The total infrared luminosity may significantly overestimate the star
  formation rate of recently quenched galaxies
  The total infrared (IR) luminosity is very useful for estimating the star
formation rate (SFR) of galaxies, but converting the IR luminosity into an SFR
relies on assumptions that do not hold for all galaxies. We test the
effectiveness of the IR luminosity as an SFR indicator by applying it to
synthetic spectral energy distributions generated from three-dimensional
hydrodynamical simulations of isolated disc galaxies and galaxy mergers. In
general, the SFR inferred from the IR luminosity agrees well with the true
instantaneous SFR of the simulated galaxies. However, for the major mergers in
which a strong starburst is induced, the SFR inferred from the IR luminosity
can overestimate the instantaneous SFR during the post-starburst phase by
greater than two orders of magnitude. Even though the instantaneous SFR
decreases rapidly after the starburst, the stars that were formed in the
starburst remain dust-obscured and thus produce significant IR luminosity.
Consequently, use of the IR luminosity as an SFR indicator may cause one to
conclude that post-starburst galaxies are still star-forming, whereas in
reality, star formation was recently quenched.
