The dust attenuation law in $z\sim 6$ quasars

TL;DR

This study combines simulations and radiative transfer to analyze dust attenuation in $z ilde{6}$ quasars, finding that models with reduced small grains fit observed data and produce flat attenuation curves similar to the Milky Way.

Contribution

It introduces a novel approach by integrating hydrodynamical simulations with radiative transfer to constrain dust grain size distributions in high-redshift quasars.

Findings

Small grains are largely removed in models fitting the data.

Attenuation curves are flat and consistent with recent observations.

Effective dust-to-metal ratio is close to Milky Way value.

Abstract

We investigate the attenuation law in $z\sim 6$ quasars by combining cosmological zoom-in hydrodynamical simulations of quasar host galaxies, with multi-frequency radiative transfer calculations. We consider several dust models differing in terms of grain size distributions, dust mass and chemical composition, and compare the resulting synthetic Spectral Energy Distributions (SEDs) with data from bright, early quasars. We show that only dust models with grain size distributions in which small grains ($a < 0.1~\mu$m, corresponding to $\approx 60\%$ of the total dust mass) are selectively removed from the dusty medium provide a good fit to the data. Removal can occur if small grains are efficiently destroyed in quasar environments and/or early dust production preferentially results in large grains. Attenuation curves for these models are close to flat, and consistent with recent data; they correspond to an effective dust-to-metal ratio $f_d \simeq 0.38$, i.e. close to the Milky Way value.