Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST and literature data

TL;DR

This paper combines Gaia EDR3, HST, and literature data to derive highly accurate distances to 162 Galactic globular clusters, achieving 1% precision for about 20 clusters and discussing implications for the local Hubble constant.

Contribution

It introduces a multi-method approach combining parallaxes, kinematics, subdwarf fitting, and stellar counts to improve globular cluster distance measurements.

Findings

Distances agree within 2% across methods

Achieved 1% accuracy for about 20 clusters

Derived distances for 162 clusters

Abstract

We have derived accurate distances to Galactic globular clusters by combining data from the Gaia Early Data Release 3 with distances based on Hubble Space telescope HST data and literature based distances. We determine distances either directly from the Gaia EDR3 parallaxes, or kinematically by combining line-of-sight velocity dispersion profiles with Gaia EDR3 and HST based proper motion velocity dispersion profiles. We furthermore calculate cluster distances from fitting nearby subdwarfs, whose absolute luminosities we determine from their Gaia EDR3 parallaxes, to globular cluster main-sequences. We finally use HST based stellar number counts to determine distances. We find good agreement in the average distances derived from the different methods down to a level of about 2%. Combining all available data, we are able to derive distances to 162 Galactic globular clusters, with the distances to about 20 nearby globular clusters determined with an accuracy of 1% or better. We finally discuss the implications of our distances for the value of the local Hubble constant.