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The gentle monster PDS 456: Kiloparsec-scale molecular outflow and its implications for QSO feedback

Accepted version
Peer-reviewed

Type

Article

Change log

Authors

Bischetti, M 
Piconcelli, E 
Feruglio, C 
Fiore, F 
Carniani, S 

Abstract

We report on the first ALMA observation of the CO(3$-2)andrestframe 340GHzcontinuumemissioninPDS456,whichisthemostluminous,radioquietQSOinthelocalUniverse(z$~0.18), with a bolometric luminosity LBol∼1047 erg s−1. ALMA angular resolution allowed us to map scales as small as ~700 pc. The molecular gas reservoir, traced by the core of the very bright CO(3$-2)emissionline,isdistributedinacompactrotatingdisk,withsizeof 1.3kpc,seenclosetofaceon(i 25deg).FastCO(3-$2) emission in the velocity range v∈[−1000,+500] km s−1 is also present. Specifically, we detect several blue-shifted clumps out to ~5 kpc from the nucleus, in addition to a compact (R≲1.2 kpc), broad emission component. These components reveal a galaxy-wide molecular outflow, with a total mass Mmolout∼2.5×108 M and a mass outflow rate M˙mol∼290 M yr−1. The corresponding depletion time is ~8 Myr, shorter than the rate at which the molecular gas is converted into stars, indicating that the detected outflow is potentially able to quench star-formation in the host. The momentum flux of the molecular outflow normalised to the radiative momentum output (i.e. LBol/c) is ≲1, comparable to that of the X-ray ultra-fast outflow (UFO) detected in PDS 456. This is at odds with the expectations for an energy-conserving expansion suggested for most of the large-scale outflows detected in low-luminosity AGN so far. We suggest three possible scenarios that may explain this observation: (i) in very luminous AGN such as our target the molecular gas phase is tracing only a fraction of the total outflowing mass; (ii) a small coupling between the shocked gas by the UFO and the host-galaxy ISM (iii) AGN radiation pressure may play an important role in driving the outflow.

Description

Keywords

galaxies: active, quasars: individual: PDS 456, galaxies: evolution, quasars: emission lines, techniques: imaging spectroscopy, techniques: interferometric

Journal Title

Astronomy and Astrophysics

Conference Name

Journal ISSN

0004-6361
1432-0746

Volume Title

628

Publisher

EDP Sciences

Rights

All rights reserved
Sponsorship
Science and Technology Facilities Council (ST/M001172/1)
European Research Council (695671)