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Mathematisch-Naturwissenschaftliche FakultätAstrophysik I.Physik

Prestellar Core Formation in Colliding Gas Flows: Simulations and Synthetic Observations

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  • Fig. 1 Number of detected cores over time in the colliding flow simulations. The upper plot represents the a-type interface and the lower plot the b-type interface simulations. The colored dots show the results of the 2D dendrogram analysis of the RADMC-3D dust emission maps for runs with different magnetic fields (0.01 μG black, 1.25 μG blue, 2.5 μG green and 5 μG red). The colored lines represent the 3D results, where the colors indicate the same magnetic field strengths as the dots. The 2D dendrogram results match the 3D results quite well.
  • Fig. 2 Histogram of core flow rate estimates obtained from three different methods. The top panel shows the 3D accretion rates, the middle panel presents flow rate estimates based on the pure RADMC-3D emission maps, and the bottom panel displays estimates derived from CASA-processed synthetic observations. The x-axis shows the core flow rate with values binned into 21 logarithmically spaced intervals ranging from 10−6 M⊙ yr−1 to 10−2 M⊙ yr−1. The y-axis represents the number of cores in each bin. The 3D accretion rates range from 10-5 to 10-2 M⊙ yr−1, with a mean value of 6 x 10-4 M⊙ yr−1. Estimates from RADMC-3D images generally underestimate the flow rates. The CASA-derived estimates are shifted to higher flow rates compared to RADMC-3D data. The order of magnitude of the flow rates is preserved in the various methods.

Author: Felix Rauprich

We study core formation and mass accretion processes using a set of magnetized colliding flow simulations from Weis et al. (2024). The simulations are classified into two groups, a- and b-type, that differ in the geometry of the hill-shaped collision interface. In the a-type interface, the spacing between the undulations is five times larger than in the b-type simulations.

To connect simulation results to real observations, we employ the radiative transfer tool RADMC-3D to generate synthetic emission maps, including 1.3 mm continuum images and molecular line cubes of 13CO and H2CO. Dense cores are identified via a dendrogram algorithm on the dust continuum maps. For each identified core, we extract cutouts that are then processed with CASA (the Common Astronomy Software Applications package, primarily used for the calibration and imaging of ALMA data)  to simulate synthetic ALMAGAL (the ALMA Survey of High-Mass Star-Forming Regions) observations. This allows us to assess how observational effects impact both core mass and accretion rate estimates.

We observe core formation in nearly all considered simulations, except in the strongest magnetic field case (5 μG), where core development is largely suppressed. Strong external magnetic fields produce isolated cores (core-fed scenario), whereas weak external magnetic fields lead to groups of cores (clump-fed scenario).

A comparison between 2D dendrogram cores and 3D simulation data shows that the dendrogram-based analysis can successfully recover the main core properties as can be seen in Figure 1, supporting its applicability in real observations.

Comparing RADMC-3D and CASA images reveals that continuum-based mass estimates are robust against observation effects, whereas molecular line emission suffers from missing flux due to large-scale structures not captured by interferometry.

In addition, we estimate gas flow rates onto the cores. There we find typical values of the order of 10-4 M⊙ yr−1, which is consistent with observational results. The observer-based method applied to both RADMC-3D and CASA images retrieves flow rates of the same order of magnitude but is affected by projection uncertainties and, in the CASA case, by blurred emission, which can lead to overestimated column densities near the core. The flow rate estimates and the influence of observer effects are presented in Figure 2.