The ALPINE-ALMA [C II] survey: a triple merger at z ∼ 4.56

January 2020 • 2020MNRAS.491L..18J

Authors • Jones, G. C. • Béthermin, M. • Fudamoto, Y. • Ginolfi, M. • Capak, P. • Cassata, P. • Faisst, A. • Le Fèvre, O. • Schaerer, D. • Silverman, J. D. • Yan, Lin • Bardelli, S. • Boquien, M. • Cimatti, A. • Dessauges-Zavadsky, M. • Giavalisco, M. • Gruppioni, C. • Ibar, E. • Khusanova, Y. • Koekemoer, A. M. • Lemaux, B. C. • Loiacono, F. • Maiolino, R. • Oesch, P. A. • Pozzi, F. • Riechers, D. • Rodighiero, G. • Talia, M. • Vallini, L. • Vergani, D. • Zamorani, G. • Zucca, E.

Abstract • We report the detection of [C II] λ158 μm emission from a system of three closely separated sources in the Cosmic Evolution Survey (COSMOS) field at z ∼ 4.56 , as part of the Atacama Large Millimeter/submillimeter Array (ALMA) Large Program to INvestigate C II at Early times (ALPINE). The two most luminous sources are closely associated, both spatially (1.6 arcsec ∼ 11 kpc) and in velocity (∼100 km s^-1), while the third source is slightly more distant (2.8 arcsec ∼ 18 kpc, ∼300 km s^-1). The second most luminous source features a slight velocity gradient, while no significant velocity gradient is seen in the other two sources. Using the observed [C II] luminosities, we derive a total log_{10}(SFR_{[C II]} [M_{⊙} yr^{-1}])=2.8± 0.2, which may be split into contributions of 59, 31, and 10 per cent from the central, east, and west sources, respectively. Comparison of these [C II] detections to recent zoom-in cosmological simulations suggests an ongoing major merger. We are thus witnessing a system in a major phase of mass build-up by merging, including an ongoing major merger and an upcoming minor merger, which is expected to end up in a single massive galaxy by z ∼ 2.5.

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Andreas Faisst

Assistant Scientist