A Study on the Universality and Linearity of the Leavitt Law in the LMC and SMC Galaxies

TL;DR

This study tests the universality and linearity of the Leavitt law in the Magellanic Clouds using Cepheid data, revealing non-linearity in certain bands and partial universality of slopes.

Contribution

It provides empirical evidence challenging the linearity and universality assumptions of the Leavitt law in specific observational bands.

Findings

Slopes in $VI$-bands and Wesenheit index behave exponentially.

Non-linearity observed in the slopes.

Long-period Cepheids' slopes are universal in $VI$-bands but not in Wesenheit index.

Abstract

The universality and linearity of the Leavitt law are hypotheses commonly adopted in studies of galaxy distances using Cepheid variables as standard candles. In order to test these hypotheses, we obtain slopes of the Leavitt law using linear regressions of fundamental-mode Cepheids observed by the Optical Gravitational Lensing Experiment project in the Magellanic Clouds. We find that the slopes in $VI$-bands and in the Wesenheit index behave exponentially, indicating non-linearity. We also find that the slopes obtained using long-period Cepheids can be considered as universal in the $VI$-bands, but not in the Wesenheit index.