# Star-formation rate and stellar mass calibrations based on infrared photometry and their dependence on stellar population age and extinction

**Authors:** Konstantinos Kouroumpatzakis, Andreas Zezas, Elias Kyritsis, Samir Salim, Jiri Svoboda  
**arXiv:** [2303.10013](https://arxiv.org/abs/2303.10013)  
**Date:** 2023-03-17  
**Summary page:** https://www.summarizepaper.com/en/paper/2303.10013v1/

## Key points

- Galaxies are characterized by their stellar mass and star-formation rate (SFR)
- Accurately measuring these properties is challenging due to factors such as age of the stellar populations and extinction
- This study explores how infrared (IR) emission of galaxies depends on these factors
- The researchers used the CIGALE spectral energy distribution fitting code to create models of galaxies with varying properties
- They found that existing calibrations for photometric IR luminosity-to-SFR and mass-to-light ratio were biased by SP age and extinction
- New calibrations were proposed that account for these biases in both extinction-dependent and independent forms, offering robust estimations while minimizing scatter throughout a wide range of SFRs and stellar masses.
- The SFR calibration offers better results in dust-free or passive galaxies where old SPs or biases from lack of dust can significantly contribute.
- Similarly, the $M_\star$ calibration yields significantly better results for dusty/high-SFR galaxies where dust emission can otherwise bias the estimations.
- The study also highlights that the relation between NIR emission and $M_\star$ depends strongly on the age of SPs, and existing calibrations based on optical or IR colors show discrepancies and large scatter in their estimations.
- New calibrations were proposed that account for SP age and extinction in both extinction dependent & independent forms to mitigate these effects & improve our understanding of galaxy properties & history.
- Overall, this study provides important insights into how galaxy properties are affected by various factors such as SP age & extinction, & offers new calibrations that can improve our understanding of galaxies' present state & history.

## Summary

Galaxies are characterized by their stellar mass ($M_\star$) and star-formation rate (SFR), which are crucial for understanding their present state and history. Accurately measuring these properties is challenging, as they depend on a range of factors such as the age of the stellar populations (SPs) and extinction. This study aims to explore how the infrared (IR) emission of galaxies depends on these factors, and to provide accurate calibrations for IR SFR and $M_\star$ that account for SP age and extinction while minimizing scatter. The researchers used the CIGALE spectral energy distribution (SED) fitting code to create models of galaxies with varying star-formation histories, dust content, and interstellar medium properties. They then fit the relations between $M_\star$ and SFR with IR and optical photometry of the model-galaxy SEDs using the MCMC method, before performing a machine-learning random forest analysis on the same data set to validate their results. The team found that existing calibrations for photometric IR luminosity-to-SFR and mass-to-light ratio were biased by SP age and extinction. To mitigate these effects, they proposed new calibrations that accounted for these biases in both extinction-dependent and independent forms. The study provides calibrations for SFR using a combination of WISE bands 1 and 3 or JWST F200W and F2100W bands, as well as mass-to-light ratio based on WISE band-1 or JWST band F200W along with optical $u-r$ or $g-r$ colors. These new calibrations offer robust estimations while minimizing scatter throughout a wide range of SFRs and stellar masses. The SFR calibration offers better results in dust-free or passive galaxies where old SPs or biases from lack of dust can significantly contribute. Similarly, the $M_\star$ calibration yields significantly better results for dusty/high-SFR galaxies where dust emission can otherwise bias the estimations. The study also highlights that the relation between NIR emission and $M_\star$ depends strongly on the age of SPs, and existing calibrations based on optical or IR colors show discrepancies and large scatter in their estimations. To address this issue, the researchers proposed new calibrations that account for SP age and extinction in both extinction dependent & independent forms in order to mitigate these effects & improve our understanding of galaxy properties & history. These new calibrations offer robust estimations while minimizing scatter throughout a wide range of SFRs & stellar masses; providing better results in dust free/passive galaxies & dusty/high SFR galaxies respectively due to accounting for biases from lack/presence of dust respectively . Overall , this study provides important insights into how galaxy properties are affected by various factors such as SP age & extinction ,& offers new calibrations that can improve our understanding of galaxies' present state & history .