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The mean star formation rates of unobscured QSOs: searching for evidence of suppressed or enhanced star formation

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posted on 2018-08-13, 14:11 authored by F. Stanley, D. M. Alexander, C. M. Harrison, D. J. Rosario, L. Wang, J. A. Aird, N. Bourne, L. Dunne, S. Dye, S. Eales, K. K. Knudsen, M. J. Micha lowski, E. Valiante, G. De Zotti, C. Furlanetto, R. Ivison, S. Maddox, M. W. L. Smith
We investigate the mean star formation rates (SFRs) in the host galaxies of \sim3000 optically selected quasi-stellar objects (QSOs) from the Sloan Digital Sky Survey within the Herschel-ATLAS fields, and a radio-luminous subsample covering the redshift range of z = 0.2-2.5. Using Wide-field Infrared Survey Explorer (WISE) and Herschel photometry (12-500 μm) we construct composite spectral energy distributions (SEDs) in bins of redshift and active galactic nucleus (AGN) luminosity. We perform SED fitting to measure the mean infrared luminosity due to star formation, removing the contamination from AGN emission. We find that the mean SFRs show a weak positive trend with increasing AGN luminosity. However, we demonstrate that the observed trend could be due to an increase in black hole (BH) mass (and a consequent increase of inferred stellar mass) with increasing AGN luminosity. We compare to a sample of X-ray selected AGN and find that the two populations have consistent mean SFRs when matched in AGN luminosity and redshift. On the basis of the available virial BH masses, and the evolving BH mass to stellar mass relationship, we find that the mean SFRs of our QSO sample are consistent with those of main sequence star-forming galaxies. Similarly the radio-luminous QSOs have mean SFRs that are consistent with both the overall QSO sample and with star-forming galaxies on the main sequence. In conclusion, on average QSOs reside on the main sequence of star-forming galaxies, and the observed positive trend between the mean SFRs and AGN luminosity can be attributed to BH mass and redshift dependencies.

Funding

We acknowledge the Faculty of Science Durham Doctoral Scholarship (FS), the Science and Technology Facilities Council (DMA and DJR, through grant code ST/L00075X/1) and the Leverhulme Trust (DMA). JAA acknowledges support from ERC Advanced Grant FEEDBACK 340442. LD and SM acknowledge support from the European Research Council Advanced Investigator grant COSMICISM, and also the ERC Consolidator Grant, Cosmic Dust. GDZ acknowledges support from ASI/INAF agreement no. 2014-024-R.1 and by PRIN–INAF 2014 ‘Probing the AGN/galaxy co-evolution through ultra-deep and ultra-high resolution radio surveys’. MJM acknowledges the support of the National Science Centre, Poland, through the POLONEZ grant 2015/19/P/ST9/04010. This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 665778. The Herschel-ATLAS (H-ATLAS) is a project with Herschel, which is an ESA Space Observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. The H-ATLAS website is http://www.h-atlas.org

History

Citation

Monthly Notices of the Royal Astronomical Society, 2017, 472, pp. 2221-2240

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy

Version

  • VoR (Version of Record)

Published in

Monthly Notices of the Royal Astronomical Society

Publisher

Oxford University Press (OUP), Royal Astronomical Society

issn

0035-8711

eissn

1365-2966

Acceptance date

2017-08-14

Copyright date

2017

Available date

2018-08-13

Publisher version

https://academic.oup.com/mnras/article/472/2/2221/4083638

Language

en

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