The Ophiuchus DIsk Survey Employing ALMA (ODISEA): Complete Size Distributions for the 100 Brightest Disks across Multiplicity and Spectral Energy Distribution Classes

Abstract The size of a protoplanetary disk is a fundamental property, yet most remain unresolved, even in nearby star-forming regions ( d ∼ 140–200 pc). We present the complete continuum size distribution for the 105 brightest protoplanetary disks ( M dust ≳ 2 M ⊕ ) in the Ophiuchus cloud, obtained from ALMA Band 8 (410 GHz) observations at 0 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>″</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 05 (7 au) to 0 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>″</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 15 (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 and the radius encircling 68% of the flux ( R 68% ) for most nonbinary 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 ∼14 au and a logarithmic standard deviation <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>σ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>log</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>0.46</mml:mn> </mml:math> (factor of 2.9 in linear scale). Disks in close-binary systems (&lt;200 au separation) have smaller radii, with a median value of ∼5 au, indicating efficient radial drift as predicted by dust evolution models. The size distribution for young embedded objects (spectral energy distribution Class I and flat spectrum, age ≲1 Myr) is similar to that of Class II objects (age ∼ a few Myr), implying that pressure bumps must be common at early disk stages to prevent millimeter-sized particle migration at astronomical unit scales.