We study the stellar population properties of the IRAC-detected 6 \lesssim z \lesssim 10 galaxy candidates from the Spitzer UltRa Faint SUrvey Program ( SURFS UP ) .
Using the Lyman Break selection technique , we find a total of 17 galaxy candidates at 6 \lesssim z \lesssim 10 from HST images ( including the full-depth images from the Hubble Frontier Fields program for MACS1149 and MACS0717 ) that have detections at S / N \geq 3 in at least one of the IRAC 3.6 \mu m and 4.5 \mu m channels .
According to the best mass models available for the surveyed galaxy clusters , these IRAC-detected galaxy candidates are magnified by factors of \sim 1.2 – 5.5 .
Due to the magnification of the foreground galaxy clusters , the rest-frame UV absolute magnitudes M _ { 1600 } are between -21.2 and -18.9 mag , while their intrinsic stellar masses are between 2 \times 10 ^ { 8 } M _ { \odot } and 2.9 \times 10 ^ { 9 } M _ { \odot } .
We identify two Ly \alpha emitters in our sample from the Keck DEIMOS spectra , one at z _ { \text { Ly } \alpha } = 6.76 ( in RXJ1347 ) and one at z _ { \text { Ly } \alpha } = 6.32 ( in MACS0454 ) .
We find that 4 out of 17 z \gtrsim 6 galaxy candidates are favored by z \lesssim 1 solutions when IRAC fluxes are included in photometric redshift fitting .
We also show that IRAC [ 3.6 ] - [ 4.5 ] color , when combined with photometric redshift , can be used to identify galaxies likely with strong nebular emission lines or have obscured AGN contributions within certain redshift windows .