Where outflows meet inflows: gas kinematics in SSA22 Ly α blob 2 decoded by advanced radiative transfer modelling

We present new spectroscopic observations of Ly alpha (Ly alpha) Blob 2 (z similar to 3.1). We observed extended Ly alpha emission in three distinct regions, where the highest Ly alpha surface brightness (SB) centre 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 centre. We further mapped the flux ratio of the blue peak to the red peak and found it is anticorrelated with Ly alpha SB with a power-law index of similar to -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 modelled 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 H i 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 per cent, i.e. minor compared to the photoionization by star-forming galaxies and/or AGNs.

Automated summary

This study presents new spectroscopic observations of Ly alpha Blob 2, revealing extended Ly alpha emission and the presence of a high surface brightness center far from known continuum sources. Radiative transfer models are used to explain the diverse Ly alpha morphologies, indicating outflow-dominated kinematics and a significant correlation between parameter pairs. The results support the scenario of Ly alpha photons being generated by a central powering source and scattering with outflowing H i gas.