Ionised outflows in z ~ 2.4 quasar host galaxies^⋆

¹ Dipartimento di Fisica e Astronomia, Università di Firenze, via G. Sansone 1, 50019 Sesto Fiorentino (Firenze), Italy
² INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
³ Cavendish Laboratory, University of Cambridge, 19 J. J. Thomson Ave., Cambridge CB3 0HE, UK
⁴ Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁵ Dipartimento di Fisica e Astronomia, Università di Bologna, viale Berti Pichat 6/2, 40127 Bologna, Italy
⁶ INAF−Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁷ Instituto de Astronomía − UNAM, Mexico City, Mexico
⁸ Institute for Astronomy, Department of Physics, ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland
⁹ INAF−Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone, Italy
¹⁰ Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy
¹¹ IRAM−Institut de Radio Astronomie Millimétrique, 300 rue de la Piscine, 38406 Saint-Martin-d’ Hères, France
¹² Dipartimento di Matematica e Fisica, Università Roma Tre, via della Vasca Navale 84, 00146 Roma, Italy
¹³ European Southern Observatory, Karl-Schwarzschild-str. 2, 85748 Garching bei München, Germany
¹⁴ Research Center for Space and Cosmic Evolution, Ehime University, Bunkyo-cho 2-5, Matsuyama, 790-8577 Ehime, Japan
¹⁵ School of Physics and Astronomy, The Sackler Faculty of Exact Sciences, Tel-Aviv University, 69978 Tel-Aviv, Israel
¹⁶ Department of Physics, University of North Texas, Denton, TX 76203, USA

Received: 19 May 2015
Accepted: 9 June 2015

Abstract

Aims. Outflows driven by active galactic nuclei (AGN) are invoked by galaxy evolutionary models to quench star formation and to explain the origin of the relations observed locally between super-massive black holes and their host galaxies. We here aim to detect extended ionised outflows in luminous quasars, where we expect the highest activity both in star formation and in black-hole accretion. Currently, there are only a few studies based on spatially resolved observations of outflows at high redshift, z > 2.

Methods. We analysed a sample of six luminous (L > 10⁴⁷ erg/s) quasars at z ~ 2.4, observed in H-band using the near-IR integral field spectrometer SINFONI at the VLT. We performed a kinematic analysis of the [Oiii] emission line at λ = 5007 Å.

Results. We detect fast, spatially extended outflows in five out of six targets. [Oiii]λ5007 has a complex gas kinematic, with blue-shifted velocities of a few hundreds of km s^-1 and line widths up to 1500 km s^-1. Using the spectroastrometric method, we infer a size of the ionised outflows of up to ~2 kpc. The properties of the ionised outflows, mass outflow rate, momentum rate, and kinetic power, are correlated with the AGN luminosity. The increase in outflow rate with increasing AGN luminosity is consistent with the idea that a luminous AGN pushes away the surrounding gas through fast outflows that are driven by radiation pressure, which depends on the emitted luminosity.

Conclusions. We derive mass outflow rates of about 6−700 M_⊙  yr^-1 for our sample, which are lower than those observed in molecular outflows. The physical properties of ionised outflows show dependences on AGN luminosity that are similar to those of molecular outflows, but indicate that the mass of ionised gas is lower than that of molecular outflows. Alternatively, this discrepancy between ionised and molecular outflows could be explained with different acceleration mechanisms.