000002317 001__ 2317
000002317 005__ 20160701171703.0
000002317 0247_ $$2DOI$$a10.1088/0004-637X/701/2/1147
000002317 037__ $$aASTROimport-474
000002317 100__ $$aAbel, N. P.
000002317 245__ $$aDust-Bounded Ultraluminous Infrared Galaxies: Model Predictions for Infrared Spectroscopic Surveys
000002317 260__ $$c2009
000002317 520__ $$aThe observed faintness of infrared fine-structure line emission along with the warm far-infrared (FIR) colors of ultraluminous infrared galaxies (ULIRGs) is a long-standing problem. In this work, we calculate the line and continuum properties of a cloud exposed to an active galactic nucleus (AGN) and starburst spectral energy distribution. We use an integrated modeling approach, predicting the spectrum of ionized, atomic, and molecular environments in pressure equilibrium. We find that the effects of high ratios of impinging ionizing radiation density to particle density (i.e., high-ionization parameters, or U) can reproduce many ULIRG observational characteristics. Physically, as U increases, the fraction of UV photons absorbed by dust increases, corresponding to fewer photons available to photoionize and heat the gas, producing what is known as a "dust-bounded" nebula. We show that high-U effects can explain the "[C II] deficit," the ~1 dex drop in the [C II] 158 µm/FIR ratio seen in ULIRGs when compared with starburst or normal galaxies. Additionally, by increasing U through increasing the ionizing photon flux, warmer dust and thus higher IRAS F(60 µm)/F(100 µm) ratios result. High-U effects also predict an increase in [O I] 63 µm/[C II] 158 µm and a gradual decline in [O III] 88 µm/FIR, similar to the magnitude of the trends observed, and yield a reasonable fit to [Ne V] 14 µm/FIR ratio AGN observations. 
000002317 700__ $$a Dudley, C.
000002317 700__ $$a Fischer, J.
000002317 700__ $$a Satyapal, S.
000002317 700__ $$a van Hoof, P. A. M.
000002317 773__ $$c1147-1160$$i2$$pThe Astrophysical Journal$$v701$$y2009
000002317 85642 $$ahttp://esoads.eso.org/abs/2009ApJ...701.1147A
000002317 905__ $$apublished in
000002317 980__ $$aREFERD