English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

The absence of broad [O III] ${\lambda\lambda}$4959,5007 forbidden emissionlines is one of the key arguments cited in the published literature for the gasdensity exceeding the critical density; 7 ${\times}$ 10$^5$ cm$^{-3}$, in thebroad line region (BLR) of active galactic nuclei. However, for NGC 3227, anequally valid alternative explanation is that O$^{2+}$ is progressively ionizedto O$^{3+}$ as the central UV-X-ray source is approached. Observationalevidence for such an ionization gradient is provided by spectra obtained withthe Space Telescope Imaging Spectrograph. Modeling the rich UV-visible spectrumof NGC 3227 with the photoionization code Cloudy supports the interpretationthat the absence of broad [O III] forbidden emission lines is due toionization, rather than high gas density, and further suggests that what weperceive as the BLR in NGC 3227 is just the illuminated portion of a muchlarger inflow. The low metallicity deduced for the inflowing gas suggests anorigin in the circumgalactic medium.

On the Absence of Broad Forbidden Emission Lines in the Low Luminosity Seyfert 1 Nucleus of NGC 3227