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

Abstract

We present Keck LRIS spectroscopy and $g$-band photometry of the metal-poor,\nlow-luminosity host galaxy of the super-Chandrasekhar mass Type Ia supernova SN\n2007if. Deep imaging of the host reveals its apparent magnitude to be\n$m_g=23.15\\pm0.06$, which at the spectroscopically-measured redshift of\n$z_{helio}=0.07450\\pm0.00015$ corresponds to an absolute magnitude of\n$M_g=-14.45\\pm0.06$. Galaxy $g-r$ color constrains the mass-to-light ratio,\ngiving a host stellar mass estimate of $\\log(M_*/M_\\odot)=7.32\\pm0.17$. Balmer\nabsorption in the stellar continuum, along with the strength of the 4000\\AA\\\nbreak, constrain the age of the dominant starburst in the galaxy to be\n$t_\\mathrm{burst}=123^{+165}_{-77}$ Myr, corresponding to a main-sequence\nturn-off mass of $M/M_\\odot=4.6^{+2.6}_{-1.4}$. Using the R$_{23}$ method of\ncalculating metallicity from the fluxes of strong emission lines, we determine\nthe host oxygen abundance to be $12+\\log(O/H)_\\mathrm{KK04}=8.01\\pm0.09$,\nsignificantly lower than any previously reported spectroscopically-measured\nType Ia supernova host galaxy metallicity. Our data show that SN 2007if is very\nlikely to have originated from a young, metal-poor progenitor.\n