Volume 652, August 2021
|Number of page(s)||26|
|Published online||11 August 2021|
ALMA multiline survey of the ISM in two quasar host–companion galaxy pairs at z > 6
Dipartimento di Fisica e Astronomia, Alma Mater Studiorum, Università di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
2 INAF-Osservatorio di Astrofisica e Scienza dello Spazio, Via Gobetti 93/3, 40129 Bologna, Italy
3 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
4 National Radio Astronomy Observatory, Pete V. Domenici Array Science Center, PO Box O, Socorro, NM 87801, USA
5 Argelander-Institut für Astronomie, University at Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
6 Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
7 Max Planck Institut für Astrophysik, Karl–Schwarzschild–Straße 1, 85748 Garching bei München, Germany
8 Department of Astronomy, School of Physics, Peking University, 5 Yiheyuan Road, Haidian District, Beijing 100871, PR China
9 Kavli Institute for Astronomy and Astrophysics, Peking University, 5 Yiheyuan Road, Haidian District, Beijing 100871, PR China
10 European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, Vitacura, Santiago 19, Chile
11 Department of Astronomy, Cornell University, Space Sciences Building, Ithaca, NY 14853, USA
12 Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
13 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
14 Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, Daejeon 34055, Korea
Accepted: 18 May 2021
We present a multiline survey of the interstellar medium (ISM) in two z > 6 quasar host galaxies, PJ231−20 (z = 6.59) and PJ308−21 (z = 6.23), and their two companion galaxies. Observations were carried out using the Atacama Large (sub-)Millimeter Array (ALMA). We targeted 11 transitions including atomic fine-structure lines (FSLs) and molecular lines: [NII]205 μm, [CI]369 μm, CO (Jup = 7, 10, 15, 16), H2O 312 − 221, 321 − 312, 303 − 212, and the OH163 μm doublet. The underlying far-infrared (FIR) continuum samples the Rayleigh-Jeans tail of the respective dust emission. By combining this information with our earlier ALMA [CII]158 μm observations, we explored the effects of star formation and black hole feedback on the ISM of the galaxies using the CLOUDY radiative transfer models. We estimated dust masses, spectral indexes, IR luminosities, and star-formation rates from the FIR continuum. The analysis of the FSLs indicates that the [CII]158 μm and [CI]369 μm emission arises predominantly from the neutral medium in photodissociation regions (PDRs). We find that line deficits agree with those of local luminous IR galaxies. The CO spectral line energy distributions (SLEDs) reveal significant high-J CO excitation in both quasar hosts. Our CO SLED modeling of the quasar PJ231−20 shows that PDRs dominate the molecular mass and CO luminosities for Jup ≤ 7, while the Jup ≥ 10 CO emission is likely driven by X-ray dissociation regions produced by the active galactic nucleus (AGN) at the very center of the quasar host. The Jup > 10 lines are undetected in the other galaxies in our study. The H2O 321 − 312 line detection in the same quasar places this object on the LH2O − LTIR relation found for low-z sources, thus suggesting that this water vapor transition is predominantly excited by IR pumping. Models of the H2O SLED and of the H2O-to-OH163 μm ratio point to PDR contributions with high volume and column density (nH ∼ 0.8 × 105 cm−3, NH = 1024 cm−2) in an intense radiation field. Our analysis suggests a less highly excited medium in the companion galaxies. However, the current data do not allow us to definitively rule out an AGN in these sources, as suggested by previous studies of the same objects. This work demonstrates the power of multiline studies of FIR diagnostics in order to dissect the physical conditions in the first massive galaxies emerging from cosmic dawn.
Key words: galaxies: high-redshift / galaxies: ISM / quasars: emission lines / quasars: supermassive black holes
© ESO 2021
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