Density distributions, magnetic field structures, and fragmentation in high-mass star formation

Abstract

The fragmentation of high-mass star-forming regions depends on a variety of physical parameters, including density, the magnetic field, and turbulent gas properties. We evaluate the importance of the density and magnetic field structures in relation to the fragmentation properties during high-mass star formation. Observing the large parsec-scale Stokes $I$ millimeter dust continuum emission with the IRAM 30\,m telescope and the intermediate-scale ($<$0.1\,pc) polarized submillimeter dust emission with the Submillimeter Array toward a sample of 20 high-mass star-forming regions allows us to quantify the dependence of the fragmentation behavior of these regions on the density and magnetic field structures. Based on the IRAM\,30\,m data, we infer density distributions $n -p $ of the regions with typical power-law slopes $p$ around sim 1.5. There is no obvious correlation between the power-law slopes of the density structures on larger clump scales (sim 1\,pc) and the number of fragments on smaller core scales ($<$0.1\,pc). Comparing the large-scale single-dish density profiles to those derived earlier from interferometric observations at smaller spatial scales, we find that the smaller-scale power-law slopes are steeper, typically around sim 2.0. The flattening toward larger scales is consistent with the star-forming regions being embedded in larger cloud structures that do not decrease in density away from a particular core. The magnetic fields of several regions appear to be aligned with filamentary structures that lead toward the densest central cores. Furthermore, we find different polarization structures; some regions exhibit central polarization holes, whereas other regions show polarized emission also toward the central peak positions. Nevertheless, the polarized intensities are inversely related to the Stokes $I$ intensities, following roughly a power-law slope of $ We estimate magnetic field strengths between sim 0.2 and sim 4.5\,mG, and we find no clear correlation between magnetic field strength and the fragmentation level of the regions. A comparison of the turbulent to magnetic energies shows that they are of roughly equal importance in this sample. The mass-to-flux ratios range between sim 2 and sim 7, consistent with collapsing star-forming regions. Finding no clear correlations between the present-day large-scale density structure, the magnetic field strength, and the smaller-scale fragmentation properties of the regions, indicates that the fragmentation of high-mass star-forming regions may not be affected strongly by the initial density profiles and magnetic field properties. However, considering the limited evolutionary range and spatial scales of the presented CORE analysis, future research directions should include density structure analysis of younger regions that better resemble the initial conditions, as well as connecting the observed intermediate-scale magnetic field structure with the larger-scale magnetic fields of the parental molecular clouds.

The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). XI. Statistical Study of Early Fragmentation

“…What dominates the fragmentation is one key question in star formation that has been investigated in some previous studies (e.g., Zhang et al 2009;Palau et al 2013Palau et al , 2015; Beuther et al 2024). We have the largest sample in IRDCs thanks to the mosaicked high-spatial resolution and highsensitivity ALMA observations.…”

Polarized Light from Massive Protoclusters (POLIMAP). I. Dissecting the Role of Magnetic Fields in the Massive Infrared Dark Cloud G28.37+0.07

“…However, measuring the magnetic field strength and morphology in IRDCs is challenging due to their relatively far distances (d  3 kpc). Advances in the polarimetric capabilities of various single-dish telescopes (e.g., SOFIA-HAWC+, JCMT-POL2, LMT-TolTEC, and IRAM-30m-NIKA2) and the full polarization capabilities of interferometric facilities such as ALMA, SMA, and VLA (e.g., Pattle et al 2017;Beltrán et al 2019;Dall'Olio et al 2019;Añez-López et al 2020;Beuther et al 2020;Cortés et al 2021;Fernández-López et al 2021;Palau et al 2021;Liu et al 2023;Maity et al 2023;Beuther et al 2024) are enabling the studies of B-fields in IRDCs.…”