Measuring the Sources of the Intergalactic Ionizing Flux

Cowie, L. L.; Barger, A. J.; Trouille, Laura

doi:10.1088/0004-637x/692/2/1476

Cited by 131 publications

(201 citation statements)

References 59 publications

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“…Resulting uncertainties in the specific emissivity are rarely discussed (see Faucher-Giguère et al 2008 for an exception), or limited to variations in the EUV spectral index ). Consequently, current estimates of the specific Lyman limit emissivity of quasars still vary by a factor ∼ 2 at z = 3-4 (Hopkins et al 2007;Siana et al 2008;Cowie et al 2009;Masters et al 2012). Figure 12 compares our stacked spectrum and various quasar composites to broken power-law parameterizations used to estimate the specific quasar Lyman limit emissivity and/or the quasar contribution to the UV background (Cowie et al 2009;Faucher-Giguère et al 2009;Haardt & Madau 2012).…”

Section: Quasar Emissivity and Photoionisation Ratementioning

confidence: 94%

“…Adopting our power-law fit fν ∝ ν −0.61 instead, we obtain Lyman limit flux ratios of f L14 ν,912 /f FG09 ν,912 = 1.12 ) and f L14 ν,912 /f HM12 ν,912 = 1.38 (Haardt & Madau 2012) as correction factors to the quasar Lyman limit emissivity ν,912(z) for a fixed luminosity function 13 . We point out that Cowie et al (2009) computed a power-law slope of -1.35 at 700 < λ < 2300Å obtained from GALEX photometry of a zem ∼ 1 AGN sample. This implies a 700Å to 2300Å flux ratio of 0.20.…”

Section: Quasar Emissivity and Photoionisation Ratementioning

confidence: 99%

“…As Fig. 8 but including recent broken power law parameterizations of the quasar continuum (Cowie et al 2009;Faucher-Giguère et al 2009;Haardt & Madau 2012). The SEDs have been normalized at the adopted rest frame wavelengths (Faucher-Giguère et al 2009: 4400Å) or assumed at 1450Å if not given by the authors (Cowie et al 2009;Haardt & Madau 2012).…”

Section: Quasar Emissivity and Photoionisation Ratementioning

confidence: 99%

“…Consequently, current estimates of the specific Lyman limit emissivity of quasars still vary by a factor ∼ 2 at z = 3-4 (Hopkins et al 2007;Siana et al 2008;Cowie et al 2009;Masters et al 2012). Figure 12 compares our stacked spectrum and various quasar composites to broken power-law parameterizations used to estimate the specific quasar Lyman limit emissivity and/or the quasar contribution to the UV background (Cowie et al 2009;Faucher-Giguère et al 2009;Haardt & Madau 2012). Most previous SED parameterizations have underestimated the quasar Lyman continuum flux because they have been based on the T02 composite spectrum without a proper IGM correction (Section 5.2).…”

Section: Quasar Emissivity and Photoionisation Ratementioning

confidence: 99%

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

Lusso

Worseck

Hennawi

et al. 2015

Monthly Notices of the Royal Astronomical Society

273

355

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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 600-2500Å) 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 (f ν ∝ ν αν ) of the full sample shows a break at ∼912Å with spectral index α ν = −0.61 ± 0.01 at λ > 912Å and a softening at shorter wavelengths (α ν = −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 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 α 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 Lyα forest at z < 3.2.

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Section: Quasar Emissivity and Photoionisation Ratementioning

confidence: 94%

Section: Quasar Emissivity and Photoionisation Ratementioning

confidence: 99%

Section: Quasar Emissivity and Photoionisation Ratementioning

confidence: 99%

Section: Quasar Emissivity and Photoionisation Ratementioning

confidence: 99%

See 2 more Smart Citations

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

Lusso

Worseck

Hennawi

et al. 2015

Monthly Notices of the Royal Astronomical Society

273

355

View full text Add to dashboard Cite

show abstract

“…Probably the most significant sources varied over time. At late times, z < 3, it has been found that the bulk of the ionizing photons originates from quasars (Faucher-Giguère et al 2008) and AGNs (Cowie et al 2009), while at higher redshifts quasars are too few in number to be the dominant source (Jiang et al 2008;Loeb 2009). The onset of the reionization has instead been connected to the appearance of the first luminous structures in the universe, the first stars and galaxies (Haehnelt et al 2001).…”

Section: Introductionmentioning

confidence: 99%

Analyzing low signal-to-noise FUSE spectra

Leitet

Bergvall

Piskunov

et al. 2011

A&A

101

105

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Context. Galaxies are believed to be the main providers of Lyman continuum (LyC) photons during the early phases of the cosmic reionization. Little is known however, when it comes to escape fractions and the mechanisms behind the leakage. To learn more, one may look at local objects, but so far only one low-z galaxy has shown any signs of emitting LyC radiation. With data from the Far Ultraviolet Spectroscopic Explorer (FUSE), we previously found an absolute escape fraction of ionizing photons ( f esc ) of 4-10% for the blue compact galaxy Haro 11. However, using a revised version of the reduction pipeline on the same data set, Grimes and collaborators were unable to confirm this and derived an upper limit of f esc 2% . Aims. We attempt to determine whether Haro 11 is emitting ionizing radiation to a significant level or not. We also investigate the performance of the reduction pipeline for faint targets such as Haro 11, and introduce a new approach to the background subtraction. Methods. The final version of the reduction pipeline, CalFUSE v3.2, was applied to the same Haro 11 data set as the two previous authors used. At these faint flux levels, both FUSE and CalFUSE are pushed to their limits, and a detailed analysis was undertaken to monitor the performance of the pipeline. We show that non-simultaneous background estimates are insuffient when working with data of low signal-to-noise ratio (S /N), and a new background model was developed based on a direct fit to the detector response. Results. We find that one has to be very careful when using CalFUSE v3.2 on low S /N data, and especially when dealing with sources where signal might originate from off-center regions. Applying the new background fit, a significant signal is detected in the LyC in both detector segments covering these wavelengths. Thus, the leakage is confirmed with a flux density of f 900 = 4.0 × 10 −15 erg s −1 cm −2 Å −1 (S /N = 4.6), measured on the airglow free regions in the LyC for the night-only data. This corresponds to an absolute escape fraction of ionizing photons from Haro 11 of f esc = 3.3 ± 0.7%. We confirm these results by investigating the two-dimensional data, the count rates, and the residual flux in C ii λ1036 Å.

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High-Redshift Galaxy Surveys and the Reionization of the Universe

Bouwens

2016

Understanding the Epoch of Cosmic Reionization

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Star-forming galaxies in the early universe provide us with perhaps the most natural way of explaining the reionization of the universe. Current observational results are sufficiently comprehensive, as to allow us to approximately calculate how the ionizing radiation from galaxies varies as a function of cosmic time. Important uncertainties in modeling reionization by galaxies revolve around the escape fraction and its luminosity and redshift dependence, a possible truncation of the galaxy luminosity function at the faint end, and an evolution in the production efficiency of Lyman-continuum photons with cosmic time. Despite these uncertainties, plausible choices for these parameters naturally predict a cosmic ionizing emissivity at z ∼ 6-10 whose evolution and overall normalization is in excellent agreement with that derived from current observational constraints. This strongly suggests that galaxies provide the necessary photons to reionize the universe.

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Measuring the Sources of the Intergalactic Ionizing Flux

Cited by 131 publications

References 59 publications

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

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

Analyzing low signal-to-noise FUSE spectra

High-Redshift Galaxy Surveys and the Reionization of the Universe

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