arXiv subjects

Pierre Didelon

Publications and source records attributed to Pierre Didelon.

4 recordsLinked to original sources

arXiv2026

Virial-based extraction of structures in numerical simulations: The vibes tool

The processes that determine the stellar initial mass function (IMF) and its connection to the core mass function (CMF) are among the major open questions in star formation. The definition of a core remains unclear, yet the way they are extracted from simulations and observations critically shapes the CMF. Nowadays, cores are mostly detected through their density or intensity only. We aim to explore a new way to define cores in 3D numerical simulations based on a direct application of the virial theorem, and break free from some limitations induced by density-based methods. We intend to improve the accuracy and the physical meaning of the extracted cores. We developed vibes, an innovative method that makes full use of the virial theorem to extract overdensities in simulation snapshots. It works by building structures iteratively around density peaks, and applying the virial theorem to the structure at each iteration. Then, the structure boundary is set from the evolution of the its energy as it spatially grows. We used STARFORGE simulations to test the sensitivity of the extraction process to the main working parameters (constraints on the structure shape, iteration step, and peak selection criteria). This sensitivity is observed to be low. We compared our extraction with two density-based extraction algorithms, hop and dendrogram, that are observed to be very sensitive to their input density threshold parameter. Vibes returns structures that are coherent to each other and physically motivated, and it appears much more stable than existing 3D extraction tools. By defining the boundary of the cores on a physical criterion rather than on a user-defined set of density parameters, we expect such extracted cores to be closer to their forsaken definition: gas reservoirs that will form a single star or a close multiple system.

astro-ph.SR↗

arXiv2021

Strong dependence of the physical properties of cores on spatial resolution in observations and simulations

During the last decade in star formation research, many studies have targeted low- and high-mass star formation regions located at different distances, with different telescopes having specific angular resolution capabilities. We present a systematic investigation of the angular resolution effects, with special attention being paid to the derived masses of sources as well as the shape of the resulting source mass functions (SMFs). We tested the impact of angular resolution, from 0.6 down to 0.02 pc, in two star-forming regions observed with Herschel (NGC6334 and Aquila), and three (magneto)-hydrodynamical simulations. We detected and measured sources at each resolution using getsf and we analysed the derived masses and sizes of the sources. We find that the number of sources does not converge from 0.6 to 0.05 pc. It increases by about two when the angular resolution increases with a similar factor. Below 0.05 pc, the number of source still increases by about 1.3 when the angular resolution increases by two, suggesting that we are close to, but not yet at, convergence. We find that the measured sizes and masses of sources linearly depend on the angular resolution with no sign of convergence to a resolution-independent value. The corresponding SMF peak also shifts with angular resolution, while the slope of the high-mass tail of the SMFs remains almost invariant. If prestellar cores, physically distinct from their background, exist in cluster-forming molecular clouds, we conclude that their mass must be lower than reported so far in the literature. We discuss various implications for the studies of star formation: the problem of determining the mass reservoirs involved in the star-formation process; the inapplicability of the Gaussian beam deconvolution to infer source sizes; and the impossibility to determine the efficiency of the mass conversion from the cores to the stars.

astro-ph.GA↗

arXiv2016

The scaling relations and star formation laws of ministarburst complexes

The scaling relations and the star formation laws for molecular cloud complexes in the Milky Way is investigated. We compare their masses $M_{\rm gas}$, mass surface densities $Σ_{M_{\rm gas}}$, radii $R$, velocity dispersions $σ$, star formation rates $SFR$, and SFR densities $Σ_{\rm SFR}$ with those of structures ranging from cores, clumps, Giant Molecular Clouds (GMCs), to Molecular Cloud Complexes (MCCs), and to Galaxies, spanning 8 orders of magnitudes in size and 13 orders of magnitudes in mass. MCC are mostly large ($R>50$ pc), massive ($\sim 10^{6}$\,\msun) gravitationally unbound cloud structures. This results in the following universal relations: $σ\sim R^{0.5}$, $M_{\rm gas}\sim R^{2}$, $Σ_{\rm SFR}\sim Σ_{M_{\rm gas}}^{1.5}$, ${SFR}\sim {M_{\rm gas}}^{0.9}$, and ${SFR}\sim σ^{2.7}$. Variations in the slopes and the coefficients of these relations are found at individual scales signifying different physics acting at different scales. Additionally, there are breaks at the MCC scale in the $σ-R$ relation and between the starburst and the normal star-forming objects in the $SFR-M_{\rm gas}$ and $Σ_{\rm SFR}$-$Σ_{\rm M_{\rm gas}}$ relations. We propose to use the Schmidt-Kennicutt diagram to distinguish the starburst from the normal star-forming structures by applying a $Σ_{M_{\rm gas}}$ threshold of $\sim100$\,\msun pc$^{-2}$ and a $Σ_{\rm SFR}$ threshold of 1\,\msun yr$^{-1}$ kpc$^{-2}$. Mini-starburst complexes have enhanced $Σ_{\rm SFR}$ ($>$1\,\msun yr$^{-1}$ kpc$^{-2}$), probably caused by dynamic events such as radiation pressure, colliding flows, or spiral arm gravitational instability. Because of the dynamical evolution, gravitational boundedness does not play a significant role in characterizing the star formation activity of MCCs, especially the mini-starburst complexes.

astro-ph.GA↗

arXiv2011

Filaments and ridges in Vela C revealed by Herschel: from low-mass to high-mass star-forming sites

We present the first Herschel PACS and SPIRE results of the Vela C molecular complex in the far-infrared and submillimetre regimes at 70, 160, 250, 350, and 500 um, spanning the peak of emission of cold prestellar or protostellar cores. Column density and multi-resolution analysis (MRA) differentiates the Vela C complex into five distinct sub-regions. Each sub-region displays differences in their column density and temperature probability distribution functions (PDFs), in particular, the PDFs of the `Centre-Ridge' and `South-Nest' sub-regions appear in stark contrast to each other. The Centre-Ridge displays a bimodal temperature PDF representative of hot gas surrounding the HII region RCW 36 and the cold neighbouring filaments, whilst the South-Nest is dominated by cold filamentary structure. The column density PDF of the Centre-Ridge is flatter than the South-Nest, with a high column density tail, consistent with formation through large-scale flows, and regulation by self-gravity. At small to intermediate scales MRA indicates the Centre-Ridge to be twice as concentrated as the South-Nest, whilst on larger scales, a greater portion of the gas in the South-Nest is dominated by turbulence than in the Centre-Ridge. In Vela C, high-mass stars appear to be preferentially forming in ridges, i.e., dominant high column density filaments.

astro-ph.GA↗