We present Spitzer/IRAC observations of nine z ^ { \prime } -band dropouts highly magnified ( 2 \lesssim \mu \lesssim 12 ) by the Bullet Cluster .
We combine archival imaging with our Exploratory program ( SURFS UP ) , which results in a total integration time of \sim 30 hr per IRAC band .
We detect ( \gtrsim 3 \sigma ) in both IRAC bands the brightest of these high-redshift galaxies , with [ 3.6 ] = 23.80 \pm 0.28 mag , [ 4.5 ] = 23.78 \pm 0.25 mag , and ( H - [ 3.6 ] ) = 1.17 \pm 0.32 mag .
The remaining eight galaxies are undetected to [ 3.6 ] \sim 26.4 mag and [ 4.5 ] \sim 26.0 mag with stellar masses of \sim 5 \times 10 ^ { 7 } M _ { \odot } .
The detected galaxy has an estimated magnification of \mu = 12 \pm 4 , which implies this galaxy has an ultraviolet luminosity of L _ { 1500 } \sim 0.3 L ^ { * } _ { z = 7 } — the lowest luminosity individual source detected in IRAC at z \gtrsim 7 .
By modeling the broadband photometry , we estimate the galaxy has an intrinsic star-formation rate of \mbox { SFR } \sim 1.3 ~ { } \mbox { M } _ { \odot } yr ^ { -1 } and stellar mass of M \sim 2.0 \times 10 ^ { 9 } ~ { } \mbox { M } _ { \odot } , which gives a specific star-formation rate of { sSFR } \sim 0.7 Gyr ^ { -1 } .
If this galaxy had sustained this star-formation rate since z \sim 20 , it could have formed the observed stellar mass ( to within a factor of \sim 2 ) , we also discuss alternate star-formation histories and argue the exponentially-increasing model is unlikely .
Finally , based on the intrinsic star-formation rate , we estimate this galaxy has a likely [ C ii ] flux of \langle f _ { [ \mbox { C~ { } { \tiny II } } ] } \rangle = 1.6 ~ { } \mbox { mJy } .