Day 1 Session 1. Chair Hee-Won Lee
Yujin Yang – KASI
Title: Lyα Emission as an Observational Probe
Abstract
Seok-Jun Chang – Sejong Univ.
Title: Lyα Radiative Transfer & Polarimetric Modeling for LABd05
Abstract
Sungyoung Hong - KIAS
Title: Statistics of Two-point Correlation and Network Topology for Lyα emitters at z ~ 2.67
Abstract
We investigate the spatial distribution of Lyα-emitting galaxies (LAEs) at z = 2.67, selected from the NOAO Deep Wide-Field Survey, using two-point statistics and topological diagnostics adopted from network science. We measure the clustering length, r0 ? 4?h?1?Mpc, and the bias, bLAE=2.2+0.2 Fitting the clustering with halo occupation distribution (HOD) models results in two disparate possibilities: (1) where the fraction of central galaxies is <1 percent in haloes of mass >10^12M⊙ and (2) where the fraction is 20 percent. We refer to these two scenarios as the ‘Dusty Core Scenario’ for Model#1, since most of the central galaxies in massive haloes are dead in Lyα emission, and the ‘Pristine Core Scenario’ for Model#2, since the central galaxies are bright in Lyα emission. Traditional two-point statistics cannot distinguish between these disparate models given the current data sets. To overcome this degeneracy, we generate mock catalogues for each HOD model using a high-resolution N-body simulation and adopt a network statistics approach, which provides excellent topological diagnostics for galaxy point distributions. We find three topological anomalies from the spatial distribution of observed LAEs, which are not reproduced by the HOD mocks. We find that Model#2 matches better all network statistics than Model#1, suggesting that the central galaxies in >1012?h?1?M⊙ haloes at z ~ 2.67 need to be less dusty to be bright as LAEs, potentially implying some replenishing channels of pristine gas such as the cold mode accretion.
Day 2 Session 1. Chair Yujin Yang
Kwang-Il Seon - KASI
Title: Lyα Radiative Transfer: The Wouthuysen-Field effect and the Lyα polarization
Abstract
A three-dimensional, Monte Carlo Lyα radiative transfer (RT) code, LaRT, is developed to study the Lyα RT, in particular, the Wouthuysen-Field (WF) effect and the polarization of Lyα. In this talk, newly-developed novel algorithms which were implemented in the code are presented. LaRT uses the Stokes vector formalism to calculate the polarization of Lyα photons and seamlessly takes into account of the continuously varying scattering phase function due to the quantum-mechanical interference between the fine-structures of hydrogen atom. LaRT is also capable of calculating the polarization due to dust scattering. The resonance-line profile at the line center is found to approach to the Boltzmann distribution with the gas kinetic temperature, even in a system with a central optical depth as low as 100. The TIGRESS simulation which well reproduces the overall properties of the the warm neutral medium (WNM) of the Milky-Way is used to study the WF effect in the Milky-Way. We also examine the effect of turbulence on the Lyα RT and show that the 21 cm spin temperature is unlikely to be affected by the turbulent velocity dispersion in astrophysical environments, as opposed to the common assumption.
Hyunmi Song – KASI
Title: Lyα Radiative Transfer through Outflowing Halo Models to Understand both the Observed Spectra and Surface Brightness Profiles of Lyα Halos around High-z Star-forming Galaxies
Abstract
With a recent observational study of extended Lyman-alpha halos around individual high-z star-forming galaxies by Leclercq et al. (2017) using MUSE, we perform radiative transfer calculations to see if Lyman-alpha scattering can explain the spatial extents of the halos together with their spectra. We adopt a spherically-symmetric halo model in which Lyman-alpha sources and neutral hydrogen (HI) medium have exponential density distributions. The HI medium is set to have outflowing motion based on a momentum-driven wind scenario in a gravitational potential well. We run our Lyman-alpha radiative transfer code, LaRT, upon this halo model for various sets of parameters regarding the HI medium such as temperature, optical depth, density scale radius, outflow velocities, and dust content. We analyze simulation results to see the impact of each parameter on Lyman-alpha spectra and surface brightness profiles, and degeneracies between the parameters. We also find a parameter set that best reproduces simultaneously the observed spectra and surface brightness profiles of the MUSE Lyman-alpha halos.
Hee-Won Lee – Sejong Univ.
Title: Atomic Physics and the Kramers-Heisenberg Formula for Lyα
Abstract
Lyα is a special spectroscopic tool to probe the physical condition of the intergalactic medium of the early universe. The enormous line center optical depth of Lyα requires accurate treatment of atomic physics associated with Lyα. The cross section of far UV radiation near Lyα is given by the Kramers-Heisenberg formula, which exhibits asymmetric deviation from Lorentzian due to contributions of np levels with n>2. In particular, the local minimum of the cross section is found at 108.0 nm, blueward of which Rayleigh cross section locally vanishes due to destructively interfering contributions of np levels. Local enhancement of the transmitted radiation associated with the local minimum of the cross section may be used to put tight constraints on the neutrality of the intergalactic medium at the reionization era.
Day 2 Session 2. – Kyungjin Ahn
Sang-Hyeon Ahn – KASI
Title: The Role of Dust Cavity in Star-forming Regions to form a Singly Peaked Lyα Emission
Abstract
Thiem Hoang – KASI
Title: A New Mechanism of Dust Destruction by Radiative Torque Disruption and its Applications
Abstract
Day 2 Session 3. – Chair Kwang-Il Seon
Kyungjin Ahn – Chosun Univ.
Title: Similarity and Differences between 21-cm and Lyα Line Stacking
Abstract
We present our first effort on stacking Lyα line spectra from multiple radiation sources, to overcome the difficulties stemming from the dimness of high-redshift sources. As long as the redshifts of sources are known, this can enable one to probe physical states of the intergalactic medium. It may be possible to even perform 3D imaging of Lyα blobs of high-redshift sources. We compare this to another stacking proposal from the epoch-of-reionization community, namely the statistical 3D imaging of 21-cm lines through stacking multiple HII-region-related signals.
Hyo Jeong Kim – Chosun Univ.
Title: Transfer of Lyα Photons through Partially Ionized Universe
Abstract
We present out study on the random scattering histories of Lyman alpha photons in the intergalactic medium of the early universe. The simulation of Monte Carlo radiative transfer of Lyman alpha photons through the intergalactic medium presents the full three-dimensional density, ionization fraction, temperature, and peculiar velocity fields. The code is tested with models having analytical solutions, idealized geometry or simplified velocity fields. We apply the code to the data cube of 3D cosmology reionization simulation, Cosmic Dawn II simulation (CODA II, Ocvirk et al 2016). CODA II simulation at different redshifts give different ionization conditions. The emergent spectral line shapes are strongly dependent on the ionized fraction so can place constraints on the ionization and temperature state of any observed part of the universe.
Taysun Kimm – Yonsei Univ.
Title: Escape of LyC and Lyα Photons from Simulated Turbulent Clouds
Abstract
Understanding how ionizing radiation propagates from molecular clouds to the intergalactic space is the key to the study of reionization and the emergence of Lyα emission from galaxies. In this contribution, I will present our new efforts to better understand the escape of the UV photons from turbulent clouds with different masses, star formation efficiencies, and spectral energy distributions using radiation-hydrodynamic simulations. I will also show predicted Lya profiles from turbulent clouds and discuss a few interesting differences identified when compared with the properties of the local green pea galaxies.
Day 3 Session 1. – Chair Taysun Kimm
Hyunjin Shim – KNU
Title: Constraining Lyα Escape Fraction Based on the Star Formation Rates of High-redshift Galaxies
Abstract
In order to estimate f_esc (Lyα), we need the intrinsic Lyα emission that is inferred from the intrinsic star formation rates of galaxies. Different star formation rate indicators has its pros and cons, but multi-wavelengths observation of galaxies provides relatively good estimates and thus good limits in f_esc at high redshifts. I will review results from several recent deep surveys.
Graziano Rossi - Sejong Univ.
Title : Neutrinos and High-Redshift Cosmic Web with the Lyman-Alpha Forest
Abstract
Yujin Yang – KASI
Title: Lyα Emission as an Observational Probe
Abstract
Seok-Jun Chang – Sejong Univ.
Title: Lyα Radiative Transfer & Polarimetric Modeling for LABd05
Abstract
Sungyoung Hong - KIAS
Title: Statistics of Two-point Correlation and Network Topology for Lyα emitters at z ~ 2.67
Abstract
We investigate the spatial distribution of Lyα-emitting galaxies (LAEs) at z = 2.67, selected from the NOAO Deep Wide-Field Survey, using two-point statistics and topological diagnostics adopted from network science. We measure the clustering length, r0 ? 4?h?1?Mpc, and the bias, bLAE=2.2+0.2 Fitting the clustering with halo occupation distribution (HOD) models results in two disparate possibilities: (1) where the fraction of central galaxies is <1 percent in haloes of mass >10^12M⊙ and (2) where the fraction is 20 percent. We refer to these two scenarios as the ‘Dusty Core Scenario’ for Model#1, since most of the central galaxies in massive haloes are dead in Lyα emission, and the ‘Pristine Core Scenario’ for Model#2, since the central galaxies are bright in Lyα emission. Traditional two-point statistics cannot distinguish between these disparate models given the current data sets. To overcome this degeneracy, we generate mock catalogues for each HOD model using a high-resolution N-body simulation and adopt a network statistics approach, which provides excellent topological diagnostics for galaxy point distributions. We find three topological anomalies from the spatial distribution of observed LAEs, which are not reproduced by the HOD mocks. We find that Model#2 matches better all network statistics than Model#1, suggesting that the central galaxies in >1012?h?1?M⊙ haloes at z ~ 2.67 need to be less dusty to be bright as LAEs, potentially implying some replenishing channels of pristine gas such as the cold mode accretion.
Day 2 Session 1. Chair Yujin Yang
Kwang-Il Seon - KASI
Title: Lyα Radiative Transfer: The Wouthuysen-Field effect and the Lyα polarization
Abstract
A three-dimensional, Monte Carlo Lyα radiative transfer (RT) code, LaRT, is developed to study the Lyα RT, in particular, the Wouthuysen-Field (WF) effect and the polarization of Lyα. In this talk, newly-developed novel algorithms which were implemented in the code are presented. LaRT uses the Stokes vector formalism to calculate the polarization of Lyα photons and seamlessly takes into account of the continuously varying scattering phase function due to the quantum-mechanical interference between the fine-structures of hydrogen atom. LaRT is also capable of calculating the polarization due to dust scattering. The resonance-line profile at the line center is found to approach to the Boltzmann distribution with the gas kinetic temperature, even in a system with a central optical depth as low as 100. The TIGRESS simulation which well reproduces the overall properties of the the warm neutral medium (WNM) of the Milky-Way is used to study the WF effect in the Milky-Way. We also examine the effect of turbulence on the Lyα RT and show that the 21 cm spin temperature is unlikely to be affected by the turbulent velocity dispersion in astrophysical environments, as opposed to the common assumption.
Hyunmi Song – KASI
Title: Lyα Radiative Transfer through Outflowing Halo Models to Understand both the Observed Spectra and Surface Brightness Profiles of Lyα Halos around High-z Star-forming Galaxies
Abstract
With a recent observational study of extended Lyman-alpha halos around individual high-z star-forming galaxies by Leclercq et al. (2017) using MUSE, we perform radiative transfer calculations to see if Lyman-alpha scattering can explain the spatial extents of the halos together with their spectra. We adopt a spherically-symmetric halo model in which Lyman-alpha sources and neutral hydrogen (HI) medium have exponential density distributions. The HI medium is set to have outflowing motion based on a momentum-driven wind scenario in a gravitational potential well. We run our Lyman-alpha radiative transfer code, LaRT, upon this halo model for various sets of parameters regarding the HI medium such as temperature, optical depth, density scale radius, outflow velocities, and dust content. We analyze simulation results to see the impact of each parameter on Lyman-alpha spectra and surface brightness profiles, and degeneracies between the parameters. We also find a parameter set that best reproduces simultaneously the observed spectra and surface brightness profiles of the MUSE Lyman-alpha halos.
Hee-Won Lee – Sejong Univ.
Title: Atomic Physics and the Kramers-Heisenberg Formula for Lyα
Abstract
Lyα is a special spectroscopic tool to probe the physical condition of the intergalactic medium of the early universe. The enormous line center optical depth of Lyα requires accurate treatment of atomic physics associated with Lyα. The cross section of far UV radiation near Lyα is given by the Kramers-Heisenberg formula, which exhibits asymmetric deviation from Lorentzian due to contributions of np levels with n>2. In particular, the local minimum of the cross section is found at 108.0 nm, blueward of which Rayleigh cross section locally vanishes due to destructively interfering contributions of np levels. Local enhancement of the transmitted radiation associated with the local minimum of the cross section may be used to put tight constraints on the neutrality of the intergalactic medium at the reionization era.
Day 2 Session 2. – Kyungjin Ahn
Sang-Hyeon Ahn – KASI
Title: The Role of Dust Cavity in Star-forming Regions to form a Singly Peaked Lyα Emission
Abstract
Thiem Hoang – KASI
Title: A New Mechanism of Dust Destruction by Radiative Torque Disruption and its Applications
Abstract
Day 2 Session 3. – Chair Kwang-Il Seon
Kyungjin Ahn – Chosun Univ.
Title: Similarity and Differences between 21-cm and Lyα Line Stacking
Abstract
We present our first effort on stacking Lyα line spectra from multiple radiation sources, to overcome the difficulties stemming from the dimness of high-redshift sources. As long as the redshifts of sources are known, this can enable one to probe physical states of the intergalactic medium. It may be possible to even perform 3D imaging of Lyα blobs of high-redshift sources. We compare this to another stacking proposal from the epoch-of-reionization community, namely the statistical 3D imaging of 21-cm lines through stacking multiple HII-region-related signals.
Hyo Jeong Kim – Chosun Univ.
Title: Transfer of Lyα Photons through Partially Ionized Universe
Abstract
We present out study on the random scattering histories of Lyman alpha photons in the intergalactic medium of the early universe. The simulation of Monte Carlo radiative transfer of Lyman alpha photons through the intergalactic medium presents the full three-dimensional density, ionization fraction, temperature, and peculiar velocity fields. The code is tested with models having analytical solutions, idealized geometry or simplified velocity fields. We apply the code to the data cube of 3D cosmology reionization simulation, Cosmic Dawn II simulation (CODA II, Ocvirk et al 2016). CODA II simulation at different redshifts give different ionization conditions. The emergent spectral line shapes are strongly dependent on the ionized fraction so can place constraints on the ionization and temperature state of any observed part of the universe.
Taysun Kimm – Yonsei Univ.
Title: Escape of LyC and Lyα Photons from Simulated Turbulent Clouds
Abstract
Understanding how ionizing radiation propagates from molecular clouds to the intergalactic space is the key to the study of reionization and the emergence of Lyα emission from galaxies. In this contribution, I will present our new efforts to better understand the escape of the UV photons from turbulent clouds with different masses, star formation efficiencies, and spectral energy distributions using radiation-hydrodynamic simulations. I will also show predicted Lya profiles from turbulent clouds and discuss a few interesting differences identified when compared with the properties of the local green pea galaxies.
Day 3 Session 1. – Chair Taysun Kimm
Hyunjin Shim – KNU
Title: Constraining Lyα Escape Fraction Based on the Star Formation Rates of High-redshift Galaxies
Abstract
In order to estimate f_esc (Lyα), we need the intrinsic Lyα emission that is inferred from the intrinsic star formation rates of galaxies. Different star formation rate indicators has its pros and cons, but multi-wavelengths observation of galaxies provides relatively good estimates and thus good limits in f_esc at high redshifts. I will review results from several recent deep surveys.
Graziano Rossi - Sejong Univ.
Title : Neutrinos and High-Redshift Cosmic Web with the Lyman-Alpha Forest
Abstract