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.
Classical spectro‐interferometry allowed us to obtain a large‐scale Hα survey of the central portions of the late‐type Sc galaxy M33. A series of 28 small‐to‐intermediate size H ii regions, kinematically dominated by Champagne flows, quiescent wind effects, potentially embedded globules and filaments, and photoablation flows, are identified and delimited. The main goal of this work is to compare and check for an eventual correlation between two statistical parameters obtained for each targeted object, namely the standard deviation of the velocity centroid distribution (σc) and the mean non‐thermal linewidth (〈σi, kin〉). These parameters, by definition, allow for a comparison between the kinematical disorder on the plane of the sky and along the line‐of‐sight. The slope of the σc versus 〈σi, kin〉 diagram, approaching unity, indicates that variations of the kinematical disorder are roughly equivalent on all spatial axes. H ii regions should therefore be regarded as strictly tridimensional objects. We attempt to reproduce the observed relation using non‐turbulent, hydrodynamical models of expanding H ii regions. Simulations indicate that the two parameters are generally correlated, as observed, in a monotonically increasing trend although the areas populated in the theoretical σc−〈σi, kin〉 space diagram do not match the observations. A certain reconciliation between models and observations is reached if one allows turbulent motions to have a sizeable kinematical impact in the ionized medium, i.e. confirming that all H ii regions in the survey have a strong turbulent component. This could apply to all optical nebulae hence in agreement with high Reynolds numbers typically found in the ionized interstellar medium. A photometric investigation of bright stars found in our nebula sample indicates that Champagne‐like objects coexist with wind‐blown bubbles in the σc versus 〈σi, kin〉 diagram. This suggests that objects characterized by multiple Champagne flows and those that are wind‐dominated can develop turbulent velocity motions of comparable amplitudes.
Large H ii regions, with angular dimensions exceeding 10 pc, usually enclose numerous massive O‐stars. Stellar winds from such stars are expected to play a sizeable role in the dynamical, morphological and chemical evolution of the targeted nebula. Kinematically, stellar winds remain hardly observable, i.e. the typical expansion velocities of wind‐blown bubbles being often confused with other dynamical processes also regularly found H ii regions. However, supersonic shock waves, developed by stellar winds, should favour shock excitation and leave a well‐defined spectral signature in the ionized nebular content. In this work, the presence of stellar winds, observed through shock excitation, is investigated in the brightest portions of the Galactic IC 1805 nebula, a giant H ii region encompassing at least 10 O‐stars from main‐sequence O9 to giant and supergiant O4. The use of the imaging Fourier transform spectrometer SpIOMM enabled the simultaneous acquisition of the spectral information associated with the Hα λ6563 Å, [N ii] λλ6548, 6584 Å, and [S ii] λλ6716, 6731 Å ionic lines. Diagnostic diagrams, first introduced by Sabbadin and collaborators, were used to circumscribe portions of the nebula likely subject to shock excitation from other areas dominated by photoionization. The gas compression, expected from supersonic shocks, is investigated by comparing the pre‐ and post‐shocked material’s densities computed from the line ratio. The typical line ratio slightly exceeds the theoretical value of 3 expected in low‐density regimes. To explain such behaviour, a scenario based on collisional de‐excitations affecting the [N ii] λ6548 Å line is proposed.
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