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Title: Active galactic nuclei emission line diagnostics and the mass-metallicity relation up to redshift z ∼ 2: The impact of selection effects and evolution

Emission line diagnostic diagrams probing the ionization sources in galaxies, such as the Baldwin-Phillips-Terlevich (BPT) diagram, have been used extensively to distinguish active galactic nuclei (AGN) from purely star-forming galaxies. However, they remain poorly understood at higher redshifts. We shed light on this issue with an empirical approach based on a z ∼ 0 reference sample built from ∼300,000 Sloan Digital Sky Survey galaxies, from which we mimic selection effects due to typical emission line detection limits at higher redshift. We combine this low-redshift reference sample with a simple prescription for luminosity evolution of the global galaxy population to predict the loci of high-redshift galaxies on the BPT and Mass-Excitation (MEx) diagnostic diagrams. The predicted bivariate distributions agree remarkably well with direct observations of galaxies out to z ∼ 1.5, including the observed stellar mass-metallicity (MZ) relation evolution. As a result, we infer that high-redshift star-forming galaxies are consistent with having normal interstellar medium (ISM) properties out to z ∼ 1.5, after accounting for selection effects and line luminosity evolution. Namely, their optical line ratios and gas-phase metallicities are comparable to that of low-redshift galaxies with equivalent emission-line luminosities. In contrast, AGN narrow-line regions may show a shift toward lowermore » metallicities at higher redshift. While a physical evolution of the ISM conditions is not ruled out for purely star-forming galaxies and may be more important starting at z ≳ 2, we find that reliably quantifying this evolution is hindered by selections effects. The recipes provided here may serve as a basis for future studies toward this goal. Code to predict the loci of galaxies on the BPT and MEx diagnostic diagrams and the MZ relation as a function of emission line luminosity limits is made publicly available.« less
Authors:
; ; ; ; ; ; ; ; ;  [1] ; ; ;  [2] ;  [3] ;  [4] ;  [5]
  1. CEA-Saclay, DSM/IRFU/SAp, F-91191 Gif-sur-Yvette (France)
  2. UPMC-CNRS, UMR 7095, Institut d'Astrophysique de Paris, F-75014 Paris (France)
  3. University of California Observatories/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States)
  4. Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands)
  5. National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States)
Publication Date:
OSTI Identifier:
22356649
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 788; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCOUNTING; DISTRIBUTION; EMISSION; EVOLUTION; EXCITATION; GALAXIES; GALAXY NUCLEI; LUMINOSITY; MASS; METALLICITY; RED SHIFT; SENSITIVITY; SKY; STARS; VISIBLE RADIATION