IMF-induced intrinsic uncertainties on measuring galaxy distances based on the number of giant stars: the case of the ultra-diffuse galaxy NGC 1052-DF2

TL;DR

This paper investigates how IMF assumptions introduce uncertainties in galaxy distance measurements using the SBF technique, highlighting potential biases especially for low-mass galaxies like NGC 1052-DF2.

Contribution

It demonstrates that IMF variations significantly affect SBF-based distance estimates, revealing a bias that can lead to underestimating galaxy distances.

Findings

IMF assumptions cause 8-12 Mpc distance uncertainties

IGIMF model suggests possible 11 Mpc distance for NGC 1052-DF2

Bias in SBF distances persists despite changes in giant star luminosity thresholds

Abstract

The surface brightness fluctuation (SBF) technique is one of the distance measurement methods that has been applied on the low surface brightness galaxy NGC 1052-DF2 yielding a distance of about 20 Mpc implying it to be a dark matter deficient galaxy. We assume the number of giant stars above a given luminosity threshold to represent the SBF magnitude. The SBF magnitude depends on the distance, but this is degenerate with the star formation history (SFH). Using a stellar population synthesis model we calculate the number of giant stars for stellar populations with different galaxy-wide stellar initial mass functions (gwIMFs), ages, metallicities and SFHs. If the gwIMF is the invariant canonical IMF, the 1$\sigma$ (3$\sigma$) uncertainty in colour allows a distance as low as 12 Mpc (8 Mpc). If instead the true underlying gwIMF is the integrated galaxy-wide IMF (IGIMF) then overestimating distances for low-mass galaxies would be a natural result, allowing NGC 1052-DF2 to have a distance of 11 Mpc within the 1$\sigma$ colour uncertainty. Finally, we show that our main conclusion on the existence of a bias in the SBF distance estimation is not much affected by changing the luminosity lower limit for counting giant stars.