The Distance to M101 Hosting Type Ia SN 2011fe Based on the Tip of the Red Giant Branch

TL;DR

This paper determines the distance to galaxy M101 hosting SN 2011fe using the TRGB method with HST data, and refines the supernova's absolute magnitudes to estimate the Hubble constant.

Contribution

The study provides a precise TRGB-based distance to M101 and recalibrates SN 2011fe's luminosity, leading to a new estimate of the Hubble constant.

Findings

Distance modulus (m-M)_0=29.30±0.01 (random)±0.12 (systematic)

SN 2011fe is ~0.2 mag brighter in optical than previous calibrations

Hubble constant estimated at 65.0±0.5 (random)±5.7 (systematic) km/s/Mpc

Abstract

We present a new determination of the distance to M101, host of the type Ia SN 2011fe, based on the tip of the red giant branch method (TRGB). Our determination is based on {\it Hubble Space Telescope} archival $F555W$ and $F814W$ images of nine fields within the galaxy. Color-magnitude diagrams of arm-free regions in all fields show a prominent red giant branch (RGB). We measure the $I$-band magnitudes of the TRGB, obtaining a mean value of $I_{\rm TRGB}=25.28\pm0.01$ (where the error is a standard error), using an edge-detection method. We derive a weighted mean value of distance modulus $(m-M)_0=29.30\pm0.01 ({\rm random})\pm0.12 ({\rm systematic})$, corresponding to a linear distance of $7.24\pm0.03\pm0.40 $ Mpc. While previous estimates for M101 show a large range (TRGB distances of $(m-M)_0=29.05$ to 29.42 and Cepheid distances of $(m-M)_0=29.04$ to 29.71), our measurements of the TRGB distances for nine fields show a small dispersion of only 0.02. We combine our distance estimate and photometry in the literature to derive absolute peak magnitudes in optical and near-infrared bands of SN 2011fe. Absolute maximum magnitudes of SN 2011fe are $\sim0.2$ mag brighter in the optical band and much more in the NIR than the current calibrations of SNe Ia in the literature. From the optical maximum magnitudes of SN 2011fe we obtain a value of the Hubble constant, $H_0=65.0\pm0.5({\rm random})\pm5.7({\rm systematic})$ \kmsMpc, slightly smaller than other recent determinations of $H_0$.