Scaling Relations Associated with Millimeter Continuum Sizes in Protoplanetary Disks

TL;DR

This study analyzes millimeter continuum sizes in 105 protoplanetary disks, confirming known correlations and revealing new size relationships with host properties, suggesting optically thick or thin emission scenarios with consistent disk optical depth profiles.

Contribution

It provides a homogenized analysis of archival SMA and ALMA data, extending size-luminosity relations and exploring new correlations with host and accretion properties.

Findings

Continuum luminosity scales linearly with emitting surface area.

Disks are larger around more massive hosts with higher accretion rates.

Size-luminosity relation extends to lower luminosities.

Abstract

We present a combined, homogenized analysis of archival Submillimeter Array (SMA) and Atacama Large Millimeter/submillimeter Array (ALMA) observations of the spatially resolved 340 GHz (870 $\mu$m) continuum emission from 105 nearby protoplanetary disks. Building on the previous SMA survey, we infer surface brightness profiles using a simple model of the observed visibilities to derive the luminosities ($L_{\rm mm}$) and effective sizes ($R_{\rm eff}$) of the continuum emission. With this sample, we confirm the shapes, normalizations, and dispersions for the strong correlations between $L_{\rm mm}$, $M_\ast$ (or $L_\ast$), and $\dot{M}_\ast$ found in previous studies. We also verify the continuum size--luminosity relation determined from the SMA survey alone (extending to an order of magnitude lower $L_{\rm mm}$), demonstrating that the amount of emission scales linearly with the emitting surface area. Moreover, we identify new, although weaker, relationships between $R_{\rm eff}$ and the host and accretion properties, such that disks are larger around more massive hosts with higher accretion rates. We explore these inter-related demographic properties with some highly simplified approximations. These multi-dimensional relationships can be explained if the emission is optically thick with a filling factor of $\sim$0.3, or if the emission is optically thin and disks have roughly the same optical depth profile shapes and normalizations independent of host properties. In both scenarios, we require the dust disk sizes to have a slightly sub-linear relationship with the host mass and a non-negligible dispersion ($\sim$0.2 dex at a given $M_\ast$).