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The ALPINE-ALMA [CII] survey. The contribution of major mergers to the galaxy mass assembly at z ∼ 5

Romano, M. and Cassata, P. and Morselli, L. and Jones, G. C. and Ginolfi, M. and Zanella, A. and Béthermin, M. and Capak, P. and Faisst, A. and Le Fèvre, O. and Schaerer, D. and Silverman, J. D. and Yan, L. and Bardelli, S. and Boquien, M. and Cimatti, A. and Dessauges-Zavadsky, M. and Enia, A. and Fujimoto, S. and Gruppioni, C. and Hathi, N. P. and Ibar, E. and Koekemoer, A. M. and Lemaux, B. C. and Rodighiero, G. and Vergani, D. and Zamorani, G. and Zucca, E. (2021) The ALPINE-ALMA [CII] survey. The contribution of major mergers to the galaxy mass assembly at z ∼ 5. Astronomy and Astrophysics, 653 . Art. No. A111. ISSN 0004-6361. doi:10.1051/0004-6361/202141306.

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Context. Galaxy mergers are thought to be one of the main mechanisms of the mass assembly of galaxies in the Universe, but there is still little direct observational evidence of how frequent they are at z ≳ 4. Recently, many works have suggested a possible increase in the fraction of major mergers in the early Universe, reviving the debate on which processes (e.g., cold accretion, star formation, mergers) most contribute to the mass build-up of galaxies through cosmic time. Aims. To estimate the importance of major mergers in this context, we make use of the new data collected by the ALMA Large Program to INvestigate [CII] at Early times (ALPINE) survey, which attempted to observe the [CII] 158 μm emission line from a sample of 75 main-sequence star-forming galaxies at 4.4 <  z <  5.9. Methods. We used, for the first time, the morpho-kinematic information provided by the [CII] emission, along with archival multiwavelength data to obtain the fraction of major mergers (f_(MM)) at z ∼ 5. By combining the results from ALPINE with those at lower redshifts from the literature, we also studied the evolution of the merger fraction through cosmic time. We then used different redshift-evolving merger timescales (T_(MM)) to convert this fraction into the merger rate per galaxy (R_(MM)) and in the volume-averaged merger rate (Γ_(MM)). Results. We find a merger fraction of f_(MM) ∼ 0.44 (0.34) at z ∼ 4.5 (5.5) from ALPINE. By combining our results with those at lower redshifts, we computed the cosmic evolution of the merger fraction which is described by a rapid increase from the local Universe to higher redshifts, a peak at z ∼ 3, and a slow decrease toward earlier epochs. Depending on the timescale prescription used, this fraction translates into a merger rate ranging between ∼0.1 and ∼4.0 Gyr⁻¹ at z ∼ 5, which in turn corresponds to an average number of major mergers per galaxy between 1 and 8 in ∼12.5 yr (from z = 6 to the local Universe). When convolved with the galaxy number density at different epochs, the merger rate density becomes approximately constant over time at 1 <  z < 4, including values from 10⁻⁴ to 10⁻³ Gyr−1 Mpc⁻³, depending on the assumed T_(MM). We finally compare the specific star formation and star-formation rate density with the analogous quantities from major mergers, finding a good agreement at z > 4 if we assume a merger timescale that quickly decreases with increasing redshift. Conclusions. Our new constraints on the merger fraction from the ALPINE survey at z ∼ 5 reveal the presence of a significant merging activity in the early Universe. Whether this population of mergers can provide a relevant contribution to the galaxy mass assembly at these redshifts and through the cosmic epochs is strongly dependent on the assumption of the merger timescale. However, our results show that an evolving T_(MM) ∝ (1 + z)⁻² agrees well with state-of-the-art cosmological simulations, suggesting a considerable role of mergers in the build-up of galaxies at early times.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Romano, M.0000-0002-9948-3916
Cassata, P.0000-0002-6716-4400
Morselli, L.0000-0003-0753-2571
Jones, G. C.0000-0002-0267-9024
Ginolfi, M.0000-0002-8231-821X
Zanella, A.0000-0001-8600-7008
Béthermin, M.0000-0002-3915-2015
Capak, P.0000-0003-3578-6843
Faisst, A.0000-0002-9382-9832
Le Fèvre, O.0000-0001-5891-2596
Schaerer, D.0000-0001-7144-7182
Silverman, J. D.0000-0002-0000-6977
Yan, L.0000-0003-1710-9339
Bardelli, S.0000-0002-8900-0298
Boquien, M.0000-0003-0946-6176
Cimatti, A.0000-0002-4409-5633
Dessauges-Zavadsky, M.0000-0003-0348-2917
Enia, A.0000-0002-0200-2857
Fujimoto, S.0000-0001-7201-5066
Gruppioni, C.0000-0002-5836-4056
Hathi, N. P.0000-0001-6145-5090
Koekemoer, A. M.0000-0002-6610-2048
Lemaux, B. C.0000-0002-1428-7036
Rodighiero, G.0000-0002-9415-2296
Vergani, D.0000-0003-0898-2216
Zamorani, G.0000-0002-2318-301X
Zucca, E.0000-0002-5845-8132
Additional Information:© ESO 2021. Article published by EDP Sciences. Received 13 May 2021; Accepted 22 July 2021; Published online 21 September 2021. We warmly thank the referee for her or his careful reading of the paper and constructive suggestions that contributed to improve the quality of this work. This paper is based on data obtained with the ALMA Observatory, under Large Program 2017.1.00428.L. ALMA is a partnership of ESO (representing its member states), NSF(USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. A. C. acknowledges the support from grant PRINMIUR 2017 – 20173ML3WW_s. The Cosmic Dawn Center is funded by the Danish National Research Foundation under grant No. 140. G. C. J. acknowledges ERC Advanced Grant 695671 “QUENCH” and support by the Science and Technology Facilities Council (STFC). This work was supported by the Programme National Cosmology et Galaxies (PNCG) of CNRS/INSU with INP and IN2P3, co-funded by CEA and CNES. E. I. acknowledges partial support from FONDECYT through grant N° 1171710. This paper is dedicated to the memory of Olivier Le Fèvre, PI of the ALPINE survey.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Ministero dell'Istruzione, dell'Universita e della Ricerca (MIUR)20173ML3WW_s
Danish National Research Foundation140
European Research Council (ERC)695671
Science and Technology Facilities Council (STFC)UNSPECIFIED
Programme National Galaxies et Cosmologie (PNCG)UNSPECIFIED
Centre National de la Recherche Scientifique (CNRS)UNSPECIFIED
Institut National des Sciences de l'Univers (INSU)UNSPECIFIED
Institut National de Physique Nucléaire et de Physique des Particules (IN2P3)UNSPECIFIED
Commissariat a l'Energie Atomique (CEA)UNSPECIFIED
Centre National d'Études Spatiales (CNES)UNSPECIFIED
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1171710
Subject Keywords:galaxies: evolution – galaxies: formation – galaxies: high-redshift – galaxies: kinematics and dynamics – early Universe
Record Number:CaltechAUTHORS:20211020-145122379
Persistent URL:
Official Citation:The ALPINE-ALMA [CII] survey - The contribution of major mergers to the galaxy mass assembly at z ∼ 5. M. Romano, P. Cassata, L. Morselli, G. C. Jones, M. Ginolfi, A. Zanella, M. Béthermin, P. Capak, A. Faisst, O. Le Fèvre, D. Schaerer, J. D. Silverman, L. Yan, S. Bardelli, M. Boquien, A. Cimatti, M. Dessauges-Zavadsky, A. Enia, S. Fujimoto, C. Gruppioni, N. P. Hathi, E. Ibar, A. M. Koekemoer, B. C. Lemaux, G. Rodighiero, D. Vergani, G. Zamorani and E. Zucca. A&A, 653 (2021) A111; DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:111551
Deposited By: Tony Diaz
Deposited On:20 Oct 2021 22:52
Last Modified:21 Oct 2021 16:30

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