From the Outside Looking in: What can Milky Way Analogues Tell us About the Star Formation Rate of Our Own Galaxy?

TL;DR

This study compares the Milky Way's star formation rate to a carefully selected sample of similar galaxies, finding it to be typical rather than unusually low, based on multiple indicators and a well-defined sample.

Contribution

The paper introduces a rigorous method for selecting Milky Way analogues and assesses the galaxy's SFR in context, showing it is not atypical among similar galaxies.

Findings

Milky Way's SFR is within 2σ of the mean SFR of analogues.

Selected 176 galaxies with similar structural features to the Milky Way.

Milky Way's SFR estimates align with recent measurements.

Abstract

The Milky Way has been described as an anaemic spiral, but is its star formation rate (SFR) unusually low when compared to its peers? To answer this question, we define a sample of Milky Way Analogues (MWAs) based on stringent cuts on the best literature estimates of non-transient structural features for the Milky Way. This selection yields only 176 galaxies from the whole of the SDSS DR7 spectroscopic sample which have morphological classifications in GZ2, from which we infer SFRs from two separate indicators. The mean SFRs found are $\log(\rm{SFR}_{SED}/\rm{M}_{\odot}~\rm{yr}^{-1})=0.53$ with a standard deviation of 0.23 dex from SED fits, and $\log(\rm{SFR}_{W4}/\rm{M}_{\odot}~\rm{yr}^{-1})=0.68$ with a standard deviation of 0.41 dex from a mid-infrared calibration. The most recent estimate for the Milky Way's star formation rate of $\log(\rm{SFR}_{MW}/\rm{M}_{\odot}~\rm{yr}^{-1})=0.22$ fits well within 2$\sigma$ of these values, where $\sigma$ is the standard deviation of each of the SFR indicator distributions. We infer that the Milky Way, while being a galaxy with a somewhat low SFR, is not unusual when compared to similar galaxies.