SIMBAD references

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/arcmin2; [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 0.6<z<1.3 EROs and at least 22% of z>1.3 EROs are dusty star-forming galaxies.