We use data taken as part of HST/WFC3 observations of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey ( CANDELS ) to identify massive and evolved galaxies at 3 < z < 4.5 .
This is performed using the strength of the Balmer break feature at rest-frame 3648Å , which is a diagnostic of the age of the stellar population in galaxies .
Using WFC3 H-band selected catalog for the CANDELS GOODS-S field and deep multi-waveband photometry from optical ( HST ) to mid-infrared ( Spitzer ) wavelengths , we identify a population of old and evolved post-starburst galaxies based on the strength of their Balmer breaks ( Balmer Break Galaxies- BBGs ) .
The galaxies are also selected to be bright in rest-frame near-IR wavelengths and hence , massive .
We identify a total of 16 BBGs .
Fitting the spectral energy distribution ( SED ) of the BBGs show that the candidate galaxies have average estimated ages of \sim 800 Myr and average stellar masses of \sim 5 \times 10 ^ { 10 } M _ { \odot } , consistent with being old and massive systems .
Two of our BBG candidates are also identified by the criteria that is sensitive to star forming galaxies ( LBG selection ) .
We find a number density of \sim 3.2 \times 10 ^ { -5 } \ > Mpc ^ { -3 } for the BBGs corresponding to a mass density of \sim 2.0 \times 10 ^ { 6 } \ > M _ { \odot } / Mpc ^ { 3 } in the redshift range covering the survey .
Given the old age and the passive evolution , it is argued that some of these objects formed the bulk of their mass only a few hundred million years after the Big Bang .