2003/05/27 by M. L. Luhman, S. Satyapal, Shobita Satyapal +6 · 2 citations
Physics and Astronomy · #Astrophysics and Star Formation Studies #Galaxies: Formation, Evolution, Phenomena #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/376965
published as Astrophys.J. 594 (2003) 758-775 · to be published in The Astrophysical Journal, 58 pages
arxiv created 2003/05/27 · openalex publication_date 2003/09/05 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/01
We present a study of the [C II] 157.74 μm fine-structure line in a sample of 15 ultraluminous infrared (IR) galaxies (IR luminosity L IR ⩾ 10 12 L ☉ ; ULIRGs) using the Long Wavelength Spectrometer (LWS) on the Infrared Space Observatory ( ISO ). We confirm the observed order of magnitude deficit (compared to normal and starburst galaxies) in the strength of the [C II] line relative to the far-infrared (FIR) dust continuum emission found in our initial report, but here with a sample that is twice as large. This result suggests that the deficit is a general phenomenon affecting 4 out of 5 ULIRGs. We present an analysis using observations of generally acknowledged photodissociation region (PDR) tracers ([C II], [O I] 63 and 145 μm, and FIR continuum emission), which suggests that a high ultraviolet flux G 0 incident on a moderate density n PDR could explain the deficit. However, comparisons with other ULIRG observations, including CO (1-0), [C I] (1-0), and 6.2 μm polycyclic aromatic hydrocarbon (PAH) emission, suggest that high G 0 / n PDRs alone cannot produce a self-consistent solution that is compatible with all of the observations. We propose that non-PDR contributions to the FIR continuum can explain the apparent [C II] deficiency. Here, unusually high G 0 and/or n physical conditions in ULIRGs as compared to those in normal and starburst galaxies are not required to explain the [C II] deficit. Dust-bounded photoionization regions, which generate much of the FIR emission but do not contribute significant [C II] emission, offer one possible physical origin for this additional non-PDR component. Such environments may also contribute to the observed suppression of FIR fine-structure emission from ionized gas and PAHs, as well as the warmer FIR colors found in ULIRGs. The implications for observations at higher redshifts are also revisited.