KECK OBSERVATIONS OF THE YOUNG METAL-POOR HOST GALAXY OF THE SUPER-CHANDRASEKHAR-MASS TYPE Ia SUPERNOVA SN 2007if

We present Keck LRIS spectroscopy and g-band photometry of the metal-poor, low-luminosity host galaxy of the super-Chandrasekhar-mass Type Ia supernova SN 2007if. Deep imaging of the host reveals its apparent magnitude to be mg = 23.15 ± 0.06, which at the spectroscopically measured redshift of zhelio = 0.07450 ± 0.00015 corresponds to an absolute magnitude of Mg = −14.45 ± 0.06. Galaxy g − r color constrains the mass-to-light ratio, giving a host stellar mass estimate of log(M*/M☉) = 7.32 ± 0.17. Balmer absorption in the stellar continuum, along with the strength of the 4000 Å break, constrains the age of the dominant starburst in the galaxy to be tburst = 123+165−77 Myr, corresponding to a main-sequence turnoff mass of M/M☉ = 4.6+2.6−1.4. Using the R23 method of calculating metallicity from the fluxes of strong emission lines, we determine the host oxygen abundance to be 12 + log(O/H)KK04 = 8.01 ± 0.09, significantly lower than any previously reported spectroscopically measured Type Ia supernova host galaxy metallicity. Our data show that SN 2007if is very likely to have originated from a young, metal-poor progenitor.