Power spectrum analysis of far-IR background fluctuations in 160 μm maps from the multiband imaging photometer for spitzer

We describe data reduction and analysis of fluctuations in the cosmic far-IR background ( CFIB) in observations with the Multiband Imaging Photometer for Spitzer ( MIPS) instrument 160 m detectors. We analyzed observations of an 8.5 square degree region in the Lockman Hole, part of the largest low-cirrus mapping observation with this instrument. We measured the power spectrum of the CFIB in these observations by fitting a power law to the IR cirrus component, the dominant foreground contaminant, and subtracting this cirrus signal. The CFIB power spectrum in the range 0.2 arcmin(-1) < k < 0.5 arcmin(-1) is consistent with previous measurements of a relatively flat component. However, we find a large power excess at low k, which falls steeply to the flat component in the range 0.03 arcmin(-1) < k < 0.1 arcmin(-1). This low-k power spectrum excess is consistent with predictions of a source clustering "signature". This is the first report of such a detection in the far-IR.