Locally Optimally Emitting Clouds and the Origin of Quasar Emission Lines

Baldwin, J. A.; Ferland, Gary J.; Korista, K. T.; Verner, D. A.

doi:10.1086/309827

Cited by 332 publications

(426 citation statements)

References 27 publications

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“…Regardless of the variation across selection criteria, luminosities and redshifts, a remarkable similarity in the overall shape is visible over a wide wavelength range. The simultaneous existence of lines arising in such different environments around objects differing by many orders of magnitude in luminosity is caused by the varying conditions in the emitting clouds which ensure that each ionic species has optimal conditions to produce line emission (Baldwin et al 1995). Significant differences between the composites are visible blueward of Lyα where different methods for IGM absorption correction has been employed.…”

Section: Comparison To Existing Compositesmentioning

confidence: 99%

An X-Shooter composite of bright 1 <z< 2 quasars from UV to infrared

Selsing

Fynbo

Christensen

et al. 2015

A&A

165

180

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Quasi-stellar object (QSO) spectral templates are important both to QSO physics and for investigations that use QSOs as probes of intervening gas and dust. However, combinations of various QSO samples obtained at different times and with different instruments so as to expand a composite and to cover a wider rest frame wavelength region may create systematic effects, and the contribution from QSO hosts may contaminate the composite. We have constructed a composite spectrum from luminous blue QSOs at 1 < z < 2.1 selected from the Sloan Digital Sky Survey (SDSS). The observations with X-Shooter simultaneously cover ultraviolet (UV) to nearinfrared (NIR) light, which ensures that the composite spectrum covers the full rest-frame range from Lyβ to 11 350 Å without any significant host contamination. Assuming a power-law continuum for the composite we find a spectral slope of α λ = 1.70 ± 0.01, which is steeper than previously found in the literature. We attribute the differences to our broader spectral wavelength coverage, which allows us to effectively avoid fitting any regions that are affected either by strong QSO emissions lines (e.g., Balmer lines and complex [Fe II] blends) or by intrinsic host galaxy emission. Finally, we demonstrate the application of the QSO composite spectrum for evaluating the reddening in other QSOs.

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Section: Comparison To Existing Compositesmentioning

confidence: 99%

An X-Shooter composite of bright 1 <z< 2 quasars from UV to infrared

Selsing

Fynbo

Christensen

et al. 2015

A&A

165

180

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“…Estimated Lyα flux does not include the strong wings beyond ±0.5 eV from the core of the line. pare the estimated line flux ratios to the fluxes from the compilation of Baldwin et al (1995). All the fluxes are expressed in the units of Lyα flux.…”

Section: Appearance Of the Blrmentioning

confidence: 99%

Gamma-ray opacity of the anisotropic stratified broad-line regions in blazars

Abolmasov

Poutanen

2016

Mon. Not. R. Astron. Soc.

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The GeV-range spectra of blazars are shaped not only by non-thermal emission processes internal to the relativistic jet but also by external pair-production absorption on the thermal emission of the accretion disc and the broad-line region (BLR). For the first time, we compute here the pair-production opacities in the GeV range produced by a realistic BLR accounting for the radial stratification and radiation anisotropy. Using photoionization modelling with the CLOUDY code, we calculate a series of BLR models of different sizes, geometries, cloud densities, column densities and metallicities. The strongest emission features in the model BLR are Lyα and He II Lyα. Contribution of recombination continua is smaller, especially for hydrogen, because Ly continuum is efficiently trapped inside the large optical depth BLR clouds and converted to Lyman emission lines and higher-order recombination continua. The largest effects on the gamma-ray opacity are produced by the BLR geometry and localization of the gamma-ray source. We show that when the gamma-ray source moves further from the central source, all the absorption details move to higher energies and the overall level of absorption drops because of decreasing incidence angles between the gamma-rays and BLR photons. The observed positions of the spectral breaks can be used to measure the geometry and the location of the gamma-ray emitting region relative to the BLR. Strong dependence on geometry means that the soft photons dominating the pair-production opacity may be actually produced by a different population of BLR clouds than the bulk of the observed broad line emission.

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“…Korista, Ferland & Baldwin (1997a) suggested that the BLR does not see the same SED we do. They adopt a baseline of 0.1 for the BLR CF, and use the Locally Optimally emitting Cloud (LOC) model of the BLR, where a single slab of gas produces line emission from a rather limited range of ionization states (Baldwin et al 1995). However, adopting the observed BLR CF of ≃0.3 (see above), and noting that a single slab produces line emission from a very broad range of ionization states (Baskin et al 2014a), alleviate the need in a different SED for the BLR.…”

Section: Similar Relations For the Broad Line Region C Iv Emissionmentioning

confidence: 99%

On the origins of C iv absorption profile diversity in broad absorption line quasars

Baskin

Laor

Hamann

2015

Monthly Notices of the Royal Astronomical Society

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There is a large diversity in the C iv broad absorption line (BAL) profile among BAL quasars (BALQs). We quantify this diversity by exploring the distribution of the C iv BAL properties, FWHM, maximum depth of absorption and its velocity shift (v md ), using the SDSS DR7 quasar catalogue. We find the following: (i) Although the median C iv BAL profile in the quasar rest-frame becomes broader and shallower as the UV continuum slope (α UV at 1700-3000Å) gets bluer, the median individual profile in the absorber rest-frame remains identical, and is narrow (FWHM = 3500 km s −1 ) and deep. Only 4 per cent of BALs have FWHM > 10, 000 km s −1 . (ii) As the He ii emission equivalent-width (EW) decreases, the distributions of FWHM and v md extend to larger values, and the median maximum depth increases. These trends are consistent with theoretical models in which softer ionizing continua reduce overionization, and allow radiative acceleration of faster BAL outflows. (iii) As α UV becomes bluer, the distribution of v md extends to larger values. This trend may imply faster outflows at higher latitudes above the accretion disc plane. (iv) For non-BALQs, the C iv emission line decreases with decreasing He ii EW, and becomes more asymmetric and blueshifted. This suggests an increasing relative contribution of emission from the BAL outflow to the C iv emission line as the ionizing spectral energy distribution (SED) gets softer, which is consistent with the increasing fraction of BALQs as the ionizing SED gets softer.

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Locally Optimally Emitting Clouds and the Origin of Quasar Emission Lines

Cited by 332 publications

References 27 publications

An X-Shooter composite of bright 1 <z< 2 quasars from UV to infrared

An X-Shooter composite of bright 1 <z< 2 quasars from UV to infrared

Gamma-ray opacity of the anisotropic stratified broad-line regions in blazars

On the origins of C iv absorption profile diversity in broad absorption line quasars

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