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The ALPINE-ALMA [C II] survey. Small Lyα-[C II] velocity offsets in main-sequence galaxies at 4.4 < z < 6

Cassata, P. and Morselli, L. and Faisst, A. and Ginolfi, M. and Béthermin, M. and Capak, P. and Le Fevre, O. and Schaerer, D. and Silverman, J. and Yan, L. and Lemaux, B. C. and Romano, M. and Talia, M. and Bardelli, S. and Boquien, M. and Cimatti, A. and Dessauges-Zavadsky, M. and Fudamoto, Y. and Fujimoto, S. and Giavalisco, M. and Hathi, N. P. and Ibar, E. and Jones, G. and Koekemoer, A. M. and Méndez-Hernández, H. and Mancini, C. and Oesch, P. A. and Pozzi, F. and Riechers, D. A. and Rodighiero, G. and Vergani, D. and Zamorani, G. and Zucca, E. (2020) The ALPINE-ALMA [C II] survey. Small Lyα-[C II] velocity offsets in main-sequence galaxies at 4.4 < z < 6. Astronomy and Astrophysics, 643 . Art. No. A6. ISSN 0004-6361.

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Context. The Lyman-α line in the ultraviolet (UV) and the [C II] line in the far-infrared (FIR) are widely used tools to identify galaxies in the early Universe and to obtain insights into interstellar medium (ISM) properties in high-redshift galaxies. By combining data obtained with ALMA in band 7 at ∼320 GHz as part of the ALMA Large Program to INvestigate [C II] at Early Times (ALPINE) with spectroscopic data from DEIMOS at the Keck Observatory, VIMOS and FORS2 at the Very Large Telescope, we assembled a unique sample of 53 main-sequence star-forming galaxies at 4.4 <  z <  6 in which we detect both the Lyman-α line in the UV and the [C II] line in the FIR. Aims. The goal of this paper is to constrain the properties of the Lyα emission in these galaxies in relation to other properties of the ISM. Methods. We used [C II], observed with ALMA, as a tracer of the systemic velocity of the galaxies, and we exploited the available optical spectroscopy to obtain the Lyα-[C II] and ISM-[C II] velocity offsets. Results. We find that 90% of the selected objects have Lyα-[C II] velocity offsets in the range 0 <  Δv_(Lyα − [C II]) < 400 km s⁻¹, in line with the few measurements available so far in the early Universe, and significantly smaller than those observed at lower redshifts. At the same time, we observe ISM-[C II] offsets in the range −500 <  Δv_(ISM−[C II]) <  0 km s⁻¹, in line with values at all redshifts, which we interpret as evidence for outflows in these galaxies. We find significant anticorrelations between Δv_(Lyα−[C II]) and the Lyα rest-frame equivalent width EW₀(Lyα) (or equivalently, the Lyα escape fraction f_(esc)(Lyα)): galaxies that show smaller Δv_(Lyα−[C II]) have larger EW₀(Lyα) and f_(esc)(Lyα). Conclusions. We interpret these results in the framework of available models for the radiative transfer of Lyα photons. According to the models, the escape of Lyα photons would be favored in galaxies with high outflow velocities, producing large EW₀(Lyα) and small Δv_(Lyα-[C II]), in agreement with our observations. The uniform shell model would also predict that the Lyα escape in galaxies with slow outflows (0 <  v_(out) <  300 km s⁻¹) is mainly determined by the neutral hydrogen column density (NHI) along the line of sight, while the alternative model by Steidel et al. (2010, ApJ, 717, 289) would more highly favor a combination of NHI at the systemic velocity and covering fraction as driver of the Lyα escape. We suggest that the increase in Lyα escape that is observed in the literature between z ∼ 2 and z ∼ 6 is not due to a higher incidence of fast outflows at high redshift, but rather to a decrease in average NHI along the line of sight, or alternatively, a decrease in HI covering fraction.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Cassata, P.0000-0002-6716-4400
Morselli, L.0000-0003-0753-2571
Faisst, A.0000-0002-9382-9832
Ginolfi, M.0000-0002-8231-821X
Béthermin, M.0000-0002-3915-2015
Capak, P.0000-0003-3578-6843
Le Fevre, O.0000-0001-5891-2596
Schaerer, D.0000-0001-7144-7182
Silverman, J.0000-0002-0000-6977
Yan, L.0000-0003-1710-9339
Lemaux, B. C.0000-0002-1428-7036
Romano, M.0000-0002-9948-3916
Talia, M.0000-0003-4352-2063
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
Fudamoto, Y.0000-0001-7440-8832
Fujimoto, S.0000-0001-7201-5066
Giavalisco, M.0000-0002-7831-8751
Hathi, N. P.0000-0001-6145-5090
Koekemoer, A. M.0000-0002-6610-2048
Méndez-Hernández, H.0000-0003-3057-9677
Mancini, C.0000-0002-4297-0561
Oesch, P. A.0000-0001-5851-6649
Pozzi, F.0000-0002-7412-647X
Riechers, D. A.0000-0001-9585-1462
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:© 2020 ESO. Article published by EDP Sciences. Received 16 January 2020; Accepted 14 June 2020; Published online 27 October 2020. This paper is dedicated to the memory of Olivier Le Fèvre, PI of the ALPINE survey. This paper is based on data obtained with the ALMA observatory, under the 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. Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under ESO programme ID 179.A-2005 and on data products produced by CALET and the Cambridge Astronomy Survey Unit on behalf of the UltraVISTA consortium. A significant fraction of the spectrographic data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. We thank the indigenous Hawaiian community for allowing us to be guests on their sacred mountain, a privilege, without which, this work would not have been possible. We are most fortunate to be able to conduct observations from this site. PC and LM acknowledge support from the BIRD 2018 research grant from the Università degli Studi di Padova. PC, AC, CG, FL, FP, MT, GR acknowledge the grant PRIN MIUR 2017. JDS was supported by JSPS KAKENHI Grant Number JP18H04346, and the World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan. DAR acknowledges support from the National Science Foundation under grant numbers AST-1614213 and AST-1910107 and from the Alexander von Humboldt Foundation through a Humboldt Research Fellowship for Experienced Researchers. EI acknowledges partial support from FONDECYT through grant N° 1171710. The authors thank Anne Verhamme for useful discussions that helped improving this manuscript, and the anonymous referee for the very constructive and insightful report.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
Università degli Studi di PadovaUNSPECIFIED
Ministero dell'Istruzione, dell'Università e della Ricerca (MIUR)UNSPECIFIED
Japan Society for the Promotion of Science (JSPS)JP18H04346
Ministry of Education, Culture, Sports, Science and Technology (MEXT)UNSPECIFIED
Alexander von Humboldt FoundationUNSPECIFIED
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1171710
Subject Keywords:galaxies: ISM – galaxies: high-redshift – submillimeter: galaxies
Record Number:CaltechAUTHORS:20201028-134551223
Persistent URL:
Official Citation:The ALPINE-ALMA [C II] survey - Small Lyα-[C II] velocity offsets in main-sequence galaxies at 4.4 < z < 6. P. Cassata, L. Morselli, A. Faisst, M. Ginolfi, M. Béthermin, P. Capak, O. Le Fèvre, D. Schaerer, J. Silverman, L. Yan, B. C. Lemaux, M. Romano, M. Talia, S. Bardelli, M. Boquien, A. Cimatti, M. Dessauges-Zavadsky, Y. Fudamoto, S. Fujimoto, M. Giavalisco, N. P. Hathi, E. Ibar, G. Jones, A. M. Koekemoer, H. Méndez-Hernandez, C. Mancini, P. A. Oesch, F. Pozzi, D. A. Riechers, G. Rodighiero, D. Vergani, G. Zamorani and E. Zucca. A&A, 643 (2020) A6; DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:106334
Deposited By: Tony Diaz
Deposited On:29 Oct 2020 16:03
Last Modified:30 Nov 2020 15:58

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