Tomography of the environment of the COSMOS/AzTEC-3 submillimeter galaxy
  at z=5.3 revealed by Lyalpha and MUSE observations
  We study the members of the protocluster around AzTEC3 submillimeter galaxy
at z=5.3. We analyzed the data from the MUSE instrument in an area of 1.4x1.4
arcmin^2 around AzTEC3 and derived information on the Lya line in emission. We
compared the Lya profile of various regions of the environment with the zELDA
radiative transfer model, revealing the neutral gas distribution and
kinematics. We identified 10 Lya emitting sources, including 2 regions with
extended emission: one embedding AzTEC3 and LBG3, a star-forming galaxy located
12 kpc north of the SMG and another toward LBG-1, a star-forming galaxy located
90 kpc to the southeast. The sources appear distributed in an elongated
configuration of about 70'' in extent. The number of sources confirms the
overdensity around AzTEC3. For the AzTEC3+LBG3 system, the Lya emission appears
redshifted and more spatially extended than the [CII] line emission. Similarly,
the Lya line spectrum is broader in velocity than [CII] for LBG1. In the former
spectrum, the Lya emission is elongated to the north of LBG3 and to the south
of AzTEC3, where a faint Lya emitting galaxy is also located. The elongated
structures could resemble tidal features due to the interaction of the two
galaxies with AzTEC3. Also, we find a bridge of gas, revealed by the Lya
emission between AzTEC3 and LBG3. The Lya emission toward LBG1 embeds its three
components. The HI kinematics support the idea of a merger of the three
components. Given the availability of CO and [CII] observations from previous
campaigns, and our Lya information, we find evidence of starburst-driven
phenomena and interactions around AzTEC-3. The stellar mass of the galaxies of
the overdensity and the Lya luminosity of the HI nebula associated with AzTEC-3
imply a dark matter halo of 10^12 Msun at z=5.3 that could evolve into a
cluster of 2x10^14 Msun at z=0.
