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Linking the formation of molecular clouds and high-mass stars: A multi-tracer and multi-scale study

Abstract : Star formation is a complex process involving many physical processes acting from the very large scales of the galaxy to the very small scales of individual stars. Among the highly debated topics, the gas to star-formation-rate (SFR) relation is an interesting topic for both the galactic and extragalactic communities. Although it is studied extensively for external galaxies, how this relation behaves with respect to the molecular clouds of the Milky Way is still unclear. The detailed mechanisms of the formation of molecular clouds and stars, especially high-mass stars, are still not clear. To tackle these two questions, we investigate the molecular cloud formation and the star formation activities in the W43 molecular cloud complex and the $\rm G035.39-00.33$ filament. The first goal is to infer the connections of the gas-SFR relations of these two objects to those of other galactic molecular clouds and to extragalactic ones. The second goal is to look for indications that the converging flows theory has formed the W43 molecular cloud since it is the first theory to explain star formation self-consistently, from the onset of molecular clouds to the formation of seeds of (high-mass) stars. We use a large dataset of continuum tracers at 3.6--870~\micron extracted from Galaxy-wide surveys such as \gls{hobys}, EPOS, \gls{higal}, \gls{atlasgal}, \gls{glimpse}, and \gls{mipsgal} to trace the cloud structure, mass and star formation activities of both the W43 molecular cloud complex and the $\rm G035.39-00.33$ filament. To explore the detailed formation mechanisms of the molecular cloud in W43 from low-density to very high-density gas, we take advantage of the existing \hi, $^{13}$CO~1--0 molecular line data from the \gls{vgps} and \gls{grs} surveys in combination with the new dedicated molecular line surveys with the \gls{30m}. We characterise the W43 molecular complex as being a massive complex ($M_{\mbox{\tiny total}}\sim 7.1 \times 10^6~\msun$ over spatial extent of $\sim 140$~pc), which has a high concentration of dense clumps ($M_{\mbox{\tiny clumps}}\sim 8.4\times 10^5~\msun, 12\%)$. It spans over a large breadth of velocity $\sim$22~\kms. This study also shows that it lies at a distance of $\sim 6$~kpc from the Sun, which is the meeting point of the Scutum-Centaurus Galactic arm and the bar. W43 harbours some of the densest cores in the Galactic Plane (W43--MM1, W43--MM2 with $\nhtwo\sim8\times 10^8$ and $4\times 10^8$\cmc), is undergoing a mini-starburst event (\emph{SFR}$\, \sim 0.01~\msun\, \mbox{yr}^{-1}$ $\sim 10^6$~yr ago to $0.1~\msun\, \mbox{yr}^{-1}$ in the near future) and has extended SiO emission.The large scale \hi gas displays an atomic gas envelope with diameter $\sim 290$~pc surrounding W43, which may be the remnant of the atomic gas clouds that formed the molecular cloud. We show that the IRDC $\rm G035.39-00.33$ filament is a cold ($13-16$~K) and dense ($\nhtwo$ up to $9\times 10^{22}~\cmd$) filament, which qualifies it as a ''ridge''. This ridge harbours a total of 28 dense cores (\textit{FWHM}$\sim$0.15~pc), among which are 13 MDCs with masses of 20--50~$\msun$ and densities of 2--20 $\times 10^{5}~\cmc$. They are potential sites of forming immediate to high-mass stars. Given their concentration in the IRDC $\rm G035.39-00.33$ they may be participating in a mini-burst of star formation activity with \textit{SFE}$\sim$ $15\%$, \textit{SFR}$\sim300~\msun\,$Myr$^{-1}$, and $\Sigma_{SFR}\sim 40~\msun\,$yr$^{-1}\,$kpc$^{-2}$. Both W43 and $\rm G035.39-00.33$ house extended SiO emission spreading over a few parsecs, which has no associated star formation activity. We propose that these regions originate from low-velocity shocks within converging flows. In W43, the evidence is even stronger with the extended SiO emission lying at the centre of the global collapses as shown by HCO$^{+}$ isotopologues. Using {\it herschel} data, we show that both W43 molecular complex and the IRDC $\rm G035.39-00.33$ filament seem to be forming stars, especially high-mass stars, very efficiently. Especially, W43 which is found to be one of the most extreme molecular complexes of the Milky Way in term of size and mass. We propose to divide the gas density-SFR diagram into two regimes: galactic mini-starbursts and normal star-forming molecular clouds, following the division made between mini-starburst normal spiral galaxies in the extragalactic context. With respect to SiO extended emission, both regions exhibit signatures of converging flows, thus they provide the perfect laboratory for testing this scenario.
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Contributor : Quang Nguyen Luong <>
Submitted on : Saturday, April 21, 2012 - 6:10:32 PM
Last modification on : Friday, April 10, 2020 - 5:09:43 PM
Long-term archiving on: : Sunday, July 22, 2012 - 2:21:32 AM


  • HAL Id : tel-00690127, version 1


Quang Nguyen Luong. Linking the formation of molecular clouds and high-mass stars: A multi-tracer and multi-scale study. Galactic Astrophysics [astro-ph.GA]. Université Paris-Diderot - Paris VII, 2012. English. ⟨tel-00690127⟩



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