Kavli Affiliate: Roberto Maiolino
| First 5 Authors: Santiago Arribas, Michele Perna, Bruno Rodríguez Del Pino, Isabella Lamperti, Francesco D’Eugenio
| Summary:
The SPT0311-58 system resides in a massive dark matter halo at z ~ 6.9. It
hosts two dusty galaxies (E and W) with a combined star formation rate (SFR) of
~3500 Msun/yr. Its surrounding field exhibits an overdensity of sub-mm sources,
making it a candidate proto-cluster. We use spatially-resolved spectroscopy
provided by the JWST/NIRSpec Integral Field Unit (IFU) to probe a field of view
(FoV) ~ 17 x 17 kpc^2 around this object, with a spatial resolution ~ 0.5 kpc.
These observations have revealed ten new galaxies at z ~ 6.9, characterised
by dynamical masses spanning from ~10^9 to 10^10 Msun and a range in radial
velocities of ~ 1500 km/s, in addition to the already known E and W galaxies.
The implied large number density, and the wide spread in velocities, indicate
that SPT0311-58 is at the core of a proto-cluster, immersed in a very massive
dark matter halo of ~ 6 x 10^12 Msun. We study the dynamical stage of the
system and find that it likely is not fully virialized, although most of the
galaxies are gravitationally bound to the halo. The galaxies exhibit a great
diversity of properties. We derive their ongoing Halpha-based unobscured SFR,
and find that its contribution to the total SF varies significantly across the
galaxies in the system. Their ionization conditions range from those typical of
galaxies at similar redshift recently studied with JWST to those found in lower
redshift objects. The metallicity spans more than 0.8 dex across the FoV,
reaching in some cases nearly solar values. The detailed IFU spectroscopy of
the E galaxy reveals that it is actively assembling its stellar mass, showing a
metallicity gradient (~ 0.1 dex/kpc) that can be explained by accretion of low
metallicity gas from the intergalactic medium. The kinematic maps indicate
departures from regular rotation, high turbulence, and a possible pre-collision
minor merger. (Abridged)
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