Star formation rates and stellar masses of z=7-8 galaxies from IRAC observations of the WFC3/IR ERS and the HUDF field

Understand

We investigate the Spitzer/IRAC properties of 36 z~7 z-dropout galaxies and 3 z~8 Y-dropout galaxies derived from deep/wide-area WFC3/IR data of the Early Release Science, the ultradeep HUDF09, and wide-area NICMOS data.

• We fit stellar population synthesis models to the SEDs to derive mean redshifts, stellar masses, and ages.
• The z~7 galaxies are best characterized by substantial ages (>100 Myr) and M/L_V~0.2.
• The main trend with decreasing luminosity is that of bluing of the far-UV slope from beta~-2.0 to beta~-3.0.