Non-linear dense core formation in the dark cloud L1517

Abstract

We present a solution for the observed core fragmentation of filaments in the Taurus L1517 dark cloud which previously could not be explained (Hacar & Tafalla 2011). Core fragmentation is a vital step for the formation of stars. Observations suggest a connection to the filamentary structure of the cloud gas, but it remains unclear which process is responsible. We show that the gravitational instability process of an infinite, isothermal cylinder can account for the exhibited fragmentation under the assumption that the perturbation grows on the dominant wavelength. We use numerical simulations with the code RAMSES, estimate observed column densities and line-of-sight velocities, and compare them to the observations. A critical factor for the observed fragmentation is that cores grow by redistributing mass within the filament and thus the density between the cores decreases over the fragmentation process. This often leads to wrong dominant wavelength estimates, as it is strongly dependent on the initial central density. We argue that non-linear effects also play an important role on the evolution of the fragmentation. Once the density perturbation grows above the critical line-mass, non-linearity leads to an enhancement of the central core density in comparison to the analytical prediction. Choosing the correct initial conditions with perturbation strengths of around 20%, leads to inclination corrected line-of-sight velocities and central core densities within the observational measurement error in a realistic evolution time.

Filamentary Fragmentation and Accretion in High-mass Star-forming Molecular Clouds

“…Ideally, n c is the undisturbed density before gravitational collapse starts, which is inaccessible in these already starforming clouds. It is inappropriate to use the density between dense cores as an approximation either, as pointed out by Heigl et al (2016). Therefore, we take a range of densities detected in dense cores, 2×10 5 -2×10 6 cm −3 , to approximate n c .…”

Fibers in the NGC 1333 proto-cluster

“…For each of the 14 fibers recovered, we have manually looked for local maxima in their (recovered) total N 2 H + emission maps. We identified as individual fragments all these local maxima with at least a 30 % increase in emission with respect to the immediate surroundings, assumed as the mean intensity I 0 at a distance of 60 arcsec of these peaks, as expected for a centrally condensed, collapsing core entering in the non-linear regime (Inutsuka & Miyama 1997;Heigl et al 2016). When found, the characteristics of these local overdensities (central position, FWHM, mass, ...) are extracted using a 2D gaussian fit of the total integrated emission at these positions after subtracting an emission floor given by I 0 .…”

“…In the prevalent filamentary paradigm of star formation, a vast theoretical framework describes the core formation mechanisms via filament fragmentation (e.g., Larson 1985;Nagasawa 1987;Inutsuka & Miyama 1997;Fiege & Pudritz 2000;Heigl et al 2016). According to these models, the mass of the cores is determined by the evolution of Jeans-unstable density perturbations within individual filaments.…”

Kelvin–Helmholtz instability in self-gravitating streams

“…We here examine the evolution of streams undergoing GI in our simulations, and in particular the properties of clumps formed within them. Regardless of whether GI is dominated by surface or body modes in the linear regime, the end result is always expected to be the collapse of dense, long-lived clumps along the stream axis (N87, H98, Heigl et al 2016Heigl et al , 2018b. Figure 11 shows the evolution of three simulations, each with (M b , δ c ) = (1.0, 100).…”