Emergence of high-mass stars in complex fiber networks (EMERGE) IV. Environmental dependence of the fiber widths

TL;DR

This study investigates how the widths of interstellar filaments vary across different star-forming regions, revealing an inverse relationship between fiber width and density, influenced by environmental conditions.

Contribution

It provides the first observational evidence of systematic variation in filament widths across regions, linking fiber properties to environmental factors.

Findings

Median fiber FWHM of ~0.05 pc observed

Inverse dependence of FWHM on central column density

Fibers adjust widths based on environmental pressure

Abstract

Despite their variety of scales throughout the interstellar medium, filaments in nearby low-mass clouds show a characteristic width of $\sim$ 0.1 pc from the analysis of {\it Herschel} observations. The origin of this characteristic width, however, has been a matter of intense discussions during the last decade. We explored a possible variation in this typical width with the EMERGE Early ALMA Survey, which includes seven star-forming regions in Orion (OMC-1/-2/-3/-4 South, LDN 1641N, NGC 2023, Flame Nebula). These targets, which exhibit different physical conditions, star formation histories, mass, and density regimes, were homogeneously surveyed at a resolution of $\sim$ 2000 au in N$_2$H$^+$ (1$-$0) with ALMA+IRAM-30m observations. We characterised the column density and temperature radial profiles of the 152 fibers identified in the survey using the automatic fitting routine FilChap. These Orion fibers show a departure from the isothermal condition with significant outward temperature gradients with $\nabla T_\mathrm{K} > 30$ K pc$^{-1}$. They also show a median full width at half maximum ($FWHM$) of $\sim 0.05$ pc, with a corresponding median aspect ratio of $\sim2$. More relevantly, we observe a systematic variation in these fiber $FWHM$ between different regions in our sample, and a direct inverse dependence of these $FWHM$ on their central column density, $N_0$, above $\gtrsim 10^{22}$ cm$^{-2}$. This dependency agrees with the expected $N_0-FWHM$ anti-correlation predicted in previous theoretical studies. Our homogeneous analysis returns the first observational evidence of an intrinsic and systematic variation in the fiber widths across different star-forming regions. While sharing comparable mass, length, and kinematic properties in all of our targets, fibers appear to adjust their $FWHM$ to their density and to the pressure in their host environment.