3D structure of HII region Sh2-235 from tunable-filter optical observations

TL;DR

This study uses tunable-filter optical observations to analyze the three-dimensional structure and physical conditions of the HII region Sh2-235, revealing its inhomogeneous neutral material distribution and photodissociation regions.

Contribution

First detailed 3D structural analysis of Sh2-235 using tunable-filter optical data combined with infrared observations.

Findings

HII region is obscured by neutral material with AV = 2-4 mag

Maximum electron density >=300 cm(-3) in the south-west

Identified two-sided photodissociation regions with specific UV field strengths

Abstract

We present observations of the H-alpha, H-beta, [SII] 6716, 6731 and [NII] 6583 emission lines in the galactic HII region Sh2-235 with the Mapper of Narrow Galaxy Lines (MaNGaL), a tunable filter at the 1-m telescope of Special Astrophysical Observatory of the Russian Academy of Sciences. We show that the HII region is obscured by neutral material with AV = 2-4 mag. The area with the highest AV is situated to the south-west from the ionizing star and coincides with a maximum detected electron density of >=300 cm(-3). The combination of these results with archive AKARI far-infrared data allows us to estimate the contribution of the front and rear walls to the total column density of neutral material in S235, and explain the three-dimensional structure of the region. The HII region consist of a denser, more compact portion deeply embedded in the neutral medium and the less dense and obscured gas. The front and rear walls of the HII region are inhomogeneous, with the material in the rear wall having a higher column density. We find a two-sided photodissociation region in the dense clump S235 East 1, illuminated by a UV field with G0=50-70 and 200 Habing units in the western and eastern parts, respectively.