The ACS Nearby Galaxy Survey Treasury III: Cepheids in the Outer Disk of M81

TL;DR

This study uses deep HST imaging to identify and analyze Cepheid variables in the outer disk of galaxy M81, providing a precise distance measurement of 3.60 Mpc.

Contribution

First detailed identification of Cepheids in M81's outer disk using ACS data, enabling accurate distance estimation.

Findings

Distance modulus of 27.78 ± 0.05 (random) ± 0.14 (systematic)

Distance to M81 is 3.60 ± 0.23 Mpc

Successful classification of Cepheid types using light curve templates

Abstract

The ACS Nearby Galaxy Survey Treasury (ANGST) has acquired deep ACS imaging of a field in the outer disk of the large spiral galaxy M81. These data were obtained over a total of 20 HST orbits, providing a baseline long enough to reliably identify Cepheid variable stars in the field. Fundamental mode and first overtone types have been distinguished through comparative fits with corresponding Cepheid light curve templates derived from principal component analysis of confirmed Cepheids in the LMC, SMC, and Milky Way. A distance modulus of 27.78 pm 0.05_random pm 0.14_systematic with a corresponding distance of 3.60 pm 0.23 Mpc has been calculated from a sample of 11 fundamental mode and 2 first overtone Cepheids (assuming an LMC distance modulus of mu_LMC=18.41 pm 0.10_r pm 0.13_s).