# Thermal Jeans fragmentation within 1000 AU in OMC-1S

## TL;DR

This study uses high-resolution ALMA and VLA observations to analyze the fragmentation process in OMC-1S, revealing a two-level fragmentation pattern likely governed by thermal Jeans processes at scales down to 40 AU.

## Contribution

It provides the first detailed analysis of core fragmentation at scales as small as 40 AU in OMC-1S, identifying characteristic spatial scales and a two-level fragmentation process.

## Key findings

- Identification of a ~560 AU characteristic scale for core grouping.
- Detection of a ~2900 AU filament scale indicating two-level fragmentation.
- Evidence that thermal Jeans processes govern fragmentation at 40 AU scales.

## Abstract

We present subarcsecond 1.3 mm continuum ALMA observations towards the Orion Molecular Cloud 1 South (OMC-1S) region, down to a spatial resolution of 74 AU, which reveal a total of 31 continuum sources. We also present subarcsecond 7 mm continuum VLA observations of the same region, which allow to further study fragmentation down to a spatial resolution of 40 AU. By applying a Mean Surface Density of Companions method we find a characteristic spatial scale at ~560 AU, and we use this spatial scale to define the boundary of 19 `cores' in OMC-1S as groupings of millimeter sources. We find an additional characteristic spatial scale at ~2900 AU, which is the typical scale of the filaments in OMC-1S, suggesting a two-level fragmentation process. We measured the fragmentation level within each core and find a higher fragmentation towards the southern filament. In addition, the cores of the southern filament are also the densest (within 1100 AU) cores in OMC-1S. This is fully consistent with previous studies of fragmentation at spatial scales one order of magnitude larger, and suggests that fragmentation down to 40 AU seems to be governed by thermal Jeans processes in OMC-1S.