J/MNRAS/449/4204ivo://CDS.VizieR/J/MNRAS/449/4204doi:10.26093/cds/vizier.74494204CDSLusso E.Worseck G.Hennawi J.F.Prochaska J.X.Vignali C.Stern J.,O'meara J.M.2024-08-14T20:21:25Z2017-12-18T08:58:39ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frquasarsactive-galactic-nucleispectroscopyultraviolet-astronomyThe ionizing continuum from active galactic nuclei is fundamental for interpreting their broad emission lines and understanding their impact on the surrounding gas. Furthermore, it provides hints on how matter accretes on to supermassive black holes. Using Hubble Space Telescope's Wide Field Camera 3, we have constructed the first stacked ultraviolet (rest-frame wavelengths 600-2500{AA}) spectrum of 53 luminous quasars at z=~2.4, with a state-of-the-art correction for the intervening Lyman forest and Lyman continuum absorption. The continuum slope (f_{nu}_{prop.to}{nu}^{alpha}{nu}^) of the full sample shows a break at ~912{AA} with spectral index {alpha}_{nu}_=-0.61+/-0.01 at {lambda}>912{AA} and a softening at shorter wavelengths ({alpha}_{nu}_=-1.70+/-0.61 at {lambda}<=912{AA}). Our analysis proves that a proper intergalactic medium absorption correction is required to establish the intrinsic continuum emission of quasars. We interpret our average ultraviolet spectrum in the context of photoionization, accretion disc models, and quasar contribution to the ultraviolet background. We find that observed broad line ratios are consistent with those predicted assuming an ionizing slope of {alpha}_ion_=-2.0, similar to the observed ionizing spectrum in the same wavelength range. The continuum break and softening are consistent with accretion disc plus X-ray corona models when black hole spin is taken into account. Our spectral energy distribution yields a 30 per cent increase to previous estimates of the specific quasar emissivity, such that quasars may contribute significantly to the total specific Lyman limit emissivity estimated from the Ly{alpha} forest at z<3.2.2015MNRAS.449.4204Lhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/MNRAS/449/4204CatalogResearchIsServedByTAP VizieR generic servicerelated-toIII/157 : An Ultraviolet Atlas of Quasar and Blazar SpectraVII/252 : SDSS-DR5 quasar catalog (Schneider+, 2007)J/ApJ/690/1181 : UV-bright quasars (Syphers+, 2009)J/ApJ/736/42 : HST QSO Catalog (Ribaudo+, 2011)J/ApJS/195/16 : HST survey for Lyman limit systems. I. (O'Meara+, 2011)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/MNRAS/449/4204https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/MNRAS/449/4204http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/MNRAS/449/4204https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/MNRAS/449/4204https://vizier.iucaa.in/viz-bin/votable?-source=J/MNRAS/449/4204http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/MNRAS/449/4204GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapUVdefaultJ/MNRAS/449/4204/table1WFC3/UVIS stacked spectrum corrected for IGM absorptionrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintlambdaRest-frame wavelength {lambda}({AA})0.1nmem.wldoubleFlambdaMean intergalactic medium (IGM) corrected flux per {AA} normalized to the flux at 1450{AA}, for the full WFC3 sample (f_{lambda},f_)phot.flux;arith.ratiofloate_FlambdaUncertainty in Flambdastat.errorfloatFlambdaRQMean IGM corrected flux per {AA} normalized to the flux at 1450{AA}, for the radio-quiet sample (f_{lambda},rq_)phot.flux;arith.ratiofloate_FlambdaRQUncertainty in FlambdaRQstat.errorfloat