Modeling the Dust Properties ofz∼ 6 Quasars with ART2—All‐Wavelength Radiative Transfer with Adaptive Refinement Tree

Yuexing Li,Xiaohui Fan,Philip F Hopkins,Naoki Yoshida,Lars Hernquist,Thomas J Cox,Linhua Jiang,Volker Springel,Douglas P Finkbeiner

doi:10.1086/529364

Abstract

The detection of large quantities of dust in z ∼ 6 quasars by infrared and radio surveys presents puzzles for the formation and evolution of dust in these early systems. Previously, Li et al. showed that luminous quasars at z≳ 6 can form through hierarchical mergers of gas-rich galaxies, and that these systems are expected to evolve from starburst through quasar phases. Here, we calculate the dust properties of simulated quasars and their progenitors using a three-dimensional Monte Carlo radiative transfer code, ART2 (All-wavelength Radiative Transfer with Adaptive Refinement Tree). ART2 incorporates a radiative equilibrium algorithm which treats dust emission self-consistently, an adaptive grid method which can efficiently cover a large dynamic range in both spatial and density scales, a multiphase model of the interstellar medium which accounts for the observed scaling relations of molecular clouds, and a supernova-origin model for dust which can explain the existence of dust in cosmologically young objects. By applying ART2 to the hydrodynamic simulations of Li et al., we reproduce the observed spectral energy distribution (SED) and inferred dust properties of SDSS J1148+5251, the most distant Sloan quasar. We find that the dust and infrared emission are closely associated with the formation and evolution of the quasar host. The system evolves from a cold to a warm ultraluminous infrared galaxy (ULIRG) owing to heating and feedback from stars and the active galactic nucleus (AGN). Furthermore, the AGN activity has significant implications for the interpretation of observation of the hosts. Our results suggest that vigorous star formation in merging progenitors is necessary to reproduce the observed dust properties of z ∼ 6 quasars, supporting a merger-driven origin for luminous quasars at high redshifts and the starburst-to-quasar evolutionary hypothesis.

Highlights

High-redshift quasars are important for understanding the formation and evolution of galaxies and supermassive black holes (SMBHs) in the early universe
In the past few years, nearly two dozen luminous quasars have been discovered by the Sloan Digital Sky Survey (SDSS; York et al 2000) and the Canada-France High-z Quasar Survey (CFHQS; Willott et al 2007) at z $ 6, corresponding to a time when the universe was less than a billion years old ( Fan et al 2003, 2004, 2006a, 2006b)
We have developed an improved version of this code by implementing an adaptive Cartesian grid on top of the code released by Wood

Summary

Introduction

High-redshift quasars are important for understanding the formation and evolution of galaxies and supermassive black holes (SMBHs) in the early universe. Deep infrared and radio surveys (e.g., Robson et al 2004; Bertoldi et al 2003a; Carilli et al 2004; Charmandaris et al 2004; Beelen et al 2006; Hines et al 2006) have revealed a large amount of cold dust in SDSS J1148+5251 ( hereafter J1148+5251), the most distant Sloan quasar detected at redshift z 1⁄4 6:42 ( Fan et al 2003). The detection of dust is reported in the first four CFHQS quasars at z > 6, including the new record holder CFHQS J2329À0301 at z 1⁄4 6:43 (Willott et al 2007). Maiolino et al (2004) argue, from the observed dust extinction curve of SDSS J1048+4637 at z 1⁄4 6:2, that the dust in these high-z systems may be produced by supernovae

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Discussion

Conclusion