Unraveling the link between Type II supernova luminosity and host galaxy velocity dispersion

Type II supernovae (SNe II) have emerged as valuable cosmological probes, serving as alternative and independent tools to Type Ia supernova (SN Ia) cosmology. However, the Hubble diagram dispersion for SNe II is significantly larger than for SNe Ia. In this study, we investigate the SN II luminosity and the host galaxy velocity dispersion with the purpose of improving the scatter in the SN II Hubble diagram. We selected a sample of SNe II discovered by the Dark Energy Survey (DES), and we measured the spectra of their host galaxies using the VLT/FORS2 and Magellan-Baade/MagE spectrographs. From those galaxy spectra, we calculated the stellar velocity dispersion in the central region. Using the effective Sérsic radius from the DES imaging, we standardized the velocity dispersion values to a common aperture. From their i-band light curves, we determined a characteristic plateau brightness for our SNe. For this purpose, we developed an algorithm designed to parameterize the plateau phase. After computing the SN absolute magnitudes using the standard cosmology, we found a modest correlation with the host galaxy velocity dispersion ($R^2=0.57$). These findings could significantly contribute to SN II cosmology, paving the way for SNe II as more robust cosmological probes.