The ALPINE-ALMA [C II] survey: Star-formation-driven outflows and circumgalactic enrichment in the early Universe

¹ Observatoire de Genève, Universitè de Genève, 51 Ch. des Maillettes, 1290 Versoix, Switzerland
e-mail: michele.ginolfi@unige.ch
² Cavendish Laboratory, University of Cambridge, 19 J. J. Thomson Ave., Cambridge CB3 0HE, UK
³ Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁴ Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
⁵ Osservatorio di Astrofisica e Scienza dello Spazio – Istituto Nazionale di Astrofisica, Via Gobetti 93/3, 40129 Bologna, Italy
⁶ University of Bologna, Department of Physics and Astronomy (DIFA), Via Gobetti 93/2, 40129 Bologna, Italy
⁷ Institute for Cosmic Ray Research, The University of Tokyo, Kashiwa-no-ha, Kashiwa 277-8582, Japan
⁸ Department of Astronomy, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan
⁹ IPAC, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA
¹⁰ University of Padova, Department of Physics and Astronomy, Vicolo Osservatorio 3, 35122 Padova, Italy
¹¹ Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI), The University of Tokyo, Kashiwa 277-8583, Japan
¹² Caltech Optical Observatories, Cahill Center for Astronomy and Astrophysics, 1200 East California Boulevard, Pasadena, CA 91125, USA
¹³ Centro de Astronomia (CITEVA), Universidad de Antofagasta, Avenida Angamos 601, Antofagasta, Chile
¹⁴ Instituto de Fisica y Astronomia, Universidad de Valparaiso, Gran Bretana 1111, Playa Ancha, Valparaiso, Chile
¹⁵ Department of Physics and Astronomy, University of Massachusetts, Amherst, MA 01003, USA
¹⁶ Department of Physics, University of California, Davis, One Shields Ave., Davis, CA 95616, USA
¹⁷ Department of Astronomy, University of Florida, 211 Bryant Space Sciences Center, Gainesville, FL 32611, USA
¹⁸ Cosmic Dawn Center (DAWN), Denmark
¹⁹ Niels Bohr Institute, University of Copenhagen, Lyngbyvej 2, 2100 Copenhagen, Denmark
²⁰ Leiden Observatory, Leiden University, PO Box 9500, 2300 RA Leiden, The Netherlands

Received: 8 October 2019
Accepted: 15 November 2019

Abstract

We study the efficiency of galactic feedback in the early Universe by stacking the [C II] 158 μm emission in a large sample of normal star-forming galaxies at 4 <  z <  6 from the ALMA Large Program to INvestigate [C II] at Early times (ALPINE) survey. Searching for typical signatures of outflows in the high-velocity tails of the stacked [C II] profile, we observe (i) deviations from a single-component Gaussian model in the combined residuals and (ii) broad emission in the stacked [C II] spectrum, with velocities of |v|≲500 km s⁻¹. The significance of these features increases when stacking the subset of galaxies with star formation rates (SFRs) higher than the median (SFR_med = 25 M_⊙ yr⁻¹), thus confirming their star-formation-driven nature. The estimated mass outflow rates are comparable to the SFRs, yielding mass-loading factors of the order of unity (similarly to local star-forming galaxies), suggesting that star-formation-driven feedback may play a lesser role in quenching galaxies at z >  4. From the stacking analysis of the datacubes, we find that the combined [C II] core emission (|v|< 200 km s⁻¹) of the higher-SFR galaxies is extended on physical sizes of ∼30 kpc (diameter scale), well beyond the analogous [C II] core emission of lower-SFR galaxies and the stacked far-infrared continuum. The detection of such extended metal-enriched gas, likely tracing circumgalactic gas enriched by past outflows, corroborates previous similar studies, confirming that baryon cycle and gas exchanges with the circumgalactic medium are at work in normal star-forming galaxies already at early epochs.