100 mum and 160 mum emission as resolved star-formation rate estimators in M33 (HERM33ES)

TL;DR

This study develops new relations to estimate star-formation rates in M33 using 100 and 160 micron infrared emission, revealing that 100 micron emission is a nearly linear SFR indicator across various regions.

Contribution

The paper introduces calibrated relations for SFR estimation from 100 and 160 micron emission in resolved star-forming regions, extending previous galaxy-wide relations.

Findings

100 micron emission is a nearly linear SFR estimator.

160 micron emission is slightly superlinear as an SFR estimator.

Star formation influences dust temperature at high SFR densities.

Abstract

Over the past few years several studies have provided estimates of the SFR (star-formation rate) or the total infrared luminosity from just one infrared band. However these relations are generally derived for entire galaxies, which are known to contain a large scale diffuse emission that is not necessarily related to the latest star-formation episode. We provide new relations to estimate the SFR from resolved star-forming regions at 100 mum and 160 mum. We select individual star-forming regions in the nearby (840 kpc) galaxy M33. We estimate the SFR combining the emission in Halpha and at 24 mum to calibrate the emission at 100 mum and 160 mum as SFR estimators, as mapped with PACS/Herschel. The data are obtained in the framework of the HERM33ES open time key project. There is less emission in the HII regions at 160 mum than at 100 mum. Over a dynamic range of almost 2 dex in Sigma(SFR) we find that the 100 mum emission is a nearly linear estimator of the SFR, whereas that at 160 mum is slightly superlinear. The behaviour of individual star-forming regions is surprisingly similar to that of entire galaxies. At high Sigma(SFR), star formation drives the dust temperature, whereas uncertainties and variations in radiation-transfer and dust-heated processes dominate at low Sigma(SFR). Detailed modelling of both galaxies and individual star forming regions will be needed to interpret similarities and differences between the two and assess the fraction of diffuse emission in galaxies.