EPoS Contribution
EPoS Contribution
Gravitationally Unstable Condensations Revealed by ALMA in a Prestellar Core in the Orion A Cloud

Satoshi Ohashi
RIKEN, Wako-shi, JP
We have investigated a prestellar core, TUKH122, embedded in a filament in the Orion A cloud using ALMA 3 mm dust continuum, N2H+ (J=1-0), and CH3OH (J=2-1) molecular line observations. This core is likely on the verge of star formation because the turbulence is almost dissipated and is 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 ~5" corresponding to 0.01 pc and identify 6 condensations with a mass range of 0.1-0.4 Msun and a radius of <0.01 pc. These condensations are gravitationally bound following a virial analysis and are embedded in the parent filament with a line mass of Mline ~ 140 Msun/pc and a radial density profile of r-1.6. The separation of condensations found in this starless core is ~0.035 pc, which is almost an order of shorter than that in isolated low-mass star forming regions. The 0.035 pc length is consistent with the thermal Jeans length at a density of 4.4×105 cm-3, which is similar to the central part of the core. Furthermore, this separation is similar to that found in protostellar cores in the Orion A cloud (e.g., OMC-2/3), suggesting that the fragmentation is set on the prestellar stage by thermal Jeans length. We also find a tendency that the N2H+ molecule seems to deplete at the dust peak condensation. This condensation may be beginning to collapse because the linewidth becomes broader. The CH3OH emission shows a large shell-like distribution and surrounds these condensations, suggesting that the CH3OH molecule formed on dust grains is released into gas phase by non-thermal desorption such as photoevaporation caused by cosmic-ray induced UV radiation.
Caption: (Right): The N2H+ velocity-integrated intensity image toward TUKH122 core obtained form ALMA-ACA combined data. The velocity range is 3.4-4.0 km/s. The contours represent the 3 mm dust continuum map. (Left): The CH3OH velocity-integrated inteinsity image toward TUKH122 core obtained form ALMA-ACA combined data.
P. Sanhueza, NAOJ, JP
N. Sakai, RIKEN, JP
R. Kandori, NAOJ, JP
M. Choi, KASI, KR
T. Hirota, NAOJ, JP
Q. Nguyen-Luong, KASI, KR
K. Tatematsu, NAOJ, JP
Suggested Session: Cores