Volume 617, September 2018
|Number of page(s)||20|
|Published online||20 September 2018|
Molecular gas in the northern nucleus of Mrk 273: Physical and chemical properties of the disc and its outflow
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
2 Chalmers University of Technology, Department of Space, Earth and Environment, Onsala Space Observatory, 43992 Onsala, Sweden
3 Universidad de Alcalá, Departamento de Física y Matemáticas, Campus Universitario, 28871 Alcalá de Henares, Madrid, Spain
4 European Southern Observatory, Alonso de Córdova 3107, Vitacura 763 0355 Santiago, Chile
5 Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura 763 0355 Santiago, Chile
6 Observatorio de Madrid, OAN-IGN, Alfonso XII, 3, 28014 Madrid, Spain
7 Astron. Dept., King Abdulaziz University, PO Box 80203 21589 Jeddah, Saudi Arabia
8 Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden, The Netherlands
9 San Jose State University, 1 Washington Square, San Jose, CA, 95192 USA
10 George Mason University, Department of Physics & Astronomy, MS 3F3, 4400 University Drive, Fairfax, VA, 22030 USA
11 Institut de Radio Astronomie Millimétrique, 300 rue de la Piscine, Dom. Univ., 38406 St. Martin d’Hères, France
Accepted: 25 May 2018
Aiming to characterise the properties of the molecular gas in the ultra-luminous infrared galaxy Mrk 273 and its outflow, we used the NOEMA interferometer to image the dense-gas molecular tracers HCN, HCO+, HNC, HOC+ and HC3N at ∼86 GHz and ∼256 GHz with angular resolutions of 4ʺ̣9 × 4ʺ̣5 (∼3.7 × 3.4 kpc) and 0ʺ̣61 × 0ʺ̣55 (∼460 × 420 pc). We also modelled the flux of several H2O lines observed with Herschel using a radiative transfer code that includes excitation by collisions and far-infrared photons. The disc of the Mrk 273 north nucleus has two components with decoupled kinematics. The gas in the outer parts (R ∼ 1.5 kpc) rotates with a south-east to north-west direction, while in the inner disc (R ∼ 300 pc) follows a north-east to south-west rotation. The central 300 pc, which hosts a compact starburst region, is filled with dense and warm gas, and contains a dynamical mass of (4 −5) × 109 M⊙, a luminosity of L′HCN = (3–4) × 108 K km s−1 pc2, and a dust temperature of 55 K. At the very centre, a compact core with R ∼ 50 pc has a luminosity of LIR = 4 × 1011 L⊙ (30% of the total infrared luminosity), and a dust temperature of 95 K. The core is expanding at low velocities ∼50–100 km s−1, probably affected by the outflowing gas. We detect the blue-shifted component of the outflow, while the red-shifted counterpart remains undetected in our data. Its cold and dense phase reaches fast velocities up to ∼1000 km s−1, while the warm outflowing gas has more moderate maximum velocities of ∼600 km s−1. The outflow is compact, being detected as far as 460 pc from the centre in the northern direction, and has a mass of dense gas ≤8 × 108 M⊙. The difference between the position angles of the inner disc (∼70°) and the outflow (∼10°) indicates that the outflow is likely powered by the AGN, and not by the starburst. Regarding the chemistry in Mrk 273, we measure an extremely low HCO+/HOC+ ratio of 10 ± 5 in the inner disc of Mrk 273.
Key words: galaxies: individual: Mrk 273 / galaxies: nuclei / ISM: molecules / line: profiles / astrochemistry / galaxies: kinematics and dynamics
© ESO 2018
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