1. Direct observational evidence of multi-epoch massive star formation in G24.47+0.49
- Author
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Saha, Anindya, Tej, Anandmayee, Liu, Hong-Li, Liu, Tie, Garay, Guido, Goldsmith, Paul F., Lee, Chang Won, He, Jinhua, Juvela, Mika, Bronfman, Leonardo, Baug, Tapas, Vazquez-Semadeni, Enrique, Sanhueza, Patricio, Li, Shanghuo, Chibueze, James O., Bhadari, N. K., Dewangan, Lokesh K., Das, Swagat Ranjan, Xu, Feng-Wei, Issac, Namitha, Hwang, Jihye, and Toth, L. Viktor
- Subjects
Astrophysics - Astrophysics of Galaxies ,Astrophysics - Solar and Stellar Astrophysics - Abstract
Using new continuum and molecular line data from the ALMA Three-millimeter Observations of Massive Star-forming Regions (ATOMS) survey and archival VLA, 4.86 GHz data, we present direct observational evidence of hierarchical triggering relating three epochs of massive star formation in a ring-like H II region, G24.47+0.49. We find from radio flux analysis that it is excited by a massive star(s) of spectral type O8.5V-O8V from the first epoch of star formation. The swept-up ionized ring structure shows evidence of secondary collapse, and within this ring a burst of massive star formation is observed in different evolutionary phases, which constitutes the second epoch. ATOMS spectral line (e.g., HCO$^+$(1-0)) observations reveal an outer concentric molecular gas ring expanding at a velocity of $\sim$ 9 $\rm km\,s^{-1}$, constituting the direct and unambiguous detection of an expanding molecular ring. It harbors twelve dense molecular cores with surface mass density greater than 0.05 $\rm g\,cm^{-2}$, a threshold typical of massive star formation. Half of them are found to be subvirial, and thus in gravitational collapse, making them third epoch of potential massive star-forming sites., Comment: 18 pages, 7 figures, accepted for publication in The Astrophysical Journal Letters
- Published
- 2024