Monte Carlo Simulation of Lyα Scattering and Application to Damped Lyα Systems

By Zheng Zheng, J. Miralda-Escudé. 2002

157 citations recorded by the source corpus.

A Monte Carlo code to solve the transfer of Lyα photons is developed that can predict the Lyα image and two-dimensional Lyα spectra of a hydrogen cloud with any given geometry, Lyα emissivity, neutral hydrogen density distribution, and bulk velocity field. We apply the code to several simple cases of a uniform cloud to show how the Lyα image and emitted line spectrum are affected by the column density, internal velocity gradients, and emissivity distribution. We then apply the code to two models for damped Lyα absorption systems: a spherical, static, isothermal cloud and a flattened, axially symmetric, rotating cloud. If the emission is due to fluorescence of the external background radiation, the Lyα image should have a core corresponding to the region where hydrogen is self-shielded. The emission-line profile has the characteristic double peak with a deep central trough. We show how rotation of the cloud causes the two peaks to shift in wavelength as the slit is perpendicular to the rotation axis and how the relative amplitude of the two peaks is changed. In reality, damped Lyα systems are likely to have a clumpy gas distribution with turbulent velocity fields, which should smooth the line emission profile but should still leave the rotation signature of the wavelength shift across the system.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/347e641b6bb432abab15a33d5e48b7c8a0249f96

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Citations in the corpus

The impact of The IGM on high-redshift Lyα emission lines (2007, background): “…collapsing gas clouds is expected to be blueshifted relative to the true line center, by an amount that depends on the infall velocity and the total column density of neutral hydrogen in the infalling gas (Zheng & Miralda-Escudé 2002; Tasitsiomi 2006; Dijkstra et al. 2006a; Verhamme et al. 2006).”
Lyman α radiative transfer in a multiphase medium (2005, methodology): “The Monte Carlo algorithm we use is similar to the code used by Ahn et al. (2001, 2002, 2003) and Zheng & Miralda-Escudé (2002).”
3D Lyman-alpha radiation transfer. I. Understanding Lyman-alpha line profile morphologies (2006, methodology): “For test purposes we have also compared the surface brightness profiles with the results of Zheng & Miralda-Escude (2002), and find a good agreement.”
THE STRUCTURE AND KINEMATICS OF THE CIRCUMGALACTIC MEDIUM FROM FAR-ULTRAVIOLET SPECTRA OF z ≃ 2–3 GALAXIES (2010, background): “…transfer in the context of galactic outflows (Verhamme et al. 2006, 2008; Schaerer & Verhamme 2008; Hansen & Oh 2006; Dijkstra et al. 2006b,a; Zheng & Miralda-Escudé 2002), and even in the highlyidealized geometric configurations considered in these papers, a given line profile does not…”
The Universe Is Reionizing at z ∼ 7: Bayesian Inference of the IGM Neutral Fraction Using Lyα Emission from Galaxies (2017, background): “This produces the fiducial double-peaked Lyα lineshape, for which the red (blue) peak is enhanced for outflows (inflows) (Zheng & Miralda-Escude 2002; Verhamme et al. 2006).”
Lyα Emitting Galaxies as a Probe of Reionisation (2014, methodology): “Moreover, as the Lyα photons are diffusing outward through an expanding medium, they loose energy because the do ’work’ on the outflowing gas (Zheng & Miralda-Escudé 2002).”
Quasars Probing Quasars. I. Optically Thick Absorbers near Luminous Quasars (2006, background): “…in ionization equilibrium with a photoionizing background reemit 60% of the ionizing radiation they absorb as fluorescent Ly recombination line photons (Gould & Weinberg 1996; Zheng & Miralda-Escudé 2002; Cantalupo et al. 2005; Adelberger et al. 2006; J. A. Kollmeier et al. 2006, in preparation).”
Using Lyman-α to detect galaxies that leak Lyman continuum (2014, background): “For comparison, the Lyα optical depth at the line centre of such a low column density medium is still τ0 = 5.88 × 10−14(12.85/b) NHI ∼ 104 (5) for a Doppler parameter of b = 12.85 km s−1, corresponding to an ISM temperature of T = 104 K (e.g. Zheng & Miralda-Escudé 2002).”
A Population of Faint Extended Line Emitters and the Host Galaxies of Optically Thick QSO Absorption Systems (2007, background): “The result may be observable as emission broadened in frequency space and extended in the spatial direction beyond the extent of the actual source of Ly photons (e.g., Adams 1972; Neufeld 1990; Zheng & Miralda-Escudé 2002; Dijkstra et al. 2006a; Tasitsiomi 2006).”
Lyα COOLING EMISSION FROM GALAXY FORMATION (2010, methodology): “…of Lyα radiative transfer reflecting the fact that the photons can escape the medium either on the blue side or on the red side of the line center, where the opacity is typically too extreme (e.g., Neufeld 1990; Zheng & Miralda-Escudé 2002a; Dijkstra et al. 2006; Verhamme et al. 2006).”
Fluorescent Lyα Emission from the High-Redshift Intergalactic Medium (2005, methodology): “…shown in the central panel of Figure 7 clearly show that the gas velocity field within and in the vicinity of the shielding layers has a complicated structure which does not show the characteristic pattern of ordered rotation or symmetric infall considered by Zheng & Miralda-Escudé (2002b).”
The Connection between Galaxies and Intergalactic Absorption Lines at Redshift 2 ≲ z ≲ 3 (2005, background): “It is expected in a wide range of models in which the stars are surrounded by outflowing gas (e.g., Tenorio-Tagle et al. 1999; Zheng & Miralda-Escudé 2002) and is not (as far as we know) expected in any other class of realistic models.”
Lyα Radiation from Collapsing Protogalaxies. I. Characteristics of the Emergent Spectrum (2005, methodology): “In this paper we attack this problemwithMonte Carlo computations, similar to those used in previous papers (e.g., Ahn et al. 2000, 2002; Zheng & Miralda-Escudé 2002, hereafter ZM02; Cantalupo et al. 2005) of Ly transfer through a range of models that represent collapsing protogalactic gas clouds.”