Lyman-alpha Imaging at 20 pc Resolution in a Low Mass Lensed Galaxy at z=1.85
Abstract
Because Lyman-alpha photons are resonantly scattered by neutral hydrogen, the strength and spatial extent of Lya emission in galaxies depend on the HI column density and covering fraction, properties that are of primary interest to the escape of ionizing radiation. Lya emission is particularly important to the study of low mass, low metallicity galaxies: such objects are likely to be responsible for the reionization of the universe, and Lya emission is more common in these galaxies. With this proposal, we request 7 orbits of WFC3/UVIS imaging to obtain a high resolution map of Lya emission in the low mass, low metallicity z=1.85 gravitationally lensed galaxy SL2SJ021737-051329. With oxygen abundance <10% of solar, stellar mass <10^8 Msun, and extremely strong Lya emission with rest-frame equivalent width ~120 A, this object is a prime example of a low mass Lya-emitter, and its gravitational magnification by a factor of ~35 results in remarkably high WFC3/UVIS spatial resolution of ~20 pc. Existing HST broadband and IR grism observations will allow us to compare the spatial extent of the Lya emission with both the rest-frame UV continuum and the rest-frame optical nebular line emission, in order to map the resonant scattering of Lya photons from their origin in star-forming regions, obtain constraints on the location of the scattering gas, and relate this information to the kinematics and geometry of the galaxy. The proposed observations, in combination with the spectroscopic information we have already obtained, will provide the most comprehensive and highest resolution picture of Lya emission at z > 1 to date.
- Publication:
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HST Proposal
- Pub Date:
- June 2016
- Bibcode:
- 2016hst..prop14632E