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Cold gas studies of a z = 2.5 protocluster

Published online by Cambridge University Press:  29 March 2021

Minju M. Lee Open the ORCID record for Minju M. Lee [Opens in a new window] ,
Ichi Tanaka  and
Rohei Kawabe
Minju M. Lee
Affiliation:
Max-Planck-Institut für Extraterrestrische Physik (MPE), Giessenbachstr. 1, D-85748 Garching, Germany
Ichi Tanaka
Affiliation:
Subaru Telescope, National Astronomical Observatory of Japan, 650 North Aohoku Place, Hilo, HI 96720, USA
Rohei Kawabe
Affiliation:
National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan The Graduate University for Advanced Studies (SOKENDAI), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan Department of Astronomy, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan
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Abstract

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We present studies of a protocluster at z =2.5, an overdense region found close to a radio galaxy, 4C 23.56, using ALMA. We observed 1.1 mm continuum, two CO lines (CO (4–3) and CO (3–2)) and the lower atomic carbon line transition ([CI](3P1-3P0)) at a few kpc (0″.3-0″.9) resolution. The primary targets are 25 star-forming galaxies selected as Hα emitters (HAEs) that are identified with a narrow band filter. These are massive galaxies with stellar masses of > 1010 Mʘ that are mostly on the galaxy main sequence at z =2.5. We measure the molecular gas mass from the independent gas tracers of 1.1 mm, CO (3–2) and [CI], and investigate the gas kinematics of galaxies from CO (4–3). Molecular gas masses from the different measurements are consistent with each other for detection, with a gas fraction (fgas = Mgas/(Mgas+ Mstar)) of ≃ 0.5 on average but with a caveat. On the other hand, the CO line widths of the protocluster galaxies are typically broader by ˜50% compared to field galaxies, which can be attributed to more frequent, unresolved gas-rich mergers and/or smaller sizes than field galaxies, supported by our high-resolution images and a kinematic model fit of one of the galaxies. We discuss the expected scenario of galaxy evolution in protoclusters at high redshift but future large surveys are needed to get a more general view.

Keywords

galaxies: clusters: generalgalaxies: evolutiongalaxies: high-redshiftgalaxies: ISMgalaxies: kinematics and dynamicslarge-scale structure of universe
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 15 , Symposium S359: Galaxy Evolution and Feedback across Different Environments , March 2019 , pp. 136 - 140
Copyright
© The Author(s), 2021. Published by Cambridge University Press on behalf of International Astronomical Union

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