Can Supermassive Black Holes Form in Metal-enriched High-Redshift Protogalaxies?

By K. Omukai, R. Schneider, Zoltán Haiman. 2008

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Primordial gas in protogalactic DM halos with virial temperatures Tvir≳ 104 K begins to cool and condense via atomic hydrogen. Provided that this gas is irradiated by a strong UV flux and remains free of H2 and other molecules, it has been proposed that the halo with Tvir ∼ 104 K may avoid fragmentation and lead to the rapid formation of an SMBH as massive as M ≈ 105–106 M☉. This “head start” would help explain the presence of SMBHs with inferred masses of several times 109 M☉, powering the bright quasars discovered in the SDSS at redshift z≳ 6. However, high-redshift DM halos with Tvir ∼ 104 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 Zcr ≈ 3 × 10−4 Z☉ (in the absence of dust) and as low as Zcr ≈ 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≲ 102–103 M☉.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/beedd5c4eb0e77ca6699f648a8e07090c5b83b16

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Citations in the corpus

Ubiquitous seeding of supermassive black holes by direct collapse (2012, background): “This could also reduce the number of DCBHs we find in our study, if the metal enrichment is high enough to alter thecooling properties of the gas (Omukai et al. 2008).”
Photodissociation of H2 in protogalaxies: modelling self‐shielding in three‐dimensional simulations (2011, methodology): “To further investigate the implications of inaccurate self–shielding models, we have repeated the one–zone calculations in SBH10, altering only how fsh is specified.”
Formation of supermassive black holes (2010, background): “Fragmentation and formation of low mass stars starts as soon as gas is polluted by metals created in the first PopIII stars (Omukai et al, 2008).”
Titans of the early Universe: The Prato statement on the origin of the first supermassive black holes (2018, background): “They report that even at an extremely short distance, ∼300pc, and with instantaneous metal mixing, the irradiating galaxy is not able to sufficiently pollute the DCBH candidate halo (Omukai et al. 2008; Latif et al. 2016c) to prohibit DCBH formation.”
FORMATION OF THE FIRST NUCLEAR CLUSTERS AND MASSIVE BLACK HOLES AT HIGH REDSHIFT (2008, background): “…of efficient star formation can foster the formation of very compact nuclear star clusters (Clark et al. 2008, Schneider et al. 2006) where star collisions can lead to the formation of a supermassive star, possibly leaving a BH remnant with mass in the range ∼ 102 − 104 M⊙ (Omukai et al. 2008).”
Fluctuations in the high-redshift Lyman–Werner background: close halo pairs as the origin of supermassive black holes (2008, background): “Possibly the most stringent requirement for the directcollapse black hole model, is the intensity of the photodissociating background, which must exceed J21,LW > Jcrit ∼ 103 (Bromm & Loeb 2003, where J21,LW denotes the intensity in the LW background in units of 10−21 erg s−1 Hz−1 sr−1 cm−2, evaluate”
FORMATION OF PRIMORDIAL SUPERMASSIVE STARS BY RAPID MASS ACCRETION (2013, background): “10−5Z⊙, since fragmentation induced by dust cooling would prohibit the monolithic collapse of massive clouds at higher metalicities (Omukai et al. 2008).”
The First Billion Years project: the impact of stellar radiation on the co-evolution of Populations II and III (2012, background): “As it is likely that the gas must be of primordial composition in order for a supermassive star, and subsequently a black hole, to form (Omukai et al. 2008) we expect that it is in these haloes in which supermassive black hole seed formation will occur.”
FORMATION RATES OF POPULATION III STARS AND CHEMICAL ENRICHMENT OF HALOS DURING THE REIONIZATION ERA (2009, background): “Quasi-stars are in fact able to form only if the gas is not polluted by metals (Omukai et al. 2008).”
Supermassive black hole formation by direct collapse: keeping protogalactic gas H2 free in dark matter haloes with virial temperatures Tvir > rsim 104 K (2009, background): “Although it cools efficiently, this gas remains relatively hot, at a temperature near T ∼ 8000 K, and consequently might be able to avoid fragmentation and collapse directly into a supermassive black hole (SMBH).”
Black hole formation in the early Universe (2013, background): “While molecular hydrogen can potentially cool below a few thousand K, the presence of strong UV flux emitted by the first generation of stars has important implications for structure formation (Omukai 2001; Omukai et al. 2008; Wolcott-Green et al. 2011).”
Formation of Supermassive Black Hole Seeds (2016, background): “On the other hand for higher metallicities fragmentation already occurs at densities < 103 cm−3 and results in the core collapse time longer than 3 Myrs (Omukai et al. 2008; Devecchi & Volonteri 2009; Devecchi et al. 2012).”
THE MASS SPECTRUM OF THE FIRST STARS (2014, background): “More massive halos of 107 M could collapse due to the H−/Lyα cooling even in the presence of a strong LW radiation field (e.g., Omukai et al. 2008).”
Pathways to massive black holes and compact star clusters in pre-galactic dark matter haloes with virial temperatures ≳10 000 K (2008, methodology): “Finally if either metal or H2 cooling become efficient in the self-gravitating disc and c© 0000 RAS, MNRAS 000, 000–000 fragmentation is efficient a very compact star cluster should form (e.g. Omukai et al. 2008; Bernadetta & Volonteri 2008) .”