Analysis of Spatial Structure of the SPica H II Region

TL;DR

This study presents FUV spectral imaging of the Spica H II region, revealing its spatial structure, density variations, and interaction with surrounding superbubbles, along with spectral analysis and modeling of the ionizing star.

Contribution

First FUV spectral images of the Spica H II region are analyzed, providing new insights into its spatial structure, density, and ionization properties compared to prior optical studies.

Findings

Enhanced emissions in the southern part indicate higher H I density.

The Al II profile suggests multiple resonant scattering effects.

Modeling yields ionizing luminosity and temperature consistent with previous estimates.

Abstract

Far ultraviolet (FUV) spectral images of the Spica H II region are first presented here for the Si II* 1533.4A and Al II 1670.8A lines and then compared with the optical Halpha image. The H alpha and Si II* images show enhanced emissions in the southern part of the H II region where H I density increases outwards. This high density region, which we identify as part of the "interaction ring" of the Loop I superbubble and the Local Bubble, seems to bound the southern H II region. On the other hand, the observed profile of Al II shows a broad central peak, without much difference between the northern and southern parts, which we suspect results from multiple resonant scattering. The extended tails seen in the radial profiles of the FUV intensities suggest that the nebula may be embedded in a warm ionized gas. Simulation with a spectral synthesis code yields the values of the Lyman continuum luminosity and the effective temperature of the central star similar to previous estimates with 10^46.2 photons s^-1 and 26,000 K, respectively, but the density of the northern H II region, 0.22 cm^-3, is much smaller than previous estimates for the H alpha brightest region.