The stellar population of a z~3.25 Lyα emitting group associated with a damped Lyα absorber

We present near-infrared observations, acquired with the Wide Field Camera 3 (WFC3) on board of the Hubble Space Telescope (HST), of a Lyα double-clumped emitting nebula at z ≈ 3.25 associated with a damped Lyα absorber (DLA). With the WFC3/F160W data we observe the stellar continuum around $3600$ A in the rest frame for a galaxy embedded in the West clump of the nebula, GW, for which we estimate a star formation rate SFR_GW = 5.0 ± 0.4 M_ yr⁻¹ and maximum stellar mass M_GW < 9.9 ± 0.7 × 10⁹ M_. With the enhanced spatial resolution of HST, we discover the presence of an additional faint source, GE, in the center of the East clump, with a star formation rate of SFR_GE = 0.70 ± 0.20 M_ yr⁻¹ and maximum stellar mass M_GE < 1.4 ± 0.4 × 10⁹ M_. We show that the Lyα emission in the two clumps can be explained by recombination following in-situ photoionization by the two galaxies, assuming escape fractions of ionizing photons of 0.24 for GW and 0.34 for GE. The fact that GW is offset by ≈ 8 kpc from the West clump does not fully rule out the presence of additional fainter star-forming sources that would further contribute to the photon budget inside this ≈ 10¹² M_ galaxy group that extends over a region encompassing over 30 × 50 kpc.