The stellar population of a z ∼ 3.25 Ly α -emitting group associated with a damped Ly α absorber

We present near-infrared observations, acquired with the Wide Field Camera 3 (WFC3) on board the Hubble Space Telescope (HST), of a Lyα-emitting double-clumped nebula at z ≈ 3.25 associated with a damped Lyα absorber (DLA). With the WFC3/F160W data we observe the stellar continuum around 3600 å in the rest frame of a galaxy embedded in the west clump of the nebula, GW, for which we estimate a star formation rate (SFR) of SFRGjavax.xml.bind.JAXBElement@79b0480e = 5.0 ± 0.4 MȮ yr- 1 and a maximum stellar mass MGjavax.xml.bind.JAXBElement@79d096e1 < 9.9 ± 0.7 × 109 MȮ. 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 SFRGjavax.xml.bind.JAXBElement@543c74cf = 0.70 ± 0.20 MȮ yr- 1 and a maximum stellar mass MGjavax.xml.bind.JAXBElement@7f4ebd24 < 1.4 ± 0.4 × 109 MȮ. 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 means we cannot fully rule out the presence of additional fainter star-forming sources, which would further contribute to the photon budget inside this ≈ 1012 MȮ galaxy group that extends over a region of 30 × 50 kpc.