The Araucaria Project. The Distance to the Sculptor Group Galaxy NGC 7793 from Near-Infrared Photometry of Cepheid Variables

TL;DR

This study refines the distance measurement to NGC 7793 using near-infrared photometry of Cepheid variables, reducing uncertainties caused by dust and metallicity effects, and confirms previous distance estimates with improved accuracy.

Contribution

It provides a more precise distance to NGC 7793 by combining near-infrared and optical Cepheid data, accounting for reddening and metallicity effects.

Findings

Distance modulus of 27.66 mag with low uncertainty

Mean reddening E(B-V)=0.08 mag indicating intrinsic dust

Agreement with previous Tully-Fisher and TRGB distances

Abstract

Following the earlier discovery of classical Cepheid variables in the Sculptor Group spiral galaxy NGC 7793 from an optical wide-field imaging survey, we have performed deep near-infrared $J$- and $K$-band follow-up photometry of a subsample of these Cepheids to derive the distance to this galaxy with a higher accuracy than what was possible from optical photometry alone, by minimizing the effects of reddening and metallicity on the distance result. Combining our new near-infrared period-luminosity relations with the previous optical photometry we obtain a true distance modulus to NGC 7793 of $(27.66 \pm 0.04)$ mag (statistical) $\pm 0.07$ mag (systematic), i.e. a distance of $(3.40 \pm 0.17)$ Mpc. We also determine the mean reddening affecting the Cepheids to be $E(B-V)=(0.08 \pm 0.02)$ mag, demonstrating that there is significant dust extinction intrinsic to the galaxy in addition to the small foreground extinction. A comparison of the new, improved Cepheid distance to earlier distance determinations of NGC 7793 from the Tully-Fisher and TRGB methods yields agreement within the reported uncertainties of these previous measurements.