The ionization mechanism of the low-ionization gas in quiescent red-sequence galaxies has been a long-standing puzzle. Direct temperature measurements would put strong constraints on this issue. We carefully selected a sample of quiescent red-sequence galaxies from Sloan Digital Sky Survey. We bin them into three bins with different [NII]/H α and [NII]/[O II] ratios, and we measure the temperature-sensitive [O III] λ4363, [N II] λ5755, [S II] λλ4068, 4076, and [OII] λλ7320, 7330 lines in the stacked spectra. The [SII] doublet ratios indicate the line-emitting gas is in the low-density regime (~10-200 cm-3). We found the temperatures in the S+ zones to be around 8000 K, the temperatures in the O+ zone to be around 1.1- 1.5 × 104 K, and the temperatures in the N+ zones to be around 1-1.4× 104 K. The [OIII] λ4363 line is not robustly detected. We found that the extinction corrections derived from Balmer decrements would yield unphysical relationships between the temperatures of the S+ zones and O+ zones, indicating that the extinction is significantly overestimated by the measured Balmer decrements. We compared these line ratios with model predictions for three ionization mechanisms: photoionization by hot evolved stars, shocks, and turbulent mixing layers. For the photoionization and shock models, the hot temperatures inferred from [S II] and [N II] coronal-to-strong line ratios require metallicities to be significantly subsolar. However, the [NII]/[O II] line ratios require them to be supersolar. None of the models could simultaneously explain all of the observed line ratios, neither could their combinations do.
|Number of pages||18|
|Journal||Monthly Notices of the Royal Astronomical Society|
|State||Published - Nov 21 2018|
Bibliographical noteFunding Information:
I thank the referee, Luc Binette, whose comments helped to significantly improve this paper. I am also grateful for the hospitality of the Tsinghua Center for Astrophysics at Tsinghua University during an extended visit. RY acknowledges the support of NSF Grant AST-1715898.
Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbuka-gakusho, the Max Planck Society, and the Higher Education Funding Council for England. The SDSS website is http://www.sdss.org/.
I thank the referee, Luc Binette, whose comments helped to significantly improve this paper. I am also grateful for the hospitality of the Tsinghua Center for Astrophysics at Tsinghua University during an extended visit. RY acknowledges the support of NSF Grant AST-1715898. Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education FundingCouncil for England. The SDSSwebsite is http://www.sdss.org/. The SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions. The Participating Institutions are the American Museum of Natural History, Astrophysical Institute Potsdam, University of Basel, University of Cambridge, Case Western Reserve University, University of Chicago, Drexel University, Fermilab, the Institute for Advanced Study, the Japan Participation Group, Johns Hopkins University, the Joint Institute for Nuclear Astrophysics, the Kavli Institute for Particle Astrophysics and Cosmology, the Korean Scientist Group, the Chinese Academy of Sciences (LAMOST), Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, Ohio State University, University of Pittsburgh, University of Portsmouth, Princeton University, the United States Naval Observatory, and the University of Washington.
© 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society.
- (galaxies:) quasars: emission lines
- Galaxies: ISM
- Galaxies: abundances
- Galaxies: elliptical and lenticular
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science