2024/07/10 by Roberto Galván-Madrid, Galván-Madrid, Roberto, D. Díaz-González +53
Engineering · #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Solar and Stellar Astrophysics (astro-ph.SR) #Spacecraft and Cryogenic Technologies
paper · pdf · doi:10.48550/arxiv.2407.07359
openalex publication_date 2024/07/10 · openalex created_date 2024/07/13 · openalex updated_date 2026/07/28
We use the H41α recombination line to create templates of the millimeter free-free emission in the ALMA-IMF continuum maps, which allows to separate it from dust emission. This method complements spectral-index information and extrapolation from centimeter wavelength maps. We use the derived maps to estimate the properties of up to 34 HII regions across the ALMA-IMF protoclusters. The hydrogen ionizing-photon rate Q0 and spectral types follow the evolutionary trend proposed by Motte et al. The youngest protoclusters lack detectable ionized gas, followed by protoclusters with increasing numbers of OB stars. The total Q0 increases from ∼ 1045 s-1 to > 1049 s-1. We used the adjacent He41α line to measure the relative number abundances of helium, finding values consistent with the Galactic interstellar medium, although a few outliers are discussed. A search for sites of maser amplification of the H41α line returned negative results. We looked for possible correlations between the electron densities (ne), emission measures (EM), and Q0 with HII region size D. The latter are the better correlated, with Q0 ∝ D2.49±0.18. This favors interpretations where smaller ultracompact HII regions are not necessarily the less dynamically evolved versions of larger ones, but rather are ionized by less massive stars. Moderate correlations were found between dynamical width ΔVdyn with D and Q0. ΔVdyn increases from about one to two times the ionized-gas sound speed. Finally, an outlier HII region south of W43-MM2 is discussed. We suggest that this source could harbor an embedded stellar or disk wind.