Ambipolar diffusion and the molecular abundances in pre-stellar cores

Priestley, F. D.; Wurster, James; Viti, S.

doi:10.1093/mnras/stz1869

Cited by 20 publications

(29 citation statements)

References 37 publications

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“…Federrath (2016) find that the inclusion of magnetic fields does not significantly affect the properties of filaments formed in their simulations. However, dynamically important magnetic fields can have a major effect on the abundances of key molecules, particularly in the densest regions (Tassis et al 2012;Priestley et al 2018Priestley et al , 2019. Other models of filament formation, such as cloud-cloud collisions (e.g.…”

Section: Discussionmentioning

confidence: 99%

“…For isothermal gas where hydrogen is already in molecular form, the chemical evolution is almost completely decoupled from the hydrodynamics. We can therefore post-process our SPH results with a time-dependent chemical code, as in Priestley, Wurster & Viti (2019). We use a subset of 10 000 SPH particles, 1 chosen randomly from those with initial positions inside the cloud, and input their density evolution as a function of time into UCL CHEM (Holdship et al 2017), which uses the UMIST12 reaction network (McElroy et al 2013) with additional molecular freeze-out and grain surface reactions as described in Holdship et al (2017).…”

Section: E T H O Dmentioning

confidence: 99%

“…In some previous work on prestellar cores, the visual extinction A V at each point in the cloud has either been calculated exactly exploiting imposed symmetries (e.g. Aikawa et al 2005;Tassis et al 2012;Priestley, Viti & Williams 2018), or has been assumed to be large enough, due to external shielding, to make the radiation field negligible (Priestley et al 2019). The former situation does not apply to turbulent clouds, while on scales of 1 pc, the second is not justifiable either.…”

Section: E T H O Dmentioning

confidence: 99%

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Synthetic line and continuum observations of simulated turbulent clouds: the apparent widths of filaments

Priestley

Whitworth

2020

Monthly Notices of the Royal Astronomical Society

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Filamentary structures are ubiquitous in observations of real molecular clouds, and also in simulations of turbulent, self-gravitating gas. However, making comparisons between observations and simulations is complicated by the difficulty of estimating volume-densities observationally. Here, we have post-processed hydrodynamical simulations of a turbulent isothermal molecular cloud, using a full time-dependent chemical network. We have then run radiative transfer models to obtain synthetic line and continuum intensities that can be compared directly with those observed. We find that filaments have a characteristic width of ∼ 0.1 pc, both on maps of their true surface density, and on maps of their 850 μm dust-continuum emission, in agreement with previous work. On maps of line emission from CO isotopologues, the apparent widths of filaments are typically several times larger because the line intensities are poorly correlated with the surface density. On maps of line emission from dense-gas tracers such as N2H+ and HCN, the apparent widths of filaments are $\lesssim 0.1\, {\rm pc}$. Thus, current observations of molecular-line emission are compatible with the universal 0.1 pc filament width inferred from Herschel observations, provided proper account is taken of abundance, optical-depth, and excitation considerations. We find evidence for ∼0.4 km s−1 radial velocity differences across filaments. These radial velocity differences might be a useful indicator of the mechanism by which a filament has formed or is forming, for example the turbulent cloud scenario modelled here, as against other mechanisms such as cloud-cloud collisions.

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Section: Discussionmentioning

confidence: 99%

Section: E T H O Dmentioning

confidence: 99%

Section: E T H O Dmentioning

confidence: 99%

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Synthetic line and continuum observations of simulated turbulent clouds: the apparent widths of filaments

Priestley

Whitworth

2020

Monthly Notices of the Royal Astronomical Society

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“…Following Priestley et al (2019), we use the PHANTOM smoothed particle (magneto)hydrodynamics (SPH) code (Price et al 2018) to run models of spherical, static, uniform density pre-stellar cores with a constant magnetic field in the z-direction. The ambipolar diffusion coefficient is calculated using the NICIL library (Wurster 2016); as NICIL does not include molecular ions, which are the dominant ionized species at the densities we investigate, we assume that the ion density is given by…”

Section: E T H O Dmentioning

confidence: 99%

“…In Priestley, Wurster & Viti (2019), we post-processed a fully three-dimensional non-ideal magnetohydrodynamical (MHD) model with a time-dependent chemical network in order to determine the molecular structure of initially subcritical and supercritical collapse models. While several molecules differ by orders of magnitude in abundance in the central regions of the pre-stellar cores, due to enhanced freeze-out in the subcritical models, we found the molecular column density profiles were too similar to distinguish the two cases, due to intervening material along the line of sight.…”

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confidence: 99%

Investigating the role of magnetic fields in star formation using molecular line profiles

Yin

Priestley

Wurster

2021

Monthly Notices of the Royal Astronomical Society

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Determining the importance of magnetic fields in star forming environments is hampered by the difficulty of accurately measuring both field strength and gas properties in molecular clouds. We post-process three-dimensional non-ideal magnetohydrodynamic simulations of prestellar cores with a time-dependent chemical network, and use radiative transfer modelling to calculate self-consistent molecular line profiles. Varying the initial mass-to-flux ratio from sub- to super-critical results in significant changes to both the intensity and shape of several observationally important molecular lines. We identify the peak intensity ratio of N2H+ to CS lines, and the CS J = 2 − 1 blue-to-red peak intensity ratio, as promising diagnostics of the initial mass-to-flux ratio, with N2H+/CS values of >0.6 (<0.2) and CS blue/red values of <3 (>5) indicating subcritical (supercritial) collapse. These criteria suggest that, despite presently being magnetically supercritical, L1498 formed from subcritical initial conditions.

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Chemistry and dynamics of the prestellar core L1544

Sipilä

Caselli

Redaelli

et al. 2022

A&A

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We aim to quantify the effect of chemistry on the infall velocity in the prestellar core L1544. Previous observational studies have found evidence for double-peaked line profiles for the rotational transitions of several molecules, which cannot be accounted for with the models presently available for the physical structure of the source, without ad hoc up-scaling of the infall velocity. We ran one-dimensional hydrodynamical simulations of the collapse of a core with L1544-like properties (in terms of mass and outer radius), using a state-of-the-art chemical model with a very large chemical network combined with an extensive description of molecular line cooling, determined via radiative transfer simulations, with the aim of determining whether these expansions of the simulation setup (as compared to previous models) can lead to a higher infall velocity. After running a series of simulations where the simulation was sequentially simplified, we found that the infall velocity is almost independent of the size of the chemical network or the approach to line cooling. We conclude that chemical evolution does not have a large impact on the infall velocity, and that the higher infall velocities that are implied by observations may be the result of the core being more dynamically evolved than what is now thought, or alternatively the average density in the simulated core is too low. However, chemistry does have a large influence on the lifetime of the core, which varies by about a factor of two across the simulations and grows longer when the chemical network is simplified. Therefore, although the model is subject to several sources of uncertainties, the present results clearly indicate that the use of a small chemical network leads to an incorrect estimate of the core lifetime, which is naturally a critical parameter for the development of chemical complexity in the precollapse phase.

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Ambipolar diffusion and the molecular abundances in pre-stellar cores

Cited by 20 publications

References 37 publications

Synthetic line and continuum observations of simulated turbulent clouds: the apparent widths of filaments

Synthetic line and continuum observations of simulated turbulent clouds: the apparent widths of filaments

Investigating the role of magnetic fields in star formation using molecular line profiles

Chemistry and dynamics of the prestellar core L1544

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