The Distance to M51

TL;DR

This paper presents a precise measurement of the distance to the Whirlpool galaxy M51 using Hubble Space Telescope data and the tip of the red giant branch method, improving accuracy over previous estimates.

Contribution

The study introduces a new, more accurate distance measurement to M51 employing a well-calibrated indicator, Bayesian analysis, and optimized photometry techniques.

Findings

Distance modulus to M51 is 29.67±0.02 mag.

Distance to M51 is 8.58±0.10 Mpc.

Method reduces uncertainties compared to previous estimates.

Abstract

Great investments of observing time have been dedicated to the study of nearby spiral galaxies with diverse goals ranging from understanding the star formation process to characterizing their dark matter distributions. Accurate distances are fundamental to interpreting observations of these galaxies, yet many of the best studied nearby galaxies have distances based on methods with relatively large uncertainties. We have started a program to derive accurate distances to these galaxies. Here we measure the distance to M51 - the Whirlpool galaxy - from newly obtained Hubble Space Telescope optical imaging using the tip of the red giant branch method. We measure the distance modulus to be 8.58+/-0.10 Mpc (statistical), corresponding to a distance modulus of 29.67+/-0.02 mag. Our distance is an improvement over previous results as we use a well-calibrated, stable distance indicator, precision photometry in a optimally selected field of view, and a Bayesian Maximum Likelihood technique that reduces measurement uncertainties.