Dense cores and filaments in M16: Enhanced formation efficiency in the stellar feedback-driven shell

TL;DR

This study analyzes dense cores and filaments in M16, showing enhanced formation efficiency in feedback-driven shells, providing evidence for positive feedback in star formation.

Contribution

It offers the first detailed observational evidence linking shell-driven feedback to increased filament and core formation in a massive star-forming region.

Findings

Filaments have a median width of 0.4 pc and are mostly supercritical.

Filament formation efficiency is 2.3 times higher within the shell.

Fragmentation timescale is comparable to the shell's dynamical age.

Abstract

We present a comprehensive analysis of dense cores and filamentary structures in the M16 Eagle Nebula using high-resolution ($11.7^{\prime\prime}$) surface density and temperature maps derived from \textit{Herschel} observations. Using the \textit{hires} algorithm for map construction and the \textit{getsf} method for source and filament extraction, we identified 233 cores and 111 filaments in this massive star-forming region. The filaments exhibit a median width of 0.4\,pc -- and a median linear density of 61\,$M_\odot$\,pc$^{-1}$, with 76\% being supercritical for gravitational fragmentation. Our radial analysis of the $\sim$60\,pc diameter shell driven by the central NGC 6611 cluster reveals strong enhancements in structure formation: filament formation efficiency (FFE) is 2.3 times higher within the shell (peaking at 22\%), while core density shows a concurrent 1.5-fold enhancement. The moderate correlation between core density and FFE ($r=0.67$) indicates coupled formation processes. Theoretical analysis demonstrates that observed surface densities exceed the critical threshold for fragmentation by a factor of $\sim$8, with a fragmentation timescale ($\sim$1.5--2.0\,Myr) comparable to the shell's dynamical age ($\sim$1.0--1.3\,Myr), indicating we are observing fragmentation in progress. These results reveal a hierarchical fragmentation sequence -- shell compression $\rightarrow$ filament formation $\rightarrow$ core formation -- providing clear observational evidence for positive feedback where massive star formation triggers secondary structure formation in the surrounding molecular cloud.