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

¹ Eureka Scientific, Inc., 2452 Delmer Street Suite 100, Oakland, CA 94602-3017, USA e-mail: Bruce_Grossan@lbl.gov
² Institute for Nuclear and Particle Astrophysics, 50R-5008, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720-8158, USA e-mail: Bruce_Grossan@lbl.gov
³ University of California at Berkeley, Department of Physics, LeConte Hall, Berkeley, CA 94720, USA
⁴ 50-5005, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720-8158, USA e-mail: GFSmoot@lbl.gov

Received: 24 April 2006
Accepted: 29 August 2007

Abstract

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 μm 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.