The Ophiuchus DIsk Survey Employing ALMA (ODISEA): Complete Size Distributions for the 100 Brightest Disks Across Multiplicity and SED Classes

TL;DR

This study provides the first complete size distribution of the 105 brightest protoplanetary disks in Ophiuchus, revealing median sizes around 14 au and smaller sizes in binary systems, with implications for dust evolution and early disk structures.

Contribution

It presents the largest flux-limited, resolved disk sample in a star-forming region, measuring disk sizes across different evolutionary stages and binary configurations using high-resolution ALMA data.

Findings

Disk sizes follow a log-normal distribution with median ~14 au.

Disks in close binaries are significantly smaller (~5 au).

Similar size distributions in Class I and Class II disks suggest early pressure bumps.

Abstract

The size of a protoplanetary disk is a fundamental property, yet most remain unresolved, even in nearby star-forming regions (d $\sim$ 140-200 pc). We present the complete continuum size distribution for the $105$ brightest protoplanetary disks (M$_{\text{dust}}$ $\gtrsim$ 2 M$_{\oplus}$) in the Ophiuchus cloud, obtained from ALMA Band 8 (410 GHz) observations at 0.05$^{\prime\prime}$ (7 au) to 0.15$^{\prime\prime}$ (21 au) resolution. This sample includes 54 Class II and 51 Class I and Flat Spectrum sources, providing a comprehensive distribution across evolutionary stages. We measure the Half Width at Half Maximum (HWHM) and the radius encircling $68\%$ of the flux ($R_{68\%}$) for most non-binary disks, yielding the largest flux-limited sample of resolved disks in any star-forming region. The distribution is log-normal with a median value of $\sim$14 au and a logarithmic standard deviation $\sigma_{\log} = 0.46$ (factor of 2.9 in linear scale). Disks in close binary systems ($<$ 200 au separation) have smaller radii, with median value of $\sim$5 au, indicating efficient radial drift as predicted by dust evolution models. The size distribution for young embedded objects (SED Class I and Flat Spectrum, age $\lesssim$ 1 Myr) is similar to that of Class II objects (age $\sim$ a few Myr), implying that pressure bumps must be common at early disk stages to prevent mm-sized particle migration at au scales.