A 3D physico-chemical model of a pre-stellar core. II. Dynamic chemical evolution in a pre-stellar core model using tracer particles

Abstract

This work explores the differences between static and dynamically evolving physico-chemical models of pre-stellar cores. A 3D MHD model of a pre-stellar core embedded in a dynamic star-forming cloud is post-processed using sequentially dust radiative transfer, a gas-grain chemical model, and a non-LTE line-radiative transfer model. The chemical evolution is modeled along $\sim$20,000 tracer particle trajectories to capture the impact of a realistic dynamical evolution as the core is formed. The emission morphology of CH$_3$OH and $c$-C$_3$H$_2$ and the intensities of CH$_3$OH, $c$-C$_3$H$_2$, CS, SO, HCN, HCO$^+$ and N$_2$H$^+$ are compared with observations of L1544. Our results show a distinct difference in chemical morphology between the dynamical and static models. The dynamical model reproduces the observed spatial distribution of CH$_3$OH and $c$-C$_3$H$_2$ toward L1544, whereas the static model fails to reproduce this morphology. In contrast, when comparing modeled and observed intensities across a broad range of molecules, the static model shows good agreement with observations for L1544. The dynamical model systematically predicts lower abundances and modeled intensities for six of the seven species presented here. For sulphur-bearing species, the intensities are in better agreement with observations when the initial abundances are undepleted in heavier elements. This study reveals distinct differences between dynamical and static physico-chemical models. The static model predicts higher abundances and intensities for the majority of the molecules studied here, compared with the dynamical model. This discrepancy may stem from the specific choices of initial conditions, which could limit the dynamical models ability to fully capture the physical and chemical history. The intensities predicted by the static model are comparable to those observed toward L1544.

Figures (17)

• Figure 1: Projected H$_2$ column densities in the molecular cloud simulation. The white crosses show the location of protostars formed in this snapshot from the simulation (t = 305 kyr). The red diamond marks the protostar that is studied here during the pre-stellar phase. The pre-stellar core studied in this work is centered in the figure for clarity because the box has periodic boundary conditions.
• Figure 2: Four snapshots showing the accretion onto the pre-stellar core at different stages of the simulation. The red dots mark the position of the tracer particle accreted onto the pre-stellar core. Only 20% of the tracer particles are plotted for clarity. The color map shows the projected column density, similar to Fig. \ref{['fig:ramses']}. Zero-age is defined as the onset of star formation in the simulation.
• Figure 3: LM model with 10$^{6}$ yr static phase and $A_\mathrm{v,eff}^\mathrm{amb} = 2$ mag (#3 LM). Top: Integrated intensity levels for CH$_3$OH (white contours) and $c$-C$_3$H$_2$ (red contours) along the three principal axes of the simulation. The color map shows the continuum emission at 1.1 mm. Middle: Slice plot showing the local $\log$$A_\mathrm{v,eff}$ for each principal axes. The upper range of the color map is limited to 10 mag for clarity. Bottom: Slice plot showing the local dust temperature for each principal axes. The red and black contours show the 10 K and 7 K limits, respectively.
• Figure 4: Comparison of the fiducial static model and the fiducial dynamic model, both with the updated network from this work. Top: Static model with LM abundances. The contours show the integrated-intensity levels for CH$_3$OH (white) and $c$-C$_3$H$_2$ (red) along the three principal axes of the simulation. The color map shows the continuum emission at 1.1 mm. Bottom: Similar to the top panel but for dynamical model $\#7$ LM.
• Figure 5: Comparison of the 18 dynamical models. The red and white contours indicate the integrated emission contours for $c$-C$_3$H$_2$ and CH$_3$OH, respectively. The background shows the continuum map of the core at 1.1 mm. The $c$-C$_3$H$_2$ emission generally peaks at the dust continuum peak, while CH$_3$OH is offset toward the more shielded part of the core.