Signatures of Gravitational Instability in Resolved Images of Protostellar Disks

TL;DR

This study uses simulations to identify observational signatures of gravitational instability in protostellar disks, revealing how spiral arms and fragments can be detected in NIR and mm wavelengths, aiding understanding of early star formation.

Contribution

The paper demonstrates how GI-induced structures in protostellar disks produce observable features in NIR and mm wavelengths, linking simulations with recent observations.

Findings

Spiral arms are detectable up to 1 kpc in NIR imaging.

Fragments with masses >=1 MJ are detectable by ALMA within 10 minutes.

GI features resemble structures observed in FU Ori systems.

Abstract

Protostellar (class 0/I) disks, having masses comparable to those of their nascent host stars, and fed continuously from their natal infalling envelopes, are prone to gravitational instability (GI). Motivated by advances in near-infrared (NIR) adaptive optics imaging and mm-wave interferometry, we explore the observational signatures of GI in disks, using hydrodynamical and Monte Carlo radiative transfer simulations to synthesize NIR scattered light images and mm dust continuum maps. Spiral arms induced by GI, located at disk radii of hundreds of AUs, are local overdensities and have their photospheres displaced to higher altitudes above the disk midplane, arms therefore scatter more NIR light from their central stars than inter-arm regions, and are detectable at distances up to 1 kpc by Gemini/GPI, VLT/SPHERE, and Subaru/HiCIAO/SCExAO. By contrast, collapsed clumps formed by disk fragmentation have such strong local gravitational fields that their scattering photospheres are at lower altitudes, such fragments appear fainter than their surroundings in NIR scattered light. Spiral arms and streamers recently imaged in four FU Ori systems at NIR wavelengths resemble GI-induced structures and support the interpretation that FUors are gravitationally unstable protostellar disks. At mm wavelengths, both spirals and clumps appear brighter in thermal emission than the ambient disk and can be detected by ALMA at distances up to 0.4 kpc with one-hour integration times at ~0.1 arcsec resolution. Collapsed fragments having masses >=1 MJ can be detected by ALMA within ~10 minutes.