Galaxy Counts at 24 Microns in the SWIRE Fields
Abstract
This paper presents galaxy source counts at 24 microns in the six Spitzer Wide-field InfraRed Extragalactic (SWIRE) fields. The source counts are compared to counts in other fields, and to model predictions that have been updated since the launch of Spitzer. This analysis confirms a very steep rise in the Euclidean-normalized differential number counts between 2 mJy and 0.3 mJy. Variations in the counts between fields show the effects of sample variance in the flux range 0.5-10 mJy, up to 100% larger than Poisson errors. Nonetheless, a "shoulder" in the normalized counts persists at around 3 mJy. The peak of the normalized counts at 0.3 mJy is higher and narrower than most models predict. In the ELAIS N1 field, the 24 micron data are combined with Spitzer-IRAC data and five-band optical imaging, and these bandmerged data are fit with photometric redshift templates. Above 1 mJy the counts are dominated by galaxies at z less than 0.3. By 300 microJy, about 25% are between z ~ 0.3-0.8, and a significant fraction are at z ~ 1.3-2. At low redshifts the counts are dominated by spirals, and starbursts rise in number density to outnumber the spirals' contribution to the counts below 1 mJy.
Keywords
Cite
@article{arxiv.0711.2026,
title = {Galaxy Counts at 24 Microns in the SWIRE Fields},
author = {David L. Shupe and Michael Rowan-Robinson and Carol J. Lonsdale and Frank Masci and Tracey Evans and Fan Fang and Sebastian Oliver and Mattia Vaccari and Giulia Rodighiero and Deborah Padgett and Jason A. Surace and C. Kevin Xu and Stefano Berta and Francesca Pozzi and Alberto Franceschini and Thomas Babbedge and Eduardo Gonzales-Solares and Brian D. Siana and Duncan Farrah and David T. Frayer and H. E. Smith and Maria Polletta and Frazer Owen and Ismael Perez-Fournon},
journal= {arXiv preprint arXiv:0711.2026},
year = {2009}
}
Comments
10 pages, 8 figures, accepted 3 November 2007 for publication in The Astronomical Journal, formatted with emulateapj style