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 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:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 32 158 WFC3/UVIS stacked spectrum corrected for IGM
absorption
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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
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Bytes Format Units Label Explanations
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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
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History:
From electronic version of the journal
(End) Tiphaine Pouvreau [CDS] 12-Dec-2017