Chemo-population multizone models for emission line evolution of star forming galaxies

¹ Dipartimento di Fisica “Enrico Fermi”, Università di Pisa, largo Pontecorvo 3, Pisa 56127, Italy e-mail: [valle;shore]@df.unipi.it
² INFN/Pisa, largo Pontecorvo 3, Pisa 56127, Italy

Received: 24 April 2006
Accepted: 31 October 2006

Abstract

Aims.We apply the nonlinear chemo-population (CP) models for galactic star formation and abundance evolution to the prediction of emission line diagnostics.

Methods.We interfaced the CP code with the photoionization code Cloudy. Using the self-consistently generated star forming rates and abundance histories we predict the time dependences of the nebular line emissivities from model H II  regions. We also simulated some effects of collisions, stripping, and accretion events on the emission line diagnostics.

Results.We find, despite using extremely simplified input fluxes (i.e. blackbodies scaled to a range of effective temperatures but without detailed model atmospheres or population synthesis), the models reproduce many features of the observations. In particular, we suggest that the line ratios for highly ionized species (e.g. [O III] vs. [N II]) are more sensitive to the galactic history, while the exclusively ionization diagnostics (e.g. [O II] vs. [O I]) are more sensitive to the underlying stellar population and the composite ultraviolet flux distribution. We discuss some reasons for this and conclude that a coupled treatment of the galactic population and chemical evolution is essential for interpretation of the data. We also find that collisional and stripped models cover a wider range in the diagnostic diagrams that provide clues to the environmental effects.