Calibration of star formation rate tracers for short- and long-lived star formation episodes

Abstract

To derive the history of star formation in the Universe a set of calibrated star formation rate tracers at different wavelengths is required. The calibration has to consistently take into account the effects of extinction, star formation regime (short or long-lived) and evolutionary state to avoid biases at different redshift ranges. We use evolutionary synthesis models optimized for intense episodes of star formation in order to compute a consistent calibration of the most usual star formation rate tracers at different energy ranges, from X-ray to radio luminosities. Nearly-instantaneous and continuous star formation regimes, and the effect of interstellar extinction are considered, as well as the effect of metallicity on the calibration of the different estimators. A consistent calibration of a complete set of star formation rate tracers is presented, computed for the most usual star-forming regions conditions: evolutionary state, star formation regime, interstellar extinction and initial mass function. We discuss the validity of the different tracers in different star formation scenarios and compare our predictions with previous calibrations of general use. Nearly-instantaneous and continuous star formation regimes must be distinguished. While the Star Formation Strength (\msun) should be used for the former, the more common Star Formation Rate (\msun yr$^{-1}$) is only valid for episodes forming stars at a constant rate during extended periods for time. Moreover, even for the latter, the evolutionary state should be taken into account, since most SFR tracers stabilize only after 100 Myr of evolution.Comment: Accepted for publication in A&A, webtool in http://www.laeff.cab.inta-csic.es/research/sfr/, 19 pages, 10 figures, 14 tables. New version including language style revisio