SIMBAD references

We present ultradeep Spitzer 70 µm observations of GOODS-North (Great Observatories Origins Deep Survey). For the first time, the turnover in the 70 µm 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 µm source counts of dN/dS∝S^–1.6, consistent with that observed for the faint 24 µm sources. An extrapolation of the 70 µm source counts to zero flux density implies a total extragalactic background light (EBL) of 7.4±1.9 nW./m2/sr. 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 σ_c=0.30±0.15 mJy (q=5) for the Spitzer 70 µm band.