Improved collision strengths and line ratios for forbidden [O III] far-infrared and optical lines

Ethan Palay (1), Sultana N. Nahar (1), Anil K. Pradhan (1), Werner Eissner (2) ((1) Department of Astronomy, The Ohio State University, Columbus, OH, USA; (2) Institut f¨ur Theoretische Physik, Teilinstitut, Stuttgart, Germany)

Far-infrared and optical [O III] lines are useful temeprature-density diagnostics of nebular as well as dust obscured astrophysical sources. Fine structure transitions among the ground state levels 1s^2.2s^2.2p^3  ^3P_{0,1,2} give rise to the 52 and 88 μm lines, whereas transitions among the ^3P_{0,1,2} , ^1D_2, ^1S_0 levels yield the well-known optical lines λλ 4363, 4959 and 5007 Å. These lines are excited primarily by electron impact excitation. But despite their importance in nebular diagnostics collision strengths for the associated fine structure transitions have not been computed taking full account of relativistic effects. We present Breit-Pauli R-matrix calculations for the collision strengths with highly resolved resonance structures. We find significant differences of up to 20% in the Maxwellian averaged rate coefficients from previous works. We also tabulate these to lower temperatures down to 100 K to enable determination of physical conditions in cold dusty environments such photo-dissociation regions and ultra-luminous infrared galaxies observed with the Herschel space observatory. We also examine the effect of improved collision strengths on temperature and density sensitive line ratios.

Complete preprint ==> http://arxiv.org/abs/1204.0812

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2 Responses to Improved collision strengths and line ratios for forbidden [O III] far-infrared and optical lines

  1. grazyna stasinska says:

    looking at your fig 5, the new emissivities of the optical lines are larger, which will make CEL oxygen abundances lower and thus will exacerbate the ORL/CEL abundance discrepancy, although, of course this should be reexamined in conjunction with the results of Nahar & Pradhan 2011 on ORL emissivities.

  2. Claudio Mendoza says:

    Anil and Sultana, although you assign the differences with the previous work by Aggarwal & Keenan (1999) to the more precise relativistic corrections in your work, i.e. the two-body Breit operators, this assertion would require some more support. For instance, you could easily compare your new data with BPRM without the Breit operators or with the fully relativistic DARC suite. The comparison with Aggarwal & Keenan brings in other factors such as different target representation, CC expansion and energy mesh.

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