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Unbound Tails and Compressed Heads: A JCMT Study of the SFO 38 Cloud

Puja Porel, Archana Soam, Janik Karoly, Eun Jung Chung, Chang Won Lee, Shinyoung Kim, Shivani Gupta, Neha Sharma

TL;DR

This study uses JCMT-HARP CO $J=3-2$ observations to dissect SFO 38, a bright-rimmed cloud exposed to UV from HD 206267, testing radiatively driven implosion (RDI) as a driver of star formation. Through LTE-based physical-property calculations, virial analyses, and turbulence assessments, the authors find that the dense southern head is gravitationally bound and actively forming stars, while the NW and NE tails are unbound and expanding under external pressure, with no current star formation. They quantify a mass-transfer rate from head to NW tail of about $3.6 imes10^{-4}$ M$_\,odot$ yr$^{-1}$ using a cylindrical-filament framework, illustrating how RDI can both trigger and quench star formation within a single cloud. Overall, the work highlights the dual role of radiative feedback in sculpting the star-formation efficiency of bright-rimmed clouds like SFO 38, promoting core collapse in the head while dispersing material in the tails.

Abstract

SFO 38, located in the Cepheus molecular cloud within the northern part of the HII region IC 1396, is shaped by intense ultraviolet radiation from the nearby O6.5V-type star HD 206267 and represents a classic example of a bright-rimmed cloud (BRC) undergoing radiatively driven implosion (RDI). While previous studies have examined the southern globule using CS and 13CO (1-0), we present a refined analysis using high-resolution JCMT-HARP observations in the 12CO, 13CO, and C18O (J = 3-2) lines, deriving key physical parameters along with virial mass and turbulence properties of the southern head. We also perform the first detailed investigation of the northeastern and northwestern tails, determining their morphological dimensions and internal conditions, including excitation temperature, column density, mass, and volume density. Spectral and stability analyses reveal that the tail regions are gravitationally unbound and dynamically expanding, explaining the lack of active star formation. Our results further shed light on the evolutionary fate of these structures, assessing whether they may accumulate sufficient material to become future sites of star formation or remain quiescent. Overall, this work highlights the dual role of RDI in this BRC: while it triggers star formation in the dense head, it simultaneously disperses and dynamically reshapes the extended tails.

Unbound Tails and Compressed Heads: A JCMT Study of the SFO 38 Cloud

TL;DR

This study uses JCMT-HARP CO observations to dissect SFO 38, a bright-rimmed cloud exposed to UV from HD 206267, testing radiatively driven implosion (RDI) as a driver of star formation. Through LTE-based physical-property calculations, virial analyses, and turbulence assessments, the authors find that the dense southern head is gravitationally bound and actively forming stars, while the NW and NE tails are unbound and expanding under external pressure, with no current star formation. They quantify a mass-transfer rate from head to NW tail of about M yr using a cylindrical-filament framework, illustrating how RDI can both trigger and quench star formation within a single cloud. Overall, the work highlights the dual role of radiative feedback in sculpting the star-formation efficiency of bright-rimmed clouds like SFO 38, promoting core collapse in the head while dispersing material in the tails.

Abstract

SFO 38, located in the Cepheus molecular cloud within the northern part of the HII region IC 1396, is shaped by intense ultraviolet radiation from the nearby O6.5V-type star HD 206267 and represents a classic example of a bright-rimmed cloud (BRC) undergoing radiatively driven implosion (RDI). While previous studies have examined the southern globule using CS and 13CO (1-0), we present a refined analysis using high-resolution JCMT-HARP observations in the 12CO, 13CO, and C18O (J = 3-2) lines, deriving key physical parameters along with virial mass and turbulence properties of the southern head. We also perform the first detailed investigation of the northeastern and northwestern tails, determining their morphological dimensions and internal conditions, including excitation temperature, column density, mass, and volume density. Spectral and stability analyses reveal that the tail regions are gravitationally unbound and dynamically expanding, explaining the lack of active star formation. Our results further shed light on the evolutionary fate of these structures, assessing whether they may accumulate sufficient material to become future sites of star formation or remain quiescent. Overall, this work highlights the dual role of RDI in this BRC: while it triggers star formation in the dense head, it simultaneously disperses and dynamically reshapes the extended tails.
Paper Structure (16 sections, 24 equations, 7 figures, 3 tables)

This paper contains 16 sections, 24 equations, 7 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Archive Data
  3. Results
  4. Examining Moment Maps and Spectral Features
  5. Analysis
  6. Physical Properties of the Southern head
  7. Excitation temperature and optical depth
  8. Mass and stability analysis
  9. Turbulence parameters
  10. Physical Properties of NW and NE tails
  11. Excitation temperature and optical depth
  12. Mass and stability analysis
  13. Turbulent properties
  14. Spectral Profile-Based Gas Kinematics Study of the Northwestern and Northeastern Tails of SFO 38
  15. Discussion
  16. ...and 1 more sections

Figures (7)

  • Figure 1: The WISE 12-micron intensity map, encompassing a region approximately 3.4$^\circ \times$ 3.4$^\circ$ in a two-dimensional projection, is displayed at an angular resolution of 6.5$\arcsec$. The map highlights the locations of prominent bright-rimmed clouds: SFO 36, SFO 37, and SFO 39, marked by red, white, and yellow plus symbols, respectively. A red rectangular box, approximately 19$^\prime \times$ 16$^\prime$ in size, delineates the bright-rimmed cloud SFO 38, which has been observed with the JCMT telescope for $^{12}$CO, $^{13}$CO, and C$^{18}$O J = 3-2 transitions. The position of the ionizing source, the O6.5V-type star HD 206267, is marked with a white star symbol, signifying its pivotal role in driving the photoionization and shaping the morphology of SFO 38.
  • Figure 2: Left: The integrated intensity (moment-0) map of $^{12}$CO (3-2) is presented for the bright-rimmed cloud SFO 38, constructed over the velocity range from -6.38 km s$^{-1}$ to 9.29 km s$^{-1}$. Contours are drawn above the 3$\sigma$ level of the background noise, where $\sigma \approx 1.46$ K km s$^{-1}$ represents the standard deviation of the background noise. The contour levels are set at 3$\sigma$, 6$\sigma$, 10$\sigma$, 20$\sigma$, 30$\sigma$, 40$\sigma$, 50$\sigma$, 60$\sigma$, and 70$\sigma$ values. Middle: The integrated intensity (moment-0) map of $^{13}$CO (3-2) is shown for cloud SFO 38, created within the velocity range of -2.16 km s$^{-1}$ to 2.44 km s$^{-1}$. Contours are drawn above the 3$\sigma$ threshold of the background noise, where $\sigma \approx 0.71$ K km s$^{-1}$ denotes the standard deviation of the background noise. The contour levels are spaced at intervals of 6$\sigma$. Right: The integrated intensity (moment-0) map of C$^{18}$O (3-2) is depicted for the cloud SFO 38, created over the velocity range from -1.63 km s$^{-1}$ to 2.21 km s$^{-1}$. The contours are drawn above the 3$\sigma$ level of the background noise, where $\sigma \approx 0.83$ K km s$^{-1}$ represents the standard deviation of the background noise. The contour levels are set at intervals of 3$\sigma$. The red star symbols denote the location of the embedded IRAS source, while the black arrow represents the direction of incident ionizing radiation originating from the massive O-type star HD 206267.
  • Figure 3: Left: Spatial segmentation of the SFO 38 cloud into three distinct morphological components. The black, blue, and green rectangular overlays on the $^{13}$CO (J=3--2) moment 0 map correspond to the southern head, northwestern tail, and northeastern tail regions, respectively. Right: Spectral profiles extracted from the southern head (top), northwestern tail (middle), and northeastern tail (bottom) are displayed, with $^{12}$CO (J=3--2) and $^{13}$CO (J=3--2) emissions shown in black and blue, respectively. Each $^{12}$CO spectrum is scaled by a factor of 1.5 relative to the $^{13}$CO spectrum, which is baseline-adjusted to 0 K, to enhance visualization and clearly distinguish the spectral profiles of both tracers. The vertical dashed lines show different velocity peaks seen in the $^{12}$CO emission.
  • Figure 4: Left: The intensity-weighted velocity (moment-1) map for $^{12}$CO (3–2) emission, constructed over the velocity range from $-6.38$ km s$^{-1}$ to $9.29$ km s$^{-1}$, is displayed. This map is superimposed with the $^{12}$CO integrated intensity contours of the bright-rimmed cloud SFO 38. The contour levels are set to be the same as those in Figure \ref{['Fig: moment 0 map']}. Right: The intensity-weighted velocity (moment-1) map for $^{13}$CO (3–2) emission, generated within the velocity range of $-2.16$ km s$^{-1}$ to $2.44$ km s$^{-1}$, is presented. Overlaid are the $^{13}$CO integrated intensity contours for the SFO 38 cloud, with contour levels set to be the same as those in Figure \ref{['Fig: moment 0 map']}. The green star symbols denote the location of the embedded IRAS source, while the black arrow represents the direction of incident ionizing radiation originating from the massive O-type star HD 206267.
  • Figure 5: Upper left:Excitation temperature map within $^{13}$CO (3--2) emission region in the SFO 38 bright-rimmed cloud. Upper right: Hydrogen column density map based on $^{13}$CO emission. Lower: 3-dimensional non-thermal velocity dispersion map based on $^{13}$CO emission. Each map is overlaid with the C$^{18}$O integrated intensity contours. The red star symbols show the position of the IRAS source.
  • ...and 2 more figures