The Universal Initial Mass Function In The XUV Disk of M83

TL;DR

This study uses deep Subaru Halpha and GALEX data to analyze the initial mass function of stellar clusters in M83's XUV disk, supporting the standard IMF over truncated models and confirming its consistency with observed flux ratios.

Contribution

It provides the first complete census of young stellar clusters in M83's XUV disk and demonstrates that the standard, stochastic IMF explains their properties better than truncated models.

Findings

Standard IMF is preferred over truncated IMF.

FUV and Halpha cluster counts align with a Salpeter IMF.

Halpha/FUV flux ratio supports the standard IMF.

Abstract

We report deep Subaru Halpha observations of the XUV disk of M83. These new observations enable the first complete census of very young stellar clusters over the entire XUV disk. Combining Subaru and GALEX data with a stellar population synthesis model, we find that (1) the standard, but stochastically-sampled, initial mass function (IMF) is preferred over the truncated IMF, because there are low mass stellar clusters (10^{2-3}Msun) that host massive O-type stars; that (2) the standard Salpeter IMF and a simple aging effect explain the counts of FUV-bright and Halpha-bright clusters with masses >10^3Msun; and that (3) the Halpha to FUV flux ratio over the XUV disk supports the standard IMF. The Subaru Prime Focus Camera (Suprime-Cam) covers a large area even outside the XUV disk -- far beyond the detection limit of the HI gas. This enables us to statistically separate the stellar clusters in the disk from background contamination. The new data, model, and previous spectroscopic studies provide overall consistent results with respect to the internal dust extinction (Av~0.1 mag) and low metallicity (~0.2Zsun) using the dust extinction curve of SMC.