HST-COS OBSERVATIONS OF AGNs. III. SPECTRAL CONSTRAINTS IN THE LYMAN CONTINUUM FROM COMPOSITE COS/G140L DATA

Journal Article · Wed Jan 20 04:00:00 EST 2016 · Astrophysical Journal

DOI:https://doi.org/10.3847/0004-637X/817/1/56· OSTI ID:22521669

Tilton, Evan M.; Shull, J. Michael; Danforth, Charles W. ^[1]

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1. CASA, Department of Astrophysical and Planetary Sciences, University of Colorado, 389-UCB, Boulder, CO 80309 (United States)

The rest-frame ultraviolet (UV) spectra of active galactic nuclei (AGNs) are important diagnostics of both accretion disk physics and their contribution to the metagalactic ionizing UV background. Though the mean AGN spectrum is well characterized with composite spectra at wavelengths greater than 912 Å, the shorter-wavelength extreme-UV (EUV) remains poorly studied. In this third paper in a series on the spectra of AGNs, we combine 11 new spectra taken with the Cosmic Origins Spectrograph on the Hubble Space Telescope with archival spectra to characterize the typical EUV spectral slope of AGNs from λ{sub rest} ∼ 850 Å down to λ{sub rest} ∼ 425 Å. Parameterizing this slope as a power law, we obtain F{sub ν} ∝ ν{sup −0.72±0.26}, but we also discuss the limitations and systematic uncertainties of this model. We identify broad emission features in this spectral region, including emission due to ions of O, Ne, Mg, and other species, and we limit the intrinsic He i 504 Å photoelectric absorption edge opacity to τ{sub He} {sub i} < 0.047.

• OSTI ID: 22521669
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 817; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABSORPTION SPECTRA
ACCRETION DISKS
EMISSION SPECTRA
GALAXIES
GALAXY NUCLEI
LIMITING VALUES
LYMAN LINES
MAGNESIUM IONS
NEON IONS
OPACITY
OXYGEN IONS
QUASARS
RED SHIFT
SPACE
TELESCOPES
ULTRAVIOLET RADIATION
ULTRAVIOLET SPECTRA