Angular momentum loss of primordial gas in Lyman-alpha radiation field

Abstract

We present results on the radiation drag exerted by an isotropic and homogenous background of Lya photons on neutral gas clouds orbiting within HII regions around Population III stars of different masses. The Doppler shift causes a frequency difference between photons moving in the direction of the cloud and opposite to it resulting in a net momentum loss of the cloud in the direction of motion. We find that half of the angular momentum of gas with v_theta <~ 20 km/s near (r <~ 3 kpc) a Population III star of 120 Msun at z=20 is lost within ~ 10^6 yr. The radiation drag is a strong function of cloud velocity that peaks at v ~ 20 km/s reflecting the frequency dependence of the photon cross section. Clouds moving with velocities larger than ~ 100 km/s loose their angular momentum on time scales of ~ 10^8 yr. At lower redshifts radiation drag becomes inefficient as the Lya photon density in HII regions decreases by a factor (1+z)^3 and angular momentum is lost on time scales > 10^8 yr even for low velocity clouds. Our results suggest that a sweet spot exists for the loss of angular momentum by radiation drag for gas clouds at z > 10 and with v ~ 20 km/s. Comparison to dynamical friction forces acting on typical gas clouds suggest that radiation drag is the dominant effect impacting the orbit. We propose that this effect can suppress the formation of extended gas discs in the first galaxies and help gas accretion near galactic centres and central black holes.

8 pages, 6 figures, accepted for publication in MNRAS

References in corpus (12)

• 3D Lyman-alpha radiation transfer. I. Understanding Lyman-alpha line profile morphologies
• Protostar Formation in the Early Universe
• Keeping the Universe ionised: Photo-heating and the clumping factor of the high-redshift intergalactic medium
• Early Cosmological HII/HeIII Regions and Their Impact on Second-Generation Star Formation
• The HII Region of a Primordial Star
• Lyman alpha Radiative Transfer in Cosmological Simulations using Adaptive Mesh Refinement
• The First Galaxies: Assembly of Disks and Prospects for Direct Detection
• Secondary Star Formation in a Population III Object
• Lyman Alpha Driven Outflows Around Star Forming Galaxies
• Radiative Regulation of Population III Star Formation
• Formation Criteria and the Mass of Secondary Population III Stars
• The effect of recombination radiation on the temperature and ionization state of partially ionized gas

Cited by in corpus (5)

• Upper limits on the mass and luminosity of Population III-dominated galaxies
• Lyman-$\alpha$ feedback prevails at Cosmic Dawn: Implications for the first galaxies, stars, and star clusters
• On the effect of Lyman alpha trapping during the initial collapse of massive black hole seeds
• Poynting-Robertson effect as a dissipative system in general relativity
• Suppression of globular cluster formation in metal-poor gas clouds by Lyman-alpha radiation feedback