The first ultraviolet quasar-stacked spectrum at z ≃ 2.4 from WFC3

By E. Lusso, G. Worseck, J. Hennawi, J. Xavier Prochaska, C. Vignali, J. Stern, John M. O’Meara. 2015

193 citations recorded by the source corpus.

The ionising continuum from active galactic nuclei (AGN) is fundamental for interpreting their broad emission lines and understanding their impact on the surrounding gas. Furthermore, it provides hints on how matter accretes onto supermassive black holes. Using HST'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 ($f_\nu \propto \nu^{\alpha_\nu}$) of the full sample shows a break at ~912\AA\ with spectral index $\alpha_\nu=-0.61\pm0.01$ at $\lambda>912$\AA\ and a softening at shorter wavelengths ($\alpha_\nu=-1.70 \pm 0.61$ at $\lambda\leq 912$\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 photoionisation, accretion disk models, and quasar contribution to the ultraviolet background. We find that observed broad line ratios are consistent with those predicted assuming an ionising slope of $\alpha_\mathrm{ion}=$-2.0, similar to the observed ionising spectrum in the same wavelength range. The continuum break and softening are consistent with accretion disk plus X-ray corona models when black hole spin is taken into account. Our spectral energy distribution yields a 30% 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.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/65d4e1a7c32789e7bfac5776af424fce4a5f5051

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Citations in the corpus

Quantitative Constraints on the Reionization History from the IGM Damping Wing Signature in Two Quasars at z > 7 (2018, methodology): “For the ionizing spectrum of each quasar, we first use the Lusso et al. (2015) template to convert from the 2 We assume that the gas is of primordial composition, i.e. there is no cooling due to elements heavier than helium.”
Conditions for Reionizing the Universe with a Low Galaxy Ionizing Photon Escape Fraction (2019, methodology): “We thus calculate the emissivity of He II ionizing photons (energies>4 Ryd), again assuming a spectral index of αAGN=1.7, and solve for the IGM volume-ionized fraction of He III using = á ñ -”
The bolometric quasar luminosity function at z = 0–7 (2020, methodology): “The Kcorrections have been unified to that in Lusso et al. (2015), which is based on the stacked spectra of 53 quasars observed at z ∼ 2.4.”
Evolution of the AGN UV luminosity function from redshift 7.5 (2018, methodology): “…law fν ∝ ναν with a break at 912 Å, fν ∝ { ν−0.61 if λ ≥ 912 Å, ν−1.70 if λ < 912 Å (19) as derived from a stacked spectrum of 53 luminous (M1450 ' −27) z ' 2.4 quasars (Lusso et al. 2015), and consistent with recent composite spectra of low-z quasars with a wide range in luminosity (Shull et…”
Inferring the astrophysics of reionization and cosmic dawn from galaxy luminosity functions and the 21-cm signal (2018, methodology): “We note that to convert units we assume the ionizing specific luminosity follows a power-law, Lν ∝ ναν , and adopt α = −1.5 which is similar quantity in Lusso et al. (2015) The resulting constraints are shown in Figure C2.”
THE FINAL SDSS HIGH-REDSHIFT QUASAR SAMPLE OF 52 QUASARS AT z > 5.7 (2016, unknown): “We assume a broken power-law quasar SED as (Lusso et al. 2015), ⎧⎨⎩ n l n l µ > < n - -”
Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). V. Quasar Luminosity Function and Contribution to Cosmic Reionization at z = 6 (2018, unknown): “In Equation 12, we used a broken power-law quasar SED (fν ∝ ν−1.70 at λ < 912 Å and ∝ ν−0.61 at λ > 912 Å) presented by Lusso et al. (2015), and integrated from the H I Lyman limit (frequency ν = νLL) to the He II Lyman limit (ν = 4νLL).”
Nuclear activity versus star formation: emission-line diagnostics at ultraviolet and optical wavelengths (2015, background): “…detected routinely in quasars and galaxies out to high redshifts, although the lack of published measurements prevented us from inserting them in the present study (e.g., Humphrey et al. 2007; Hainline et al. 2011; Pâris et al. 2012; Alexandroff et al. 2013; Pâris et al. 2014; Lusso et al. 2015).”
Consistent modelling of the meta-galactic UV background and the thermal/ionization history of the intergalactic medium (2018, methodology): “The 1 Ry emissivity data were inferred by MH15 by converting the optical emissivity derived in the mentioned studies, using a power-law spectral index, αUV = −0.61, after Lusso et al. (2015).”
A JWST/NIRSpec First Census of Broad-line AGNs at z = 4–7: Detection of 10 Faint AGNs with M BH ∼ 106–108 M ⊙ and Their Host Galaxy Properties (2023, methodology): “The photoionization rate, Γ, is estimated from ϵ 912 us-ing an equation presented in Lusso et al. (2015).”
Modeling the Radio Background from the First Black Holes at Cosmic Dawn: Implications for the 21 cm Absorption Amplitude (2018, methodology): “We compute the ionizing flux by extrapolating from 2500Å to 912Å using a power law of −0.65 and assume a steeper spectrum blueward of 912Å with a spectral index of −1.7 (Lusso et al. 2015).”
COSMIC REIONIZATION AFTER PLANCK: COULD QUASARS DO IT ALL? (2015, methodology): “We have converted the integrated optical emissivity inferred from these studies, ǫλ (in units of erg s−1Mpc−3 Hz−1), into a 1 ryd emissivity, ǫ912, using a power-law spectral energy distribution, ǫ912 = ǫλ(λ/912) −αuv f̄esc, with αuv = 0.61 following Lusso et al. (2015).”