Intrinsic color diversity of nearby type Ia supernovae

TL;DR

This study investigates the intrinsic color diversity of nearby Type Ia supernovae by analyzing their photometric properties, host galaxy types, and spectroscopic classifications, revealing intrinsic color variations especially in Broad Line sub-types.

Contribution

It provides new insights into the intrinsic color diversity of SNe Ia and its dependence on spectroscopic sub-types and host galaxy morphology, clarifying the role of dust extinction.

Findings

Redder SNe Ia are found in early-type spirals and ellipticals.

Dust extinction in most SNe Ia resembles Milky Way extinction when peculiar red BL SNe are excluded.

Intrinsic color diversity is evident in BL sub-type SNe Ia, especially in less dusty environments.

Abstract

It has been reported that the extinction law for Type Ia Supernovae (SNe Ia) may be different from the one in the Milky Way, but the intrinsic color of SNe Ia and the dust extinction are observationally mixed. In this study, we examine photometric properties of SNe Ia in the nearby universe ($z \lesssim 0.04$) to investigate the SN Ia intrinsic color and the dust extinction. We focus on the Branch spectroscopic classification of 34 SNe Ia and morphological types of host galaxies. We carefully study their distribution of peak colors on the $B-V$, $V-R$ color-color diagram, as well as the color excess and absolute magnitude deviation from the stretch-color relation of the bluest SNe Ia. We find that SNe Ia which show the reddest color occur in early-type spirals and the trend holds when divided into Branch sub-types. The dust extinction becomes close to the Milky-Way like extinction if we exclude some peculiar red Broad Line (BL) sub-type SNe Ia. Furthermore, two of these red BLs occur in elliptical galaxies, less-dusty environment, suggesting intrinsic color diversity in BL sub-type SNe Ia.