173 research outputs found
Opacity Limit for Supermassive Protostars
No full textWe present a model for the evolution of supermassive protostars from their formation at until their growth to . To calculate the initial properties of the object in the optically thick regime, we follow two approaches: one based on idealized thermodynamic considerations, and another based on a more detailed one-zone model. Both methods derive a similar value of for the density of the object when opacity becomes important, i.e., the opacity limit. The subsequent evolution of the growing protostar is determined by the accretion of gas onto the object and can be described by a mass–radius relation of the form during the early stages, and of the form when internal luminosity becomes important. For the case of a supermassive protostar, this implies that the radius of the star grows from to during its evolution. Finally, we use this model to construct a subgrid recipe for accreting sink particles in numerical simulations. A prime ingredient thereof is a physically motivated prescription for the accretion radius and the effective temperature of the growing protostar embedded inside it. From the latter, we can conclude that photoionization feedback can be neglected until very late in the assembly process of the supermassive object
Light, medium-weight or heavy? The nature of the first supermassive black hole seeds
No full textObservations of hyper-luminous quasars at z>6 reveal the rapid growth of supermassive black holes (SMBHs >10^9 m M_{odot}) 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) photo-dissociating radiation and of metal/dust enrichment. This allows us to set the physical conditions for BH 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 (<10^3 m M_odot) form at a higher rate, the mass growth of a SMBH at z<15 is driven by efficient gas accretion (at a sub-Eddington rate) onto its heavy progenitors (). This conclusion holds independently of the critical level of LW radiation and even when medium-weight seeds are allowed to form in higher metallicity galaxies, via the so-called super-competitive accretion scenario. Our study suggests that the genealogy of SMBHs is characterized by a rich variety of BH progenitors, which represent only a small fraction (< 10 - 20%) of all the BHs that seed galaxies at z > 15
Systematic Broad-band X-ray Study of super-Eddington Accretion onto Supermassive Black Holes. I. X-ray Continuum
No full textWe present the first systematic broad-band X-ray study of super-Eddington
accretion onto SMBHs with simultaneous {\it NuSTAR} and {\it XMM-Newton} or
{\it Swift}/XRT observations of a sample of 8 super-Eddington accreting AGN
with Eddington ratio . We find that the SEAMBHs show a
steep primary continuum slope as expected for sources accreting in the super
Eddington regime, mostly dominated by relativistic reflection. The Iron
K emission lines of the sources of our sample show relativistic
broadening. In addition the equivalent widths of the narrow components of the
Iron K lines follow the 'X-ray Baldwin' effect, also known as the
'Iwasawa-Taniguchi' effect. We found a statistically significant correlation
between the photon-index of the primary power-law and the Eddington ratio,
consistent with past studies. Moreover, as expected for super-Eddington
sources, the median value of the reflection fraction of the sources we analysed
is a factor higher than the median reflection fraction value of the
type\,1 AGN from the BASS sample. We are able to estimate the coronal
temperature for three sources of our sample: Mrk\,382 (\,keV),
PG\,0026+129 (\,keV) and IRAS\,04416+1215 (\,keV). Looking at
the position of the SEAMBHs sources of our sample in the
compactness-temperature diagram it appears that in super-Eddington AGN, as for
lower Eddington ratio AGN, the X-ray corona is controlled by pair production
and annihilation.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Societ
The extreme properties of the nearby hyper-Eddington accreting active galactic nucleus in IRAS 04416+1215
No full textThe physical properties of the accretion flow and of the X-ray emitting plasma, in supermassive black holes accreting at extreme Eddington rates, are still very unclear. Here we present the analysis of simultaneous XMM-Newton and NuSTAR observations of the hyper-Eddington Seyfert 1 galaxy IRAS 04416+1215, carried out in 2020. The main goal of these observations is to investigate the properties of the X-ray corona, as well as the structure of the accretion flow and of the circumnuclear environment, in this regime of extreme accretion. IRAS 04416+1215 has one of the highest Eddington ratio (lambda(Edd) similar or equal to 472) in the local Universe. It shows an interesting spectral shape, very similar to the standard narrow-line Seyfert 1 galaxy's spectra, with the presence of multiphase absorption structure composed of three phases, whose estimate of the minimum and maximum distances suggests two different interpretations, one consistent with the three X-ray winds being cospatial, and possibly driven by magnetohydrodynamical processes, the other consistent with the multiphase winds being also multiscale. The X-ray spectrum of IRAS 04416+1215 also has a prominent soft excess component and a hard X-ray emission dominated by a reflection component. Moreover, our detailed spectral analysis shows that IRAS 04416+1215 has the lowest coronal temperature measured so far by NuSTAR (kT(e) = 3-22 keV, depending on the model). This is consistent with a hybrid coronal plasma, in which the primary continuum emission is driven by pair production due to high-energy tail of the energy distribution of non-thermal electrons
Graphium sarpedon subsp. sirkari Page & Treadaway 2013
No full textGraphium sarpedon sirkari Page & Treadaway, 2013 INDIA: 1♂, HOLOTYPE [illustration], Shillong, Khasi Hills, Assam, N. India, April–June 1968, leg. S. K. Sirkar. [SMF]. MYANMAR: 1♂, Hkasi (1,050 m), Tarung Hka River, N. Sagaing State, 2007-VII-14, Prasobsuk Sukkit leg. [AMC]; 1♂, same locality, 2007-VIII-4, Prasobsuk Sukkit leg. [AMC]; 1♂, same locality, 2008-VII-25, Prasobsuk Sukkit leg. [AMC]; 1♂, between Pangmandim & Gawai, Mayhka River, N. Kachin State, 1996-IX-14, Prasobsuk Sukkit leg. [AMC]; 1♂, Chudu Razi Hills, east of Kawnglanghpu, N.E. Kachin State, 2004-VI-24, Prasobsuk Sukkit leg. [AMC]; 2♂♂, same locality, 2005-VI-26, Prasobsuk Sukkit leg. [AMC]; 1♂, same locality, 2006-VII-17, Prasobsuk Sukkit leg. [AMC]; 2♂♂, same locality, 2007-VII-5, Prasobsuk Sukkit leg. [AMC]; 1♂, same locality, 2008-VI-24, Prasobsuk Sukkit leg. [AMC]. CHINA: 1♂, Fugong, N.W. Yunnan, 2012-VII-17, Prasobsuk Sukkit leg. [AMC].Published as part of Cotton, Adam M., Doleck, Tenzing, Zhang, Xin, Inayoshi, Yutaka, Lohman, David J. & Hu, Shao-Ji, 2022, Graphium septentrionicolus Page & Treadaway, 2013 (Lepidoptera: Papilionidae) is a distinct species, pp. 211-224 in Zootaxa 5154 (2) on page 223, DOI: 10.11646/zootaxa.5154.2.6, http://zenodo.org/record/664141
Pulsational instability of supergiant protostars: do they grow supermassive by accretion?
No full textSupermassive stars (SMSs; M* ≳ 10[5] M⊙) and their remnant black holes are promising progenitors for supermassive black holes (SMBHs) observed in the early universe at z ≳ 7. It has been postulated that SMSs form through very rapid mass accretion on to a protostar at a high rate exceeding 0.01 M⊙ yr[−1]. According to recent studies, such rapidly accreting protostars evolve into ‘supergiant protostars’, i.e. protostars consisting of a bloated envelope and a contracting core, similar to giant star. However, like massive stars as well as giant stars, both of which are known to be pulsationally unstable, supergiant protostars may also be unstable to launch strong pulsation-driven outflows. If this is the case, the stellar growth via accretion will be hindered by the mass-loss. We here study the pulsational stability of the supergiant protostars in the mass range M* ≲ 10[3] M⊙ through the method of the linear perturbation analysis. We find that the supergiant protostars with M* ≳ 600 M⊙ and very high accretion rate M˙acc≳1.0M⊙yr[−1] are unstable due to the κ mechanism. The pulsation is excited in the He+ ionization layer in the envelope. Even under a conservative assumption that all the pulsation energy is converted into the kinetic energy of the outflows, the mass-loss rate is ∼10[−3] M⊙ yr[−1], which is lower than the accretion rate by more than two orders of magnitude. We thus conclude that the supergiant protostars should grow stably via rapid accretion at least in the mass range we studied. As long as the rapid accretion is maintained in the later stage, protostars will become SMSs, which eventually produce seeds for the high-z SMBHs
Formation of an embryonic supermassive star in the first galaxy
No full textWe studied the gravitational collapse of a warm (similar to 8000 K) primordial-gas cloud as a candidate progenitor for a supermassive star (SMS; a parts per thousand(3) 10(5) M-aS (TM)) using a three-dimensional hydrodynamical simulation including all the relevant cooling processes of both H-2 and H, which can potentially induce cloud fragmentation. This is the first simulation of this kind to resolve protostar formation. We find that from a weakly turbulent initial condition, the cloud undergoes runaway collapse without a major episode of fragmentation. Although the H-2 fraction jumps by a large factor via the three-body reaction at similar to 10(-13) g cm(-3), its cooling remains inefficient due to the optical thickness, and the temperature remains a parts per thousand(3) 3000 K. When the central core of the cloud becomes opaque to continuum radiation at similar to 10(-8) g cm(-3), a hydrostatic protostar with a parts per thousand integral 0.2 M-aS (TM) is formed. The protostar grows to the mass a parts per thousand integral 1 M-aS (TM) and the radius a parts per thousand integral 2 au within similar to 1 yr via rapid accretion of dense filamentary flows. With high accretion rate, similar to 2 M-aS (TM) yr(-1), the protostar is expected to turn into an SMS within its lifetime, eventually collapsing to a seed for the supermassive black hole observed in the early Universe at z similar to 7
- …
