Gravitational lensing effects on sub-millimetre galaxy counts

TL;DR

This paper investigates how gravitational lensing influences sub-millimetre galaxy counts, focusing on halo properties, cosmological parameters, and a two-halo population model, confirming lensing as a key factor in observed excess counts.

Contribution

It introduces a simplified, realistic model incorporating halo profiles and a two-population approach to better understand lensing effects on galaxy counts.

Findings

Ellipticity has minimal impact on magnification cross section.

Halo density profiles significantly affect lensing probabilities.

Lensing explains the excess in bright sub-millimetre galaxy counts.

Abstract

We study the effects on the number counts of sub-millimetre galaxies due to gravitational lensing. We explore the effects on the magnification cross section due to halo density profiles, ellipticity and cosmological parameter (the power-spectrum normalisation $\sigma_8$). We show that the ellipticity does not strongly affect the magnification cross section in gravitational lensing while the halo radial profiles do. Since the baryonic cooling effect is stronger in galaxies than clusters, galactic haloes are more concentrated. In light of this, a new scenario of two halo population model is explored where galaxies are modeled as a singular isothermal sphere profile and clusters as a Navarro, Frenk and White (NFW) profile. We find the transition mass between the two has modest effects on the lensing probability. The cosmological parameter $\sigma_8$ alters the abundance of haloes and therefore affects our results. Compared with other methods, our model is simpler and more realistic. The conclusions of previous works is confirm that gravitational lensing is a natural explanation for the number count excess at the bright end.