168 research outputs found
Hasora mavis Evans, 1934 syn. n. is confirmed to be the female of H. leucospila leucospila (Mabille, 1891) (Hesperiidae, Coeliadinae) by DNA barcoding
No full textXue, Guoxi, Ikari, Etsuo, Inayoshi, Yutaka, Li, Meng (2019): Hasora mavis Evans, 1934 syn. n. is confirmed to be the female of H. leucospila leucospila (Mabille, 1891) (Hesperiidae, Coeliadinae) by DNA barcoding. Zootaxa 4695 (4): 391-393, DOI: https://doi.org/10.11646/zootaxa.4695.4.
Extremely Dense Gas around Little Red Dots and High-redshift Active Galactic Nuclei: A Nonstellar Origin of the Balmer Break and Absorption Features
No full textThe James Webb Space Telescope (JWST) has uncovered low-luminosity active galactic nuclei (AGNs) at high redshifts of z ≳ 4–7, powered by accreting black holes with masses of ∼10 ^6−8 M _⊙ . One remarkable distinction of these JWST-identified AGNs, compared to their low-redshift counterparts, is that at least ∼20% of them present H α and/or H β absorption, which must be associated with extremely dense (≳10 ^9 cm ^−3 ) gas in the broad-line region or its immediate surroundings. These Balmer absorption features unavoidably imply the presence of a Balmer break caused by the same dense gas. In this Letter, we quantitatively demonstrate that a Balmer break can form in AGN spectra without stellar components, when the accretion disk is heavily embedded in dense neutral gas clumps with densities of ∼10 ^9−11 cm ^−3 , where hydrogen atoms are collisionally excited to the n = 2 states and effectively absorb the AGN continuum at the bluer side of the Balmer limit. The nonstellar origin of a Balmer break offers a potential solution to the large stellar masses and densities inferred for little red dots (LRDs) when assuming that their continuum is primarily due to stellar light. Our calculations indicate that the observed Balmer absorption blueshifted by a few hundred km s ^−1 , which suggests the presence of dense outflows in the nucleus at rates exceeding the Eddington value. Other spectral features such as higher equivalent widths of broad H α emission and presence of O i lines observed in high-redshift AGNs including LRDs align with the predicted signatures of a dense super-Eddington accretion disk
First Direct Observation of Biological Molecules in Liquid by Environmental Phase Contrast Transmission Electron Microscopy
No full textExtended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.</jats:p
Improved Generalization by Adding both Auto-Association and Hidden-Layer-Noise to Neural-Network-Based-Classifiers
No full textMassive Black Hole Seed Formation in Strong X-Ray Environments at High Redshift
No full textDirect collapse of pristine gas in early galaxies is a promising pathway for forming supermassive black holes (SMBHs) powering active galactic nuclei at the Epoch of Reionization (EoR). This seeding mechanism requires suppression of molecular hydrogen (H _2 ) cooling during primordial star formation via intense far-ultraviolet radiation from nearby starburst galaxies clustered in overdense regions. However, nondetection of 21 cm signals from the EoR reported by the Hydrogen Epoch of Reionization Array (HERA) experiment suggests that such galaxies may also emit X-rays more efficiently than in the local Universe, promoting H _2 production and thereby potentially quenching massive black hole (BH) seed formation. In this study, we examine the thermal and chemical evolution of collapsing gas in dark matter halos using a semi-analytic model incorporating observationally calibrated X-ray intensities. We find that strong X-ray irradiation, as suggested by HERA, significantly suppresses direct collapse and leads most halos to experience H _2 cooling. Nevertheless, massive BH seeds with M _BH ≳ 10 ^4 M _⊙ still form by z ≃ 15, particularly in regions with baryonic streaming motion, and their abundance reaches ∼ 10 ^−4 Mpc ^−3 , sufficient to explain the SMBHs identified by James Webb Space Telescope spectroscopy at 3 < z < 6. While the formation of highly overmassive BHs with masses comparable to their host galaxies is prohibited by X-ray ionization, our model predicts that BH-to-stellar mass ratios of ≃0.01–0.1 were already established at seeding
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
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