Widespread QSO-driven outflows in the early Universe^⋆

¹ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monte Porzio Catone, Roma, Italy
e-mail: manuela.bischetti@inaf.it
² Cavendish Laboratory, University of Cambridge, 19 J. J. Thomson Avenue, Cambridge CB3 0HE, UK
³ Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁴ INAF – Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, 34143 Trieste, Italy

Received: 3 June 2018
Accepted: 16 July 2019

Abstract

We present the stacking analysis of a sample of 48 quasi-stellar objects (QSOs) at 4.5 <  z <  7.1 detected by the Atacama Large Millimetre Array (ALMA) in the [CII] λ158 μm emission line to investigate the presence and the properties of massive, cold outflows associated with broad wings in the [CII] profile. The high sensitivity reached through this analysis allows us to reveal very broad [CII] wings tracing the presence of outflows with velocities in excess of 1000 km s⁻¹. We find that the luminosity of the broad [CII] emission increases with L_AGN, while it does not significantly depend on the star formation rate of the host galaxy, indicating that the central active galactic nucleus (AGN) is the main driving mechanism of the [CII] outflows in these powerful, distant QSOs. From the stack of the ALMA cubes, we derive an average outflow spatial extent of ∼3.5 kpc. The average atomic neutral mass outflow rate inferred from the stack of the whole sample is Ṁ_out ∼ 100 M_⊙ yr⁻¹, while for the most luminous systems it increases to ∼200 M_⊙ yr⁻¹. The associated outflow kinetic power is about 0.1% of L_AGN, while the outflow momentum rate is ∼L_AGN/c or lower, suggesting that these outflows are either driven by radiation pressure onto dusty clouds or, alternatively, are driven by the nuclear wind and energy conserving but with low coupling with the interstellar medium. We discuss the implications of the resulting feedback effect on galaxy evolution in the early Universe.