Deep Hubble Space Telescope Imaging on the Extended Ly α Emission of a QSO at z = 2.19 with a Damped Lyman Alpha System as a Natural Coronagraph

Recent observations suggest that proximate damped Lyα (PDLA) systems can be used to study the host galaxies of quasi-stellar objects (QSOs), because the PDLAs can block the bright point-spread function from central QSOs. Using six orbits of narrowband imaging with Hubble Space Telescope (HST)/WFC3, we present the first high-resolution narrowband image of the Lyα emission in the PDLA trough of the QSO SDSS J115432.67–021537.9. We detect one major component and one minor component in the narrowband imaging. Combining the ${HST}$/WFC3 imaging with deep Magellan/MagE spectra, we measure that the Lyα flux ${F}_{\mathrm{Ly}\alpha }$ = $1.56\pm 0.10\,\times {10}^{-16}\,\mathrm{erg}\,{{\rm{s}}}^{-1}\,{\mathrm{cm}}^{-2}$, which is among the luminous (≈2.7 ${\text{}}{L}_{\mathrm{Ly}\alpha }^{\star }$) Lyα emitters at $z=$ 2.19. The $\mathrm{Ly}\alpha $-based star formation rate is ∼7 ${M}_{\odot }\,{\mathrm{yr}}^{-1}$. These observational results favor that the star formation from the host galaxy could be the main mechanism powering the Lyα emission. This new method sheds light on the study of the kinematic structure and the spatial distribution of the extended Lyα emitting regions around the QSO host.