We present a study of three Ly \alpha emitting galaxies ( LAEs ) , selected via a narrow-band survey in the GOODS northern field , and spectroscopically confirmed to have redshifts of z \sim 5.65 .
Using HST ACS and Spitzer IRAC data , we constrain the rest-frame UV-to-optical spectral energy distributions ( SEDs ) of the galaxies .
Fitting stellar population synthesis models to the observed SEDs , we find best-fit stellar populations with masses between \sim 10 ^ { 9 } -10 ^ { 10 } { M } _ { \sun } and ages between \sim 5 - 100 Myr , assuming a simple starburst star formation history .
However , stellar populations as old as 700 Myr are admissible if a constant star formation rate model is considered .
Very deep near-IR observations may help to narrow the range of allowed models by providing extra constraints on the rest-frame UV spectral slope .
Our narrow-band selected objects and other IRAC-detected z \sim 6 i ^ { \prime } -dropout galaxies have similar 3.6 µm magnitudes and z ^ { \prime } - [ 3.6 ] colors , suggesting that they posses stellar populations of similar masses and ages .
This similarity may be the result of a selection bias , since the IRAC-detected LAEs and i ^ { \prime } -dropouts probably only sample the bright end of the luminosity function .
On the other hand , our LAEs have blue i ^ { \prime } - z ^ { \prime } colors compared to the i ^ { \prime } -dropouts , and would have been missed by the i ^ { \prime } -dropout selection criterion .
A better understanding of the overlap between the LAE and the i ^ { \prime } -dropout populations is necessary in order to constrain the properties of the overall high-redshift galaxy population , such as the total stellar mass density at z \sim 6 .