SUNRISE: The rich molecular inventory of high-redshift dusty galaxies revealed by broadband spectral line surveys
Journal article, 2023
Understanding the nature of high-redshift dusty galaxies requires a comprehensive view of their interstellar medium (ISM) and molecular complexity. However, the molecular ISM at high redshifts is commonly studied using only a few species beyond 12C16O, limiting our understanding. In this paper, we present the results of deep 3 mm spectral line surveys using the NOrthern Extended Millimeter Array (NOEMA) targeting two strongly lensed dusty galaxies observed when the Universe was less than 1.8 Gyr old: APM 08279+5255, a quasar at redshift z = 3.911, and NCv1.143 (H-ATLAS J125632.7+233625), a z = 3.565 starburst galaxy. The spectral line surveys cover rest-frame frequencies from about 330 to 550 GHz for both galaxies. We report the detection of 38 and 25 emission lines in APM 08279+5255 and NCv1.143, respectively. These lines originate from 17 species, namely CO, 13CO, C18O, CN, CCH, HCN, HCO+, HNC, CS, C34S, H2O, H3O+, NO, N2H+, CH, c-C3H2, and the vibrationally excited HCN and neutral carbon. The spectra reveal the chemical richness and the complexity of the physical properties of the ISM. By comparing the spectra of the two sources and combining the analysis of the molecular gas excitation, we find that the physical properties and the chemical imprints of the ISM are different: the molecular gas is more excited in APM 08279+5255, which exhibits higher molecular gas temperatures and densities compared to NCv1.143; the molecular abundances in APM 08279+5255 are akin to the values of local active galactic nuclei (AGN), showing boosted relative abundances of the dense gas tracers that might be related to high-temperature chemistry and/or the X-ray-dominated regions, while NCv1.143 more closely resembles local starburst galaxies. The most significant differences between the two sources are found in H2O: the 448 GHz ortho-H2O(423 - 330) line is significantly brighter in APM 08279+5255, which is likely linked to the intense far-infrared radiation from the dust powered by AGN. Our astrochemical model suggests that, at such high column densities, far-ultraviolet radiation is less important in regulating the ISM, while cosmic rays (and/or X-rays and shocks) are the key players in shaping the molecular abundances and the initial conditions of star formation. Both our observed CO isotopologs line ratios and the derived extreme ISM conditions (high gas temperatures, densities, and cosmic-ray ionization rates) suggest the presence of a top-heavy stellar initial mass function. From the ~330-550 GHz continuum, we also find evidence of nonthermal millimeter flux excess in APM 08279+5255 that might be related to the central supermassive black hole. Such deep spectral line surveys open a new window into the physics and chemistry of the ISM and the radiation field of galaxies in the early Universe.
infrared: galaxies
galaxies: ISM
submillimeter: galaxies
ISM: molecules
radio lines: ISM
galaxies: high-redshift
Author
Chentao Yang
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
A.A. Omont
Institut d 'Astrophysique de Paris
S. Martin
European Southern Observatory Santiago
Atacama Large Millimeter-submillimeter Array (ALMA)
T. G. Bisbas
Zhejiang Lab
P. Cox
Institut d 'Astrophysique de Paris
A. Beelen
Laboratoire d'Astrophysique de Marseille
E. Gonzalez-Alfonso
University of Alcalá
R. Gavazzi
Laboratoire d'Astrophysique de Marseille
Institut d 'Astrophysique de Paris
Susanne Aalto
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
P. Andreani
European Southern Observatory (ESO)
University of Oslo
Aristotle University of Thessaloniki
C. Ceccarelli
Institut de Planétologie et d’Astrophysique de Grenoble (IPAG)
Y. Gao
Xiamen University
Mark Gorski
Northwestern University
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
M. Guelin
Institut de Radioastronomie Millimétrique (IRAM)
Hai Fu
University of Iowa
R. J. Ivison
European Southern Observatory (ESO)
University of Edinburgh
Macquarie University
Dublin Institute for Advanced Studies
Kirsten Knudsen
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
M. Lehnert
École Normale Supérieure de Lyon
H. Messias
Atacama Large Millimeter-submillimeter Array (ALMA)
European Southern Observatory Santiago
Sebastien Muller
Chalmers, Space, Earth and Environment, Onsala Space Observatory
R. Neri
Institut de Radioastronomie Millimétrique (IRAM)
D. A. Riechers
University of Cologne
P. van der Werf
Leiden University
Zhi-Yu Zhang
Nanjing University
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 680 A95Exploring the Hidden Dusty Nuclei of Galaxies (HIDDeN)
European Research Council (ERC) (789410), 2018-10-01 -- 2023-09-30.
Subject Categories
Astronomy, Astrophysics and Cosmology
Atom and Molecular Physics and Optics
Roots
Basic sciences
DOI
10.1051/0004-6361/202347610