Fomalhaut debris disk emission at 7 millimeters: constraints on the collisional models of planetesimals

TL;DR

This study uses 7 mm observations of the Fomalhaut debris disk to analyze dust emission and grain size distribution, providing constraints on collisional models of planetesimals and supporting classical steady-state cascade predictions.

Contribution

First spatially resolved 7 mm observations of the Fomalhaut debris disk combined with sub-mm data to constrain dust grain size distribution and test collisional models.

Findings

Derived a grain size distribution slope q = 3.48 ± 0.14.

Results support classical collisional cascade models.

More recent models with size-dependent velocity or tensile strength are inconsistent.

Abstract

We present new spatially resolved observations of the dust thermal emission at 7 mm from the Fomalhaut debris disk obtained with the Australia Telescope Compact Array. These observations provide the longest wavelength detection of the Fomalhaut debris disk to date. We combined the new data to literature sub-mm data to investigate the spectral index of the dust thermal emission in the sub-millimeter and constrained the $q$-slope of the power-law grain size distribution. We derived a value for $q = 3.48 \pm 0.14$ for grains with sizes around 1 mm. This is consistent with the classical prediction for a collisional cascade at the steady-state. The same value cannot be explained by more recent collisional models of planetesimals in which either the velocity distribution of the large bodies or their tensile strength is a strong function of the body size.