Keck Observations of the Young Metal-Poor Host Galaxy of the Super-Chandrasekhar-Mass Type Ia Supernova SN 2007if

TL;DR

This study presents detailed spectroscopic and photometric analysis of the metal-poor host galaxy of the super-Chandrasekhar-mass Type Ia supernova SN 2007if, revealing its low mass, young stellar population, and low metallicity, suggesting a young, metal-poor progenitor.

Contribution

First detailed spectroscopic and photometric characterization of the host galaxy of SN 2007if, highlighting its low mass, young age, and low metallicity, which informs supernova progenitor models.

Findings

Host galaxy has an absolute magnitude of M_g=-14.45.

Host galaxy's metallicity is significantly lower than previously reported for Type Ia hosts.

SN 2007if likely originated from a young, metal-poor progenitor.

Abstract

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 $m_g=23.15\pm0.06$, which at the spectroscopically-measured redshift of $z_{helio}=0.07450\pm0.00015$ corresponds to an absolute magnitude of $M_g=-14.45\pm0.06$. Galaxy $g-r$ color constrains the mass-to-light ratio, giving a host stellar mass estimate of $\log(M_*/M_\odot)=7.32\pm0.17$. Balmer absorption in the stellar continuum, along with the strength of the 4000\AA\ break, constrain the age of the dominant starburst in the galaxy to be $t_\mathrm{burst}=123^{+165}_{-77}$ Myr, corresponding to a main-sequence turn-off mass of $M/M_\odot=4.6^{+2.6}_{-1.4}$. Using the R$_{23}$ method of calculating metallicity from the fluxes of strong emission lines, we determine the host oxygen abundance to be $12+\log(O/H)_\mathrm{KK04}=8.01\pm0.09$, 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.