The Heterogeneous Nature of the Warm Ionized Medium in the Galaxy
Gregory Madsen
University of Wisconsin, Madison
Abstract
The warm ionized medium (WIM) is an important component of the
interstellar medium in our Galaxy, characterized by its low density
(~0.1 cm^-3), warm temperature (T ~ 10^4 K), and large scale height (~1
kpc). However, the origin and physical conditions within the WIM are not
well understood. Basic questions such as how the WIM is ionized and
heated have yet to be fully answered. In this talk, I will present new
multiple emission line observations of [N II], [S II], and [O III]
toward a variety of newly revealed H-alpha emitting structures in the
WIM, obtained with the Wisconsin H-Alpha Mapper (WHAM). These features
span a wide range in surface brightness, scale, environment, and
morphology.
By comparing the relative strengths of the emission lines, we infer the
temperature and ionization conditions within the emitting gas and their
variations between the different emission regions.
We find that in the WIM, the gas is warmer, in a lower ionization state,
and ionized by a softer spectrum than the gas in classical H II regions
surrounding O stars, the presumed ionization source for the WIM, and
discuss the implications this has for the nature and origin of the WIM.