Spectral Energy Distributions of QSOs at z > 5: Common Active Galactic Nucleus-heated Dust and Occasionally Strong Star-formation

Author(s)

C. Leipski, K. Meisenheimer, Fabian Walter, Helmut Dannerbauer, U. Klaas, Giuseppe De Rosa, X. Fan, M. Haas, Oliver Krause, Hans-Walter Rix

Abstract

We present spectral energy distributions (SEDs) of 69 QSOs at z > 5, covering a rest frame wavelength range of 0.1 μm to ∼80 μm, and centered on new Spitzer and Herschel observations. The detection rate of the QSOs with Spitzer is very high (97% at λ

_rest ≲ 4 μm), but drops toward the Herschel bands with 30% detected in PACS (rest frame mid-infrared) and 15% additionally in the SPIRE (rest frame far-infrared; FIR). We perform multi-component SED fits for Herschel-detected objects and confirm that to match the observed SEDs, a clumpy torus model needs to be complemented by a hot (∼1300 K) component and, in cases with prominent FIR emission, also by a cold (∼50 K) component. In the FIR-detected cases the luminosity of the cold component is of the order of 10

¹³ LȮ which is likely heated by star formation. From the SED fits we also determine that the active galactic nucleus (AGN) dust-to-accretion disk luminosity ratio declines with UV/optical luminosity. Emission from hot (∼1300 K) dust is common in our sample, showing that nuclear dust is ubiquitous in luminous QSOs out to redshift 6. However, about 15% of the objects appear under-luminous in the near infrared compared to their optical emission and seem to be deficient in (but not devoid of) hot dust. Within our full sample, the QSOs detected with Herschel are found at the high luminosity end in L

_UV/opt and L

_NIR and show low equivalent widths (EWs) in Hα and in Lyα. In the distribution of Hα EWs, as determined from the Spitzer photometry, the high-redshift QSOs show little difference to low-redshift AGN.

Organisation(s)

Department of Astrophysics

External organisation(s)

Max-Planck-Institut für Astronomie, Ohio State University, University of Arizona, Ruhr-Universität Bochum (RUB)

Journal

The Astrophysical Journal

Volume

785

No. of pages

22

ISSN

0004-637X

DOI

https://doi.org/10.1088/0004-637X/785/2/154

Publication date

04-2014

Peer reviewed

Yes

Austrian Fields of Science 2012

103003 Astronomy, 103004 Astrophysics

Keywords

ASJC Scopus subject areas

Astronomy and Astrophysics, Space and Planetary Science

Portal url

https://ucrisportal.univie.ac.at/en/publications/0d15959a-fe3e-48be-bc4c-0a872e34000a