Abstract
Early-time spectroscopy of supernovae (SNe), acquired within days of
explosion, yields crucial insights into their outermost ejecta layers,
facilitating the study of their environments, progenitor systems, and explosion
mechanisms. Recent efforts in early discovery and follow-up of SNe have shown
the potential insights that can be gained from early-time spectra. The
Time-Domain Extragalactic Survey (TiDES), conducted with the 4-meter
Multi-Object Spectroscopic Telescope (4MOST), will provide spectroscopic
follow-up of transients discovered by the Legacy Survey of Space and Time
(LSST). Current simulations indicate that early-time spectroscopic studies
conducted with TiDES data will be limited by the current SN selection criteria.
To enhance TiDES's capability for early-time SN spectroscopic studies, we
propose an additional set of selection criteria focusing on early-time (young)
SNe (YSNe). Utilising the Zwicky Transient Facility live transient alerts, we
developed criteria to select YSNe while minimising the sample's contamination
rate to 28 percent. The developed criteria were applied to LSST simulations,
yielding a sample of 1167 Deep Drilling Field survey SNe and 67388 Wide Fast
Deep survey SNe for follow-up with 4MOST. We demonstrate that our criteria
enables the selection of SNe at early-times, enhancing TiDES's future
early-time spectroscopic SN studies. Finally, we investigated 4MOST-like
observing strategies to increase the sample of spectroscopically observed YSNe.
We propose that a 4MOST-like observing strategy that follows LSST with a delay
of 3 days is optimal for the TiDES SN survey, while a 1 day delay is most
optimal for enhancing the early-time science in conjunction with our YSN
selection criteria.