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Published April 2018 | Published + Submitted
Journal Article Open

Molecular outflow and feedback in the obscured quasar XID2028 revealed by ALMA


We imaged, with ALMA and ARGOS/LUCI, the molecular gas and dust and stellar continuum in XID2028, which is an obscured quasi-stellar object (QSO) at z = 1.593, where the presence of a massive outflow in the ionised gas component traced by the [OIII]5007 emission has been resolved up to 10 kpc. This target represents a unique test case to study QSO feedback in action at the peak epoch of AGN-galaxy co-evolution. The QSO was detected in the CO(5 − 4) transition and in the 1.3 mm continuum at ~30 and ~20σ significance, respectively; both emissions are confined in the central (<2 kpc) radius area. Our analysis suggests the presence of a fast rotating molecular disc (v ~ 400 km s^(−1)) on very compact scales well inside the galaxy extent seen in the rest-frame optical light (~10 kpc, as inferred from the LUCI data). Adding available measurements in additional two CO transitions, CO(2 − 1) and CO(3 − 2), we could derive a total gas mass of ~10^(10) M⊙, thanks to a critical assessment of CO excitation and the comparison with the Rayleigh–Jeans continuum estimate. This translates into a very low gas fraction (<5%) and depletion timescales of 40–75 Myr, reinforcing the result of atypical gas consumption conditions in XID2028, possibly because of feedback effects on the host galaxy. Finally, we also detect the presence of high velocity CO gas at ~5σ, which we interpret as a signature of galaxy-scale molecular outflow that is spatially coincident with the ionised gas outflow. XID2028 therefore represents a unique case in which the measurement of total outflowing mass, of ~500–800 M⊙ yr^(−1) including the molecular and atomic components in both the ionised and neutral phases, was attempted for a high-z QSO.

Additional Information

© 2018 ESO. Article published by EDP Sciences. Received 25 July 2017; Accepted 12 December 2017; Published online 16 April 2018. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2015.1.00299.S (PI: Brusa), #2015.1.00137.S (PI: Scoville), and #20015.1.00171.S (PI: Daddi). ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), NSC, and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ. XID2028 is an interesting target from several perspectives (e.g. massive MS galaxy; bright FIR/Herschel source with substantial SFR), and as such, in addition to our deep dedicated follow-up, it has also been targeted independently by two different ALMA snapshot programmes as part of large samples (100+) of high-z galaxies. A careful scrutiny of the ALMA archive and an open collaboration with the PIs of the programmesallowed us to make the best use of ALMA data. We thank the ARGOS team for obtaining the K-band imaging of XID2028 during a commissioning run. We gratefully thank the staff of the Italian ARC node for their support in data reduction. This research was finalised at the Munich Institute for Astro- and Particle Physics (MIAPP) ofthe DFG cluster of excellence "Origin and Structure of the Universe", during the programme "In & Out: What rules the galaxy baryon cycle?" (July 2017). MB, MP, and GL acknowledge support from the FP7 Career Integration Grant "eEASy" ("SMBH evolution through cosmic time: from current surveys to eROSITA-Euclid AGN Synergies", CIG 321913). EL is supported by a European Union COFUND/Durham Junior Research Fellowship (under EU grant agreement no. 609412). MTS was supported by a Royal Society Leverhulme Trust Senior Research Fellowship (LT150041). CF acknowledges support from the European Union Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 664931. SC acknowledges financial support from the Science and Technology Facilities Council (STFC). We acknowledge financial support from INAF under the contract PRIN-INAF-2014 ("Windy Black Holes combing Galaxy evolution"). We gratefully thank Maurilio Pannella, Renzo Sancisi, Margherita Talia, Anna Cibinel, Roberto Decarli, Andrea Lapi, Gergö Popping, David Rosario, Kartik Sheth, and John Silverman for useful discussions, and Darshan Kakkad for providing data prior to publication. We thank the anonymous referee for her/his constructive criticisms, which considerably improved the presentation of the results.

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August 19, 2023
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