Physical properties of a Coma-analog protocluster at z = 6.5

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Chanchaiworawitk, Krittapas
Guzmán, Rafael
Salvador-Solé, Eduard
Calvi, Rosa
Manrique, Alberto
Herrero, Artemio
Marín-Franch, Antonio
Mas-Hesse, Miguel
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We present evidence for the discovery of a protocluster of starburst galaxies (Lyα emitters, or LAEs) near the end of the epoch of reionization. The recent trend in the search for high-redshift protoclusters focuses on utilizing bias tracers, such as luminous starburst galaxies, as signposts of overdensities. Thus, we conducted a photometric selection of LAE candidates around a pair of spatially close, luminous LAEs at z = 6.5 in the Subaru/XMM-Newton Deep Survey field, using OSIRIS in its imaging mode at the 10.4 m Gran Telescopio Canarias in La Palma, Spain. The spectroscopic follow-up was done with OSIRIS in its multiobject spectroscopy capability. We have spectroscopically confirmed 10 LAEs via their recognizable Lyα emission feature. The redshifts of these LAEs shed light on their 3D distributions within the observing window defined by the photometric selection. We have derived the galaxy number density contrast of δ_(gal) = 3.18_(-1.99)^(+3.47), which led to the expected mass of the overdensity of 8.40 _(-1.39)^(+2.98) x 10^(14) Mꙩ. We also found evidence for the presence of a virialized core with M_(200) = 4.06_(-1.90)^(+2.77) x 10^(13) Mꙩ within this overdensity. Based on the extended Press–Schechter formalism, this overdensity would continue to grow in the linear regime and collapse to form a galaxy cluster at z_(coll) = 0.84_(-0.43)^(+0.57). By the time this protocluster reaches z = 0, it will be a massive cluster of galaxies with mass 1.54_(-0.69)^(+1.12) x 10^(15) Mꙩ, comparable to the Coma cluster. Thus, our careful analysis has pointed to evidence that this protocluster would evolve into a Coma-analog cluster in the present-day universe.
© 2019. The American Astronomical Society. We are grateful for all of the referee’s suggestions and comments, which greatly improved the scientific quality and information flow of this work. K.C. would like to recognize and thank the Royal Thai Government Scholarship in the section of the Ministry of Sciences & Technologies for the National Astronomical Research Institute of Thailand (NARIT) and the University of Florida’s Graduate School Doctoral Dissertation Award for guidance and financial support during the phase of completing this work and his thesis. E.S.S. acknowledges funding and support from the Spanish MINECO under the projects MDM-2014-0369 of ICCUB (Unidad de Excelencia “María de Maeztu”), AYA2015-70498-C02-2-R and AYA2017-88085-R (both cofunded with FEDER funds), and the Catalan DEC grant 2017SGR643. R.C. and J.M.R.E. acknowledge support from the Spanish Ministry of Science under grant AYA2015-70498-C2-1. J.M.R.E. also acknowledges support from the Spanish Ministry of Science through grant AYA2017-84061-P. R.C., J.M.R.E., and A.H. acknowledge the Spanish Ministry of Science’s support through the Severo Ochoa grant SEV2015-0548. A.H. acknowledges support by the Spanish Ministry of Science through grant AYA2015-68012-C2-1 and by the Gobierno de Canarias through grant ProID2017010115. J.G. acknowledges support by the Spanish Ministry of Science through grant AYA2016- 75808-R. J.M.M.H. is partially funded by Spanish State Research Agency grants ESP2017-87676-C5-1-R and MDM2017-0737 (Unidad de Excelencia ‘María de Maeztu’ CAB).
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