Programme by Session

The extragalactic background light (EBL) is defined as the total flux received today from all sources of photon production since the epoch of recombination. Understanding this form of energy is essential as it encodes all energy production pathways.

Here, we measure the energy output from discrete components in the universe, i.e. galaxies, using the input catalogue for the Wide Area VISTA Extragalactic Survey (WAVES, Driver et al. 2015) a deep spectroscopic campaign on 4MOST. We calculate galaxy number counts in 9 bandpasses (0.4 micron - 2.1 micron) and model the EBL contribution from these resolved extragalactic sources. We compare our results obtained from discrete integrated galaxy counts (IGL) to that measured from very high energy (VHE) astrophysics, which samples all photons. A comparison between our measurements and the total EBL from VHE represents the fraction of photons arising from diffuse components in the Universe, and provides an estimate of the total missing mass in galaxy samples.

Currently, the uncertainty in the IGL measurements is 20%, of which the most dominant component is caused by cosmic variance. This is comparable to the predicted difference between IGL and VHE measured. Adding data from the WAVES input catalogue which is the combination of the ESO VIKING+KiDS datasets covering ~1200 sq_deg of the extragalactic sky, are essential in reducing this error component. With significantly reduced errors the comparison between our IGL measurements and those derived from VHE will allow us to parameterise the total missing mass in galaxy samples for the very first time.