MEASURING THE STELLAR MASSES OF z ∼ 7 GALAXIES WITH THE SPITZER ULTRAFAINT SURVEY PROGRAM (SURFS UP)

We present Spitzer/IRAC observations of nine z-band dropouts highly magnified (2 [ ~] 7. By modeling the broadband photometry, we estimate the galaxy has an intrinsic star formation rate (SFR) of SFR ~ 1.3 M sub([miidot in circle]) yr super(-1) and stellar mass of M ~ 2.0 x 10 super(9) M sub(middot in circle]), which gives a specific star formation rate of sSFR ~ 0.7 Gyr super(-1). If this galaxy had sustained this SFR since z ~ 20, it could have formed the observed stellar mass (to within a factor of ~2). We also discuss alternate star formation histories and argue that the exponentially increasing model is unlikely. Finally, based on the intrinsic SFR, we estimate that this galaxy has a likely [CII] flux of [left angle bracket][functionof] sub([CII])[right angle bracket] = 1.6mJy.