Bibcode
Cerviño, M.; Bongiovanni, A.; Hidalgo, S.
Bibliographical reference
Astronomy and Astrophysics, Volume 589, id.A108, 13 pp.
Advertised on:
4
2016
Journal
Citations
9
Refereed citations
7
Description
Aims: Star formation rate (SFR) inferences are based on the
so-called constant SFR approximation, where synthesis models are
required to provide a calibration. We study the key points of such an
approximation with the aim to produce accurate SFR inferences.
Methods: We use the intrinsic algebra of synthesis models and explore
how the SFR can be inferred from the integrated light without any
assumption about the underlying star formation history (SFH).
Results: We show that the constant SFR approximation is a simplified
expression of deeper characteristics of synthesis models: It
characterizes the evolution of single stellar populations (SSPs), from
which the SSPs as a sensitivity curve over different measures of the SFH
can be obtained. As results, we find that (1) the best age to calibrate
SFR indices is the age of the observed system (i.e., about 13 Gyr for z
= 0 systems); (2) constant SFR and steady-state luminosities are not
required to calibrate the SFR; (3) it is not possible to define a single
SFR timescale over which the recent SFH is averaged, and we suggest to
use typical SFR indices (ionizing flux, UV fluxes) together with
untypical ones (optical or IR fluxes) to correct the SFR for the
contribution of the old component of the SFH. We show how to use galaxy
colors to quote age ranges where the recent component of the SFH is
stronger or softer than the older component. Conclusions: Despite
of SFR calibrations are unaffected by this work, the meaning of results
obtained by SFR inferences does. In our framework, results such as the
correlation of SFR timescales with galaxy colors, or the sensitivity of
different SFR indices to variations in the SFH, fit naturally. This
framework provides a theoretical guide-line to optimize the available
information from data and numerical experiments to improve the accuracy
of SFR inferences.