The Cepheid Period-Luminosity Relation at Mid-Infrared Wavelengths: I. First-Epoch LMC Data

TL;DR

This study establishes the first mid-infrared Period-Luminosity relations for LMC Cepheids using single-epoch Spitzer data, showing consistent slopes and low scatter, which could enhance distance measurements.

Contribution

It provides the initial mid-infrared PL relations for LMC Cepheids, demonstrating their potential for more accurate cosmic distance estimations.

Findings

Nearly identical slopes across wavelengths

Low scatter of +/-0.16 mag independent of period

Mid-IR PL relations less affected by reddening

Abstract

We present the first mid-infrared Period-Luminosity (PL) relations for Large Magellanic Cloud (LMC) Cepheids. Single-epoch observations of 70 Cepheids were extracted from Spitzer IRAC observations at 3.6, 4.5, 5.8 and 8.0 microns, serendipitously obtained during the SAGE (Surveying the Agents of a Galaxy's Evolution) imaging survey of the LMC. All four mid-infrared PL relations have nearly identical slopes over the period range 6 - 88 days, with a small scatter of only +/-0.16 mag independent of period for all four of these wavelengths. We emphasize that differential reddening is not contributing significantly to the observed scatter, given the nearly two orders of magnitude reduced sensitivity of the mid-IR to extinction compared to the optical. Future observations, filling in the light curves for these Cepheids, should noticeably reduce the residual scatter. These attributes alone suggest that mid-infrared PL relations will provide a practical means of significantly improving the accuracy of Cepheid distances to nearby galaxies.