First Submillimeter Lights from Dome A: Tracing the Carbon Cycle in the Feedback of Massive Stars

Abstract

The cycling of carbon between its ionized, atomic, and molecular phases shapes the chemical compositions and physical conditions of the interstellar medium (ISM). However, ground-based studies of the full carbon cycle have been limited by atmospheric absorption. Dome~A, the most promising site for submillimeter astronomy, has long resisted successful submillimeter astronomical observations. Using the 60~cm Antarctic Terahertz Explorer, we present the first successful CO ($4-3$) and [CI] ($^3P_1 - ^3P_0$) mapping observations of two archetypal triggered massive star-formation regions at Dome~A. These data, together with archival [CII], provide the first complete characterization of all three carbon phases in these environments. We find elevated C$^{0}$/CO abundance ratios in high-extinction regions, plausibly driven by deep penetration of intense radiation fields from massive stars into a clumpy ISM. These findings mark a major milestone for submillimeter astronomy at Dome~A and offer valuable insights into the impact of massive star feedback on the surrounding ISM.

Figures (11)

• Figure 1: Map of Antarctica with elevation contour lines2020RAA....20..168S, with Dome A higlighted. Reproduced by permission of RAA. All rights reserved. The right inset shows a photo of ATE60 deployed at Dome A in January 2025 during the 41st CHINARE. The red building discernible in the distant background is the Chinese Kunlun Station.
• Figure 2: Three-color composite images of RCW 79 (left) and RCW 120 (right) overlaid with ATE60 [CI] integrated intensity contours. The SARAO (South African Radio Astronomy Observatory) MeerKAT Galactic Plane Survey (SMGPS) 1.3 GHz radio continuum emission, Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) 8 $\mu$m emission, and Multiband Imaging Photometer for Spitzer Galactic Plane Survey (MIPSGAL) 24 $\mu$m emission are shown in red, green, and blue, respectively. For RCW 79 and RCW 120, the [CI] integrated intensity maps span velocity ranges of $-48$ km s$^{-1}$ to $-43$ km s$^{-1}$ and $-13$ km s$^{-1}$ to $-3$ km s$^{-1}$, respectively. Contours are drawn at 4.5 K km s$^{-1}$ with increments of 1.5 K kms$^{-1}$ for RCW 79, and at 15 K km s$^{-1}$ with increments of 4.5 K kms$^{-1}$ for RCW 120.
• Figure 3: Distribution and spectra of C$^{+}$, C$^{0}$, and CO in RCW 79 and RCW 120. (A) CO ($4-3$) integrated intensity map of RCW 79 overlaid with its [CI] integrated intensity contours (blue). The integrated velocity range for CO ($4-3$) is from $-40$ km s$^{-1}$ to $-30$ km s$^{-1}$. The [CI] contours are the same as those in Figure \ref{['fig:3col']}. (B) Similar to panel (A) but overlaid with the [CII] integrated intensity contours (green). The integrated velocity range for [CII] is $-70$ km s$^{-1}$ to $-10$ km s$^{-1}$. The contours start at 25 K km s$^{-1}$ and increase in steps of 10 K km s$^{-1}$. (C) and (D) similar to (A) and (B), respectively, but for RCW 120. The CO ($4$–$3$) and [CII] integrated velocity ranges are $-13$ to $-3$ km s$^{-1}$ and $-30$ to $10$ km s$^{-1}$, respectively; [CII] contours start at 25 K km s$^{-1}$ and increase by 10 K km s$^{-1}$. In panels (A)–(D), the color scale shows the CO ($4$–$3$) integrated intensity, and the beam size is indicated in the lower right corner. (E) [CII], [CI], and CO ($4-3$) spectra of RCW 79 averaged over the region indicated by the CO ($4-3$) integrated intensity map in panels (A)--(B). (F) Similar to panel (E) but for RCW 120. In panel (E), the [CII] spectrum has been scaled down for a better comparison, with the scaling factor provided in the legend. The [CII] 158 $\mu$m data are taken from the SOFIA legacy program FEEDBACK 2021SciA....7.9511L2023AA...679L...5B2020PASP..132j4301S.
• Figure 4: Observed spectra of the selected targets. (A) Integrated-intensity map of $^{13}$CO ($1-0$) overlaid with [CI] contours for RCW 79. The $^{13}$CO ($1-0$) integrated velocity range is from $-$60 km s$^{-1}$ to $-$30 km s$^{-1}$. (B) Integrated-intensity map of $^{13}$CO ($3-2$) overlaid with [CI] contours for RCW 120. The $^{13}$CO ($3-2$) integrated velocity range is from $-$13 km s$^{-1}$ to $-$3 km s$^{-1}$. In panels (A) and (B), the beam sizes are indicated in the lower right corner and the [CI] contours are the same as in Figure \ref{['fig:cycle']}. Panels (C)--(F) present observed spectra of the selected targets which are extracted from the pixels indicated by pluses in panels (A) and (B). The transitions are labeled in each panel and the $^{13}$CO transitions are scaled by a factor of 3 for comparison.
• Figure S1: Posterior probability distributions of $T_{\rm K}$, $n_{\rm H_2}$, log($N_{\rm ^{13}CO}$), and $N_{\rm C^0}/N_{\rm ^{13}CO}$ for RCW 120A from the RADEX models, with the maximum posterior possibility point in the parameter space highlighted by orange lines and points. Contours represent the 0.5, 1.0, 1.5, and 2.0$\sigma$ confidence intervals. The vertical dashed lines represent the 1$\sigma$ dispersion.