Gas dynamics in an AGN-host galaxy at z ≃ 2.6: Regular rotation, noncircular motions, and mass models

¹ School of Astronomy and Space Science, Nanjing University, Nanjing 210023, China
² Key Laboratory of Modern Astronomy and Astrophysics, Nanjing University, Ministry of Education, Nanjing 210023, China
³ INAF – Arcetri Astrophysical Observatory, Large E. Fermi 5, 50125 Florence, Italy
⁴ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
⁵ Department of Physics & Astronomy, The University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada
⁶ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monteporzio Catone, Italy
⁷ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁸ Université de la Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Bd de l’Observatoire, CS 34229, 06304 Nice Cedex 4, France
⁹ Research Center for Astronomical Computing, Zhejiang Laboratory, Hangzhou 311100, China
¹⁰ Department of Astronomy, University of California at Berkeley, Berkeley, CA 94720, USA
¹¹ Department of Physics, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong
¹² Centre de Recherche Astrophysique de Lyon, ENS de Lyon, Université Lyon 1, CNRS, UMR5574, 69230 Saint-Genis-Laval, France

^⋆ Corresponding author; federico.lelli@inaf.it

Received: 21 May 2024
Accepted: 4 November 2024

Abstract

The gas dynamics of galaxies provide critical insights into the evolution of both baryons and dark matter (DM) across cosmic time. In this context, galaxies at cosmic noon, that is, in the period characterized by the most intense star formation and black hole activities, are particularly significant. We present an analysis of the gas dynamics of PKS 0529–549. This galaxy lies at z ≃ 2.6 and hosts a radio-loud active galactic nucleus (AGN). We used new ALMA observations of the [C I] (2−1) line at a spatial resolution of 0.18″ (∼1.5 kpc). We found that (1) the molecular gas forms a rotation-supported disk with V_rot/σ_v = 6 ± 3 and displays a flat rotation curve out to 3.3 kpc; (2) there are several noncircular components, including a kinematically anomalous structure near the galaxy center, a gas tail to the southwest, and possibly a second weaker tail to the east; and finally, (3) the dynamical estimates of the gas and stellar masses from fitting the rotation curve are inconsistent with photometric estimates made using standard gas conversion factors and stellar population models, respectively. These discrepancies may be due to systematic uncertainties in the photometric masses or in the dynamical masses, or they might be caused by a more massive radio-loud AGN-host galaxy that is hidden behind the gas-rich [C I] emitting starburst galaxy along the line of sight. Our work shows that in-depth investigations of 3D line cubes are crucial for revealing the complexity of gas dynamics in high-z galaxies, in which regular rotation may coexist with noncircular motions and possibly tidal structures.