GS34-6+65: A Large Galactic Supershell Originating in an Active Star Formation Region and Extending to the Halo

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Session 36 -- ISM: Structure, Molecular Clouds
Display presentation, Wednesday, June 14, 1995, 9:20am - 6:30pm

[36.12] GS34-6+65: A Large Galactic Supershell Originating in an Active Star Formation Region and Extending to the Halo

Witold Maciejewski (U. Wisconsin---Madison), Edward M. Murphy, Felix J. Lockman (NRAO), Blair D. Savage (U. Wisconsin---Madison)

The Galactic supershell GS34-6+65 (Heiles 1979) was mapped in the H\,{\small I}$\;$ 21 cm emission line with the NRAO 140 ft radiotelescope. The observations cover galactic longitudes 30$^{\circ} \;$ to 40$^{\circ} \;$ and latitudes -1$^{\circ} \;$ to -15$^{\circ} \;$ with 10 arcmin spacing in both coordinates. Centered at $l$=35, $b$=-5 and $v_{\rm rad}$=+56km/s, the supershell consists of an irregular spherical shell about 7$^{\circ} \;$ in diameter, which reaches 9.5$^{\circ} \;$ below the galactic plane, and of a well defined, massive cone at low latitudes which connects to the molecular cloud CO[35,44] (Dame et al.1986) through a narrow (20 pc wide) channel of reduced H\,{\small I}$\;$ emission. On the basis of an investigation of objects near the line of sight to the supershell and information from the galactic rotation curve, we derive a distance of $\sim$3.7 kpc, which implies that the shell has a diameter of $\sim$450 pc and extends at least 600 pc into the Galactic halo. The distance also indicates that the supershell originates in the Sagittarius arm. The concentration of supernova remnants, star forming regions and H\,{\small II}$\;$ regions in this direction implies that the supershell is a remnant of multiple supernovae and that strong star formation activity persists in this region of the Galaxy, though the large column density (greater than $10^{22}$ H/cm$^2$) prevents us from seeing the stars. We interpret W48 as a region of star formation induced by a shock wave related to the cone. We consider simple models to take into account geometrical and dynamical effects resulting in observed H\,{\small I}$\;$ emission at given radial velocity. We estimate the swept up mass in the shell to be 7.3$\times10^4$M$_{\odot} \;$ and the mass in the cone -- 1.3$\times10^5$M$_{\odot} \;$. The estimated kinetic energy of the supershell, 5.0$\times10^{51}$ergs, imposes a minimum limit of about 5.0$\times10^{52}$ ergs on the total energy of the event creating the supershell.\\

REFERENCES: \\ Dame, T. M., Elmegreen, B. G., Cohen, R. S., Thaddeus, P. 1986, Astroph. Journ. , 305 , 892\\ Heiles, C. 1979, Astroph. Journ. , 229 , 533

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