Effect of cosmic ray/X-ray ionization on supermassive black hole formation

Abstract

We study effects of external ionization by cosmic rays (CRs) and X-rays on the thermal evolution of primordial clouds under strong far-ultraviolet (FUV) radiation. A strong FUV radiation dissociates H2 and quenches its cooling. Even in such an environment, a massive cloud with Tvir>10^4 K can contract isothermally at 8000 K by Lyman alpha cooling. This cloud collapses monolithically without fragmentation, and a supermassive star (>10^5 Msun) is believed to form at the center, which eventually evolves to a supermassive black hole (SMBH). However, candidates of FUV sources, including star-forming galaxies, are probably sources of strong CRs and X-rays, as well. We find that the external ionization promotes H2 production and elevates the threshold FUV intensity Jcr needed for the SMBH formation for CR energy density U_CR>10^-14 erg/cm^3 or X-ray intensity J_X>10^-24 erg/s/cm^2/sr/Hz at 1 keV. The critical FUV flux increases in proportion to U_CR^{1/2} (J_X^{1/2}) in the high CR (X-ray, respectively) limit. With the same value of FUV intensity at the Lyman limit (13.6 eV), the H^- photodissociation rate, with threshold of 0.755 eV, increases and the H2 molecules decrease with decreasing effective temperature of the FUV sources T*. The lower value of T* thus results in the lower critical FUV flux at 13.6 eV. Using an empirical relation between intensities of FUV and CR/X-ray from nearby star-forming galaxies, we find that external ionization effect remarkably enhances the critical FUV flux for sources with T* as high as 10^5 K and composed of stars with <100 Msun to a level that is not realized in any halo. This indicates that, to induce SMBH formation, the FUV sources must be either Pop II/I galaxies with low brightness temperature, Pop III galaxies with a very top-heavy IMF, or Pop III galaxies too young to harbor sources of CR/X-ray, e.g., supernova remnants or high-mass X-ray binaries.

14 pages, 8 figures, 2 tables, accepted for publication in MNRAS

References in corpus (12)

• Formation of z ~ 6 quasars from hierarchical galaxy mergers
• Accretion onto the First Stellar Mass Black Holes
• H3+ in Diffuse Interstellar Clouds: a Tracer for the Cosmic-Ray Ionization Rate
• Fluctuations in the High-Redshift Lyman-Werner Background: Close Halo Pairs as the Origin of Supermassive Black Holes
• Can Supermassive Black Holes Form in Metal-Enriched High-Redshift Protogalaxies ?
• The First Galaxies: Assembly, Cooling and the Onset of Turbulence
• Resolving the Formation of Protogalaxies. I. Virialization
• Accretion onto Intermediate-Mass Black Holes in Dense Protogalactic Clouds
• The formation of compact massive self-gravitating discs in metal-free haloes with virial temperatures of ~ 13000-30000 K
• Formation of Massive Primordial Stars in a Reionized Gas
• Suppression of HD-cooling in protogalactic gas clouds by Lyman-Werner radiation
• Impact of Cosmic Rays on Population III Star Formation

Cited by in corpus (45)

• The Assembly of the First Massive Black Holes
• Formation of the First Stars
• Formation of Primordial Supermassive Stars by Rapid Mass Accretion
• Ubiquitous seeding of supermassive black holes by direct collapse
• Black hole formation in the early universe
• Titans of the Early Universe: The Prato Statement on the Origin of the First Supermassive Black Holes
• Rapidly Accreting Supergiant Protostars: Embryos of Supermassive Black Holes?
• The critical radiation intensity for direct collapse black hole formation: dependence on the radiation spectral shape
• From the first stars to the first black holes
• Formation of an embryonic supermassive star in the first galaxy
• How realistic UV spectra and X-rays suppress the abundance of direct collapse black holes
• Supermassive black hole formation by the cold accretion shocks in the first galaxies
• The Growth of the Stellar Seeds of Supermassive Black Holes
• Cosmological Simulations of Early Blackhole Formation: Halo Mergers, Tidal Disruption, and the Conditions for Direct Collapse
• A UV flux constraint on the formation of direct collapse black holes
• The Direct Collapse of a Massive Black Hole Seed Under the Influence of an Anisotropic Lyman-Werner Source
• On the formation of the first quasars
• Does disk fragmentation prevent the formation of supermassive stars in protogalaxies?
• H_2 Suppression with Shocking Inflows: Testing a Pathway for Supermassive Black Hole Formation
• The suppression of direct collapse black hole formation by soft X-ray irradiation
• Protostellar Feedback and Final Mass of the Second-Generation Primordial Stars
• Simulating the formation of massive seed black holes in the early Universe. II: Impact of rate coefficient uncertainties
• The Early Growth of the First Black Holes
• Direct collapse black hole formation via high-velocity collisions of protogalaxies
• Rapid growth of seed black holes during early bulge formation
• The impact of reionization on the formation of supermassive black hole seeds
• Pulsational instability of supergiant protostars: Do they grow supermassive by accretion?
• Forming Super-Massive Black Hole Seeds under the Influence of a Nearby Anisotropic Multi-Frequency Source
• The First Stars: formation under X-ray feedback
• Massive black hole and Population III galaxy formation in over-massive dark matter halos with violent merger histories
• Modelling the cosmological Lyman-Werner background radiation field in the Early Universe
• Ab Initio Cosmological Simulations of CR7 as an Active Black Hole
• Conditions for HD Cooling in the First Galaxies Revisited: Interplay between Far-Ultraviolet and Cosmic Ray Feedback in Population III Star Formation
• Positive or Negative? The Impact of X-ray Feedback on the Formation of Direct Collapse Black Hole Seeds
• Enhanced direct collapse due to Lyman alpha feedback
• The First Stars: formation under cosmic ray feedback
• Photoevaporation of Minihalos during Cosmic Reionization: Primordial and Metal-Enriched Halos
• Triggering the formation of direct collapse black holes by their congeners
• Extreme Primordial Star Formation Enabled by High Redshift Quasars
• Supermassive black hole seeds from sub-keV dark matter
• Effects of binary stellar populations on direct collapse black hole formation
• The Dawn of Black Holes
• Population III Star Formation in an X-ray background: II. Protostellar Discs, Multiplicity and Mass Function of the Stars
• Population III Star Formation in an X-ray background: I. Critical Halo Mass of Formation and Total Mass in Stars
• Radiative feedback on supermassive star formation: the massive end of the Population III initial mass function