Hubble Space Telescope Imaging of Lyα Emission at z ≈ 4.4
Finkelstein, Steven L.; Grogin, Norman A.; Hathi, Nimish P.; Koekemoer, Anton M.; Mutchler, Max; Anderson, Jay; McCarthy, Patrick J.; Calzetti, Daniela; Whitmore, Bradley C.; Bond, Howard E.; Young, Erick T.; Ryan, Russell E.; Windhorst, Rogier A.; Cohen, Seth H.; Frogel, Jay A.; O'Connell, Robert W.; Balick, Bruce; Disney, Michael J.; Dopita, Michael A.; Hall, Donald N. B.; Holtzman, Jon A.; Kimble, Randy A.; Paresce, Francesco; Silk, Joseph I.; Trauger, John T.; Walker, Alistair R.; Saha, Abhijit; Malhotra, Sangeeta; Rhoads, James E.; Finkelstein, Keely D.; Luppino, Gerard
United States, United Kingdom, Australia, Italy, Chile
Abstract
We present the highest redshift detections of resolved Lyα emission, using Hubble Space Telescope (HST)/Advanced Camera for Surveys F658N narrowband-imaging data taken in parallel with the Wide Field Camera 3 Early Release Science program in the GOODS Chandra Deep Field-South. We detect Lyα emission from three spectroscopically confirmed z = 4.4 Lyα emitting galaxies (LAEs), more than doubling the sample of LAEs with resolved Lyα emission. Comparing the light distribution between the rest-frame ultraviolet continuum and narrowband images, we investigate the escape of Lyα photons at high redshift. While our data do not support a positional offset between the Lyα and rest-frame ultraviolet (UV) continuum emission, the half-light radius in one out of the three galaxies is significantly (>1σ) larger in Lyα than in the rest-frame UV continuum. Stacking the three LAEs in both the narrowband and UV continuum images, we find that the Lyα light appears larger than the rest-frame UV at 4.2σ significance. This Lyα flux detected with HST is a factor of 4-10 less than observed in similar filters from the ground. These results together imply that the Lyα emission is not strictly confined to its indigenous star-forming regions. Rather, for at least one object the Lyα emission is more extended, with the missing HST flux possibly existing in a diffuse outer halo. This suggests that the radiative transfer of Lyα photons in high-redshift LAEs is complicated, with the interstellar-medium geometry and/or outflows playing a significant role in galaxies at these redshifts.
Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program no. 11359.