The Discovery of Raman Scattering in H Ii Regions

Abstract

We report here on the discovery of faint extended wings of Hα observed out to an apparent velocity of ∼ 7600 km s −1 in the Orion Nebula (M42) and in five H II regions in the Large and the Small Magellanic Clouds. We show that, these wings are caused by Raman scattering of both the O I and Si II resonance lines and stellar continuum UV photons with H I followed by radiative decay to the H I n = 2 level. The broad wings also seen in Hβ and in Hγ result from Raman scattering of the UV continuum in the H I n = 4 and n = 5 levels respectively.The Raman scattering fluorescence is correlated with the intensity of the narrow permitted lines of O I and Si II. In the case of Si II, this is explained by radiative pumping of the same 1023.7Å resonance line involved in the Raman scattering by the Lyβ radiation field. The subsequent radiative cascade produces enhanced Si II λλ5978.9, 6347.1 and 6371.4Å permitted transitions. Finally we show that in O I, radiative pumping of the 1025.76Å resonance line by the Lyman series radiation field is also the cause of the enhancement in the permitted lines of this species lying near Hα in wavelength, but here the process is a little more complex. We argue that all these processes are active in the zone of the H II region near the ionisation front.

Chemical abundances of Seyfert 2 AGNs – III. Reducing the oxygen abundance discrepancy

“…A different approach is considering the presence of shocks caused by supersonic turbulence, jets, and/or winds as a secondary ionization source (Zhang et al 2013). This extra ionization and heating of the gas (Dopita & Sutherland 1995;Dopita et al 1996) drives to high temperatures which in turn leads to derive unrealistically low abundance values through the Te-method. If shocks have really an important contribution to the ionization/heating of AGNs, some correlation between temperatute and shock indicators should be derived.…”

Raman Scattering as the Key Link Between Unidentified Infrared Bands, Diffuse Interstellar Bands, and Extended Red Emission

“…Together with the article by Nussbaumer et al (1989) his discovery stimulated a new line of research. Emission lines Raman scattered by hydrogen have since been found in planetary nebulae (PNe, Pequignot et al 1997;Lee et al 2006) and galaxies (Dopita et al 2016). Scholars have also been interested in Raman scattering of the ultraviolet continuum (Lee & Hyung 2000;Jung & Lee 2004;Dopita et al 2016).…”

“…Emission lines Raman scattered by hydrogen have since been found in planetary nebulae (PNe, Pequignot et al 1997;Lee et al 2006) and galaxies (Dopita et al 2016). Scholars have also been interested in Raman scattering of the ultraviolet continuum (Lee & Hyung 2000;Jung & Lee 2004;Dopita et al 2016). The work of Chang et al (2015) suggests that hydrogen Raman scattering of the ultraviolet continuum clusters around hydrogen transitions, with strong minima in between.…”

3D Grid-Based Monte Carlo Code for Radiative Transfer through Raman and Rayleigh Scattering with Atomic Hydrogen -- STaRS

“…Additional examples include Raman scattering of C IIλλ1036 and 1037 forming optical features at 7023 Å and 7054 Å, which were reported in the symbiotic nova V1016 Cygni by Schild & Schmid (1996). Dopita et al (2016) investigated the H II regions in the Orion Nebula (M42) and five H II regions in the Large and Small Magellanic Clouds to discover Raman-scattered features at 6565 Å and 6480 Å formed through Raman scattering of O I λ1025.76 and Si II λ1023.70, respectively.…”