Volume 646, February 2021
|Number of page(s)||21|
|Published online||16 February 2021|
IV. CO(J = 3–2) properties of active galactic nucleus hosts at cosmic noon revealed by ALMA⋆
Department of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT, UK
2 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
3 INAF – Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, 34143 Trieste, Italy
4 School of Mathematics, Statistics and Physics, Newcastle University NE1 7RU, UK
5 European Southern Observatory, Alonso de Cordova 3107, Casilla 19, Santiago 19001, Chile
6 INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
7 INAF IASF-Milano, Via Alfonso Corti 12, 20133 Milano, Italy
8 Dipartimento di Fisica e Astronomia dell’Università degli Studi di Bologna, via P. Gobetti 93/2, 40129 Bologna, Italy
9 INAF/OAS, Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, via P. Gobetti 93/3, 40129 Bologna, Italy
10 MPE, Giessenbach-Str. 1, 85748 Garching bei München, Germany
11 Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy
12 Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway
13 INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
14 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
15 Dipartimento di Fisica e Astronomia, Università di Firenze, Via G. Sansone 1, 50019 Sesto Fiorentino (Firenze), Italy
16 Centro de Astrobiología (CAB, CSIC–INTA), Departamento de Astrofísica, Cra. de Ajalvir Km. 4, 28850 Torrejón de Ardoz, Madrid, Spain
17 INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monte Porzio Catone (Roma), Italy
18 Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
19 Graduate school of Science and Engineering, Saitama Univ. 255 Shimo-Okubo, Sakura-ku, Saitama City, Saitama 338-8570, Japan
Accepted: 25 November 2020
Feedback from active galactic nuclei (AGN) is thought to be key in shaping the life cycle of their host galaxies by regulating star-formation activity. Therefore, to understand the impact of AGN on star formation, it is essential to trace the molecular gas out of which stars form. In this paper we present the first systematic study of the CO properties of AGN hosts at z ≈ 2 for a sample of 27 X-ray selected AGN spanning two orders of magnitude in AGN bolometric luminosity (log Lbol / erg s−1 = 44.7 − 46.9) by using ALMA Band 3 observations of the CO(3-2) transition (∼1″ angular resolution). To search for evidence of AGN feedback on the CO properties of the host galaxies, we compared our AGN with a sample of inactive (i.e., non-AGN) galaxies from the PHIBSS survey with similar redshift, stellar masses, and star-formation rates (SFRs). We used the same CO transition as a consistent proxy for the gas mass for the two samples in order to avoid systematics involved when assuming conversion factors (e.g., excitation corrections and αCO). By adopting a Bayesian approach to take upper limits into account, we analyzed CO luminosities as a function of stellar masses and SFRs, as well as the ratio LCO(3–2)′/M∗ (a proxy for the gas fraction). The two samples show statistically consistent trends in the LCO(3–2)′−LFIR and LCO(3–2)′−M∗ planes. However, there are indications that AGN feature lower CO(3-2) luminosities (0.4–0.7 dex) than inactive galaxies at the 2–3σ level when we focus on the subset of parameters where the results are better constrained (i.e., LFIR ≈ 1012.2 L⊙ and M* > 1011 M⊙) and on the distribution of the mean log(LCO(3–2)′/M∗). Therefore, even by conservatively assuming the same excitation factor r31, we would find lower molecular gas masses in AGN, and assuming higher r31 would exacerbate this difference. We interpret our result as a hint of the potential effect of AGN activity (such as radiation and outflows), which may be able to heat, excite, dissociate, and/or deplete the gas reservoir of the host galaxies. Better SFR measurements and deeper CO observations for AGN as well as larger and more uniformly selected samples of both AGN and inactive galaxies are required to confirm whether there is a true difference between the two populations.
Key words: galaxies: active / galaxies: evolution / galaxies: ISM / quasars: general / submillimeter: ISM / galaxies: high-redshift
Data are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (184.108.40.206) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/646/A96
© ESO 2021
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