2024ApJ...963...83H

The giant spiral galaxy M101 is host to the nearest recent Type Ia supernova (SN 2011fe) and thus has been extensively monitored in the near-infrared to study the late-time light curve of the SN. Leveraging this existing baseline of observations, we derive the first Mira-based distance to M101 by discovering and classifying a sample of 211 Miras with periods ranging from 240-400 days in the SN field. Combined with new Hubble Space Telescope (HST) WFC3/IR channel observations, our data set totals 11 epochs of F110W (HST YJ) and 13 epochs of F160W (HST H) data spanning ∼2900 days. We adopt absolute calibrations of the Mira period-luminosity relation based on geometric distances to the Large Magellanic Cloud and the water megamaser host galaxy NGC 4258, and find μ_M101 = 29.10 ± 0.06 mag. This distance is in 1σ agreement with most other recent Cepheid and tip of the red giant branch distance measurements to M101. Including the previous Mira SN Ia host, NGC 1559, and SN 2005df, we determine the fiducial SN Ia peak luminosity, ${M}_{B}^{0}=-19.27\,\pm \,0.09$ mag. With the Hubble diagram of supernovae Ia, we derive H₀ = 72.37 ± 2.97 km s^–1 Mpc^–1, a 4.1% measurement of H₀ using Miras. We find excellent agreement with recent Cepheid distance ladder measurements of H₀ and confirm previous indications that the local universe value of H₀ is higher than the early universe value at ∼95% confidence. Currently, the Mira-based H₀ measurement is still dominated by the statistical uncertainty in the SN Ia peak magnitude.