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Article Dans Une Revue Monthly Notices of the Royal Astronomical Society Année : 2010

Alternative diagnostic diagrams and the `forgotten' population of weak line galaxies in the SDSS

Résumé

A numerous population of weak line galaxies (WLGs) is often left out of statistical studies on emission-line galaxies (ELGs) due to the absence of an adequate classification scheme, since classical diagnostic diagrams, such as [OIII]/Hbeta versus [NII]/Halpha (the BPT diagram), require the measurement of at least four emission lines. This paper aims to remedy this situation by transposing the usual divisory lines between star-forming (SF) galaxies and active galactic nuclei (AGN) hosts and between Seyferts and LINERs to diagrams that are more economical in terms of line quality requirements. By doing this, we rescue from the classification limbo a substantial number of sources and modify the global census of ELGs. More specifically, (1) we use the Sloan Digital Sky Survey Data Release 7 to constitute a suitable sample of 280000 ELGs, one-third of which are WLGs. (2) Galaxies with strong emission lines are classified using the widely applied criteria of Kewley et al., Kauffmann et al. and Stasinska et al. to distinguish SF galaxies and AGN hosts and Kewley et al. to distinguish Seyferts from LINERs. (3) We transpose these classification schemes to alternative diagrams keeping [NII]/Halpha as a horizontal axis, but replacing Hbeta by a stronger line (Halpha or [OII]), or substituting the ionization-level sensitive [OIII]/Hbeta ratio with the equivalent width of Halpha (WHalpha). Optimized equations for the transposed divisory lines are provided. (4) We show that nothing significant is lost in the translation, but that the new diagrams allow one to classify up to 50 per cent more ELGs. (5) Introducing WLGs in the census of galaxies in the local Universe increases the proportion of metal-rich SF galaxies and especially LINERs.

Dates et versions

hal-03742168 , version 1 (02-08-2022)

Identifiants

Citer

Roberto Cid Fernandes, Grazyna Stasinska, M. S. Schlickmann, Abílio Mateus, Natalia Vale Asari, et al.. Alternative diagnostic diagrams and the `forgotten' population of weak line galaxies in the SDSS. Monthly Notices of the Royal Astronomical Society, 2010, 403, pp.1036-1053. ⟨10.1111/j.1365-2966.2009.16185.x⟩. ⟨hal-03742168⟩
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