# An updated Type II supernova Hubble diagram

## TL;DR

This study refines the use of Type II supernovae as distance indicators by applying and updating the expanding photosphere and standardized candle methods with new high-redshift data, exploring alternative spectral velocity indicators and the potential of Type II-L SNe.

## Contribution

It provides updated Hubble diagrams for Type II SNe, introduces an epoch-dependent relation for spectral line velocities, and evaluates Type II-L SNe as potential distance indicators.

## Key findings

- Both EPM and SCM yield consistent distances.
- Type II-L SNe show promise as distance indicators.
- High-redshift SN II-P PS1-13bni confirms supernova utility in cosmology.

## Abstract

We present photometry and spectroscopy of nine Type II-P/L supernovae (SNe) with redshifts in the 0.045 < z < 0.335 range, with a view to re-examining their utility as distance indicators. Specifically, we apply the expanding photosphere method (EPM) and the standardized candle method (SCM) to each target, and find that both methods yield distances that are in reasonable agreement with each other. The current record-holder for the highest-redshift spectroscopically confirmed SN II-P is PS1-13bni (z = 0.335 +0.009 -0.012), and illustrates the promise of Type II SNe as cosmological tools. We updated existing EPM and SCM Hubble diagrams by adding our sample to those previously published. Within the context of Type II SN distance measuring techniques, we investigated two related questions. First, we explored the possibility of utilising spectral lines other than the traditionally used Fe II 5169 to infer the photospheric velocity of SN ejecta. Using local well-observed objects, we derive an epoch-dependent relation between the strong Balmer line and Fe II 5169 velocities that is applicable 30 to 40 days post-explosion. Motivated in part by the continuum of key observables such as rise time and decline rates exhibited from II-P to II-L SNe, we assessed the possibility of using Hubble-flow Type II-L SNe as distance indicators. These yield similar distances as the Type II-P SNe. Although these initial results are encouraging, a significantly larger sample of SNe II-L would be required to draw definitive conclusions.