The Paschen Jump as a Diagnostic of the Diffuse Nebular Continuum Emission in Active Galactic Nuclei*

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Documents

  • Hengxiao Guo
  • Aaron J. Barth
  • Kirk T. Korista
  • Michael R. Goad
  • Edward M. Cackett
  • Misty C. Bentz
  • William N. Brandt
  • D. Gonzalez-Buitrago
  • Gary J. Ferland
  • Jonathan M. Gelbord
  • Luis C. Ho
  • Keith Horne
  • Michael D. Joner
  • Gerard A. Kriss
  • Ian McHardy
  • Missagh Mehdipour
  • Daeseong Park
  • Raymond Remigio
  • U. Vivian
  • Vestergaard, Marianne

Photoionization modeling of active galactic nuclei (AGN) predicts that diffuse continuum (DC) emission from the broad-line region makes a substantial contribution to the total continuum emission from ultraviolet through near-infrared wavelengths. Evidence for this DC component is present in the strong Balmer jump feature in AGN spectra, and possibly from reverberation measurements that find longer lags than expected from disk emission alone. However, the Balmer jump region contains numerous blended emission features, making it difficult to isolate the DC emission strength. In contrast, the Paschen jump region near 8200 angstrom is relatively uncontaminated by other strong emission features. Here, we examine whether the Paschen jump can aid in constraining the DC contribution, using Hubble Space Telescope Space Telescope Imaging Spectrograph spectra of six nearby Seyfert 1 nuclei. The spectra appear smooth across the Paschen edge, and we find no evidence of a Paschen spectral break or jump in total flux. We fit multicomponent spectral models over the range 6800-9700 angstrom and find that the spectra can still be compatible with a significant DC contribution if the DC Paschen jump is offset by an opposite spectral break resulting from blended high-order Paschen emission lines. The fits imply DC contributions ranging from similar to 10% to 50% at 8000 angstrom, but the fitting results are highly dependent on assumptions made about other model components. These degeneracies can potentially be alleviated by carrying out fits over a broader wavelength range, provided that models can accurately represent the disk continuum shape, Fe ii emission, high-order Balmer line emission, and other components.

Original languageEnglish
Article number60
JournalAstrophysical Journal
Volume927
Issue number1
Number of pages12
ISSN0004-637X
DOIs
Publication statusPublished - 1 Mar 2022

    Research areas

  • LAG-LUMINOSITY RELATIONSHIP, ACCRETION-DISK, SPACE TELESCOPE, BROAD EMISSION, SEYFERT 1, FE-II, H-I, QUASARS, SPECTRA, GALAXY

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