ASYMMETRIC ABSORPTION PROFILES OF Lyα AND Lyβ IN DAMPED Lyα SYSTEMS

Lee, Heewon

doi:10.1088/0004-637x/772/2/123

Cited by 20 publications

(28 citation statements)

References 30 publications

(39 reference statements)

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“…For a photon in the vicinity of Lyα, the 2p state provides a dominant contribution. A minor contribution from the remaining p states affects the final cross section in a complicated way so that the cross section is larger for radiation redward of Lyα than blueward (Lee 2013).…”

Section: Discussion and Summarymentioning

confidence: 99%

Polarization of Rayleigh scattered Lyα in active galactic nuclei

Chang

Lee

Yang

2016

Mon. Not. R. Astron. Soc.

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The unification scheme of active galactic nuclei (AGNs) invokes an optically thick molecular torus component hiding the broad emission line region. Assuming the presence of a thick neutral component in the molecular torus characterized by a H i column density > 10 22 cm −2 , we propose that far UV radiation around Lyα can be significantly polarized through Rayleigh scattering. Adopting a Monte Carlo technique we compute polarization of Rayleigh scattered radiation near Lyα in a thick neutral region in the shape of a slab and a cylindrical shell. It is found that radiation near Lyα Rayleigh reflected from a very thick slab can be significantly polarized in a fairly large range of wavelength ∆λ ∼ 50Å exhibiting a flux profile similar to the incident one. Rayleigh transmitted radiation in a slab is characterized by the central dip with a complicated polarization behavior. The optically thick part near Lyα center is polarized in the direction perpendicular to the slab normal, which is in contrast to weakly polarized wing parts in the direction parallel to the slab normal. A similar polarization flip phenomenon is also found in the case of a tall cylindrical shell, in which the spatial diffusion along the vertical direction near the inner cylinder wall for core photons leads to a tendency of the electric field aligned to the direction perpendicular to the vertical axis. Observational implications are briefly discussed including spectropolarimetry of the quasar PG 1630+377 by Koratkar et al. in 1990 where Lyα is strongly polarized with no other emission lines polarized.

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Section: Discussion and Summarymentioning

confidence: 99%

Polarization of Rayleigh scattered Lyα in active galactic nuclei

Chang

Lee

Yang

2016

Mon. Not. R. Astron. Soc.

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“…The Raman wing feature is fitted with a Lorentzian function, because the Raman cross section near Lyβ is roughly approximated by a Lorentzian function due to the proximity of resonance (e.g., Lee 2013). The Thomson wing profile is fitted with a Gaussian function because the free electron region is assumed to follow a Maxwell-Boltzmann distribution.…”

Section: Simulated Broad Balmer Wing Profilesmentioning

confidence: 99%

Broad Wings around Hα and Hβ in the Two S-type Symbiotic Stars Z Andromedae and AG Draconis

Chang

Lee

et al. 2018

ApJ

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Symbiotic stars often exhibit broad wings around Balmer emission lines, whose origin is still controversial. We present the high resolution spectra of the S type symbiotic stars Z Andromedae and AG Draconis obtained with the ESPaDOnS and the 3.6 m Canada France Hawaii Telescope to investigate the broad wings around Hα and Hβ. When Hα and Hβ lines are overplotted in the Doppler space, it is noted that Hα profiles are overall broader than Hβ in these two objects. Adopting a Monte Carlo approach, we consider the formation of broad wings of Hα and Hβ through Raman scattering of far UV radiation around Lyβ and Lyγ and Thomson scattering by free electrons. Raman scattering wings are simulated by choosing an H I region with a neutral hydrogen column density N HI and a covering factor CF . For Thomson wings, the ionized scattering region is assumed to cover fully the Balmer emission nebula and is characterized by the electron temperature T e and the electron column density N e . Thomson wings of Hα and Hβ have the same width that is proportional to T 1/2 e . However, Raman wings of Hα are overall three times wider than Hβ counterparts, which is attributed to different cross section for Lyβ and Lyγ. Normalized to have the same peak values and presented in the Doppler factor space. Hα wings of Z And and AG Dra are observed to be significantly wider than Hβ counterpart, favoring the Raman scattering origin of broad Balmer wings.

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“…However, current measurement of the power-spectrum on these scales do not allow for stringent constraints (see Mesinger, McQuinn, & Spergel 2012, for a discussion). 2013;Planck Collaboration et al 2013). For a reionisation history in which the Universe transitions from fully neutral to fully ionised at redshift z reion over a redshift range z = 0.5, this translates to z reion = 11.1 ± 1.1.…”

Section: Introductionmentioning

confidence: 99%

Lyα Emitting Galaxies as a Probe of Reionisation

Dijkstra

2014

Publ. Astron. Soc. Aust.

265

171

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The Epoch of Reionization (EoR) represents a milestone in the evolution of our Universe. Star-forming galaxies that existed during the EoR likely emitted a significant fraction (∼ 5 − 40%) of their bolometric luminosity as Lyα line emission. However, neutral intergalactic gas that existed during the EoR was opaque to Lyα emission that escaped from galaxies during this epoch, which makes it difficult to observe. The neutral intergalactic medium (IGM) may thus reveal itself by suppressing the Lyα flux from background galaxies. Interestingly, a 'sudden' reduction in the observed Lyα flux has now been observed in galaxies at z > 6. This review contains a detailed summary of Lyα radiative processes: I describe (i) the main Lyα emission processes, including collisional-excitation & recombination (and derive the origin of the famous factor '0.68'), and (ii) basic radiative transfer concepts, including e.g. partially coherent scattering, frequency diffusion, resonant versus wing scattering, optically thick versus 'extremely' optically thick (static/outflowing/collapsing) media, and multiphase media. Following this review, I derive expressions for the Gunn-Peterson optical depth of the IGM during (inhomogeneous) reionisation and post-reionisation. I then describe why current observations appear to require a very rapid evolution of volume-averaged neutral fraction of hydrogen in the context of realistic inhomogeneous reionisation models, and discuss uncertainties in this interpretation. Finally, I describe how existing & futures surveys and instruments can help reduce these uncertainties, and allow us to fully exploit Lyα emitting galaxies as a probe of the EoR.

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ASYMMETRIC ABSORPTION PROFILES OF Lyα AND Lyβ IN DAMPED Lyα SYSTEMS

Cited by 20 publications

References 30 publications

Polarization of Rayleigh scattered Lyα in active galactic nuclei

Polarization of Rayleigh scattered Lyα in active galactic nuclei

Broad Wings around Hα and Hβ in the Two S-type Symbiotic Stars Z Andromedae and AG Draconis

Lyα Emitting Galaxies as a Probe of Reionisation

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