HOLISMOKES: XVIII. Cosmology with strongly lensed type II supernovae: Effects of instrumental setups on H0

The upcoming Rubin Observatory and subsequent follow-up observations should improve the determination of the Hubble constant (H0) via time-delay cosmography of strongly lensed type II supernovae (LSNe II), by enabling the detection of many more such events. In our previous work, we developed a method for determining the supernova (SN) phase from spectral absorption features. Because obtaining spectra of faint targets such as distant SN II is expensive, we examined how low-resolution spectra influence the precision of time-delay retrieval, and consequently the precision on H0. We considered spectral resolutions R = λ/∆λ R = λ ∆ λ between 100 and 250, and we investigated three signal-to-noise ratio (S/N) values of 10, 15, and 20, for each resolution. Furthermore, we forecast the precision on H0 achievable with S/N = 10 and compared the observing time required to reach it with ground-based and space-based facilities. We find that the time delay can be determined without bias and with uncertainties as low as 1.3 days for the investigated resolutions and S/N values when we combine time-delay measurements of multiple absorption lines. For a typical LSN II system (absolute magnitude ∼−17 mag in the rest-frame V band, source redshift of zs = 0.8), the required exposure times range from multiple hours for ground-based observations to a few minutes for space-based observations with the JWST. Our predictions on the precision of H0 for a single lensed SN range from 14.2% for R = 100 and S/N = 10 to 7.5% for R = 250 and S/N = 20, enabling a 1% determination of H0 from ∼20 lensed SNe in the coming years.