Absolute Calibration of Cluster Mira Variables to Provide a New Anchor for the Hubble Constant Determination

TL;DR

This study uses Mira variables in globular clusters to calibrate the cosmic distance scale, leading to a precise local measurement of the Hubble constant that supports existing tension with early universe estimates.

Contribution

It introduces a new calibration method for Mira variables in globular clusters to measure the Hubble constant with high precision, providing an independent anchor for cosmic distances.

Findings

Cluster Mira PLRs are consistent across metallicities.

Distance to LMC calibrated with 1.2% accuracy.

Hubble constant measured as 73.06 km/s/Mpc.

Abstract

Mira variables in globular clusters can provide an accurate and precise absolute calibration of their period-luminosity relations (PLRs) to independently anchor the cosmic distance scale and determine the Hubble constant. We present homogeneous near-infrared ($JHK_s$) time-series photometric observations of a sample of 55 candidate long-period variables in 18 globular clusters covering a wide metallicity range ($-1.7 < \textrm{[Fe/H]} < -0.1$ dex). The Gaia proper motions, long-period variability information, and optical-infrared colors are used to identify 41 oxygen-rich Miras as members of the globular clusters. Mean luminosities of Miras in the $JHK_s$ bands are independently calibrated using the recommended distances and mean parallaxes to their host clusters. Cluster Mira PLRs exhibit scatter comparable to the Large Magellanic Cloud (LMC) variables and do not show any dependence on iron abundance for a wide range of metallicities. We establish the accuracy of cluster Miras as independent anchors by determining a distance modulus to the LMC, $18.45 \pm 0.04$ mag, in agreement with the 1.2\% precise geometric distance. Our $H$-band photometry is transformed to derive Hubble Space Telescope F160W PLR for cluster Miras providing a three-anchor baseline with the LMC and NGC 4258. We employ three-anchor solution to determine distances to two type Ia supernovae host galaxies, NGC 1559 ($31.39\pm0.05$ mag) and M101 ($29.07\pm0.04$ mag), and provide a $3.7\%$ measurement of the Hubble constant, $H_0 = 73.06\pm 2.67$ km~s$^{-1}$~Mpc$^{-1}$. Similar to Cepheids, our independent baseline solution results in a local $H_0$ determination that is systematically larger than its inference from the early universe probes, further supporting the ongoing Hubble tension.