The nature of liner-like emission in red galaxies

Renbin Yan, Michael R. Blanton

    Research output: Contribution to journalArticle

    Abstract

    Passive red galaxies frequently contain warm ionized gas and have spectra similar to low-ionization nuclear emission-line regions (LINERs). Here we investigate the nature of the ionizing sources powering this emission, by comparing nuclear spectroscopy from the Palomar survey with larger aperture data from the Sloan Digital Sky Survey. We find the line emission in the majority of passive red galaxies is spatially extended; the Hα surface brightness profile depends on radius r as r -1.28. We detect strong line ratio gradients with radius in [N II]/Hα, [S II]/Hα, and [O III]/[S II], requiring the ionization parameter to increase outward. Combined with a realistic gas density profile, this outward increasing ionization parameter convincingly rules out active galactic nuclei (AGNs) as the dominant ionizing source and strongly favors distributed ionizing sources. Sources that follow the stellar density profile can additionally reproduce the observed luminosity dependence of the line ratio gradient. Post-asymptotic giant branch stars provide a natural ionization source candidate, though they have an ionization parameter deficit. Velocity width differences among different emission lines disfavor shocks as the dominant ionization mechanism, and suggest that the interstellar medium in these galaxies contains multiple components. We conclude that the line emission in most LINER-like galaxies found in large-aperture (>100pc) spectroscopy is not primarily powered by AGN activity and thus does not trace the AGN bolometric luminosity. However, they can be used to trace warm gas in these red galaxies.

    Original languageEnglish (US)
    Article number61
    JournalAstrophysical Journal
    Volume747
    Issue number1
    DOIs
    StatePublished - Mar 1 2012

    Fingerprint

    linings
    liner
    ionization
    galaxies
    active galactic nuclei
    profiles
    apertures
    spectroscopy
    luminosity
    gas
    gradients
    radii
    asymptotic giant branch stars
    ionized gases
    gas density
    brightness
    shock
    gases
    parameter

    Keywords

    • galaxies: active
    • galaxies: elliptical and lenticular, cD
    • galaxies: ISM
    • ISM: kinematics and dynamics
    • stars: AGB and post-AGB

    ASJC Scopus subject areas

    • Space and Planetary Science
    • Astronomy and Astrophysics

    Cite this

    The nature of liner-like emission in red galaxies. / Yan, Renbin; Blanton, Michael R.

    In: Astrophysical Journal, Vol. 747, No. 1, 61, 01.03.2012.

    Research output: Contribution to journalArticle

    Yan, Renbin ; Blanton, Michael R. / The nature of liner-like emission in red galaxies. In: Astrophysical Journal. 2012 ; Vol. 747, No. 1.
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