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J/MNRAS/449/4204   WFC3/UVIS quasar-stacked spectrum at z≃2.4    (Lusso+, 2015)

The first ultraviolet quasar-stacked spectrum at z≃2.4 from WFC3. Lusso E., Worseck G., Hennawi J.F., Prochaska J.X., Vignali C., Stern J., O'meara J.M. <Mon. Not. R. Astron. Soc., 449, 4204-4220 (2015)> =2015MNRAS.449.4204L (SIMBAD/NED BibCode)
ADC_Keywords: QSOs ; Active gal. nuclei ; Spectra, ultraviolet Keywords: accretion, accretion discs - galaxies: active - quasars: general Abstract: The 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 600-2500Å) 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 (fν∝ναν) of the full sample shows a break at ∼912Å with spectral index αν=-0.61±0.01 at λ>912Å and a softening at shorter wavelengths (αν=-1.70±0.61 at λ≤912Å). 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 αion=-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 Lyα forest at z<3.2. Description: The data sample employed in the present analysis comes from a survey performed with HST using the WFC3 instrument. Quasar sample, HST observations, and reduction procedures are described in detail in O'meara et al. 2011, J/ApJS/195/16 (O11). The O11 survey consists of 53 quasars selected from SDSS Data Release 5 (Schneider et al. 2007, Cat. VII/252) with g<18.5 mag, 2.3<zem<2.6, observed with the WFC3/UVIS-G280 grism in Cycle 17. These data were taken specifically for the scientific goal of surveying the abundance of strong H I Lyman limit absorption features at 1.2<z<2.5. Flux- and wavelength-calibrated 1D spectra for each quasar in this sample are extracted using customized software (see section 3.1 in O11). WFC3/UVIS-G280 spectra span roughly λ=2000-6000Å and they have relatively high signal-to-noise ratio (S/N∼20) per pixel down to λ∼2000Å (FWHM∼60Å at λ=2500Å). File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 32 158 WFC3/UVIS stacked spectrum corrected for IGM absorption
See also: III/157 : An Ultraviolet Atlas of Quasar and Blazar Spectra (Kinney+, 1991) VII/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) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 8 F8.3 0.1nm lambda Rest-frame wavelength λ(Å) 10- 14 F5.3 --- Flambda Mean intergalactic medium (IGM) corrected flux per Å normalized to the flux at 1450Å, for the full WFC3 sample (fλ,f) 16- 20 F5.3 --- e_Flambda Uncertainty in Flambda 22- 26 F5.3 --- FlambdaRQ Mean IGM corrected flux per Å normalized to the flux at 1450Å, for the radio-quiet sample (fλ,rq) 28- 32 F5.3 --- e_FlambdaRQ Uncertainty in FlambdaRQ
History: From electronic version of the journal
(End) Tiphaine Pouvreau [CDS] 12-Dec-2017
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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