• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.79.1-79.1
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• 2012

Due to the quantum interference of many atomic levels, the exact scattering cross section around a given resonance transition deviates from the Lorentz function when the frequency of the incident radiation is quite far from the resonance frequency. This atomic effect is quite significant in the case of damped Ly alpha systems, where HI column density is in excess of 10^20 cm^-2. In this poster, we present the deviation quantitatively taking into consideration of the Rayleigh and Raman scattering around Lyman alpha and Lyman beta.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.35-38
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• 1996

Much of our knowledge about the formation and evolution of high-redshift galaxies has come from studying the absorption signatures they impress on the spectra of background QSOs. The damped Lyman $\alpha$ (DLA) systems, in particular, have proved to be valuable probes of the metallicity and dust at redshifts z $\~$2-3 in what are the likely progenitors of galaxies like our own. At z $\~$ 2 we find that the typical metallicity of the universe was 1/15 solar. In addition, we find clear evidence for the existence of trace amounts of interstellar dust in DLA galaxies and show that this is consistent with recent high resolution spectra of DLAs with the Keck telescope, despite claims to the contrary.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.35.3-35.3
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• 2018

Incorporating the fully quantum mechanical computation of scattering cross-section and statistical moment analysis of absorption profiles, we investigate the Lyman line asymmetry of extremely high column density systems. Recent high redshift observations detected strong damped Lyman alpha systems (DLAs) whose column density is larger than N_HI ~ [10]^21.3 cm^(-2). Absorption profiles of these DLAs are characterized by the broad and asymmetric damping wing. For accurate description of radiation damping, the second-order time-dependent perturbation theory is adopted. To quantitatively address line asymmetry, we define a distribution function for each Lyman line, and compute statistical moments (mean, standard deviation, skewness and kurtosis) regarding column densities N_HI > [10]^18 cm^(-2). In this work, we present statistical properties of the intrinsic line profiles, and compare them with the Lorentzian cases.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.38.1-38.1
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• 2016

Gamma ray burst, the most brightest explosion phenomena in the current universe is well suited for study of high redshift universe. We report the afterglow multi-wavelength observation and GTC spectroscopy follow up of GRB 140304A which was exploded at z=5.283. The spectrum was shown damped Lyman alpha features and a series of absorption lines S, Si, SiII*, Oi, CII, CII*, SiIV are clearly detected at common redshift. Clear optical flares are detected when X-ray flare happened and a possible gamma-ray excess also. At this conference, we report on implications for the GRB host and environments using its absorption features which place the results in context to other well studied high redshift GRBs and studies about the ejecta using its observed flaring activities.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.41.1-41.1
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• 2021

Neutral (HI) gas clouds associated with galaxies are responsible for fuelling the star-formation in the universe. In literature, the extremely strong damped Lyman-alpha absorbers (or ESDLAs) have been known to be sensitive to the effects of HI-H2 transition and star-formation in galaxies. Yet, ESDLAs are rare to probe due to the smaller cross section they subtend on the sky (similar to galaxies). In my talk, I will focus primarily on my study of the nature of ESDLAs that are observed as absorption signature along the line-of-sight (LOS) of a quasar (QSO). I will further look at the HI-H2 transition and interesting results relevant to diffuse molecular gas and the multi-phase medium (gas in different ionization states) that are associated with ESDLAs. Furthermore, I will also discuss how the ESDLA environments differ from the high star-forming and molecular environments detected in blind optical and radio surveys consecutively.