The critical radiation intensity for direct collapse black hole formation: dependence on the radiation spectral shape

It has been proposed that supermassive black holes (SMBHs) are originated from direct-collapse black holes (DCBHs) that are formed at z gtrsim 10 in the primordial gas in the case that H2 cooling is suppressed by strong external radiation. In this work, we study the critical specific intensity J^crit required for DCBH formation for various radiation spectral shapes by a series of one-zone calculations of a collapsing primordial- gas cloud. We calculate the critical specific intensity at the Lyman-Werner (LW) bands J^crit_LW,21 (in units of 10^-21 erg s^-1 Hz^-1 sr^-1 cm^-2) for realistic spectra of metal-poor galaxies. We find J^crit is not sensitive to the age or metallicity for the constant star formation galaxies with J^crit_LW,21 = 1300-1400, while J^crit decreases as galaxies become older or more metal-enriched for the instantaneous starburst galaxies. However, such dependence for the instantaneous starburst galaxies is weak for the young or extremely metal-poor galaxies: J^crit_LW,21 = 1000-1400 for the young galaxies and J^crit_LW,21 approx 1400 for the extremely metal-poor galaxies. The typical value of J^crit for the realistic spectra is higher than those expected in the literature, which affects the estimated DCBH number density n_DCBH. By extrapolating the result of Dijkstra, Ferrara and Mesinger, we obtain n_DCBH sim 10^-10 cMpc^-3 at z = 10, although there is still large uncertainty in this estimation.Comment: 11 pages, 6 figures, submitted to MNRA

Equivalence of Probability Laws for a Class of Infinitely Divisible Random Measures

This is the extended exposition of the previous paper [2]. Given an infinitely divisible (or ID) random measure A on a measurable space T, we provide a certain method to construct a version of A based on a Poisson random measure on the product space S = T×(R＼{0}). In particular, the present paper contains a new result about a class of ID random measures on T which are realized by R-valued signed measures on T. As an application we discuss the law equivalence of ID random measures on T by using our constructive method with Kakutani's theorem on the equivalence of infinite product probability measures.Article信州大学理学部紀要 31(2): 71-80(1997)departmental bulletin pape

Conjugate Sets of Gaussian Random Fields on a Hilbert Space

Article信州大学理学部紀要 21(2): 65-69(1987)departmental bulletin pape

An Elementary Construction of Processes with Independent Increments

Article信州大学理学部紀要 26(1): 17-23(1991)departmental bulletin pape

Fragmentation of star-forming clouds enriched with the first dust

The thermal and fragmentation properties of star-forming clouds have important consequences on the corresponding characteristic stellar mass. The initial composition of the gas within these clouds is a record of the nucleosynthetic products of previous stellar generations. In this paper we present a model for the evolution of star-forming clouds enriched by metals and dust from the first supernovae, resulting from the explosions of metal-free progenitors with masses in the range 12 - 30 Msun and 140 - 260 Msun. Using a self-consistent approach, we show that: (i) metals depleted onto dust grains play a fundamental role, enabling fragmentation to solar or sub-solar mass scales already at metallicities Zcr = 10^{-6} Zsun; (ii) even at metallicities as high as 10^{-2} Zsun, metals diffused in the gas-phase lead to fragment mass scales which are ~ 100 Msun; (iii) C atoms are strongly depleted onto amorphous carbon grains and CO molecules so that CII plays a minor role in gas cooling, leaving OI as the main gas-phase cooling agent in low-metallicity clouds. These conclusions hold independently of the assumed supernova progenitors and suggest that the onset of low-mass star formation is conditioned to the presence of dust in the parent clouds.Comment: 9 pages, 5 figures, accepted for publication in MNRA

Oscillation dynamics underlie functional switching of NF-κB for B-cell activation.

Transcription factor nuclear factor kappa B (NF-κB) shows cooperative switch-like activation followed by prolonged oscillatory nuclear translocation in response to extracellular stimuli. These dynamics are important for activation of the NF-κB transcriptional machinery, however, NF-κB activity regulated by coordinated actions of these dynamics has not been elucidated at the system level. Using a variety of B cells with artificially rewired NF-κB signaling networks, we show that oscillations and switch-like activation of NF-κB can be dissected and that, under some conditions, these two behaviors are separated upon antigen receptor activation. Comprehensive quantitative experiments and mathematical analysis showed that the functional role of switch activation in the NF-κB system is to overcome transient IKK (IκB kinase) activity to amplify nuclear translocation of NF-κB, thereby inducing the prolonged NF-κB oscillatory behavior necessary for target gene expression and B-cell activation