Speaker
Description
Through recent efforts using narrowband observations and integral field spectrographs, high redshift (3<z<6) Lyman alpha (Lya) emitting galaxies have been found to almost ubiquitously have spatially extended Lya emission, known as a Lya halo, extending significantly further out than their star formation (as traced by UV emission). At these redshifts, Lya is the highest surface brightness tracer of gas around star-forming galaxies and understanding this gas and its Lya emission is crucial to understanding how galaxies interact with their surroundings. The Lyman Alpha Reference Sample (LARS) survey has shown that z ~0 galaxies appear to have significantly smaller Lya halo extents than their high redshift counterparts. In order to determine if this is a true physical evolution between z~0 and z~3, we received 55 orbits of HST time to observe the Lya emission of seven intermediate (0.23<z<0.3) redshift galaxies selected to be similar to galaxies observed at high redshift and where the redshift window was optimized for low contamination Lya observations. We are now able to present the first preliminary results from this project. Our imaging shows relatively small Lya halo extents consistent with those of LARS but that do not seem consistent with halos found at high redshift. This has profound implications since it means that some dramatic change has occurred in the properties of the circumgalactic media of starforming galaxies between the local universe and z~3, which we do not yet understand.
