H II regions and supernova remnants associated with molecular clouds: A pilot study with the SARAO MeerKAT Galactic Plane Survey

TL;DR

This work investigates whether feedback from massive stars in H II regions and SNRs triggers star formation by cross-matching MeerKAT SMGPS 1.3 GHz continuum data with the SEDIGISM $^{13}$CO(2-1) cloud survey in the G342 Galactic plane tile. A velocity-window association method, anchored by emission fractions $f_W$ with a threshold of $f_W\geq0.3$, links 131 SMGPS sources to 90 SEDIGISM molecular clouds across 131 complexes and validates CO-derived velocities against available radio-recombination line velocities. The associated clouds are statistically more massive, denser, and dynamically broader than unassociated clouds, with L_radio scaling as $L_{\rm radio}\propto M_{\rm complex}^{0.76}$ and increasing $L_{\rm radio}/M_{\rm complex}$ with source size, implying evolutionary effects and progressive disruption of natal gas; however, no definitive, population-level trigger signature emerges due to sample size and data coverage. The study also yields first kinematic distance estimates for two SNRs, S30047 and S30048, demonstrating the potential of this approach to anchor distances and environmental context for remnants. Altogether, the paper establishes a robust framework for a larger, Galactic-scale assessment of feedback and triggered star formation, leveraging together high-resolution radio continuum and CO datasets.

Abstract

Massive stars (mass beyond 8 solMass) release vast amounts of energy into the interstellar medium through their stellar winds, photoionising radiation and supernova explosions. These processes may compress nearby regions, triggering further star formation, but the significance of triggered star formation across the Galactic disc is not well understood. This pilot study combines 1.3 GHz continuum data from the South African Radio Astronomy Observatory (SARAO) MeerKAT Galactic Plane Survey (SMGPS) with 13CO (2-1) data from the Structure, Excitation, and Dynamics of the Inner Galactic Interstellar Medium (SEDIGISM) survey to identify and examine molecular clouds associated with H II regions and supernovae remnants (SNRs). We focus on their physical properties and massive star formation potential. We identify 268 molecular clouds from the SEDIGISM tile covering the Galactic plane region between 341 and 343 longitude deg and latitude deg equal to or less 0.5, of which 90 clouds (34 per cent) are associated with SMGPS extended sources. Compared to unassociated clouds, we find that associated clouds exhibit significantly higher mean mass (9600 solMass vs. 2500 solMass ) and average gas surface density (104 solMass / pc^2 vs. 67 solMass / pc^2 ), and slightly elevated but comparable virial parameters. We also find that the size-linewidth scaling relation is steeper for associated clouds compared to unassociated clouds. In addition, radio luminosity shows a positive correlation with total complex mass, and the ratio L_radio/L_complex increases with source size, consistent with an evolutionary sequence where expanding H II regions progressively disrupt their natal molecular environment. These findings suggest an enhanced dynamical activity for the associated clouds and support the hypothesis that feedback from massive stars influences molecular cloud properties and may trigger star formation.

Figures (15)

• Figure 1: Top: A section of SARAO MeerKAT 1.3 GHz Galactic Plane Survey intensity image within Galactic longitude range of approximately 341.0 to 343.0 degrees and Galactic latitude $|b|\leq 0.5$ degrees, displayed on a square-root intensity scale. The green, white, and blue polygons outline SMGPS extended Hii regions, diffuse Hii region, and supernova remnants (SNRs), respectively. Bottom: Zeroth moment map of the G342 SEDIGISM $^{13}$CO (2--1) tile, integrated between-150.0 and 50.0 km s$^{-1}$, on a linear intensity scale. The same extended SMGPS sources are overlaid on it with white, red, and magenta polygons identifying extended Hii regions, diffuse Hii regions and SNRs, respectively.
• Figure 2: An example of the SMGPS-SEDIGISM association methodology for the extended SMGPS radio source S30009 2025AA...Bordiu. Top panel: SMGPS intensity map with the lime outline tracing the region of the source on a square-root intensity scale. Middle panel: Mean $^{13}$CO (2--1) spectrum extracted over the entire source area, showing the velocity-coherent emission windows. The best, second best, and third best-matching windows, ranked by the emission fraction ($f_\mathrm{W}$), are represented as Best $\mathrm{W_1}$, 2nd $\mathrm{W_2}$, and 3rd $\mathrm{W_3}$, respectively. Vertical dashed lines in black colour indicate the velocity components of SEDIGISM molecular clouds intersecting the source region. Bottom panels: Moment-0 maps of the three most significant emission windows. The SMGPS source mask is shown as a white polygon, and the spectral windows' velocity ranges and emission fractions are given above each panel.
• Figure 3: Scatter plot of the centroid velocities of matched Hii regions from the SMGPS extended sources versus the systemic velocities of Hii regions from the WISE catalogue of Galactic Hii regions. The colour bar shows the emission fraction $f_\mathrm{W}$ of the associations between the interacting SMGPS extended sources with the associated molecular clouds from the best spectral emission windows. The red line indicates the one-to-one relation. The highlighted data point with red circle is a source with $f_\mathrm{W}$$<0.3$, and represents less reliable association.
• Figure 4: Mean (red) and maximum (blue) absolute velocity discrepancies (|$\Delta_v|$) between WISE RRL velocities and SMGPS-SEDIGISM associations, as a function of the emission fraction ($f_\mathrm{W}$). The dashed green vertical line marks $f_\mathrm{W}$$=0.3$, the threshold adopted in this study. Above this threshold, the mean velocity difference decreases from $\sim 10.5$ km s$^{-1}$ to $\sim 6$ km s$^{-1}$, while the maximum difference drops from $\sim 86$ km s$^{-1}$ to $\sim 35$ km s$^{-1}$. The decreasing trend suggests that a higher emission fraction corresponds to superior kinematic agreement, signifying a more reliable physical association.
• Figure 5: Histogram distribution of the number of SEDIGISM molecular clouds per complex, within the best-matching velocity window, associated with SMGPS sources.