To Stack or Not to Stack: Spectral Energy Distribution Properties of
  Lya-Emitting Galaxies at z=2.1
  We use the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey
(CANDELS) GOODS-S multi-wavelength catalog to identify counterparts for 20 Lya
Emitting (LAE) galaxies at z=2.1. We build several types of stacked Spectral
Energy Distributions (SEDs) of these objects. We combine photometry to form
average and median flux-stacked SEDs, and postage stamp images to form average
and median image-stacked SEDs. We also introduce scaled flux stacks that
eliminate the influence of variation in overall brightness. We use the SED
fitting code SpeedyMC to constrain the physical properties of individual
objects and stacks. Our LAEs at z = 2.1 have stellar masses ranging from 2x10^7
Msun - 8x10^9 Msun (median = 3x10^8 Msun), ages ranging from 4 Myr to 500 Myr
(median =100 Myr), and E(B-V) between 0.02 and 0.24 (median = 0.12). We do not
observe strong correlations between Lya equivalent width (EW) and stellar mass,
age, or E(B-V). The Lya radiative transfer (q) factors of our sample are
predominantly close to one and do not correlate strongly with EW or E(B-V),
implying that Lya radiative transfer prevents Lya photons from resonantly
scattering in dusty regions. The SED parameters of the flux stacks match the
average and median values of the individual objects, with the flux-scaled
median SED performing best with reduced uncertainties. Median image-stacked
SEDs provide a poor representation of the median individual object, and none of
the stacking methods captures the large dispersion of LAE properties.
