FOUR IRAC SOURCES WITH AN EXTREMELY RED H – 3.6 COLOR: PASSIVE OR DUSTY GALAXIES ATz> 4.5?

We report detection of four IRAC sources in the GOODS-South field with an extremely red color of H-3. 6>4. 5. The four sources are not detected in the deep HST WFC3 H-band image with H₋₈₌₈ₓ=28. 3 mag. We find that only 3 types of SED templates can produce such a red H-3. 6 color: a very dusty SED with the Calzetti extinction of AV=16 mag at z=0. 8; a very dusty SED with the SMC extinction of AV=8 mag at z=2. 02. 2; and an 1Gyr SSP with AV 0. 8 at z=5. 7. We argue that these sources are unlikely dusty galaxies at z2. 2 based on absent strong MIPS 24m emission. The old stellar population model at z>4. 5 remains a possible solution for the 4 sources. At z>4. 5, these sources have stellar masses of Log (M_*/M_) =10. 611. 2. One source, ERS-1, is also a type-II X-ray QSO with L₂-₈₊₄ₕ=1. 6 10^44 erg s^-1. One of the four sources is an X-ray QSO and another one is a HyperLIRG, suggesting a galaxy-merging scenario for the formation of these massive galaxies at high redshifts.