Protoplanetary Disk Properties in the Orion Nebula Cluster: Initial Results from Deep, High-Resolution ALMA Observations

TL;DR

This study uses high-resolution ALMA observations to analyze the properties of protoplanetary disks in the Orion Nebula Cluster, revealing that disks are generally smaller, more compact, and influenced by the cluster environment compared to other regions.

Contribution

First high-resolution, deep ALMA survey of Orion Nebula Cluster disks providing detailed measurements of disk sizes, masses, and environmental effects.

Findings

Disks are particularly compact and likely optically thick.

Smaller, lower-flux disks compared to other star-forming regions.

Weak correlation between disk flux and stellar mass; strong influence of nearby massive stars.

Abstract

We present ALMA 850 $\mu$m continuum observations of the Orion Nebula Cluster that provide the highest angular resolution ($\sim 0\rlap{.}''1 \approx 40$ AU) and deepest sensitivity ($\sim 0.1$ mJy) of the region to date. We mosaicked a field containing $\sim 225$ optical or near-IR-identified young stars, $\sim 60$ of which are also optically-identified "proplyds". We detect continuum emission at 850 $\mu$m towards $\sim 80$% of the proplyd sample, and $\sim 50$% of the larger sample of previously-identified cluster members. Detected objects have fluxes of $\sim 0.5$-80 mJy. We remove sub-mm flux due to free-free emission in some objects, leaving a sample of sources detected in dust emission. Under standard assumptions of isothermal, optically thin disks, sub-mm fluxes correspond to dust masses of $\sim 0.5$ to 80 Earth masses. We measure the distribution of disk sizes, and find that disks in this region are particularly compact. Such compact disks are likely to be significantly optically thick. The distributions of sub-mm flux and inferred disk size indicate smaller, lower-flux disks than in lower-density star-forming regions of similar age. Measured disk flux is correlated weakly with stellar mass, contrary to studies in other star forming regions that found steeper correlations. We find a correlation between disk flux and distance from the massive star $\theta^1$ Ori C, suggesting that disk properties in this region are influenced strongly by the rich cluster environment.