The clustering and number counts of galaxies

Abstract

We present a Curtis Schmidt CCD survey of two strips of the sky overlapping with the NGC and SGC 2dFGRS fields. When this survey is used in conjunction with data from the APM Galaxy Survey, DUKST, 2dFGRS and 2MASS, we find that there is a hole in the SGC distribution of galaxies of 100 x60 in angular extent which extends to z~0.1. The magnitude of this galaxy number deficiency is 30% . The two-point correlation function for our CTIO data is calculated and we find that there is excess power in our SGC function with the break occurring on larger angular scales relative to that in the NGC. When we take into account the effect of the integral constraint we find that a power law form of the two-point correlation function extending beyond ~100h(^-1) Mpc cannot be ruled out, and we show that this kind of pure power law behaviour is an example of what might be needed to explain the hole we claim exists in the SGC distribution of galaxies. We also find evidence of bias from the fact that the galaxy number deficiency in the 2dF SGC n(z) is greater when more instrinsically luminous galaxies are sampled. We also investigate the clustering properties of a sample of faint blue galaxies at z=l-2 and are able to use our CTIO clustering results in order to constrain the galaxy correlation length in the local Universe where we find that r(_0)=4.7h(^-1)Mpc. By parametrising the clustering evolution using the clustering growth parameter ϵ, we find that our faint blue galaxies are consistent with an ϵ=0.1 model, which corresponds to a scenario where clustering is approximately fixed in proper coordinates. Finally, we investigate whether the presence of dust in such faint blue galaxies could have an impact in the sub-mm wave-band. We show that by using either a 1/ƛ or Calzetti absorption law for the dust and re-distributing the evolved spiral galaxy ultraviolet (UV) radiation into the far infrared (FIR), we can account for all of the 'faint'(≤ ImJy) 850μm galaxy counts and a significant proportion of the sub-mm extra-galactic background.