Where Outflows Meet Inflows: Gas Kinematics in SSA22 Lyman-$\alpha$ Blob
  2 Decoded by Advanced Radiative Transfer Modelling
  We present new spectroscopic observations of Lyman-$\alpha$ (Ly$\alpha$) Blob
2 ($z \sim$ 3.1). We observed extended Ly$\alpha$ emission in three distinct
regions, where the highest Ly$\alpha$ surface brightness (SB) center is far
away from the known continuum sources. We searched through the MOSFIRE slits
that cover the high Ly$\alpha$ 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 Ly$\alpha$ SB with a power-law index of $\sim$ -0.4. We used radiative
transfer models with both multiphase, clumpy and shell geometries and
successfully reproduced the diverse Ly$\alpha$ 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
Ly$\alpha$ 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 Ly$\alpha$ photons are generated by a
central powering source and then scatter with outflowing, multiphase HI gas
while propagating outwards. The infalling of cool gas near the blob outskirts
shapes the observed blue-dominated Ly$\alpha$ profiles, but its energy
contribution to the total Ly$\alpha$ luminosity is less than 10%, i.e. minor
compared to the photo-ionization by star-forming galaxies and/or AGNs.
