Volume 526, February 2011
|Number of page(s)||10|
|Published online||13 January 2011|
Metallicity diagnostics with infrared fine-structure lines
Graduate School of Science and Engineering, Ehime University,
2-5 Bunkyo-cho, 790-8577,
2 Research Center for Space and Cosmic Evolution, Ehime University, 2-5 Bunkyo-cho, 790-8577 Matsuyama, Japan
3 Optical and Infrared Astronomy Division, National Astronomical Observatory of Japan, 2-21-1 Osawa, 181-8588 Mitaka, Japan
4 INAF – Osservatorio Astrofisico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Italy
5 Dipartimento di Fisica e Astronomia, Università di Firenze, Largo E. Fermi 2, 50125 Firenze, Italy
6 Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, 252-5210 Sagamihara, Japan
Received: 26 July 2010
Accepted: 4 December 2010
Although measuring the gas metallicity in galaxies at various redshifts is crucial to constrain galaxy evolutionary scenarios, only rest-frame optical emission lines have been generally used to measure the metallicity. This has prevented us to accurately measure the metallicity of dust-obscured galaxies, and accordingly to understand the chemical evolution of dusty populations, such as ultraluminous infrared galaxies. Here we propose diagnostics of the gas metallicity based on infrared fine-structure emission lines, which are nearly unaffected by dust extinction even the most obscured systems. Specifically, we focus on fine-structure lines arising mostly from Hii regions, not in photo-dissociation regions, to minimize the dependence and uncertainties of the metallicity diagnostics from various physical parameters. Based on photoionization models, we show that the emission-line flux ratio of ([Oiii]51.80+[Oiii]88.33)/[Niii]57.21 is an excellent tracer of the gas metallicity. The individual line ratios [Oiii]51.80/[Niii]57.21 or [Oiii]88.33/[Niii]57.21 can also be used as diagnostics of the metallicity, but they are more strongly dependent on the gas density. The line ratios [Oiii]88.33/[Oiii]51.80 and [Nii]121.7/[Niii]57.21 can be used to measure and, therefore, account for the dependences on the gas density and ionization parameter, respectively. We show that these diagnostic fine-structure lines are detectable with Herschel in luminous infrared galaxies out z ~ 0.4. Metallicity measurements with these fine-structure lines will be feasible at relatively high redshift (z ~ 1 or more) with SPICA, the future infrared space observatory.
Key words: galaxies: abundances / galaxies: evolution / galaxies: ISM / Hiiregions / infrared: galaxies / infrared: ISM
© ESO, 2011
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.