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Published September 2004 | Published + Submitted
Journal Article Open

Extragalactic Source Counts at 24 Microns in the Spitzer First Look Survey


We present the Spitzer Multiband Imaging Photometer 24 μm source counts in the Extragalactic First Look Survey (FLS) main, verification, and European Large Area ISO Survey N1 fields. Spitzer's increased sensitivity and efficiency in large areal coverage over previous infrared telescopes, coupled with the enhanced sensitivity of the 24 μm band to sources at intermediate redshift, dramatically improve the quality and statistics of number counts in the mid-infrared. The FLS observations cover areas of 4.4, 0.26, and 0.015 deg^2, respectively, and reach 3 σ depths of 0.11, 0.08, and 0.03 mJy. The extragalactic counts derived for each survey agree remarkably well. The counts can be fitted by a super-Euclidean power law of index α = -2.9 from 0.2 to 0.9 mJy, with a flattening of the counts at fluxes fainter than 0.2 mJy. Comparison with infrared galaxy evolution models reveals a peak's displacement in the 24 μm counts. This is probably due to the detection of a new population of galaxies with redshift between 1 and 2, previously unseen in the 15 μm deep counts.

Additional Information

© 2004 The American Astronomical Society. Received 2004 March 29; accepted 2004 May 13. We thank A. Noriega-Crespo for useful discussions and the referee M. Malkan for insightful comments. We are grateful to H. Dole and A. Franceschini for providing us with their model predictions. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407. Support for this work was provided by NASA through an award issued by JPL/Caltech.

Attached Files

Published - Marleau_2004_ApJS_154_66.pdf

Submitted - 0405635.pdf


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