2008/04/30 by K. Omukai, R. Schneider, Z. Haiman · 6 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Cosmology and Gravitation Theories #Dark matter #Galaxies: Formation, Evolution, Phenomena #Galaxy #Halo #Metallicity #Quasar #Redshift #Reionization #Star formation #Stars #Supermassive black hole #astro-ph
paper · pdf · doi:10.1086/591636
39 pages, 10 figures, ApJ in press
arxiv created 2008/07/09 · openalex publication_date 2008/10/17 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
Primordial gas in protogalactic DM halos with virial temperatures T vir ≳ 10 4 K begins to cool and condense via atomic hydrogen. Provided that this gas is irradiated by a strong UV flux and remains free of H 2 and other molecules, it has been proposed that the halo with T vir ∼ 10 4 K may avoid fragmentation and lead to the rapid formation of an SMBH as massive as M ≈ 10 5 –10 6 M ☉ . This "head start" would help explain the presence of SMBHs with inferred masses of several times 10 9 M ☉ , powering the bright quasars discovered in the SDSS at redshift z ≳ 6. However, high-redshift DM halos with T vir ∼ 10 4 K are likely already enriched with at least trace amounts of metals and dust produced by prior star formation in their progenitors. Here we study the thermal and chemical evolution of low-metallicity gas exposed to extremely strong UV radiation fields. Our results, obtained in one-zone models, suggest that gas fragmentation is inevitable above a critical metallicity, whose value is between Z cr ≈ 3 × 10 −4 Z ☉ (in the absence of dust) and as low as Z cr ≈ 5 × 10 −6 Z ☉ (with a dust-to-gas mass ratio of about 0.01Z/ Z ☉ ). We propose that when the metallicity exceeds these critical values, dense clusters of low-mass stars may form at the halo nucleus. Relatively massive stars in such a cluster can then rapidly coalesce into a single more massive object, which may produce an intermediate-mass BH remnant with a mass up to M ≲ 10 2 –10 3 M ☉ .