The mid-infrared Leavitt Law for Classical Cepheids in the Magellanic Clouds

TL;DR

This study refines the mid-infrared Period-Luminosity relations for Classical Cepheids in the Magellanic Clouds using extensive OGLE-IV and Spitzer data, calibrated with Gaia and HST parallaxes, enhancing cosmic distance measurements.

Contribution

It provides new calibrated mid-infrared Leavitt Law relations for Magellanic Cloud Cepheids, combining large datasets and advanced statistical methods for improved accuracy.

Findings

Derived precise mid-infrared Period-Luminosity relations for LMC and SMC Cepheids.

Calibrated the relations using Gaia and HST parallaxes for improved zero points.

Analyzed the linearity and period dependence of the Leavitt Law coefficients.

Abstract

The Cepheid Leavitt Law (LL), also known as the Period-Luminosity relation, is a crucial tool for assembling the cosmic distance ladder. By combining data from the OGLE-IV catalogue with mid-infrared photometry from the Spitzer Space Telescope, we have determined the $3.6$ $\mu$m and $4.5$ $\mu$m LLs for the Magellanic Clouds using around 5000 fundamental-mode Classical Cepheids. Mean magnitudes were determined using a Monte Carlo Markov Chain (MCMC) template fitting procedure, with template light curves constructed from a subsample of these Cepheids with fully-phased, well-sampled light curves. The dependence of the Large Magellanic Cloud LL coefficients on various period cuts was tested, in addition to the linearity of the relationship. The zero point of the LL was calibrated using the parallaxes of Milky Way Cepheids from the Hubble Space Telescope and Gaia Data Release 2. Our final calibrated relations are $M_{[3.6]} = -3.246(\pm 0.008)(\log(P)-1.0)-5.784(\pm 0.030)$ and $M_{[4.5]} = -3.162(\pm 0.008)(\log(P)-1.0)-5.751(\pm 0.030)$.