Resolved [CII] emission in a lensed quasar at z = 4.4^⋆

¹ INAF – Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Italy
e-mail: simona.gallerani@gmail.com
² Institut de RadioAstronomie Millimétrique, 300 rue de la Piscine, Domaine Universitaire, 38406 Saint Martin d’Hères, France
³ Cavendish Laboratory, University of Cambridge, 19 J. J. Thomson Ave., Cambridge CB3 0HE, UK
⁴ European Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago 19, Chile
⁵ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁶ School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
⁷ INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁸ INFN, Sezione di Bologna, viale Berti Pichat 6/2, 40127 Bologna, Italy
⁹ The Hakubi Project, Kyoto University, Yoshida-Ushinomiya-cho, Sakyo-ku, 606-8302 Kyoto, Japan
¹⁰ Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
¹¹ Dublin Institute of Advanced Studies, 31 Fitwilliam Place, Dublin 2, Ireland

Received: 21 December 2011
Accepted: 17 May 2012

Abstract

We present one of the first resolved maps of the [CII] 158 μm line, a powerful tracer of the star forming inter-stellar medium, at high redshift. We use the new IRAM PdBI receivers at 350 GHz to map this line in BRI 0952-0115, the host galaxy of a lensed quasar at z = 4.4 previously found to be very bright in [CII] emission. The [CII] emission is clearly resolved and our data allow us to resolve two [CII] lensed images associated with the optical quasar images. We find that the star formation, as traced by [CII], is distributed over a region of about 1 kpc in size near the quasar nucleus, and we infer a star formation surface density  ≳ 150   M_⊙   yr^-1   kpc^-2, similar to that observed in local ULIRGs. We also reveal another [CII] component, extended over  ~12 kpc, and located at about 10 kpc from the quasar. We suggest that this component is a companion disk galaxy, in the process of merging with the quasar host, whose rotation field is distorted by the interaction with the quasar host, and where star formation, although intense, is more diffuse. These observations suggest that galaxy merging at high-z can enhance star formation at the same time in the form of more compact regions, in the vicinity of the accreting black hole, and in more extended star forming galaxies.