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Title: HST-COS OBSERVATIONS OF AGNs. I. ULTRAVIOLET COMPOSITE SPECTRA OF THE IONIZING CONTINUUM AND EMISSION LINES

Abstract

The ionizing fluxes from quasars and other active galactic nuclei (AGNs) are critical for interpreting the emission-line spectra of AGNs and for photoionization and heating of the intergalactic medium. Using ultraviolet spectra from the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST), we have directly measured the rest-frame ionizing continua and emission lines for 22 AGNs. Over the redshift range 0.026 < z < 1.44, COS samples the Lyman continuum and many far-UV emission lines (Ly{alpha} {lambda}1216, C IV {lambda}1549, Si IV/O IV] {lambda}1400, N V {lambda}1240, O VI {lambda}1035). Strong EUV emission lines with 14-22 eV excitation energies (Ne VIII {lambda}{lambda}770, 780, Ne V {lambda}569, O II {lambda}834, O III {lambda}833, {lambda}702, O IV {lambda}788, 608, 554, O V {lambda}630, N III {lambda}685) suggest the presence of hot gas in the broad emission-line region. The rest-frame continuum, F{sub {nu}}{proportional_to}{nu}{sup {alpha}{sub {nu}}}, shows a break at wavelengths {lambda} < 1000 A, with spectral index {alpha}{sub {nu}} = -0.68 {+-} 0.14 in the FUV (1200-2000 A) steepening to {alpha}{sub {nu}} = -1.41 {+-} 0.21 in the EUV (500-1000 A). The COS EUV index is similar to that of radio-quiet AGNs in the 2002 HST/FOS survey ({alpha}{sub {nu}} = -1.57more » {+-} 0.17). We see no Lyman edge ({tau}{sub HI} < 0.03) or He I {lambda}584 emission in the AGN composite. Our 22 AGNs exhibit a substantial range of FUV/EUV spectral indices and a correlation with AGN luminosity and redshift, likely due to observing below the 1000 A spectral break.« less

Authors:
; ;  [1]
  1. CASA, Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309 (United States)
Publication Date:
OSTI Identifier:
22036987
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 752; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTRONOMY; ASTROPHYSICS; CORRELATIONS; EV RANGE; EXCITATION; GALAXIES; GALAXY NUCLEI; INDEXES; LUMINOSITY; LYMAN LINES; NITROGEN IONS; OXYGEN IONS; PHOTOIONIZATION; PHOTON EMISSION; QUASARS; RED SHIFT; SILICON IONS; ULTRAVIOLET RADIATION; ULTRAVIOLET SPECTRA

Citation Formats

Shull, J. Michael, Stevans, Matthew, and Danforth, Charles W., E-mail: michael.shull@colorado.edu, E-mail: matthew.stevans@colorado.edu, E-mail: charles.danforth@colorado.edu. HST-COS OBSERVATIONS OF AGNs. I. ULTRAVIOLET COMPOSITE SPECTRA OF THE IONIZING CONTINUUM AND EMISSION LINES. United States: N. p., 2012. Web. doi:10.1088/0004-637X/752/2/162.
Shull, J. Michael, Stevans, Matthew, & Danforth, Charles W., E-mail: michael.shull@colorado.edu, E-mail: matthew.stevans@colorado.edu, E-mail: charles.danforth@colorado.edu. HST-COS OBSERVATIONS OF AGNs. I. ULTRAVIOLET COMPOSITE SPECTRA OF THE IONIZING CONTINUUM AND EMISSION LINES. United States. doi:10.1088/0004-637X/752/2/162.
Shull, J. Michael, Stevans, Matthew, and Danforth, Charles W., E-mail: michael.shull@colorado.edu, E-mail: matthew.stevans@colorado.edu, E-mail: charles.danforth@colorado.edu. Wed . "HST-COS OBSERVATIONS OF AGNs. I. ULTRAVIOLET COMPOSITE SPECTRA OF THE IONIZING CONTINUUM AND EMISSION LINES". United States. doi:10.1088/0004-637X/752/2/162.
@article{osti_22036987,
title = {HST-COS OBSERVATIONS OF AGNs. I. ULTRAVIOLET COMPOSITE SPECTRA OF THE IONIZING CONTINUUM AND EMISSION LINES},
author = {Shull, J. Michael and Stevans, Matthew and Danforth, Charles W., E-mail: michael.shull@colorado.edu, E-mail: matthew.stevans@colorado.edu, E-mail: charles.danforth@colorado.edu},
abstractNote = {The ionizing fluxes from quasars and other active galactic nuclei (AGNs) are critical for interpreting the emission-line spectra of AGNs and for photoionization and heating of the intergalactic medium. Using ultraviolet spectra from the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST), we have directly measured the rest-frame ionizing continua and emission lines for 22 AGNs. Over the redshift range 0.026 < z < 1.44, COS samples the Lyman continuum and many far-UV emission lines (Ly{alpha} {lambda}1216, C IV {lambda}1549, Si IV/O IV] {lambda}1400, N V {lambda}1240, O VI {lambda}1035). Strong EUV emission lines with 14-22 eV excitation energies (Ne VIII {lambda}{lambda}770, 780, Ne V {lambda}569, O II {lambda}834, O III {lambda}833, {lambda}702, O IV {lambda}788, 608, 554, O V {lambda}630, N III {lambda}685) suggest the presence of hot gas in the broad emission-line region. The rest-frame continuum, F{sub {nu}}{proportional_to}{nu}{sup {alpha}{sub {nu}}}, shows a break at wavelengths {lambda} < 1000 A, with spectral index {alpha}{sub {nu}} = -0.68 {+-} 0.14 in the FUV (1200-2000 A) steepening to {alpha}{sub {nu}} = -1.41 {+-} 0.21 in the EUV (500-1000 A). The COS EUV index is similar to that of radio-quiet AGNs in the 2002 HST/FOS survey ({alpha}{sub {nu}} = -1.57 {+-} 0.17). We see no Lyman edge ({tau}{sub HI} < 0.03) or He I {lambda}584 emission in the AGN composite. Our 22 AGNs exhibit a substantial range of FUV/EUV spectral indices and a correlation with AGN luminosity and redshift, likely due to observing below the 1000 A spectral break.},
doi = {10.1088/0004-637X/752/2/162},
journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 752,
place = {United States},
year = {2012},
month = {6}
}