The Mira Distance Ladder

Here we provide a review of Mira variables, their basic properties, and Period-Luminosity Relations with an emphasis on their role in measuring the Hubble Constant. The usage of multiple independent distance indicators and methods is crucial to cross-checking systematic uncertainties in distance measurements and in reinforcing previous findings of the Hubble tension. To this end, Mira variables serve as an alternative Type Ia Supernova calibrator to the more commonly-used Cepheid variables or Tip of the Red Giant Branch method. They also have the potential to expand the number of local SN Ia calibrators by calibrating previously-inaccessible SNe Ia. Short-period ($P \lesssim 400$ d) O-rich Miras are a ubiquitous older population that can reach galaxies not hosting the younger Cepheids variables or out of reach to the old but fainter Tip of the Red Giant Branch. With the current and upcoming focus on infrared observations, Miras, which can be discovered and characterized using exclusively near-infrared and infrared observations, will be particularly useful in obtaining distances to astrophysical objects. Long-period Miras ($P \gtrsim 400$ d) are highly luminous variables that have the potential to measure $H_0$ directly, excluding Type Ia SNe altogether in the distance ladder.Comment: Invited chapter for the edited book "Hubble Constant Tension" (Eds. E. Di Valentino and D. Brout, Springer Singapore, expected in 2024

The Mira Distance to M101 and a 4% Measurement of H0

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 lightcurve of the supernova. 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 to 400 days in the supernova field. Combined with new HST WFC3/IR channel observations, our dataset totals 11 epochs of F110W (HST $YJ$) and 13 epochs of F160W (HST $H$) data spanning $\sim$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 $\mu_{\rm M101} =$ 29.10 $\pm$ 0.06 mag. This distance is in 1$\sigma$ agreement with most other recent Cepheid and Tip of the Red Giant Branch distance measurements to M101. Including the previous Mira-SNIa host, NGC 1559 and SN 2005df, we determine the fiducial SN Ia peak luminosity, $M^0_B = -19.27 \pm 0.09$ mag. With the Hubble diagram of SNe Ia, we derive $H_0 = 72.37 \pm 2.97$ km s$^{-1}$Mpc$^{-1}$, a $4.1\%$ measurement of $H_0$ using Miras. We find excellent agreement with recent Cepheid distance ladder measurements of $H_0$ and confirm previous indications that the local universe value of $H_0$ is higher than the early-universe value at $\sim$ $95\%$ confidence. Currently, the Mira-based $H_0$ measurement is still dominated by the statistical uncertainty in the SN Ia peak magnitude.Comment: 22 pages, 11 figures, accepted to Ap