The Population of the Galactic Center Filaments: Position Angle Distribution Reveal a Degree-scale Collimated Outflow from Sgr A* along the Galactic Plane

Abstract

We have examined the distribution of the position angle (PA) of the Galactic center filaments with lengths $L > 66''$ and $< 66''$ as well as their length distribution as a function of PA. We find bimodal PA distributions of the filaments, long and short populations of radio filaments. Our PA study shows the evidence for a distinct population of short filaments with PA close to the Galactic plane. Mainly thermal short radio filaments ($<66''$) have PAs concentrated close to the Galactic plane within $60^\circ < \rm PA <120^\circ$. Remarkably, the short filament PAs are radial with respect to the Galactic center at $l <0^\circ$, and extend in the direction toward Sgr A*. On a smaller scale, the prominent Sgr E HII complex G358.7-0.0 provides a vivid example of the nearly radial distribution of short filaments. The bimodal PA distribution suggests different origin for two distinct filament populations. We argue that alignment of the short filament population results from the ram pressure of a degree-scale outflow from Sgr A* that exceeds the internal filament pressure, and aligns them along the Galactic plane. The ram pressure is estimated to be 2$\times10^6\,$ cm$^{-3}\,$ K at a distance of 300pc, requiring biconical mass outflow rate $10^{-4}$ \msol\, yr$^{-1}$ with an opening angle of $\sim40^\circ$. This outflow aligns not only the magnetized filaments along the Galactic plane but also accelerates thermal material associated with embedded or partially embedded clouds. This places an estimate of $\sim$6 Myr as the age of the outflow.Comment: 19 pages, 8 figures, ApJL (June 2nd, 2023