Nebular excitation in z ∼ 2 star-forming galaxies from the sins and luci surveys: The influence of shocks and active galactic nuclei

Sarah F. Newman, Peter Buschkamp, Reinhard Genzel, Natascha M. Förster Schreiber, Jaron Kurk, Amiel Sternberg, Orly Gnat, David Rosario, Chiara Mancini, Simon J. Lilly, Alvio Renzini, Andreas Burkert, C. Marcella Carollo, Giovanni Cresci, Ric Davies, Frank Eisenhauer, Shy Genel, Kristen Shapiro Griffin, Erin K.S. Hicks, Dieter LutzThorsten Naab, Yingjie Peng, Linda J. Tacconi, Stijn Wuyts, Gianni Zamorani, Daniela Vergani, Benjamin J. Weiner

Research output: Contribution to journalArticlepeer-review

63 Scopus citations

Abstract

Based on high-resolution, spatially resolved data of 10 z ∼ 2 star-forming galaxies from the SINS/zC-SINF survey and LUCI data for 12 additional galaxies, we probe the excitation properties of high-z galaxies and the impact of active galactic nuclei (AGNs), shocks, and photoionization. We explore how these spatially resolved line ratios can inform our interpretation of integrated emission line ratios obtained at high redshift. Many of our galaxies fall in the "composite" region of the z ∼ 0 [N II]/Hα versus [O III]/Hβ diagnostic (BPT) diagram, between star-forming galaxies and those with AGNs. Based on our resolved measurements, we find that some of these galaxies likely host an AGN, while others appear to be affected by the presence of shocks possibly caused by an outflow or from an enhanced ionization parameter as compared with H II regions in normal, local star-forming galaxies. We find that the Mass-Excitation (MEx) diagnostic, which separates purely star-forming and AGN hosting local galaxies in the [O III]/Hβ versus stellar mass plane, does not properly separate z ∼ 2 galaxies classified according to the BPT diagram. However, if we shift the galaxies based on the offset between the local and z ∼ 2 mass-metallicity relation (i.e., to the mass they would have at z ∼ 0 with the same metallicity), we find better agreement between the MEx and BPT diagnostics. Finally, we find that metallicity calibrations based on [N II]/Hα are more biased by shocks and AGNs at high-z than the [O III]/Hβ/[N II]/Hα calibration.

Original languageEnglish (US)
Article number21
JournalAstrophysical Journal
Volume781
Issue number1
DOIs
StatePublished - Jan 20 2014
Externally publishedYes

Keywords

  • galaxies: evolution
  • galaxies: high-redshift
  • infrared: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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