15 research outputs found
On de-Sitter Geometry in Cosmic Void Statistics
Starting from the geometrical concept of a 4-dimensional de-Sitter
configuration of spheres in Euclidean 3-space and modelling voids in the
Universe as spheres, we show that a uniform distribution over this
configuration space implies a power-law for the void number density which is
consistent with results from the excursion set formalism and with data, for an
intermediate range of void volumes. The scaling dimension of the large scale
structure can be estimated as well. We also discuss the effect of restricting
the survey geometry on the void statistics. This work is a new application of
de-Sitter geometry to cosmology and also provides a new geometrical perspective
on self-similarity in cosmology.Comment: 8 pages, 4 figures, accepted by MNRAS. Minor changes, appendix adde
First emergence of cold accretion and supermassive star formation in the early universe
We investigate the first emergence of the so-called cold accretion, the
accretion flows deeply penetrating a halo, in the early universe with
cosmological N-body/SPH simulations. We study the structure of the accretion
flow and its evolution within small halos with
with sufficiently high spatial resolutions down to scale.
While previous studies only follow the evolution for a short period after the
primordial cloud collapse, we follow the long-term evolution until the cold
accretion first appears, employing the sink particle method. We show that the
cold accretion emerges when the halo mass exceeds , the halo
masses above which the accretion flow penetrates halos. We further continue
simulations to study whether the cold accretion provides the dense shock waves,
which have been proposed to give birth to supermassive stars (SMSs). We find
that the accretion flow eventually hits a compact disc near the halo centre,
creating dense shocks over a wide area of the disc surface. The resulting
post-shock gas becomes dense and hot enough with its mass comparable to the
Jeans mass , a sufficient amount to
induce the gravitational collapse, leading to the SMS formation.Comment: 17 pages, 17 figures, MNRAS submitte
Direct-collapse black hole formation induced by internal radiation of host halos
We estimate the fraction of halos that host supermassive black holes (SMBHs)
forming through the direct collapse (DC) scenario by using cosmological N -body
simulations combined with a semi-analytic model for galaxy evolution. While in
most of earlier studies the occurrence of the DC is limited only in chemically
pristine halos, we here suppose that the DC can occur also in halos with
metallicity below a threshold value --, considering the super-competitive accretion pathway for DC
black hole (DCBH) formation. In addition, we consider for the first time the
effect of Lyman-Werner (LW) radiation from stars within host halos, i.e.,
internal radiation. We find that, with low threshold metallicities of , the inclusion of internal radiation
rather reduces the number density of DCBHs from -- to
--. This is because star formation is suppressed due
to self-regulation, and the LW flux emitted by neighboring halos is reduced.
Only when is as high as , internal
radiation enhances the number density of DCBHs from to , thereby decreasing the threshold halo mass above which at least one
DCBH forms from to . We
also find that halos with -- can host more than one DCBH at . This indicates that the
DC scenario alone can explain the observed number of SMBH-hosting galaxies.Comment: 17 pages, 12 figures, 2 tables, accepted by MNRA
Light, medium-weight, or heavy? The nature of the first supermassive black hole seeds
Observations of hyper-luminous quasars at z>6 reveal the rapid growth of supermassive black holes (SMBHs >109M⊙) whose origin is still difficult to explain. Their progenitors may have formed as remnants of massive, metal-free stars (light seeds), via stellar collisions (medium-weight seeds) and/or massive gas clouds direct collapse (heavy seeds). In this work, we investigate for the first time the relative role of these three seed populations in the formation of z>6 SMBHs within an Eddington-limited gas accretion scenario. To this aim, we implement in our semi-analytical data-constrained model a statistical description of the spatial fluctuations of Lyman–Werner (LW) photodissociating radiation and of metal/dust enrichment. This allows us to set the physical conditions for black hole seeds formation, exploring their relative birth rate in a highly biased region of the Universe at z>6. We find that the inclusion of medium-weight seeds does not qualitatively change the growth history of the first SMBHs: although less massive seeds (15
H1821+643: The most X-ray and infrared luminous AGN in the Swift/BAT survey in the process of rapid stellar and supermassive black hole mass assembly
H1821+643 is the most X-ray luminous non-beamed AGN of erg s in the Swift/BAT ultra-hard X-ray survey
and it is also a hyper-luminous infrared (IR) galaxy residing in the center of a massive galaxy cluster, which is a unique
environment achieving the rapid mass assembly of black holes (BH) and host
galaxies in the local universe. We decompose the X-ray to IR spectral energy
distribution (SED) into the AGN and starburst component using the SED fitting
tool CIGALE-2022.0 and show that H1821+643 consumes a large amount of cold gas
() with star-formation rate of and BH accretion rate
of .
This high is larger than the cooling rate
() of the intra-cluster medium (ICM),
, which is one to two
order magnitude higher than the typical value of other systems, indicating that
H1821 provides the unique and extreme environment of rapid gas consumption. We
also show that H1821+643 has an efficient cooling path achieving from K
to K thanks to [OIII] 63 , which is a main coolant in
low temperature range ( K to K) with a cooling rate of
, and the
star-forming region extends over 40 kpc scale.Comment: 20 pages, 8 figures, accepted for publication in Ap