Milky Way Classical Cepheid Distances from Calibrated Infrared Period–Luminosity–Metallicity Relations

Abstract

Classical Cepheids (DCEPs) serve as fundamental standard candles for measuring cosmic distances and investigating the structure and evolution of the Milky Way disk. However, accurate distance estimation faces challenges due to severe extinction, particularly toward the Galactic center. Although the Gaia Wesenheit magnitude reduces extinction effects, its reliance on a constant optical extinction law introduces significant uncertainties in regions of heavy obscuration. Infrared period–luminosity relations, combined with 3D extinction maps, offer an alternative, but these maps become unreliable beyond approximately 5 kpc. In this work, we calibrate the period–luminosity–metallicity (PLZ) relations for DCEPs across three near-infrared bands (J, H, K_S) and four mid-infrared bands (W1, W2, [3.6], and [4.5]). This includes the first calibration of the W1 and W2 bands. To correct for extinction, we employ the infrared multi-passband optimal distance method and the BP–RP method, which complement and validate each other. These homogeneous PLZ relations, combined with reliable extinction corrections, yield the most accurate Galactic DCEP distances to date, covering 3452 DCEPs with an average relative distance error of 3.1%.