Large Scale Structure at 24 Microns in the SWIRE Survey

Abstract

We present initial results of galaxy clustering at 24μm by analyzing statistics of the projected galaxy distribution from counts-in-cells. This study focuses on the ELAIS-North1 SWIRE field. The sample covers ≃5.9 deg^2 and contains 24,715 sources detected at 24μm to a 5.6σ limit of 250μJy (in the lowest coverage regions). We have explored clustering as a function of 3.6 - 24μm and 24μm flux density using angular-averaged two-point correlation functions derived from the variance of counts-in-cells on scales 0°.05-0°.7. Using a power-law parameterization, w_2(θ)=A(θ/deg)^(1-γ), we find [A,γ] = [(5.43±0.20)×10^(-4),2.01±0.02] for the full sample (1σ errors throughout). We have inverted Limber's equation and estimated a spatial correlation length of r_0=3.32±0.19 h^(-1)Mpc for the full sample, assuming stable clustering and a redshift model consistent with observed 24μm counts. We also find that blue [f_ν(24)/f_ν(3.6)≤5.5] and red [f_ν(24)/f_ν(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). 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.

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