Evidence for extended gaseous reser v oirs around AGN at cosmic noon from ALMA CO(3 -2) obser v ations

G. C. Jones*, R. Maiolino, C. Circosta, J. Scholtz, S. Carniani, Y. Fudamoto

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Gaseous outflows are key phenomena in the evolution of galaxies, as they affect star formation (either positively or ne gativ ely), eject gas from the core or disc, and directly cause mixing of pristine and processed material. Active outflows may be detected through searches for broad spectral line emission or high-velocity gas, but it is also possible to determine the presence of past outflows by searching for extended reservoirs of chemically enriched molecular gas in the circumgalactic medium (CGM) around galaxies. In this work, we examine the CO(3 -2) emission of a set of seven z ~2.0-2.5 active galactic nuclei (AGN) host galaxies, as observed with ALMA. Through a 3D stacking analysis, we find evidence for extended CO emission of radius r ~13 kpc. We extend this analysis to the HST /ACS i -band images of the sample galaxies, finding a complex small-scale (r < 10 kpc) morphology but no robust evidence for extended emission. In addition, the dust emission (traced by rest-frame FIR emission) shows no evidence for significant spatial extension. This indicates that the diffuse CO emission revealed by ALMA is morphologically distinct from the stellar component, and thus traces an extended reservoir of enriched gas. The presence of a diffuse, enriched molecular reservoir around this sample of AGN host galaxies at cosmic noon hints at a history of AGN-driven outflows that likely had strong effects on the star formation history of these objects.

Original languageEnglish
Pages (from-to)691-708
Number of pages18
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Publication statusPublished - 2022


  • galaxies: evolution
  • galaxies: high-redshift
  • ISM: jets and outflows

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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