Ruiz-Lara, T.; Pérez, I.; Gallart, C.; Alloin, D.; Monelli, M.; Koleva, M.; Pompei, E.; Beasley, M.; Sánchez-Blázquez, P.; Florido, E.; Aparicio, A.; Fleurence, E.; Hardy, E.; Hidalgo, S. L.; Raimann, D.
Bibliographical reference
Astronomy and Astrophysics, Volume 583, id.A60, 23 pp.
Description
Context. Accurate star formation histories (SFHs) of galaxies are
fundamental for understanding the build-up of their stellar content.
However, the most accurate SFHs - those obtained from colour-magnitude
diagrams (CMDs) of resolved stars reaching the oldest main-sequence
turnoffs (oMSTO) - are presently limited to a few systems in the Local
Group. It is therefore crucial to determine the reliability and range of
applicability of SFHs derived from integrated light spectroscopy, as
this affects our understanding of unresolved galaxies from low to high
redshift. Aims: We evaluate the reliability of current full
spectral fitting techniques in deriving SFHs from integrated light
spectroscopy by comparing SFHs from integrated spectra to those obtained
from deep CMDs of resolved stars. Methods: We have obtained a
high signal-to-noise (S/N ~ 36.3 per Å) integrated spectrum of a
field in the bar of the Large Magellanic Cloud (LMC) using EFOSC2 at the
3.6-metre telescope at La Silla Observatory. For this same field,
resolved stellar data reaching the oMSTO are available. We have compared
the star formation rate (SFR) as a function of time and the
age-metallicity relation (AMR) obtained from the integrated spectrum
using STECKMAP, and the CMD using the IAC-star/MinnIAC/IAC-pop set of
routines. For the sake of completeness we also use and discuss other
synthesis codes (STARLIGHT and ULySS) to derive the SFR and AMR from the
integrated LMC spectrum. Results: We find very good agreement
(average differences ~4.1%) between the SFR (t) and the AMR obtained
using STECKMAP on the integrated light spectrum, and the CMD analysis.
STECKMAP minimizes the impact of the age-metallicity degeneracy and has
the advantage of preferring smooth solutions to recover complex SFHs by
means of a penalized χ2. We find that the use of single
stellar populations (SSPs) to recover the stellar content, using for
instance STARLIGHT or ULySS codes, hampers the reconstruction of the SFR
(t) and AMR shapes, yielding larger discrepancies with respect to the
CMD results. These discrepancies can be reduced if spectral templates
based on known and complex SFHs are employed rather than SSPs.
Based on observations obtained at the 3.6 m ESO telescope on La Silla
(Chile) and with the Hubble Space Telescope, operated by NASA.Appendices
are available in electronic form at
http://www.aanda.org
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