z-GAL: A NOEMA spectroscopic redshift survey of bright Herschel galaxies

III. Physical properties

¹ Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, 38400 Saint-Martin-d’Hères, France
e-mail: berta@iram.fr
² Aix-Marseille Université, CNRS and CNES, Laboratoire d’Astrophysique de Marseille, 38 rue Frédéric Joliot-Curie, 13388 Marseille, France
³ Sorbonne Université, UPMC Université Paris 6 and CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98b boulevard Arago, 75014 Paris, France
⁴ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
⁵ Department of Physics and Astronomy, Rutgers, The State University of New Jersey, 136 Frelinghuysen Road, Piscataway, NJ 08854-8019, USA
⁶ Cosmic Dawn Center (DAWN), Radmandsgade 62, 2200 Copenhagen N, Denmark
⁷ DTU Space, Technical University of Denmark, Elektrovej 327, 2800 Kgs. Lyngby, Denmark
⁸ Instituto Astrofísica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain
⁹ Universidad de La Laguna, Dpto. Astrofísica, 38206 La Laguna, Tenerife, Spain
¹⁰ Division of Particle and Astrophysical Science, Graduate School of Science, Nagoya University, Aichi 464-8602, Japan
¹¹ National Astronomical Observatory of Japan, 2-21-1, Osawa, Mitaka, Tokyo 181-8588, Japan
¹² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
¹³ National Centre for Nuclear Research, ul. Pasteura 7, 02-093 Warsaw, Poland
¹⁴ INAF – Osservatorio Astronomico d’Abruzzo, Via Maggini SNC, 64100 Teramo, Italy
¹⁵ Leiden University, Leiden Observatory, PO Box 9513 2300 RA Leiden, The Netherlands
¹⁶ Department of Physics and Astronomy, University of the Western Cape, Robert Sobukwe Road, Bellville 7535, South Africa
¹⁷ UK ALMA Regional Centre Node, Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
¹⁸ Dipartimento di Fisica e Astronomia “G. Galilei”, Università di Padova, vicolo dell’Osservatorio 3, 35122 Padova, Italy
¹⁹ University of California Irvine, Department of Physics & Astronomy, FRH 2174, Irvine, CA 92697, USA
²⁰ School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK
²¹ School of Physics and Astronomy, Cardiff University, Queens Building, The Parade, Cardiff CF24 3AA, UK
²² Instituto Nacional de Astrofísica, Óptica y Electrónica, Astrophysics Department, Apdo 51 y 216, Tonantzintla, Puebla 72000, Mexico
²³ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
²⁴ Department of Physics and Astronomy, Macquarie University, North Ryde, New South Wales, Australia
²⁵ School of Cosmic Physics, Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin D02 XF86, Ireland
²⁶ Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
²⁷ I. Physikalisches Institut, Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany
²⁸ Centre de Recherche Astrophysique de Lyon – CRAL, CNRS UMR 5574, UCBL1, ENS Lyon, 9 avenue Charles André, 69230 Saint-Genis-Laval, France
²⁹ University of Cape Town, Department of Astronomy, Private Bag X3 Rondebosch, 7701 Cape Town, South Africa
³⁰ INAF – Instituto di Radioastronomia – Italian ARC, Via Piero Gobetti 101, 40129 Bologna, Italy
³¹ Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura, 763-0355 Santiago de Chile, Chile
³² European Southern Observatory, Alonso de Córdova 3107, Casilla, 19001 Vitacura, Santiago, Chile
³³ Department of Physical Sciences, The Open University, Milton Keynes MK7 6AA, UK
³⁴ National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA

Received: 3 May 2023
Accepted: 14 July 2023

Abstract

The z-GAL survey observed 137 bright Herschel-selected targets with the IRAM Northern Extended Millimeter Array, with the aim to measure their redshift and study their properties. Several of them have been resolved into multiple sources. Consequently, robust spectroscopic redshifts have been measured for 165 individual galaxies in the range 0.8 < z < 6.5. In this paper we analyse the millimetre spectra of the z-GAL sources, using both their continuum and line emission to derive their physical properties. At least two spectral lines are detected for each source, including transitions of ¹²CO, [CI], and H₂O. The observed ¹²CO line ratios and spectral line energy distributions of individual sources resemble those of local starbursts. In seven sources the para-H₂O (2₁₁−2₀₂) transition is detected and follows the IR versus H₂O luminosity relation of sub-millimetre galaxies. The molecular gas mass of the z-GAL sources is derived from their ¹²CO, [CI], and sub-millimetre dust continuum emission. The three tracers lead to consistent results, with the dust continuum showing the largest scatter when compared to ¹²CO. The gas-to-dust mass ratio of these sources was computed by combining the information derived from ¹²CO and the dust continuum and has a median value of 107, similar to star-forming galaxies of near-solar metallicity. The same combined analysis leads to depletion timescales in the range between 0.1 and 1.0 Gyr, which place the z-GAL sources between the ‘main sequence’ of star formation and the locus of starbursts. Finally, we derived a first estimate of stellar masses – modulo possible gravitational magnification – by inverting known gas scaling relations: the z-GAL sample is confirmed to be mostly composed by starbursts, whereas ∼25% of its members lie on the main sequence of star-forming galaxies (within ±0.5 dex).