The Araucaria Project. The Distance to the Local Group Galaxy WLM from Near-Infrared Photometry of Cepheid Variables

TL;DR

This study uses near-infrared photometry of Cepheid variables in WLM to accurately determine its distance and reddening, achieving a 3% precision and confirming the reliability of infrared methods for small irregular galaxies.

Contribution

It provides the first tight near-infrared period-luminosity relations for WLM Cepheids and demonstrates the effectiveness of multiwavelength analysis for precise distance measurements.

Findings

Distance modulus of WLM is 24.924 mag with 3% uncertainty.

Reddening E(B-V) is 0.082 mag, mostly internal to WLM.

Infrared photometry yields highly accurate Cepheid distances.

Abstract

We have obtained deep images in the near-infrared J and K filters for several fields in the Local Group galaxy WLM. We report intensity mean magnitudes for 31 Cepheids located in these fields which we previously discovered in a wide-field optical imaging survey of WLM. The data define tight period-luminosity relations in both near-infrared bands which we use to derive the total reddening of the Cepheids in WLM and the true distance modulus of the galaxy from a multiwavelength analysis of the reddened distance moduli in the VIJK bands. From this, we obtain the values E(B-V) = 0.082 $\pm$ 0.02, and $(m-M)_{0} = 24.924 \pm 0.042$ mag, with a systematic uncertainty in the distance of about $\pm$ 3%. This Cepheid distance agrees extremely well with the distance of WLM determined from the I-band TRGB method by ourselves and others. Most of the reddening of the Cepheids in WLM (0.06 mag) is produced inside the galaxy, demonstrating again the need for an accurate determination of the total reddening and/or the use of infrared photometry to derive Cepheid distances which are accurate to 3% or better, even for small irregular galaxies like WLM.