Extremely Red Objects in the Lockman Hole

Wilson, G., Huang, J.-S., Pérez-González, P. G., Egami, E., Ivison, R. J., Rigby, J. R., Alonso-Herrero, A., Barmby, P., Dole, H., Fazio, G. G., Le Floc'h, E., Papovich, C., Rigopoulou, D., Bai, L., Engelbracht, C. W., Frayer, D., Gordon, K. D., Hines, D. C., Misselt, K. A., Miyazaki, S., Morrison, J. E., Rieke, G. H., Rieke, M. J., & Surace, J.
2004, The Astrophysical Journal Supplement Series, 154, 107

We investigate extremely red objects (EROs) using near- and mid-infrared observations in five passbands (3.6 to 24 μm) obtained from the Spitzer Space Telescope, and deep ground-based R and K imaging. The great sensitivity of the Infrared Array Camera (IRAC) camera allows us to detect 64 EROs (a surface density of 2.90+/-0.36 arcmin-2 [3.6]AB<23.7) in only 12 minutes of IRAC exposure time, by means of an R-[3.6] color cut (analogous to the traditional red R-K cut). A pure infrared K-[3.6] red cut detects a somewhat different population and may be more effective at selecting z>1.3 EROs. We find ~17% of all galaxies detected by IRAC at 3.6 or 4.5 μm to be EROs. These percentages rise to about 40% at 5.8 μm, and about 60% at 8.0 μm. We utilize the spectral bump at 1.6 μm to divide the EROs into broad redshift slices using only near-infrared colors (2.2/3.6/4.5 μm). We conclude that two-thirds of all EROs lie at redshift z>1.3. Detections at 24 μm imply that at least 11% of 0.61.3 EROs are dusty star-forming galaxies.


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