The FMOS-COSMOS survey of star-forming galaxies at z ∼ 1.6. IV. Excitation state and chemical enrichment of the interstellar medium

Journal Article · Fri Jan 20 04:00:00 EST 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/835/1/88· OSTI ID:22869368

Kashino, D. ^[1]; Silverman, J. D. ^[2]; Sanders, D.; Chu, J. ^[3]; Kartaltepe, J. S. ^[4]; Daddi, E.; Valentino, F.; Juneau, S. ^[5]; Renzini, A. ^[6]; Rodighiero, G. ^[7]; Kewley, L. J. ^[8]; Zahid, H. J. ^[9]; Arimoto, N. ^[10]; others, and

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1. Institute for Astronomy, Department of Physics, ETH Zürich, Wolfgang-Pauli-strasse 27, CH-8093 Zürich (Switzerland)
2. Kavli Institute for the Physics and Mathematics of the Universe (WPI), Todai Institutes for Advanced Study, the University of Tokyo, Kashiwanoha, Kashiwa, 277-8583 (Japan)
3. Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)
4. School of Physics and Astronomy, Rochester Institute of Technology, 84 Lomb Memorial Dr., Rochester, NY 14623 (United States)
5. Laboratoire AIM-Paris-Saclay, CEA/DSM-CNRS-Université Paris Diderot, Irfu/Service d’Astrophysique, CEA-Saclay, Service d’Astrophysique, F-91191 Gif-sur-Yvette (France)
6. INAF Osservatorio Astronomico di Padova, vicolo dell’Osservatorio 5, I-35122 Padova (Italy)
7. Dipartimento di Fisica e Astronomia, Universitá di Padova, vicolo dell’Osservatorio, 2, I-35122 Padova (Italy)
8. Research School of Astronomy and Astrophysics, Australian National University, Cotter Road, Weston Creek, ACT 2611 (Australia)
9. Smithsonian Astrophysical Observatory, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
10. Subaru Telescope, National Astronomical Observatory of Japan, National Institutes of Natural Sciences (NINS), 650 North Aohoku Place, Hilo, HI 96720 (United States)

We investigate the physical conditions of ionized gas in high-z star-forming galaxies using diagnostic diagrams based on the rest-frame optical emission lines. The sample consists of 701 galaxies with an Hα detection at 1.4≲z≲1.7, from the Fiber Multi-Object Spectrograph (FMOS)-COSMOS survey, that represent the normal star-forming population over the stellar mass range 10{sup 9.6}≲M{sub ∗}/M{sub ⊙}≲10{sup 11.6}, with those at M{sub ∗}>10{sup 11} M{sub ⊙} being well sampled. We confirm an offset of the average location of star-forming galaxies in the Baldwin–Phillips–Terlevich (BPT) diagram ([O III]/Hβ versus [N II]/Hα), primarily toward higher [O III]/Hβ, compared with local galaxies. Based on the [S ii] ratio, we measure an electron density (n{sub e}=220{sub −130}{sup +170} cm{sup −3}), which is higher than that of local galaxies. Based on comparisons to theoretical models, we argue that changes in emission-line ratios, including the offset in the BPT diagram, are caused by a higher ionization parameter both at fixed stellar mass and at fixed metallicity, with additional contributions from a higher gas density and possibly a hardening of the ionizing radiation field. Ionization due to active galactic nuclei is ruled out as assessed with Chandra. As a consequence, we revisit the mass–metallicity relation using [NII]/Hα and a new calibration including [N II]/[S II] as recently introduced by Dopita et al. Consistent with our previous results, the most massive galaxies (M{sub ∗}≳10{sup 11} M{sub ⊙}) are fully enriched, while those at lower masses have metallicities lower than local galaxies. Finally, we demonstrate that the stellar masses, metallicities, and star formation rates of the FMOS sample are well fit with a physically motivated model for the chemical evolution of star-forming galaxies.

• OSTI ID: 22869368
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 835; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
CALIBRATION
COMPARATIVE EVALUATIONS
DENSITY
DETECTION
DIAGRAMS
ELECTRON DENSITY
EMISSION
EXCITATION
GALACTIC EVOLUTION
GALAXY NUCLEI
IONIZATION
IONIZING RADIATIONS
MASS
METALLICITY
MILKY WAY
RED SHIFT
STARS
UNIVERSE