2006AJ....132.1405S

We present Spitzer Space Telescope observations of the well-studied extremely red objects (EROs) HR 10 and LBDS 53W091 from 3.6 to 160 µm. These galaxies are the prototypes of the two primary classes of EROs: dusty starbursts and old, evolved galaxies, respectively. Both galaxies, as well as LBDS 53W069, another example of an old, quiescent galaxy, are well detected out to 8 µm. However, only the dusty starburst HR 10 is detected in the far-infrared. All three EROs have stellar masses of a fewx10¹¹ M_☉. Using evolutionary model fits to their multiband photometry, we predict the infrared colors of similar EROs at 1<z<2. We find that blueward of observed 10 µm, the two ERO classes are virtually indistinguishable photometrically. Deep spectroscopy and 24 µm data allow the classes to be separated.