Radiative Compression of Dense Cores in the Pillars of Creation as Revealed by JWST Extinction Mapping

Abstract

The Pillars of Creation in M16 represent an iconic star-forming region where stellar feedback shapes molecular cloud evolution. We present a detailed investigation of dust extinction and density structure in the Pillars of Creation using multiband photometric observations from \emph{JWST} NIRCam. A high-resolution (2\arcsec) extinction map reaching depths of $A_V\sim 100$ mag has been constructed using NIRCam filters F090W, F200W, F335M, and F444W. This map clearly reveals the intricate structure of dense gas within the molecular cloud in the Pillars of Creation region. Analysis of the column density probability distribution function (N-PDF) exhibits a characteristic lognormal distribution at intermediate extinctions ($A_V\approx10-30$\,mag), which transitions to a power-law tail at high extinctions ($A_V\gtrsim$ 30\,mag) where star-forming cores reside. The power-law slope $α$ displays significant spatial variation, steepening from $α\approx 2.0$ at the pillar tips facing the NGC 6611 cluster to $α\approx$4.0 in regions distant from the cluster. This systematic gradient demonstrates that stellar feedback not only disperses molecular clouds but can also locally enhance the formation of dense, self-gravitating structures through radiative compression.

Figures (5)

• Figure 1: Color-magnitude diagrams derived from JWST/NIRCam photometry of sources detected in the Pillars of Creation region in M16. The panels show F090W versus F090W$-$F200W (a), F200W versus F200W$-$F335M (b), and F335M versus F444W$-$F335M (c). Magenta points indicate synthetic stellar populations generated using the TRILEGAL Galactic model for the same field of view. Black arrows in each panel shows the reddening vector of $A_V=10$ mag calculated using the extinction law of Hensley2023.
• Figure 2: Extinction ($A_V$) map of the Pillars of Creation in M16, derived from JWST/NIRCam photometry. The map has pixel size of 1 and is smoothed with a Gaussian kernel of FWHM = 2. The contours are drawn in black at $A_V=$ [20, 40, 60, 80] mag. A scale bar of 0.5 pc ($\sim$ 1 arcmin) is shown in the lower right corner. The seven labeled subregions (P1a, P1b, P2a, P2b, P3, P4, and the Central Dense Structure, CDS) follow the nomenclature of Dewangan2024 and Karim2023.
• Figure 3: Column-density probability density functions (N-PDFs) derived from our extinction map for the entire Pillars of Creation region and each of the seven subregions (panels labeled as in Figure \ref{['fig:ce_map']}). The lower $x$-axis shows the visual extinction $A_V$, the upper $x$-axis gives the corresponding $\eta = {\rm ln}(A_V/\langle A_V\rangle)$. The $y$-axis is the normalized probability density $p(\eta)$. Histogram with Poisson error bars shown in each bin. Red curves are the best-fit lognormal functions to the low- and moderate-density ranges, and blue lines are the best-fit power-law tails at high density. The specific fitting ranges for the log-normal and power-law components are indicated by the red and blue shaded regions, respectively. The lognormal widths $\sigma$ and power-law indices $\alpha$ are indicated in each panel.
• Figure 4: Comparison with previous large-scale observations of M16. (a) H$_2$ column density map derived from Herschel far-infrared dust emission at 36 resolution Molinari2010. (b) $\rm ^{12}CO(J=1-0)$ integrated intensity map from the FUGIN survey Umemoto2017 at $\sim$33 resolution, integrated over 19.3-27.7 km/s. (c) N-PDF for the Herschel map (panel a); (d) N-PDF for the $^{12}$CO map (panel b). The best-fit lognormal width $\sigma$ and high-$N$ power-law index $\alpha$ are labeled for each N-PDF, with $\sigma=0.13$, $\alpha=3.51$ for the Herschel N-PDF and $\sigma=0.25$, $\alpha=2.45$ for the $^{12}$CO N-PDF, respectively. The red and blue shaded regions in panels (a) and (b) show the specific fitting ranges for the log-normal and power-law components, respectively.
• Figure 5: Spatial distribution of the background field stars used to construct the continuous extinction map, overlaid on the F335M band image. The sample consists of $\sim 10^5$ stars across the observed field. Each point represents an individual star, color-coded by its derived visual extinction ($A_V$). The rectangular boxes with labels mark the limits of the subregions used for the N-PDF fitting in Figure \ref{['fig:npdf_subregions']}. The high spatial density of these probing stars, characterized by a median nearest-neighbour distance of 0.51 , provides sufficient spatial sampling to justify the 2 resolution of the smoothed extinction map presented in Figure \ref{['fig:ce_map']}.