The Twins Embedding of Type Ia Supernovae I: The Diversity of Spectra at Maximum Light

Abstract

We study the spectral diversity of Type Ia supernovae (SNe Ia) at maximum light using high signal-to-noise spectrophotometry of 173 SNe Ia from the Nearby Supernova Factory. We decompose the diversity of these spectra into different extrinsic and intrinsic components, and we construct a nonlinear parameterization of the intrinsic diversity of SNe Ia that preserves pairings of "twin" SNe Ia. We call this parameterization the "Twins Embedding". Our methodology naturally handles highly nonlinear variability in spectra, such as changes in the photosphere expansion velocity, and uses the full spectrum rather than being limited to specific spectral line strengths, ratios or velocities. We find that the time evolution of SNe Ia near maximum light is remarkably similar, with 84.6% of the variance in common to all SNe Ia. After correcting for brightness and color, the intrinsic variability of SNe Ia is mostly restricted to specific spectral lines, and we find intrinsic dispersions as low as ~0.02 mag between 6600 and 7200 A. With a nonlinear three-dimensional model plus one dimension for color, we can explain 89.2% of the intrinsic diversity in our sample of SNe Ia, which includes several different kinds of "peculiar" SNe Ia. A linear model requires seven dimensions to explain a comparable fraction of the intrinsic diversity. We show how a wide range of previously-established indicators of diversity in SNe Ia can be recovered from the Twins Embedding. In a companion article, we discuss how these results an be applied to standardization of SNe Ia for cosmology.

Accepted to ApJ

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• Constraints on Cosmological Parameters with a Sample of Type Ia Supernovae from JWST
• Carnegie Supernova Project-II: Near-infrared spectral diversity and template of Type Ia Supernovae
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• A Spectroscopic Model of the Type Ia Supernova--Host Galaxy Mass Correlation from SALT3
• The Chicago Carnegie Hubble Program: Improving the Calibration of SNe Ia with JWST Measurements of the Tip of the Red Giant Branch
• Intrinsic and extinction colour components in SNeIa and the determination of $R_V$
• Approaches to lowering the cost of large space telescopes
• The Dark Energy Survey Supernova Program results: Type Ia Supernova brightness correlates with host galaxy dust
• Normal or transitional? The evolution and properties of two type Ia supernovae in the Virgo cluster
• A Sparse Spectroscopic Supernova Survey
• An Agnostic Approach to Building Empirical Type Ia Supernova Light Curves: Evidence for Intrinsic Chromatic Flux Variation Using Nearby Supernova Factory Data