On the Diffuse Lyman-alpha Halo Around Lyman-alpha Emitting Galaxies

Abstract

Ly$\alpha$ photons scattered by neutral hydrogen atoms in the circumgalactic media or produced in the halos of star-forming galaxies are expected to lead to extended Ly$\alpha$ emission around galaxies. Such low surface brightness Ly$\alpha$ halos (LAHs) have been detected by stacking Ly$\alpha$ images of high-redshift star-forming galaxies. We study the origin of LAHs by performing radiative transfer modeling of nine $z=3.1$ Lyman-Alpha Emitters (LAEs) in a high resolution hydrodynamic cosmological galaxy formation simulation. We develop a method of computing the mean Ly$\alpha$ surface brightness profile of each LAE by effectively integrating over many different observing directions. Without adjusting any parameters, our model yields an average Ly$\alpha$ surface brightness profile in remarkable agreement with observations. We find that observed LAHs cannot be accounted for solely by photons originating from the central LAE and scattered to large radii by hydrogen atoms in the circumgalactic gas. Instead, Ly$\alpha$ emission from regions in the outer halo is primarily responsible for producing the extended LAHs seen in observations, which potentially includes both star-forming and cooling radiation. With the limit on the star formation contribution set by the ultra-violet (UV) halo measurement, we find that cooling radiation can play an important role in forming the extended LAHs. We discuss the implications and caveats of such a picture.

11 pages, 8 figures, accepted for publication in ApJ. Our conclusion is slightly updated as a result of an improved evaluation of the sky-subtraction systematics in the observed UV profile. The diffuse Lya halo can have contributions from both star formation and cooling radiation

References in corpus (7)

• Cosmic Star Formation History
• The Subaru/XMM-Newton Deep Survey (SXDS). IV. Evolution of Lya Emitters from z=3.1 to 5.7 in the 1 deg^2 Field: Luminosity Functions and AGN
• Diffuse Lyman-alpha Halos around Galaxies at z=2.2-6.6: Implications for Galaxy Formation and Cosmic Reionization
• Lyman alpha Resonant Scattering in Young Galaxies - Predictions from Cosmological Simulations
• The Impact of Galactic Feedback on the Circumgalactic Medium
• Galaxy Size Problem at z=3: Simulated Galaxies Are Too Small
• Effect of Intergalactic Medium on the Observability of Lyman Alpha Emitters during Cosmic Reionization

Cited by in corpus (6)

• Illuminating gas in-/outflows in the MUSE deepest fields: discovery of Ly-alpha nebulae around forming galaxies at z~3.3
• The Diversity of Diffuse Ly$\alpha$ Nebulae around Star-Forming Galaxies at High Redshift
• Stacking the Cosmic Web in Fluorescent Lyman alpha Emission with MUSE
• Empirically Constrained Predictions for Metal-Line Emission from the Circumgalactic Medium
• A Magellan M2FS Spectroscopic Survey of Galaxies at 5.5<z<6.8: Program Overview and a Sample of the Brightest Lyman-alpha Emitters
• Small-scale Intensity Mapping: Extended Halos as a Probe of the Ionizing Escape Fraction and Faint Galaxy Populations during Reionization