Gravitationally unstable condensations revealed by ALMA in the TUKH122 prestellar core in the Orion A cloud

TL;DR

This study used ALMA observations to reveal gravitationally bound condensations within the TUKH122 prestellar core, demonstrating ongoing fragmentation and potential early star formation processes driven by thermal Jeans instability.

Contribution

First detailed ALMA imaging of condensations in TUKH122 showing fragmentation at the prestellar stage with implications for star formation.

Findings

Identified 6 gravitationally bound condensations within TUKH122.

Condensations are separated by the thermal Jeans length.

Evidence of chemical evolution and early collapse signs.

Abstract

We have investigated the TUKH122 prestellar core in the Orion A cloud using ALMA 3 mm dust continuum, N$_2$H$^+$ ($J=1-0$), and CH$_3$OH ($J_K=2_K-1_K$) molecular line observations. Previous studies showed that TUKH122 is likely on the verge of star formation because the turbulence is almost dissipated and chemically evolved among other starless cores in the Orion A cloud. By combining ALMA 12-m and ACA data, we recover extended emission with a resolution of $\sim5"$ corresponding to 0.01 pc and identify 6 condensations with a mass range of $0.1-0.4$ $M_\odot$ and a radius of $\lesssim0.01$ pc. These condensations are gravitationally bound following a virial analysis and are embedded in the filament including the elongated core with a mass of $\sim29$ $M_\odot$ and a radial density profile of $r^{-1.6}$ derived by {\it Herschel}. The separation of these condensations is $\sim0.035$ pc, consistent with the thermal jeans length at a density of $4.4\times10^5$ cm$^{-3}$. This density is similar to the central part of the core. We also find a tendency that the N$_2$H$^+$ molecule seems to deplete at the dust peak condensation. This condensation may be beginning to collapse because the linewidth becomes broader. Therefore, the fragmentation still occurs in the prestellar core by thermal Jeans instability and multiple stars are formed within the TUKH122 prestellar core. The CH$_3$OH emission shows a large shell-like distribution and surrounds these condensations, suggesting that the CH$_3$OH molecule formed on dust grains is released into gas phase by non-thermal desorption such as photoevaporation caused by cosmic-ray induced UV radiation.