Optical and near-infrared observations of the SPT2349-56 proto-cluster core at z = 4.3. (arXiv:2006.15345v4 [astro-ph.GA] UPDATED)

Optical and near-infrared observations of the SPT2349-56 proto-cluster core at z = 4.3. (arXiv:2006.15345v4 [astro-ph.GA] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Rotermund_K/0/1/0/all/0/1">K. M. Rotermund</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chapman_S/0/1/0/all/0/1">S. C. Chapman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Phadke_K/0/1/0/all/0/1">K. A. Phadke</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hill_R/0/1/0/all/0/1">R. Hill</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pass_E/0/1/0/all/0/1">E. Pass</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Aravena_M/0/1/0/all/0/1">M. Aravena</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ashby_M/0/1/0/all/0/1">M. L. N. Ashby</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Babul_A/0/1/0/all/0/1">A. Babul</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bethermin_M/0/1/0/all/0/1">M. B&#xe9;thermin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Canning_R/0/1/0/all/0/1">R. Canning</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Breuck_C/0/1/0/all/0/1">C. de Breuck</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dong_C/0/1/0/all/0/1">C. Dong</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gonzalez_A/0/1/0/all/0/1">A. H. Gonzalez</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hayward_C/0/1/0/all/0/1">C. C. Hayward</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jarugula_S/0/1/0/all/0/1">S. Jarugula</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Marrone_D/0/1/0/all/0/1">D. P. Marrone</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Narayanan_D/0/1/0/all/0/1">D. Narayanan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Reuter_C/0/1/0/all/0/1">C. Reuter</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Scott_D/0/1/0/all/0/1">D. Scott</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Spilker_J/0/1/0/all/0/1">J. S. Spilker</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Vieira_J/0/1/0/all/0/1">J. D. Vieira</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wang_G/0/1/0/all/0/1">G. Wang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Weiss_A/0/1/0/all/0/1">A. Weiss</a>

We present Gemini-S and {it Spitzer}-IRAC optical-through-near-IR
observations in the field of the SPT2349-56 proto-cluster at $z=4.3$. We detect
optical/IR counterparts for only nine of the 14 submillimetre galaxies (SMGs)
previously identified by ALMA in the core of SPT2349-56. In addition, we detect
four $zsim4$ Lyman-break galaxies (LBGs) in the 30 arcsec diameter region
surrounding this proto-cluster core. Three of the four LBGs are new systems,
while one appears to be a counterpart of one of the nine observed SMGs. We
identify a candidate brightest cluster galaxy (BCG) with a stellar mass of
$(3.2^{+2.5}_{-1.4})times10^{11},{rm M}_{odot}$. The stellar masses of the
eight other SMGs place them on, above, and below the main sequence of star
formation at $zapprox4.5$. The cumulative stellar mass for the SPT2349-56 core
is at least $(11.5pm2.9)times10^{11},{rm M}_{odot}$, a sizeable fraction
of the stellar mass in local BCGs, and close to the universal baryon fraction
(0.16) relative to the virial mass of the core ($10^{13},{rm M}_{odot}$). As
all 14 of these SMGs are destined to quickly merge, we conclude that the
proto-cluster core has already developed a significant stellar mass at this
early stage, comparable to $z=1$ BCGs. Importantly, we also find that the
SPT2349-56 core structure would be difficult to uncover in optical surveys,
with none of the ALMA sources being easily identifiable or constrained through
$g,r,$ and $i$ colour-selection in deep optical surveys and only a modest
overdensity of LBGs over the extended core structure. SPT2349-56 therefore
represents a truly dust-obscured phase of a massive cluster core under
formation.

We present Gemini-S and {it Spitzer}-IRAC optical-through-near-IR
observations in the field of the SPT2349-56 proto-cluster at $z=4.3$. We detect
optical/IR counterparts for only nine of the 14 submillimetre galaxies (SMGs)
previously identified by ALMA in the core of SPT2349-56. In addition, we detect
four $zsim4$ Lyman-break galaxies (LBGs) in the 30 arcsec diameter region
surrounding this proto-cluster core. Three of the four LBGs are new systems,
while one appears to be a counterpart of one of the nine observed SMGs. We
identify a candidate brightest cluster galaxy (BCG) with a stellar mass of
$(3.2^{+2.5}_{-1.4})times10^{11},{rm M}_{odot}$. The stellar masses of the
eight other SMGs place them on, above, and below the main sequence of star
formation at $zapprox4.5$. The cumulative stellar mass for the SPT2349-56 core
is at least $(11.5pm2.9)times10^{11},{rm M}_{odot}$, a sizeable fraction
of the stellar mass in local BCGs, and close to the universal baryon fraction
(0.16) relative to the virial mass of the core ($10^{13},{rm M}_{odot}$). As
all 14 of these SMGs are destined to quickly merge, we conclude that the
proto-cluster core has already developed a significant stellar mass at this
early stage, comparable to $z=1$ BCGs. Importantly, we also find that the
SPT2349-56 core structure would be difficult to uncover in optical surveys,
with none of the ALMA sources being easily identifiable or constrained through
$g,r,$ and $i$ colour-selection in deep optical surveys and only a modest
overdensity of LBGs over the extended core structure. SPT2349-56 therefore
represents a truly dust-obscured phase of a massive cluster core under
formation.

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