Dust-free quasars in the early Universe

Abstract

The most distant quasars known, at redshifts z=6, generally have properties indistinguishable from those of lower-redshift quasars in the rest-frame ultraviolet/optical and X-ray bands. This puzzling result suggests that these distant quasars are evolved objects even though the Universe was only seven per cent of its current age at these redshifts. Recently one z=6 quasar was shown not to have any detectable emission from hot dust, but it was unclear whether that indicated different hot-dust properties at high redshift or if it is simply an outlier. Here we report the discovery of a second quasar without hot-dust emission in a sample of 21 z=6 quasars. Such apparently hot-dust-free quasars have no counterparts at low redshift. Moreover, we demonstrate that the hot-dust abundance in the 21 quasars builds up in tandem with the growth of the central black hole, whereas at low redshift it is almost independent of the black hole mass. Thus z=6 quasars are indeed at an early evolutionary stage, with rapid mass accretion and dust formation. The two hot-dust-free quasars are likely to be first-generation quasars born in dust-free environments and are too young to have formed a detectable amount of hot dust around them.

To be published in Nature on the 18 March 2010.

References in corpus (12)

• Biases in Virial Black Hole Masses: An SDSS Perspective
• Four quasars above redshift 6 discovered by the Canada-France High-z Quasar Survey
• Gemini Near-infrared Spectroscopy of Luminous z~6 Quasars: Chemical Abundances, Black Hole Masses, and MgII Absorption
• Black hole masses and enrichment of z ~ 6 SDSS quasars
• Thermal Emission from Warm Dust in the Most Distant Quasars
• Probing the Evolution of IR Properties of z~6 Quasars: Spitzer Observations
• The Toroidal Obscuration of Active Galactic Nuclei
• Chandra Observations of the Highest Redshift Quasars from the Sloan Digital Sky Survey
• Millimeter and Radio Observations of z~6 Quasars
• Dust properties at z=6.3 in the host galaxy of GRB 050904
• Mid-infrared spectroscopy of infrared-luminous galaxies at z~0.5-3
• The Central Engines of Narrow-Line Seyfert 1 Galaxies

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• Dust-Deficient Palomar-Green Quasars and the Diversity of AGN Intrinsic IR Emission
• Observational Signatures of High-Redshift Quasars and Local Relics of Black Hole Seeds
• Rest-frame Optical Spectra and Black Hole Masses of 3<z<6 Quasars
• Discovery of Eight z ~ 6 Quasars in the Sloan Digital Sky Survey Overlap Regions
• On the Scatter in the Radius - Luminosity Relationship for Active Galactic Nuclei
• The AKARI 2.5-5.0 Micron Spectral Atlas of Type-1 Active Galactic Nuclei: Black Hole Mass Estimator, Line Ratio, and Hot Dust Temperature
• On inferring extinction laws in z~6 quasars as signatures of supernova dust
• Quasi-stellar objects in the ALHAMBRA survey. I. Photometric redshift accuracy based on a 23 optical-NIR filter photometry
• The Infrared Medium-deep Survey. III. Survey of Luminous Quasars at 4.7 $\le$ z $\le$ 5.4
• On the Evolution of High-Redshift Active Galactic Nuclei
• The nature of massive black hole binary candidates: II. Spectral energy distribution atlas
• High Star Formation Rates of Low Eddington Ratio Quasars at $z\gtrsim 6$
• Spectral Energy Distribution Variations of Nearby Seyfert Galaxies During AGN Watch Monitoring Programs