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

Abstract

Recent observations suggest that proximate damped Ly$\alpha$ (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 (PSF) from central QSOs. Using six-orbits of narrowband imaging with $\it{HST}$/WFC3, we present the first high resolution narrowband image of the Ly$\alpha$ emission in the PDLA trough of the QSO SDSSJ115432.67-021537.9 . We detect one major component and one minor component in the narrowband imaging. Combining the $\it{HST}$/WFC3 imaging with deep Magellan/MagE spectra, we measure that the Ly$\alpha$ flux F$_{\rm{Ly\alpha}}$ = 1.56$\pm0.10 \times10^{-16}$ $\rm{erg\ s^{-1}\ cm^{-2}}$, which is among the luminous ($\approx$ 2.7 L$^{\star}_{\rm{Ly\alpha}}$) Ly$\alpha$ emitters at $\it{z} =$ 2.19. The $\rm{Ly\alpha}$-based star formation rate (SFR) is $\sim$ 7 $\textrm{M_{\sun} \ yr^{-1}}$. These observational results favor that the star formation from the host galaxy could be the main mechanism to power the Ly$\alpha$ emission. This new method sheds new light on the study of the kinematic structure and the spatial distribution of the extended Ly$\alpha$ emitting regions around the QSO host.