SMGPS: A study of Galactic HII regions with extended morphology

We present a study of ionised hydrogen (H II) regions in the Galactic Plane using data from the SARAO MeerKAT Galactic Plane Survey (SMGPS). The SMPGS is a wide-field, wide-band 1.3 GHz radio continuum survey (251 at most l at most 358 and 2 at most l at most 61 at b at most 1.5) that has enabled us to trace the diffuse emission enveloping recently formed massive stars. Our multifrequency synthesis images reveal faint and extended emission that was previously overlooked by H II region surveys. We report the distances and Lyman-photon flux (N Ly) measurements for 1,327 Galactic H II regions from which we characterise the spectral types for candidate ionising stars. The spectral types range from B2 to O4. The typical stellar spectral type responsible for ionisation is the B0, which constitutes about 16% of our catalogue, corresponding to a mean (N Ly) = 47.5 s-1. Moreover, as a result of the lack of radio recombination line (RRL) velocity measurements for faint H II regions, we identify the effective completeness limit at (N Ly) about 47.6 s-1. The multiwavelength approach reveals that the physical radius at 1.3 GHz and in the mid-infrared are well correlated with a slope of 1.15 plus or minus 0.02. We find clear power-law relations between N Ly and physical radius, and an inverse correlation between electron density and radius (n e proportional to R-0.73). However, no significant correlation is observed between the N Ly and Galactocentric distance, suggesting that the observed trends are governed primarily by local star-forming environments rather than large-scale Galactic gradients.