Revisiting the Gas Kinematics in SSA22 Lyman-α Blob 1 with Radiative Transfer Modeling in a Multiphase, Clumpy Medium
Abstract
We present new observations of Lyman-α (Lyα) 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 Lyα image and identified several prominent features. By comparing the spatial distributions and intensities of Lyα and Hβ, we find that recombination of photo-ionized HI gas followed by resonant scattering is sufficient to explain all the observed Lyα/Hβ ratios. We further decode the spatially-resolved Lyα profiles using both moment maps and Monte-Carlo radiative transfer (MCRT) modeling. By fitting a set of multiphase, 'clumpy' models to the observed Lyα 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 Lyα morphologies at different locations, and the main results are: (1) The observed Lyα 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 Lyα line center.