Formation of Primordial Galaxies under UV background Radiation

Abstract

The pancake collapse of pregalactic clouds under UV background radiation is explored with a one-dimensional sheet model. Here, attention is concentrated on elucidating the basic physics on the thermal evolution of pregalactic clouds exposed to diffuse UV radiation. So, we treat accurately the radiation transfer for the ionizing photons, with solving chemical reactions regarding hydrogen molecules as well as atoms. The self-shielding against UV radiation by H${}_2$ Lyman-Werner bands, which regulates the photo-dissociation of hydrogen molecules, is also taken into account. As a result, it is found that when the UV background radiation is at a level of $10^{-22}(\nu /{\nu }_L{)}^{-1}\mathrm{erg}{\mathrm{s}}^{-1}\mathrm{c}{\mathrm{m}}^{-2}\mathrm{H}{\mathrm{z}}^{-1}\mathrm{st}{\mathrm{r}}^{-1}$, the cloud evolution bifurcates with a critical mass as $M_{\mathrm{SB}}=2.2\times 10^{11}{M}_{\odot }[(1+z_c)/5{]}^{-4.2}$, where $z_c$ is the final collapse epoch. A cloud more massive than $M_{\mathrm{SB}}$ cools below $5\times 10^3$K due to H${}_2$ line emission at the pancake collapse and would undergo the initial starburst. The pancake possibly evolves into a virialized system in a dissipationless fashion. Consequently, this leads to the dissipationless galaxy formation at $3\lsim z_c \lsim 10$. A cloud less massive than $M_{\mathrm{SB}}$ cannot cool by H${}_2$ emission shortly after the pancake collapse, but could cool in the course of shrinking to the rotation barrier. This is likely to lead to the dissipational galaxy formation at relatively low redshifts as $0\lsim z_c \lsim 4$. The present results provide a solid physical mechanism which controls the star formation efficiency in the pregalactic clouds. In the context of a standard CDM cosmology, $M_{\mathrm{SB}}$ lies between 1$\sigma$ and 2$\sigma$ density fluctuations.

29 pages, 7 figures, uses aaspp4.sty, ApJ accepted

Cited by in corpus (23)

• The First Stars
• Dust Formation in Primordial Type II Supernovae
• Intermediate-Mass Black Holes
• Formation of early-type galaxies from cosmological initial conditions
• The Structure and Evolution of Early Cosmological HII Regions
• Escape fraction of ionizing photons from high-redshift galaxies in cosmological SPH simulations
• The Stellar Initial Mass Function in Primordial Galaxies
• Formation of Dwarf Galaxies during the Cosmic Reionization
• The Habitat Segregation between Lyman Break Galaxies and Lyman alpha Emitters around a QSO at z~5
• Ultrafaint Dwarf Galaxies - the lowest mass relics from before reionization
• Criteria for the Formation of Population III Objects in the Ultraviolet Background Radiation
• Smoothed Particle Hydrodynamics coupled with Radiation Transfer
• The proximity effect in a close group of QSOs
• The escape of ionizing photons from supernova-dominated primordial galaxies
• Cosmological Origin of the Lowest Metallicity Halo Stars
• The Nature of Blue Early-Type Galaxies in the Goods Fields
• N-Body Code with Adaptive Mesh Refinement
• Computational Cosmology: from the Early Universe to the Large Scale Structure
• Formation Criteria and the Mass of Secondary Population III Stars
• Regulated star formation in forming disk galaxies under ultraviolet radiation background
• Cosmological 3D HI Gas Map with HETDEX Ly$\alpha$ Emitters and eBOSS QSOs at $z=2$: IGM-Galaxy/QSO Connection and a $\sim$ 40-Mpc Scale Giant HII Bubble Candidate
• The Stellar IMF in Very Metal-Deficient Gas
• Can luminous Lyman alpha emitters at $z$ $\simeq$ 5.7 and $z$ $\simeq$ 6.6 suppress star formation?