The [O iii] Profiles of Far-infrared Active and Inactive Optically Selected Green Valley Galaxies

Abstract

We present a study of the [O iii ] λ 5007 line profile in a subsample of eight active galactic nuclei (AGNs) and six non-AGNs in the optically selected green valley at z < 0.5 using long-slit spectroscopic observations obtained with the 11 m Southern African Large Telescope. Gaussian decomposition of the line profile was performed to study its different components. We observe that the AGN profiles are more complex than the non-AGN ones. In particular, in most AGNs (5/8) we detect a blue wing of the line. We derive the FWHM velocities of the wing and systemic component, and find that the AGNs show higher FWHM velocities than the non-AGNs in their core component. We also find that the AGNs show blue wings with a median velocity width of approximately 600 km s ^−1 , and a velocity offset from the core component in the range −90 to −350 km s ^−1 , in contrast to the non-AGN galaxies, where we do not detect blue wings in any of their [O iii ] λ 5007 line profiles. Using the spatial information in our spectra, we show that at least three of the outflow candidate galaxies have centrally driven gas outflows extending across the whole galaxy. Moreover, these are also the galaxies which are located on the main sequence of star formation, raising the possibility that the AGNs in our sample are influencing the star formation of their host galaxies (such as positive feedback). This is in agreement with our previous work where we studied the star formation, morphology, and stellar population properties of a sample of green valley AGNs and non-AGN galaxies.

Keywords

• Green valley galaxies
• Active galaxies
• AGN host galaxies
• Infrared galaxies
• Emission line galaxies
• Optical observation