A Hubble diagram from Type II Supernovae based solely on photometry: the Photometric-Colour Method

TL;DR

This paper introduces a photometric-only method to construct a Hubble diagram using Type II supernovae, achieving competitive accuracy without spectral data, crucial for future large-scale surveys.

Contribution

The study develops the Photometric-Colour Method (PCM) for Type II supernovae, enabling distance measurements solely from photometry with reduced dispersion.

Findings

Dispersion of 0.44 mag with PCM using $(V-i)$ colour and $r$ band.

Reduced dispersion to 0.39 mag with the golden sample.

Comparison shows PCM has higher dispersion than the spectroscopic SCM.

Abstract

We present a Hubble diagram of type II supernovae using corrected magnitudes derived only from photometry, with no input of spectral information. We use a data set from the Carnegie Supernovae Project I (CSP) for which optical and near-infrared light-curves were obtained. The apparent magnitude is corrected by two observables, one corresponding to the slope of the plateau in the $V$ band and the second a colour term. We obtain a dispersion of 0.44 mag using a combination of the $(V-i)$ colour and the $r$ band and we are able to reduce the dispersion to 0.39 mag using our golden sample. A comparison of our photometric colour method (PCM) with the standardised candle method (SCM) is also performed. The dispersion obtained for the SCM (which uses both photometric and spectroscopic information) is 0.29 mag which compares with 0.43 mag from the PCM, for the same SN sample. The construction of a photometric Hubble diagram is of high importance in the coming era of large photometric wide-field surveys, which will increase the detection rate of supernovae by orders of magnitude. Such numbers will prohibit spectroscopic follow-up in the vast majority of cases, and hence methods must be deployed which can proceed using solely photometric data.