The 24 Micron Source Counts in Deep Spitzer Space Telescope Surveys
نویسندگان
چکیده
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 m imaging from Spitzer surveys, which include 5 ;10 sources to an 80% completeness of ’60 Jy. The 24 m 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 0.3 mJy. The 24 m counts exceed expectations from nonevolving models by a factor of k10 at S 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 m counts from the Infrared Space Observatory. We argue that this implies the existence of a previously undetected population of infrared-luminous galaxies at z 1 3. Integrating the counts to 60 Jy, we derive a lower limit on the 24 m background intensity of 1:9 0:6 nW m 2 sr 1 of which the majority ( 60%) stems from sources fainter than 0.4 mJy. Extrapolating to fainter flux densities, sources below 60 Jy contribute 0:8þ0:9 0:4 nW m 2 sr 1 to the background, which provides an estimate of the total 24 m background of 2:7þ1:1 0:7 nW m 2 sr . Subject headings: cosmology: observations — galaxies: evolution — galaxies: high-redshift — galaxies: photometry — infrared: galaxies Online material: machine-readable table
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