Environment of the submillimeter-bright massive starburst HFLS3 at z 6.34

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We describe the search for Lyman-break galaxies (LBGs) near the sub-millimeter bright starburst galaxy HFLS3 at z=6.34 and a study on the environment of this massive galaxy during the end of reionization.We performed two independent selections of LBGs on images obtained with the Gran Telescopio Canarias (GTC) and the Hubble Space Telescope (HST) by combining non-detections in bands blueward of the Lyman-break and color selection. A total of 10 objects fulfilling the LBG selection criteria at z>5.5 were selected over the 4.54 and 55.5 arcmin² covered by our HST and GTC images, respectively. The photometric redshift, UV luminosity, and the star-formation rate of these sources were estimated with models of their spectral energy distribution. These z 6 candidates have physical properties and number densities in agreement with previous results. The UV luminosity function at z 6 and a Voronoi tessellation analysis of this field shows no strong evidence for an overdensity of relatively bright objects (mF₁₀₅W<25.9) associated with HFLS3. However, the over-density parameter deduced from this field and the surface density of objects can not excluded definitively the LBG over-density hypothesis. Moreover we identified three faint objects at less than three arcseconds from HFLS3 with color consistent with those expected for z 6 galaxies. Deeper data are needed to confirm their redshifts and to study their association with HFLS3 and the galaxy merger that may be responsible for the massive starburst.