Abstract
The Time Domain Extragalactic Survey (TiDES) conducted on the 4-metre
Multi-Object Spectroscopic Telescope (4MOST) will perform spectroscopic
follow-up of extragalactic transients discovered in the era of the NSF-DOE Vera
C. Rubin Observatory. TiDES will conduct a 5-year survey, covering
${>}14\,000\,\mathrm{square\, degrees}$, and use around 250 000 fibre hours to
address three main science goals: (i) spectroscopic observations of ${>}30 000$
live transients, (ii) comprehensive follow-up of ${>}200 000$ host galaxies to
obtain redshift measurements, and (iii) repeat spectroscopic observations of
Active Galactic Nuclei to enable reverberation mapping studies. The live
spectra from TiDES will be used to reveal the diversity and astrophysics of
both normal and exotic supernovae across the luminosity-timescale plane. The
extensive host-galaxy redshift campaign will allow exploitation of the larger
sample of supernovae and improve photometric classification, providing the
largest-ever sample of spec-confirmed type Ia supernovae, capable of a sub-2
per cent measurement of the equation-of-state of dark energy. Finally, the
TiDES reverberation mapping experiment of 700--1\,000 AGN will complement the
SN Ia sample and extend the Hubble diagram to $z\sim2.5$