The 24 micron source counts in deep Spitzer space telescope surveys

Galaxy source counts in the infrared provide strong constraints on the evolution of the bolometric energy output from distant galaxy populations. We present the results from deep 24 mum imaging from Spitzer surveys, which include approximate to5 x 10(4) sources to an 80% completeness of similar or equal to 60 muJy. The 24 mum counts rapidly rise at near-Euclidean rates down to 5 mJy, increase with a super-Euclidean rate between 0.4 and 4 mJy, and converge below similar to 0.3 mJy. The 24 mum counts exceed expectations from nonevolving models by a factor of greater than or similar to10 at S-nu similar to 0.1 mJy. The peak in the differential number counts corresponds to a population of faint sources that is not expected from predictions based on 15 mum counts from the Infrared Space Observatory. We argue that this implies the existence of a previously undetected population of infrared-luminous galaxies at z similar to 1-3. Integrating the counts to 60 muJy, we derive a lower limit on the 24 mum background intensity of 1.9 +/- 0.6 nW m(-2) sr(-1) of which the majority (similar to60%) stems from sources fainter than 0.4 mJy. Extrapolating to fainter flux densities, sources below 60 muJy contribute 0.8(-0.4)(+0.9) nW m(-2) sr(-1) to the background, which provides an estimate of the total 24 mum background of 2.7(-0.7)(+1.1) nW m(-2) sr(-1).