Revisiting the Gas Kinematics in SSA22 Lyman-$\alpha$ Blob 1 with Radiative Transfer Modeling in a Multiphase, Clumpy Medium

TL;DR

This study uses advanced radiative transfer modeling to analyze the complex gas kinematics in the Ly$eta$ Blob 1, revealing insights into the multiphase, clumpy medium and its impact on Ly$eta$ emission profiles.

Contribution

It introduces a multiphase, clumpy radiative transfer model that successfully reproduces observed Ly$eta$ profiles and constrains key physical parameters of the gas in LAB1.

Findings

Few clumps per line-of-sight are needed to explain flux at line center.

Clump velocity dispersion broadens the Ly$eta$ spectra significantly.

Outflows in the ICM contribute to spectral broadening and absorption features.

Abstract

We present new observations of Lyman-$\alpha$ (Ly$\alpha$) Blob 1 (LAB1) in the SSA22 protocluster region ($z$ = 3.09) using the Keck Cosmic Web Imager (KCWI) and the Keck Multi-object Spectrometer for Infrared Exploration (MOSFIRE). By applying matched filtering to the KCWI datacube, we have created a narrow-band Ly$\alpha$ image and identified several prominent features. By comparing the spatial distributions and intensities of Ly$\alpha$ and H$\beta$, we find that recombination of photo-ionized HI gas followed by resonant scattering is sufficient to explain all the observed Ly$\alpha$/H$\beta$ ratios. We further decode the spatially-resolved Ly$\alpha$ profiles using both moment maps and Monte-Carlo radiative transfer (MCRT) modeling. By fitting a set of multiphase, 'clumpy' models to the observed Ly$\alpha$ profiles, we are able to reasonably constrain many parameters, namely the HI number density in the inter-clump medium (ICM), the cloud volume filling factor, the random velocity and outflow velocity of the clumps, the HI outflow velocity of the ICM and the local systemic redshift. Our model has successfully reproduced the diverse Ly$\alpha$ morphologies at different locations, and the main results are: (1) The observed Ly$\alpha$ spectra require relatively few clumps per line-of-sight as they have significant fluxes at the line center; (2) The velocity dispersion of the clumps yields a significant broadening of the spectra as observed; (3) The clump bulk outflow can also cause additional broadening if the HI in the ICM is optically thick; (4) The HI in the ICM is responsible for the absorption feature close to the Ly$\alpha$ line center.