Starburst(s) at the Galactic Center\\ Triggered by Collisions of Giant Molecular Clouds

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Session 66 -- Galactic Center
Oral presentation, Tuesday, 10, 1995, 2:00pm - 3:30pm

[66.05] Starburst(s) at the Galactic Center\\ Triggered by Collisions of Giant Molecular Clouds

\def\mo{$M_{\odot}$} L.\thinspace M. Ozernoy (Phys. Dept. and Inst. for Comp. Sci. \& Inform., George Mason U.; also Lab. for Astron. and Sol. Phys., NASA/GSFC)

Evidence both from the stellar population in the central parsec and the 10 KeV gas within the 150-pc expanding molecular ring strongly indicates that, in the recent past, the Galactic center has passed through a starburst episode. I sugggest that the presence of about 200 giant molecular clouds (GMCs) in the inner kiloparsec of the Galaxy, many of which have highly elongated orbits, could trigger, as a result of mutual cloud-cloud collisions, nuclear starbursts with the characteristic interval of starburst recurrency of $\sim$200 Myr. Each collision episode could start at comparatively large distances from the Galactic center and result in the infall of the remnants of the clouds towards it. The presence at the Galactic center of a rotating molecular Circum Nuclear Ring indicates a recent collision between the molecular clouds in the central several tens of parsecs. The ring whose mass is estimated between $10^4$ to $10^5$\mo~ (Genzel et al. 1994) seems to be what is left after a comparable mass, which had its angular momentum dissipated by the collision, fell into the central parsec. The latest starburst within the central parsec, which involved $\sim 4\cdot 10^5$\mo, has the age $\sim 7-8$ Myr and an average SN production rate to be 1 SN/$7\cdot 10^4$ yr (Tamblyn \& Rieke 1993). This implies more than 100 SN during the entire starburst, which is marginally consistent with what is required to produce the bubble of ultra hot gas. Sgr A Est which has been interpreted as a product of a SN explosion might be a part of that starburst provided that the SN exploded into a progenitor bubble created by a wind (Mezger et al. 1989). Inhomogeneities in the eventual products of GMC collisions inavoidably give rise to non-uniform dissipation and fragmentation processes and thus to non-coeval star formation. As a result, SN explosions can also occur non-instanteneously in different places. Different ages of stars which originated in various sites of the same starburst may explain why the estimates of the Galactic center starburst are somewhat contradictory.

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