Small-scale Intensity Mapping: Extended Lyα, Hα, and Continuum Emission as a Probe of Halo Star Formation in High-redshift Galaxies

Abstract

Lyα halos are observed ubiquitously around star-forming galaxies at high redshift, but their origin is still a matter of debate. We demonstrate that the emission from faint unresolved satellite sources,  -M 17 UV , clustered around the central galaxies may play a major role in generating spatially extended Lyα, continuum (UV + VIS), and Hα halos. We apply the analytic formalism developed in Mas-Ribas & Dijkstra to model the halos around Lyman Alpha Emitters (LAEs) at z=3.1, for several different satellite clustering prescriptions. In general, our UV and Lyα surface brightness profiles match the observations well at   r 20 4 0 physical kpc from the centers of LAEs. We discuss how our profiles depend on various model assumptions and how these can be tested and constrained with future Hα observations by the James Webb Space Telescope (JWST). Our analysis shows how spatially extended halos constrain (i) the presence of otherwise undetectable satellite sources, (ii) the integrated, volumetric production rates of Lyα and LyC photons, and (iii) their population-averaged escape fractions. These quantities are all directly relevant for understanding galaxy formation and evolution and, for high enough redshifts, cosmic reionization.

Small-scale Intensity Mapping: Extended Halos as a Probe of the Ionizing Escape Fraction and Faint Galaxy Populations during Reionization

“…We have predicted radial surface brightness profiles that include the contribution from (i) fluorescent emission powered by ionizing radiation leaking from the central galaxy (as in Mas-Ribas & Dijkstra 2016, for two different CGM prescriptions), and (ii), nebular emission from faint satellite sources that possibly resided within the halo of the central galaxies (as in Mas-Ribas et al 2017). We have compared our predictions with observations of Lyα halos at z=5.7 and z=6.6, and have also predicted Hα and visible continuum surface brightness profiles may be detectable within future JWST observations.…”

“…Both the production rate of ionizing photons and the conversion efficiency into Hα and Lyα line photons depend on the IMF, metallicity, stellar populations, etc., at these redshifts (Raiter et al 2010;; see also the discussion in Mas-Ribas et al 2017). The factors h X n and 1 4p account for the energy and isotropic emission of the line photons, respectively.…”

“…We calculate the Lyα and Hα surface brightness of the satellite sources as in Mas-Ribas et al (2017),…”

“…We demonstrated in Mas-Ribas et al (2017) that comparing the surface brightness profiles of the Lyα, Hα, and continuum emission can disentangle the significance of each mechanism. This is because the "size" of the halos is connected to the physical properties of the CGM and the radiative processes affecting the Lyα, Hα, and continuum radiation.…”

“…At larger distances from the central galaxy, the predicted fluorescent surface brightness profiles lie below the observations. We therefore assessed the contribution of nebular emission produced "in-situ" in satellite sources clustered around the central galaxy in Mas-Ribas et al (2017). These satellites would be too faint to be resolved individually, but their integrated emission may be detectable, analogous to the method of "intensity mapping" (see Fonseca et al 2017 and references therein), but here applied to much smaller scales.…”