Where outflows meet inflows: Gas Kinematics in SSA22 Lyman-α Blob 2 Decoded by Advanced Radiative Transfer Modelling

Abstract We present new spectroscopic observations of Lyman-α (Lyα) Blob 2 (z ∼ 3.1). We observed extended Lyα emission in three distinct regions, where the highest Lyα surface brightness (SB) center is far away from the known continuum sources. We searched through the MOSFIRE slits that cover the high Lyα SB regions, but were unable to detect any significant nebular emission near the highest SB center. We further mapped the flux ratio of the blue peak to the red peak and found it is anti-correlated with Lyα SB with a power-law index of ∼ – 0.4. We used radiative transfer models with both multiphase, clumpy and shell geometries and successfully reproduced the diverse Lyα morphologies. We found that most spectra suggest outflow-dominated kinematics, while 4/15 spectra imply inflows. A significant correlation exists between parameter pairs, and the multiphase, clumpy model may alleviate previously reported discrepancies. We also modeled Lyα spectra at different positions simultaneously and found that the variation of the inferred clump outflow velocities can be approximately explained by line-of-sight projection effects. Our results support the ‘central powering + scattering’ scenario, i.e. the Lyα photons are generated by a central powering source and then scatter with outflowing, multiphase H i gas while propagating outwards. The infalling of cool gas near the blob outskirts shapes the observed blue-dominated Lyα profiles, but its energy contribution to the total Lyα luminosity is less than 10 per cent, i.e. minor compared to the photo-ionization by star-forming galaxies and/or AGNs.