Do Disk Galaxies with Abnormally Low Mass-to-Light Ratios Exist?

TL;DR

This study investigates whether some disk galaxies have genuinely low mass-to-light ratios, suggesting possible variations in stellar populations or measurement errors, with implications for the universality of the initial mass function.

Contribution

The paper provides photometric analysis of suspected low M/L ratio galaxies, identifying cases with potentially real low ratios and discussing implications for stellar population theories.

Findings

Most low M/L ratios are due to measurement errors.

Some galaxies may have intrinsically low M/L ratios, indicating unusual stellar populations.

Results support the universality of the stellar initial mass function for most galaxies.

Abstract

We performed the photometric B, V and R observations of nine disk galaxies that were suspected in having abnormally low total mass-to-light (M/L) ratios for their observed color indices. We use our surface photometry data to analyze the possible reasons for the anomalous M/L. We infer that in most cases this is a result of errors in photometry or rotational velocity, however for some galaxies we cannot exclude the real peculiarities of the galactic stellar population. The comparison of the photometric and dynamical mass estimates in the disk shows that the low M/L values for a given color of disks are probably real for a few our galaxies: NGC 4826 (Sab), NGC 5347 (Sab), and NGC 6814 (Sb). The small number of such galaxies suggests that the stellar initial mass function is indeed universal, and that only a small fraction of galaxies may have a non-typical low-mass star depleted initial mass function. Such galaxies require more careful studies for understanding their star formation history.