Calibration of Star Formation Rate Tracers with Population Synthesis Models: the X-ray to FIR Luminosities Ratio

TL;DR

This paper revises the calibration of star formation rate (SFR) tracers across different wavelengths using population synthesis models, focusing on the X-ray to FIR luminosity ratio, and assesses their reliability for different starburst durations.

Contribution

It provides a new analysis of the X-ray to FIR luminosity ratio evolution using updated population synthesis models, comparing predictions with observational data.

Findings

Soft X-ray luminosity is a valid SFR tracer only during short starburst periods.

The study offers revised calibrations for SFR tracers based on population synthesis.

Comparison with literature data supports the limited applicability of X-ray as a universal SFR indicator.

Abstract

The study of massive star formation needs some basic tools, among which reliable SFR tracers are crucial ones. We are presently revising the calibration of SFR tracers at different wavelength ranges using last generation evolutionary population synthesis codes. The FIR luminosity produced by the heated dust in star forming regions is commonly used to characterize a starburst. The X-ray luminosity has been found to show a narrow correlation with it, and therefore it has been proposed as an additional tracer of potential interest for high $z$ galaxies, whose FIR emission is redshifted to the sub-mm range. In this communication we analyze the evolution of the X-ray to FIR luminosities ratio as predicted by the CMHK population synthesis models, both for constant stellar formation and instantaneous bursts. The results are compared to some sample data taken from the literature. The conclusion drawn from the comparison is that the empirical calibration of the soft X-ray luminosity seems a valid SFR tracer only for starbursts around a rather short period of time.