On the dynamical evolution of H II regions: an investigation of the ionized component of W4, a galactic chimney candidate. II. Kinematics and dynamics in the latitude range 3° < b ≤ 7°.
LAGROIS D. and JONCAS G.
Abstract (from CDS):
In the second of this two-paper series, we present results associated with an Hα investigation, obtained using the Fabry-Perot interferometer FaNTOmM, of the tenuous ionized material found embedded in the northern portion of W4. W4 is a promising candidate for a galactic chimney, likely connected with the galactic corona, and presents evidence of shell fragmentation. We present the quantitative method for identifying shell breakout that allows us to characterize the giant H I supershell/H II region W4 as enclosing a galactic chimney in formation. On a range of approximately 125 pc, two "south-to-north" radial velocity gradients are detected, ∇v= (-)0.17 km/s/pc (3°.5 ≤ b < 6°.3) and ∇v= (-)3.13 km/s/pc (6°.3 ≤ b ≤ 6°.5). This leads to radial velocities, slightly above the vicinity of the shell's polar cap, of -70 km/s, blueshifted by nearly 25 km/s with respect to the H I supershell. The kinematic behavior is in agreement with a rarefaction scenario if the W4 superbubble presents a tilt toward the observer. This angle of inclination is estimated between 9° and 27° with respect to the plane of the sky. A line-narrowing gradient is correlated with the radial velocity gradient. The large-scale trends in radial velocities and line widths correspond to highly accelerated, well-parallelized outflows of vented ionized material. This kinematic signature is expected from the chimney model. The dynamical age of the W4 chimney is estimated at 4.1 Myr and constraints shell instabilities to have developed at latitudes lower than the blowout threshold height. Our work contributes to the evidence that the star cluster IC 1805 partially sustains the low-galactic corona above the Perseus arm.