Limiting the dimming of distant type Ia supernovae

Abstract

Distant supernovae have been observed to be fainter than what is expected in a matterdominated universe. The most likely explanation is that the universe is dominated by anenergy component with negative pressure, namely dark energy. However, there are severalastrophysical processes that could, in principle, affect the measurements andin order to be able to take advantage of the growing supernova statistics, thecontrol of systematic effects is crucial. We discuss two of these; extinction due tointergalactic grey dust and dimming due to photon–axion oscillations and show howtheir effect on supernova observations can be constrained using observed quasarcolours and spectra. For a wide range of intergalactic dust models, we are ableto rule out any dimming larger than 0.2 magnitudes for a type Ia supernova atz = 1. The corresponding limit for intergalactic Milky Way type dust is 0.03 magnitudes. For themore speculative model of photons mixing with axions, we find that the effect isindependent of photon energy for certain combinations of parameter values and a dimmingas large as 0.6 magnitudes cannot be ruled out. These effects can have profoundimplications for the possibility of constraining dark energy properties using supernovaobservations.