Title: An updated Type II supernova Hubble diagram,
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.