The Tip of the Red Giant Branch Distances to Type Ia Supernova Host Galaxies. II. M66 and M96 in the Leo I Group (1306.2306v1)

Abstract: M66 and M96 in the Leo I Group are nearby spiral galaxies hosting Type Ia Supernovae (SNe Ia). We estimate the distances to these galaxies from the luminosity of the tip of the red giant branch (TRGB). We obtain $VI$ photometry of resolved stars in these galaxies from $F555W$ and $F814W$ images in the {\it Hubble Space Telescope} archive. From the luminosity function of these red giants we find the TRGB $I$-band magnitude to be $I_{\rm TRGB}=26.20\pm0.03$ for M66 and $26.21\pm0.03$ for M96. These values yield distance modulus $(m-M)_0=30.12\pm0.03 ({\rm random})\pm0.12 ({\rm systematic})$ for M66 and $(m-M)_0=30.15\pm0.03 ({\rm random})\pm0.12 ({\rm systematic})$ for M96. These results show that they are indeed the members of the same group. With these results we derive absolute maximum magnitudes of two SNe (SN 1989B in M66 and SN 1998bu in M96). $V$-band magnitudes of these SNe Ia are $\sim$0.2 mag fainter than SN 2011fe in M101, the nearest recent SN Ia. We also derive near-infrared magnitudes for SN 1998bu. Optical magnitudes of three SNe Ia (SN 1989B, SN 1998bu, and SN 2011fe) based on TRGB analysis yield a Hubble constant, $H_0=67.6\pm1.5 ({\rm random})\pm 3.7({\rm systematic})$ \kmsMpc. This value is similar to the values derived from recent WMAP9 results, $H_0=69.32\pm0.80$ \kmsMpc. % and from Planck results, $H_0=67.3\pm1.2$ \kmsMpc, but smaller than other recent determinations based on Cepheid calibration for SNe Ia luminosity, $H_0 = 74 \pm3$ km s$^{-1}$ Mpc$^{-1}$.