Other
Scientific paper
Mar 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008sptz.prop50093a&link_type=abstract
Spitzer Proposal ID #50093
Other
Scientific paper
Recent investigations into x-ray irradiated atomic and molecular gas (XDRs) present a challenge to interpreting IRS observations of AGNs, ULIRGs, and protoplanetary disks. XDR models predict strong [Ne II], [Ar II], and [S III] emission, spectral diagnostics which are usually assumed to emerge from H II regions. These diagnostics are widely used to infer physical properties such as galaxy energetics, density, and the shape of the spectral energy distribution. A non-H II region component represents a gap between observation and theory. IRS observations cannot distinguish between XDR and H II emission, due to insufficient spectral resolution. Without sufficient resolution, the best way to separate out the H II and XDR components of [Ne II], [Ar II], and [S III] in the IRS spectrum is to calculate the contribution of each region to the total intensity. To date, no XDR + H II region calculation exists. The goal of this proposal is to understand the role of XDRs and H II regions to important IRS spectral diagnostics. We will determine the effect of the XDR on the IRS spectroscopy by including important XDR processes into the spectral synthesis code Cloudy. These processes include charge transfer reactions between multiply ionized Ne, S, and Ar with H and H2, collisional excitation of [Ne II], [Ar II], and [S III] with H and H2, and other high energy atomic and molecular processes. We will use these theoretical tools to study, over a wide range of physical conditions, the contribution XDRs makes to the overall emission of important IRS emission-line diagnostics. In so doing, we will provide a way to separate out the XDR and H II components in IRS observations, increasing the scientific return of Spitzer. The theoretical improvements will make Cloudy the only computer simulation capable of modeling H II regions and XDRs self-consistently. In addition, since Cloudy is a publicly available code, the results of this proposal will be immediately available to the astrophysical community.
Abel Nicholas
Satyapal Shobita
Stancil Philip
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