Large Scale Structure at 24 Microns in the SWIRE Survey


Abstract in English

We present initial results of galaxy clustering at 24um by analyzing statistics of the projected galaxy distribution from counts-in-cells. This study focuses on the ELAIS-N1 SWIRE field. The sample covers ~5.9 square-degrees and contains 24,715 sources detected at 24um to a 5.6-sigma limit of 250 micro-Jy (in the lowest coverage regions). We have explored clustering as a function of 3.6 - 24um color and 24um flux density using angular-averaged two-point correlation functions derived from the variance of counts-in-cells on scales 0.05-0.7 degrees. Using a power-law parameterization, $w_{2}(theta)=A(theta/deg)^{1-gamma}$, we find [A,gamma] = [(5.43pm0.20)times10^{-4},2.01pm0.02] for the full sample (1-sigma errors throughout). We have inverted Limbers equation and estimated a spatial correlation length of $r_{0}=3.32pm0.19 h^{-1}$Mpc for the full sample, assuming stable clustering and a redshift model consistent with observed 24um counts. We also find that blue [f(24)/f(3.6)<=5.5] and red [f(24)/f(3.6)>=6.5] galaxies have the lowest and highest $r_{0}$ values respectively, implying that redder galaxies are more clustered (by a factor of ~3 on scales >0.2 degree). Overall, the clustering estimates are smaller than those derived from optical surveys, but in agreement with results from IRAS and ISO in the mid-infrared. This extends the notion to higher redshifts that infrared selected surveys show weaker clustering than optical surveys.

Download