Spectroscopic Properties of Star-Forming Host Galaxies and Type Ia Supernova Hubble Residuals in a Nearly Unbiased Sample

TL;DR

This study investigates how properties of star-forming host galaxies, such as metallicity and star-formation rate, correlate with Type Ia supernova brightness residuals, revealing potential biases in cosmological measurements.

Contribution

It introduces spectroscopic analysis of host galaxies to directly measure metallicity and star-formation rates, improving understanding of supernova-host correlations.

Findings

Supernovae are ~0.1 magnitudes brighter in high-metallicity hosts.

Significant correlation between Hubble residuals and host galaxy star-formation rate.

Spectroscopic host analysis reduces bias compared to photometric estimates.

Abstract

We examine the correlation between supernova host galaxy properties and their residuals on the Hubble diagram. We use supernovae discovered during the Sloan Digital Sky Survey II - Supernova Survey, and focus on objects at a redshift of z < 0.15, where the selection effects of the survey are known to yield a complete Type Ia supernova sample. To minimize the bias in our analysis with respect to measured host-galaxy properties, spectra were obtained for nearly all hosts, spanning a range in magnitude of -23 < M_r < -17. In contrast to previous works that use photometric estimates of host mass as a proxy for global metallicity, we analyze host-galaxy spectra to obtain gas-phase metallicities and star-formation rates from host galaxies with active star formation. From a final sample of ~ 40 emission-line galaxies, we find that light-curve corrected Type Ia supernovae are ~ 0.1 magnitudes brighter in high-metallicity hosts than in low-metallicity hosts. We also find a significant (> 3{\sigma}) correlation between the Hubble residuals of Type Ia supernovae and the specific star-formation rate of the host galaxy. We comment on the importance of supernova/host-galaxy correlations as a source of systematic bias in future deep supernova surveys.