A census of the stellar content in the protocluster core SPT2349$-$56 at $z,{=},4.3$. (arXiv:2109.04534v1 [astro-ph.GA])

A census of the stellar content in the protocluster core SPT2349$-$56 at $z,{=},4.3$. (arXiv:2109.04534v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Hill_R/0/1/0/all/0/1">Ryley Hill</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chapman_S/0/1/0/all/0/1">Scott Chapman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Phadke_K/0/1/0/all/0/1">Kedar A. Phadke</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Aravena_M/0/1/0/all/0/1">Manuel Aravena</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Archipley_M/0/1/0/all/0/1">Melanie Archipley</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bethermin_M/0/1/0/all/0/1">Matthieu Bethermin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Canning_R/0/1/0/all/0/1">Rebecca E. A. Canning</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gonzalez_A/0/1/0/all/0/1">Anthony Gonzalez</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Greve_T/0/1/0/all/0/1">Thomas R. Greve</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gururajan_G/0/1/0/all/0/1">Gayathri Gururajan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hayward_C/0/1/0/all/0/1">Christopher C. Hayward</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hezaveh_Y/0/1/0/all/0/1">Yashar Hezaveh</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jarugula_S/0/1/0/all/0/1">Sreevani Jarugula</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Marrone_D/0/1/0/all/0/1">Daniel P. Marrone</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Miller_T/0/1/0/all/0/1">Tim Miller</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Reuter_C/0/1/0/all/0/1">Cassie Reuter</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rotermund_K/0/1/0/all/0/1">Kaja Rotermund</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Scott_D/0/1/0/all/0/1">Douglas Scott</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Spilker_J/0/1/0/all/0/1">Justin Spilker</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Vieira_J/0/1/0/all/0/1">Joaquin D. Vieira</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wang_G/0/1/0/all/0/1">George Wang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Weiss_A/0/1/0/all/0/1">Axel Weiss</a>

The protocluster core SPT2349$-$56 at $z,{=},4.3$ is one of the most
actively star-forming regions known, yet constraints on the total stellar mass
of this system are highly uncertain. We have therefore carried out deep optical
and infrared observations of this system, probing rest-frame ultraviolet to
infrared wavelengths. Using the positions of the spectroscopically-confirmed
protocluster members, we identify counterparts and perform detailed source
deblending, allowing us to fit spectral energy distributions in order to
estimate stellar masses. We show that the galaxies in SPT2349$-$56 have stellar
masses proportional to their high star-formation rates, consistent with other
protocluster galaxies and field submillimetre galaxies (SMGs) around redshift
4. The galaxies in SPT2349$-$56 have on average lower molecular gas-to-stellar
mass fractions and depletion timescales than field SMGs, although with
considerable scatter. We construct the stellar-mass function for SPT2349$-$56
and compare it to the stellar-mass function of $z,{=},1$ galaxy clusters,
finding both to be best described by a Schechter function. We measure
rest-frame ultraviolet half-light radii from our {it HST/}-F160W imaging,
finding that on average the galaxies in our sample are similar in size to
typical star-forming galaxies around the same redshift. However, the brightest
{it HST/}-detected galaxy in our sample, found near the luminosity-weighted
centre of the protocluster core, remains unresolved at this wavelength.
Hydrodynamical simulations predict that the core galaxies will quickly merge
into a brightest cluster galaxy, thus our observations provide a direct view of
the early formation mechanisms of this class of object.

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