Star formation, morphologies and clustering of galaxies in a radio galaxy protocluster at z=4.1

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Abstract
We present HST/ACS griz and VLT K observations towards the radio galaxy TN J1338-1942 and 12 Lya emitters (LAEs) at z=4.1. The LAEs are young (a few 10^7 yr), dust-free galaxies based on small sizes, steep UV slopes and blue UV-optical colors with SFRs of <14 M/yr. When stacking the K-band fluxes, the LAEs seem to be less massive (masses of a few 10^8 Msun) than LBGs while having comparable UV SFRs. The LAE AGN fraction is minimal. We selected 66 z~4.1 g-dropouts with z<27. Their SFRs, sizes, morphological parameters, and UV/optical color-magnitude relations are all similar to those found for LBGs in the `field'. We quantify the number density and cosmic variance of g-dropouts using the GOODS survey, and show that our field is significantly richer than random fields. About half of the objects are clustered in a filamentary region that includes the radio galaxy and the brightest LBGs. The generally fainter LAEs appear to favour regions that are devoid of LBGs, while LBGs detected in K tend to lie in the richest region, suggesting a forming age- or mass-density relation. We compare the angular correlation function to that of mock samples with built-in z~4 LBG clustering. We find an excess signal at separations of 10^14 Msun structure,possibly a `protocluster'.

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