ON THE DYNAMICAL EVOLUTION OF H II REGIONS: AN INVESTIGATION OF THE IONIZED COMPONENT OF W4, A GALACTIC CHIMNEY CANDIDATE. I. KINEMATICS AND DYNAMICS IN THE LATITUDE RANGE 0° ⩽b⩽ 3°

Abstract

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 −1 pc −1 (3. • 5 b < 6. • 3) and ∇ v = (−)3.13 km s −1 pc −1 (6. • 3 b 6. • 5). This leads to radial velocities, slightly above the vicinity of the shell's polar cap, of −70 km s −1 , blueshifted by nearly 25 km s −1 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.

The Massive Star-Forming Regions Omnibus X-Ray Catalog

“…W4 also exhibits a 1 • loop of emission to the south of IC 1805 (Lagrois & Joncas 2009a), where the bubble created by IC 1805's predecessors is encountering denser material in the Galactic Plane. IR and radio work (Terebey et al 2003) has shown that the W4 shell is very inhomogeneous, allowing 40% of the MYSC's ionizing photons to leak out of the superbubble and ionize the surrounding ISM.…”

Origins and interpretation of the tridimensional kinematical disorder in H ii regions

“…In order to extract purely kinematic broadening effects from the observed Hα linewidths, the standard method of quadratic subtraction presented in e.g. Lagrois & Joncas (2009a) was used (see ). The broadening excess caused by thermal motions was subtracted by estimating the electron temperature for each targeted nebula.…”

Diagnostic line ratios in the IC 1805 optical gas complex

“…These filaments most likely trace out the spatial disposition, on the plane of the sky, of the eroded (sometimes fully ionized) molecular envelopes. The central structure is surrounded by diffuse ionized material likely associated with photoevaporated flows kinematically in agreement with the Champagne phase (Lagrois & Joncas 2009a). One of these flows (displaying blue shades in Fig.…”

“…Lagrois & Joncas (2009a,b) provide a high spectral‐resolution (<15 km s −1 ) kinematical investigation of the H + content on an appreciable fraction of the IC 1805 ionized extent. The northernmost portions (63°20′ ≤ δ 2000 ≤ 66°50′) of the large ovoid bubble have shown kinematical evidence for high‐latitude gas venting and the early development of a Galactic chimney.…”

“…The regular and thick lines trace out the H + and CO (2−1) structures, respectively (see fig. 1 of Lagrois & Joncas 2009a). The thin‐line box approximately delineates the gas‐rich region in the vicinity of the Melotte 15 star cluster.…”