期刊
ASTROPHYSICAL JOURNAL
卷 701, 期 2, 页码 1147-1160出版社
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/701/2/1147
关键词
galaxies: active; galaxies: starburst; infrared: galaxies; infrared: ISM; X-rays: galaxies; X-rays: ISM
资金
- National Science Foundation [0094050, 0607497]
- University of Cincinnati
- Spitzer Science Center [1356415]
- NASA Herschel Science Center [NAG5-11432]
- Office of Naval Research
- Direct For Mathematical & Physical Scien
- Division Of Astronomical Sciences [0607497] Funding Source: National Science Foundation
- Direct For Mathematical & Physical Scien
- Division Of Astronomical Sciences [0094050] Funding Source: National Science Foundation
The 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 similar to 1 dex drop in the [ C II] 158 mu m/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 mu m)/F( 100 mu m) ratios result. High-U effects also predict an increase in [ O I] 63 mu m/[ C II] 158 mu m and a gradual decline in [ O III] 88 mu m/FIR, similar to the magnitude of the trends observed, and yield a reasonable fit to [ Ne V] 14 mu m/FIR ratio AGN observations.
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