ALMA Observations of G333.6-0.2: Molecular and Ionized Gas Environment

Omar A. Abdirakhman A. Alimgazinova N. Kyzgarina M. Naurzbayeva A. Islyam Z. Turekhanova K. Demessinova A. Manapbayeva A.
August 2025 Multidisciplinary Digital Publishing Institute (MDPI)

Galaxies
2025 #13 Issue 4

We present high-angular resolution observations, conducted with the Atacama Large Millimeter/Submillimeter Array (ALMA) in Band 6, of high-excitation molecular lines of (Formula presented.), CH₃OH, and the H29 (Formula presented.) radio recombination line, towards the G333.6-0.2 ultracompact (UC) H ii region. Our observations reveal three hot molecular cores: A, B, and C, where emission is detected in ten components of the (Formula presented.) rotational ladder of (Formula presented.) and in the CH₃OH (Formula presented.) transition. Rotational diagram analysis of (Formula presented.) reveals excitation temperatures ranging from 380 to 430 K. First-order moment maps of (Formula presented.) and CH₃OH reveal distinct velocity gradients in all cores, suggesting rotating structures, with core A also showing evidence of expansion motions. The H29 (Formula presented.) recombination line shows a linewidth of (Formula presented.) km s⁻¹, dominated by dynamical and thermal broadening, indicative of large-scale motions in ionized gas. Analysis of the ionized gas properties yields an electron density of (Formula presented.) cm⁻³, an emission measure of (Formula presented.) pc cm⁻⁶, and a Lyman continuum photon flux consistent with an O5–O6 V (Zero-Age Main Sequence; ZAMS) star. Our results suggest that G333.6-0.2 is in an intermediate evolutionary stage between hypercompact (HC) and ultracompact (UC) H ii regions, hosting active high-mass star formation with rotating hot cores and ionized gas dynamics.

H ii regions , hot molecular cores , individual object (G333.6-0.2) , ionized gas , massive stars , molecular gas , star formation

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Faculty of Physics and Technology, Al-Farabi Kazakh National University, Al-Farabi Ave., 71, Almaty, 050040, Kazakhstan
Institute of Experimental and Theoretical Physics, Al-Farabi Kazakh National University, Almaty, 050040, Kazakhstan

Faculty of Physics and Technology
Institute of Experimental and Theoretical Physics

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