Way and M33 under the hypothesis
Martín
López Corredoira