Spitzer 70 micron source counts in GOODS-North

We present ultradeep Spitzer 70 mu m observations of GOODS-North (Great Observatories Origins Deep Survey). For the first time, the turnover in the 70 mu m Euclidean-normalized differential source counts is observed. We derive source counts down to a flux density of 1.2 mJy. From the measured source counts and fluctuation analysis, we estimate a power-law approximation of the faint 70 mu m source counts of dN/dS proportional to S-1.6, consistent with that observed for the faint 24 mm sources. An extrapolation of the 70 mm source counts to zero flux density implies a total extragalactic background light (EBL) of 7.4 +/- 1.9 nW m(-2) sr(-1). The source counts above 1.2 mJy account for about 60% of the estimated EBL. From fluctuation analysis, we derive a photometric confusion level of sigma(c) = 0.30 +/- 0.15 mJy (q = 5) for the Spitzer 70 mu m band.