Probing the Evolution of IR Properties of z~6 Quasars: Spitzer Observations

Abstract

We present Spitzer observations of thirteen z~6 quasars using the Infrared Array Camera (IRAC) and Multiband Imaging Photometer for Spitzer (MIPS). All the quasars except SDSS J000552.34-000655.8 (SDSS J0005-0006) were detected with high S/N in the four IRAC channels and the MIPS 24um band, while SDSS J0005-0006 was marginally detected in the IRAC 8.0um band, and not detected in the MIPS 24um band. We find that most of these quasars have prominent emission from hot dust as evidenced by the observed 24um fluxes. Their spectral energy distributions (SEDs) are similar to those of low-redshift quasars at rest-frame 0.15-3.5 um, suggesting that accretion disks and hot-dust structures for these sources already have reached maturity. However, SDSS J0005-0006 has an unusual SED that lies significantly below low-redshift SED templates at rest-frame 1 and 3.5 um, and thus shows a strong near-IR (NIR) deficit and no hot-dust emission. Type I quasars with extremely small NIR-to-optical flux ratios like SDSS J0005-0006 are not found in low-redshift quasar samples, indicating that SDSS J0005-0006 has different dust properties at high redshift. We combine the Spitzer observations with X-ray, UV/optical, mm/submm and radio observations to determine bolometric luminosities for all the quasars. We find that the four quasars with central black-hole mass measurements have Eddington ratios of order unity.

22 pages, 5 figures, accepted by AJ

References in corpus (1)

• High-resolution radio imaging of the most distant radio quasar SDSS J0836+0054

Cited by in corpus (25)

• Formation of z ~ 6 quasars from hierarchical galaxy mergers
• Dust covering factor, silicate emission and star formation in luminous QSOs
• The Evolution of Dust in the Early Universe with Applications to the Galaxy SDSS J1148+5251
• 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
• A Survey of z~6 Quasars in the SDSS Deep Stripe: I. a Flux-Limited Sample at z_{AB}<21
• Black-Hole Mass and Growth Rate at High Redshift
• Star formation in the hosts of high-z QSOs: Evidence from Spitzer PAH detections
• Thermal Emission from Warm Dust in the Most Distant Quasars
• Reliable Identification of Compton-thick Quasars at z~2: Spitzer Mid-IR spectroscopy of HDF-oMD49
• Are Optically-Selected Quasars Universally X-Ray Luminous? X-Ray/UV Relations in Sloan Digital Sky Survey Quasars
• A Population of Massive and Evolved Galaxies at z$\ga$5
• Six more quasars at redshift 6 discovered by the Canada-France High-z Quasar Survey
• Aromatic Features in AGN: Star-Forming Infrared Luminosity Function of AGN Host Galaxies
• LCDM predictions for galaxy protoclusters I: the relation between galaxies, protoclusters and quasars at z~6
• Millimeter and Radio Observations of z~6 Quasars
• Modeling the Dust Properties of z ~ 6 Quasars with ART^2 -- All-wavelength Radiative Transfer with Adaptive Refinement Tree
• Observations of Dense Molecular Gas in a Quasar Host Galaxy at z=6.42: Further Evidence for a Non-Linear Dense Gas - Star Formation Relation at Early Cosmic Times
• IRS Spectroscopy and Multi-wavelength Study of Luminous Star-forming Galaxies at z~1.9
• Jet enhanced accretion growth of supermassive black holes
• The Nature of CO Emission From z~6 Quasars
• SHARC-II 350 micron Observations of Thermal Emission from Warm Dust in z>=5 Quasars
• An Investigation into the Effects of Luminosity on the Mid-Infrared Spectral Energy Distributions of Radio-Quiet Quasars
• Studying the first galaxies with ALMA
• O/IR Polarimetry for the 2010 Decade (CGT): Science at the Edge, Sharp Tools for All