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Title: THE COSMIC BPT DIAGRAM: CONFRONTING THEORY WITH OBSERVATIONS

We compare a large sample of galaxies between 0.5 < z < 2.6 with theoretical predictions for how the optical diagnostic line ratios in galaxy ensembles change as a function of cosmic time. We show that star-forming galaxies at high redshift (z > 1.5) are consistent with a model in which the interstellar medium conditions are more extreme at high redshift than seen in the global spectra of local galaxies. We speculate that global spectra of our high-redshift galaxies may be dominated by H II regions similar to the extreme clumpy, dense star-forming complexes in the Antennae and M82. The transition to local-type conditions occurs between 0.8 < z < 1.5. We conclude that classification schemes developed for local samples should not be applied at high redshift (z {>=} 1.5). We use our theoretical models to derive a new redshift-dependent classification line that utilizes the standard optical diagnostic line ratios [O III]/H{beta} and [N II]/H{alpha}. Our new line can be used to separate star-forming galaxies from active galactic nuclei (AGN) between z = 0 to z {approx} 3.5. We anticipate that our redshift-dependent optical classification line will be useful for future large surveys with near-infrared multi-object spectrographs. We apply ourmore » classification line to a sample of gravitationally lensed galaxies at z {approx} 2.5. Although limited by small numbers, we show that our classification line is consistent with the position of AGN that have been independently confirmed via other methods.« less
Authors:
; ;  [1] ;  [2] ;  [3] ;  [4] ;  [5]
  1. Australian National University, Research School for Astronomy and Astrophysics, Mount Stromlo Observatory, Cotter Road, Weston, ACT 2611 (Australia)
  2. University of Vienna, Department of Astrophysics, Tuerkenschanzstrasse, 17, 1180 Vienna (Austria)
  3. Department of Optical and Infrared Astronomy, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588 (Japan)
  4. Department of Astronomy, Faculty of Science, Kyoto University, Kyoto, 606-8502 (Japan)
  5. Astronomical Institute, Tohoku University, 6-3 Aramaki, Aoba-ku Sendai, Japan 980-8578 (Japan)
Publication Date:
OSTI Identifier:
22136536
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 774; 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; ABUNDANCE; ANTENNAS; CLASSIFICATION; COMPARATIVE EVALUATIONS; GALAXY NUCLEI; GEOPHYSICAL SURVEYS; GRAVITATIONAL LENSES; MILKY WAY; RED SHIFT; SPECTRA; STARS; TIME DEPENDENCE