CaltechAUTHORS
Published February 11, 2013 | Version Published
Journal Article Open

Polycyclic aromatic hydrocarbon emission in powerful high-redshift radio galaxies

Creators

  • 1. ROR icon University College London
  • 2. ROR icon Astronomy and Space
  • 3. ROR icon European Southern Observatory
  • 4. ROR icon Jet Propulsion Lab
  • 5. ROR icon California Institute of Technology
  • 6. ROR icon Infrared Processing and Analysis Center
  • 7. ROR icon Institut de Recherche sur les Lois Fondamentales de l'Univers
  • 8. ROR icon Leiden University
  • 9. ROR icon Durham University
  • 10. ROR icon Tufts University
  • 11. ROR icon Haverford College
  • 12. ROR icon University of Copenhagen

Abstract

We present the mid-infrared (IR) spectra of seven of the most powerful radio-galaxies known to exist at 1.5 < z < 2.6. The radio emission of these sources is dominated by the AGN with 500 MHz luminosities in the range 10^(27.8)–10^(29.1) W Hz^(−1). The AGN signature is clearly evident in the mid-IR spectra; however, we also detect polycyclic aromatic hydrocarbon emission, indicative of prodigious star formation at a rate of up to ∼1000 M_⊙ yr^(−1). Interestingly, we observe no significant correlation between AGN power and star formation in the host galaxy. We also find most of these radio galaxies to have weak 9.7 μm silicate absorption features (τ_(9.7 μm) < 0.8) which implies that their mid-IR obscuration is predominantly due to the dusty torus that surrounds the central engine, rather than the host galaxy. The tori are likely to have an inhomogeneous distribution with the obscuring structure consisting of individual clouds. We estimate that these radio galaxies have already formed the bulk of their stellar mass and appear to lie at a stage in their evolution where the obscured AGN dominates the energy output of the system but star formation is also prevalent.

Additional Information

© 2012 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. First published online: December 5, 2012. Accepted 2012 November 6. Received 2012 November 6; in original form 2012 July 18. We thank the anonymous referee and R.C. Hickox for their useful comments which improved the manuscript. JIR acknowledges the support of a Science and Technologies Facilities Council studentship. NS is the recipient of an Australian Research Council Future Fellowship. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory (JPL), California Institute of Technology (Caltech) under contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech. The IRS was a collaborative venture between Cornell University and Ball Aerospace Corporation funded by NASA through JPL and Ames Research Center. This work benefitted from the NASA/IPAC Extragalactic Database (NED), which is operated by the JPL, Caltech, under contract with NASA.

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Additional details

Identifiers

Eprint ID
39078
Resolver ID
CaltechAUTHORS:20130625-104025806

Funding

Science and Technology Facilities Council (STFC)
Australian Research Council
NASA/JPL/Caltech
NASA Ames Research Center

Dates

Created
2013-06-25
Created from EPrint's datestamp field
Updated
2021-11-09
Created from EPrint's last_modified field