Lyα-emitting galaxies at z= 2.1: Stellar masses, dust, and star formation histories from spectral energy distribution fitting

We study the physical properties of 216 z ≃ 2.1 Lyα-emitting galaxies (LAEs) discovered in an ultra-deep narrow- MUSYC image of the ECDF-S. We fit their stacked spectral energy distribution (SED) using Charlot & Bruzual templates. We consider star formation histories (SFHs) parameterized by the e-folding time parameter τ, allowing for exponentially decreasing (τ > 0), exponentially increasing (τ < 0), and constant star formation rates (SFRs). We estimated the average flux at 5015 of our LAE sample, finding a non-detection, which translates into negligible He II line emission at z ≃ 2.1. In addition to this, the lack of high equivalent width (EW) Lyα line objects ruled out the hypothesis of a top-heavy initial mass function in LAEs. The typical LAEs of our sample are characterized by best-fit parameters and 68% confidence intervals of log(M_*/M_⊙)= 8.6[8.4-9.1], E(B - V) = 0.22[0.00-0.31], τ = -0.02[(- 4)-18]Gyr, and age_SF = 0.018[0.009-3]Gyr. Thus, we obtain robust measurements of low stellar mass and dust content, but we cannot place meaningful constraints on the age or SFH of the LAEs. We also calculate the instantaneous SFR to be 35[0.003-170] M_⊙ yr^-1, with its average over the last 100Myr before observation giving 〈SFR〉₁₀₀= 4[2-30] M _⊙ yr^-1. When we compare the results for the same SFH, typical LAEs at z ≃ 2.1 appear dustier and show higher instantaneous SFRs than z ≃ 3.1 LAEs, while the observed stellar masses of the two samples seem consistent. Because the majority are low-mass galaxies, our typical LAEs appear to occupy the low-mass end of the distribution of star-forming galaxies at z 2. We perform SED fitting on several sub-samples selected based on photometric properties and find that LAE sub-samples at z ≃ 2.1 exhibit heterogeneous properties. The typical IRAC-bright, UV-bright, and red LAEs have the largest stellar mass and dust reddening. The typical UV-faint, IRAC-faint, and high EW LAE sub-samples appear less massive (<10⁹ M _⊙) and less dusty, with E(B - V) consistent with zero.