Using Spectral Flux Ratios to Standardize SN Ia Luminosities
Abstract
We present a new method to standardize Type Ia supernova (SN Ia) luminosities to ~<0.13 magnitudes using flux ratios from a single flux-calibrated spectrum per SN. Using Nearby Supernova Factory spectrophotomery of 58 SNe Ia, we performed an unbiased search for flux ratios which correlate with SN Ia luminosity. After developing the method and selecting the best ratios from a training sample, we verified the results on a separate validation sample and with data from the literature. We identified multiple flux ratios whose correlations with luminosity are stronger than those of light curve shape and color, previously identified spectral feature ratios, or equivalent width measurements. In particular, the flux ratio R(642/443) = F(642 nm) / F(443 nm) has a correlation of 0.95 with SN Ia absolute magnitudes. Using this single ratio as a correction factor produces a Hubble diagram with a residual scatter standard deviation of 0.125 +- 0.011 mag, compared with 0.161 +- 0.015 mag when fit with the SALT2 light curve shape and color parameters x1 and c. The ratio R(642/443) is an effective correction factor for both extrinsic dust reddening and instrinsic variations such as those of SN 1991T-like and SN 1999aa-like SNe. When combined with broad-band color measurements, spectral flux ratios can standardize SN Ia magnitudes to ~0.12 mag. These are the first spectral metrics that improve over the standard normalization methods based upon light curve shape and color and they provide among the lowest scatter Hubble diagrams ever published.
Keywords
Cite
@article{arxiv.0905.0340,
title = {Using Spectral Flux Ratios to Standardize SN Ia Luminosities},
author = {S. Bailey and G. Aldering and P. Antilogus and C. Aragon and C. Baltay and S. Bongard and C. Buton and M. Childress and N. Chotard and Y. Copin and E. Gangler and S. Loken and P. Nugent and R. Pain and E. Pecontal and R. Pereira and S. Perlmutter and D. Rabinowitz and G. Rigaudier and K. Runge and R. Scalzo and G. Smadja and H. Swift and C. Tao and R. C. Thomas and C. Wu},
journal= {arXiv preprint arXiv:0905.0340},
year = {2015}
}
Comments
6 pages, 3 figures, 2 tables; accepted by A&A Letters; v2 fixed typos of literature SNe redshifts in table 2, final language and formatting edits, small improvements to literature SNe comparison