Exploring the spatially resolved initial mass function in SAMI star-forming galaxies

TL;DR

This study investigates the spatial variation of the initial mass function (IMF) in star-forming galaxies using SAMI survey data, revealing correlations with star formation activity and suggesting environmental influences on high-mass star formation.

Contribution

It provides the first spatially resolved analysis of the IMF in star-forming galaxies, linking IMF variability to local star formation rates and surface densities.

Findings

Resolved and integrated IMF slopes are closely related for certain values.

Higher star formation rates correlate with flatter IMF slopes.

Mass dependency influences the relationship between IMF slope and SFR.

Abstract

The initial mass function (IMF) is a construct that describes the distribution of stellar masses for a newly formed population of stars. It is a fundamental element underlying all of star and galaxy formation, and has been the subject of extensive investigation for more than 60 years. In the past few decades there has been a growing, and now substantial, body of evidence supporting the need for a variable IMF. In this light, it is crucial to investigate the IMF's characteristics across different spatial scales and to understand the factors driving its variability. We make use of spatially resolved spectroscopy to examine the high-mass IMF slope of star-forming galaxies within the SAMI survey. By applying the Kennicutt method and stellar population synthesis models, we estimated both the spaxel-resolved ($\alpha_{res}$) and galaxy-integrated ($\alpha_{int}$) high-mass IMF slopes of these galaxies. Our findings indicate that the resolved and integrated IMF slopes exhibit a near 1:1 relationship for $\alpha_{int}> -2.7$. We observe a wide range of $\alpha_{res}$ distributions within galaxies. To explore the sources of this variability, we analyse the relationships between the resolved and integrated IMF slopes and both the star formation rate (SFR) and SFR surface density ($\Sigma_{SFR}$). Our results reveal a strong correlation where flatter/steeper slopes are associated with higher/lower SFR and $\Sigma_{SFR}$. This trend is qualitatively similar for resolved and global scales. Additionally, we identify a mass dependency in the relationship with SFR, though none was found in the relation between the resolved slope and $\Sigma_{SFR}$. These findings suggest an scenario where the formation of high-mass stars is favoured in regions with more concentrated star formation. This may be a consequence of the reduced fragmentation of molecular clouds, which nonetheless accrete more material.