The Carnegie Supernova Project: Absolute Calibration and the Hubble Constant

TL;DR

This paper refines the calibration of Type Ia supernovae luminosities using new color relations, investigates their use for precise distance measurements, and estimates the Hubble constant as approximately 73 km/s/Mpc.

Contribution

It introduces improved intrinsic color relations for SNeIa, assesses the impact of host galaxy mass, and provides a new estimate of the Hubble constant based on the Carnegie Supernova Project data.

Findings

Intrinsic scatter in luminosity-decline-rate relation is 0.13-0.18 mag.

Hubble constant estimated at 73.2 km/s/Mpc with optical/NIR data.

Host galaxy mass effect decreases at redder wavelengths.

Abstract

We present an analysis of the final data release of the Carnegie Supernova Project I, focusing on the absolute calibration of the luminosity-decline-rate relation for Type Ia supernovae (SNeIa) using new intrinsic color relations with respect to the color-stretch parameter, $s_{BV}$, enabling improved dust extinction corrections. We investigate to what degree the so-called fast-declining SNeIa can be used to determine accurate extragalactic distances. We estimate the intrinsic scatter in the luminosity-decline-rate relation, and find it ranges from $\pm 0.13$ mag to $\pm 0.18$ mag with no obvious dependence on wavelength. Using the Cepheid variable star data from the SH0ES project (Riess et al., 2016), the SNIa distance scale is calibrated and the Hubble constant is estimated using our optical and near-infrared sample, and these results are compared to those determined exclusively from a near-infrared sub-sample. The systematic effect of the supernova's host galaxy mass is investigated as a function of wavelength and is found to decrease toward redder wavelengths, suggesting this effect may be due to dust properties of the host. Using estimates of the dust extinction derived from optical and NIR wavelengths, and applying these to H band, we derive a Hubble constant $H_0 = 73.2 \pm 2.3$ km/s/Mpc, whereas using a simple $B-V$ color-correction applied to B band yields $H_0 = 72.7 \pm 2.1$ km/s/Mpc. Photometry of two calibrating SNeIa from the CSP-II sample, SN2012ht and SN2015F, is presented and used to improve the calibration of the SNIa distance ladder.