2014/06/21 by M. Meléndez, Timothy M. Heckman, T. M. Heckman +3
Physics and Astronomy · #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Cosmic infrared background #Emission spectrum #Galaxies: Formation, Evolution, Phenomena #Galaxy #Infrared #Line (geometry) #Luminous infrared galaxy #Optics #Physics #Spectral line #Spectroscopy #Stellar, planetary, and galactic studies #astro-ph.CO #astro-ph.GA
paper · pdf · doi:10.1093/mnras/stu1242
Accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journal. The paper contains 13 pages, 16 figures
arxiv created 2014/06/21 · openalex publication_date 2014/07/21 · arxiv updated 2015/06/22 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We have carried out extensive and detailed photoionization modelling to successfully constrain the locations of different emission-line galaxies in optical and mid-infrared diagnostic diagrams. Our model grids cover a wide range in parameter space for the active galaxy continuum and starburst galaxies with different stellar population laws and metallicities. We compare the predicted AGN and star formation mid-infrared line ratios [Ne iii]15.56 μm/[Ne ii]12.81 μm and [O iv]25.89 μm/[Ne iii]15.56 μm to the observed values, and find that the best fit for the active galactic nucleus (AGN) is via a two-zone approximation. This two-zone approximation is a combination of a matter-bounded component, where [Ne iii] and [O iv] are emitted efficiently, and a radiation-bounded component that maximizes [Ne ii] emission. We overlay the predictions from this two-zone approximation on to the optical [O iii]λ5007/Hβ and [N ii]λ6583/Hα diagnostic diagram derived from the Sloan Digital Sky Survey, to find that the high-density and low-ionization radiation-bounded component in our two-zone AGN approximation model provides a good lower limit for [N ii] emission. This establishes a new theoretical demarcation line for the minimum AGN contribution in this diagram. This new classification results by a factor of ∼1.4 in a higher AGN population than predictions derived from previous divisions of star-forming galaxies. Similarly, we define a maximum AGN contribution in the [O iii]/Hβ and [N ii]/Hα diagram by using a two-zone approximation within a parameter range typical of the narrow-line region.