190 research outputs found

    The formation of globular clusters with top-heavy initial mass functions

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    We study the formation of globular clusters in massive compact clouds with the low-metallicity of Z=103 ZZ=10^{-3}~Z_{\odot} by performing three-dimensional radiative-hydrodynamics simulations. Considering the uncertainty of the initial mass function (IMF) of stars formed in low-metallicity and high-density clouds, we investigate the impacts of the IMF on the cloud condition for the GC formation with the range of the power-law index of IMF as γ=12.35\gamma = 1-2.35. We find that the threshold surface density (Σthr\Sigma_{\rm thr}) for the GC formation increases from 800 M  pc2800~M_{\odot} \; {\rm pc^{-2}} at γ=2.35\gamma = 2.35 to 1600 M  pc21600~M_{\odot}\; {\rm pc^{-2}} at γ=1.5\gamma = 1.5 in the cases of clouds with Mcl=106 MM_{\rm cl} = 10^6~M_{\odot} because the emissivity of ionizing photons per stellar mass increases as γ\gamma decreases. For γ<1.5\gamma < 1.5, Σthr\Sigma_{\rm thr} saturates with 2000 M  pc2\sim 2000~M_{\odot}\; {\rm pc^{-2}} that is quite rare and observed only in local starburst galaxies due to e.g., merger processes. Thus, we suggest that formation sites of low-metallicity GCs could be limited only in the very high-surface density regions. We also find that Σthr\Sigma_{\rm thr} can be modelled by a power-law function with the cloud mass (MclM_{\rm cl}) and the emissivity of ionizing photons (ss_*) as Mcl1/5s2/5\propto M_{\rm cl}^{-1/5} s_{*}^{2/5}. Based on the relation between the power-law slope of IMF and Σthr\Sigma_{\rm thr}, future observations with e.g., the James Webb Space Telescope can allow us to constrain the IMF of GCs.Comment: 9 pages, 6 figures, accepted for publication in MNRA

    Generation of high circular polarization of interstellar Lyman α\alpha radiation triggering biological homochirality

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    The homochirality of biological molecules on the Earth is a long-standing mystery regarding the origin of life. Circularly polarized ultraviolet (UV) light could induce the enantiomeric excess of biological molecules in the interstellar medium, leading to the homochirality on the earth. By performing 3D radiation transfer simulations with multiple scattering processes in interstellar dusty slabs, we study the generation of circular polarization (CP) of ultraviolet light at Lyman α\alpha (λ=0.1216 μm\lambda = 0.1216~{\rm \mu m}) as well as in the near-infrared (NIR, λ=2.14 μm\lambda = 2.14~{\rm \mu m}) wavelengths. Our simulations show that the distributions of CP exhibit a symmetric quadrupole pattern, regardless of wavelength and viewing angle. The CP degree of scattered light from a dusty slab composed of aligned grains is 15\sim 15 percent for Lyα\alpha and 3\sim 3 percent at NIR wavelengths in the case of oblate grains with an MRN size distribution. We find that the CP degree of Lyα\alpha is well correlated with that in the NIR regardless of viewing angles, whilst being a factor of 5\sim 5 higher. Thus, high CP of Lyα\alpha is expected in sites where NIR CP is detected. We suggest that such circularly polarized Lyα\alpha may initiate the enantiomeric excess of biological molecules in space.Comment: 10 pages, 11 figures, accepted for publication in MNRA

    Differential Expression of Survivin in Mammary Gland Diseases

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    Objective: Unlike other inhibitors of apoptosis proteins (IAP), survivin is expressed during fetal development, cannot be detected in normal adult tissues, and is re-expressed in most of the common human cancers. However, the clinicopathological significance of the expression of survivin in human breast carcinoma has not been fully elucidated. Therefore, we examined the accumulation of survivin in pathological specimens of mammary gland diseases to identify new protein markers that may lead to improvements in patient management.Methods: We investigated the expression of survivin using immunohistochemistry in 180 cases of breast disease accessioned in the Department of Pathology, International University of Health and Welfare Hospital and Nissan Tamagawa Hospital between 2003 and 2013.Results: Ninety-eight out of 141 malignant tumor cases (69.5%) stained positive for survivin, with no significant staining being detected in the remaining cases. Staining for survivin was completely absent in the epithelial cells of 34 of 39 cases of benign disease. No correlation was observed between the expression of survivin and major prognostic factors in breast carcinomas including patient age, tumor size, histological grade, axillary lymph node metastasis, local recurrence, and visceral metastasis status. However, a significant difference was observed in the expression of survivin between malignant and benign tumors and other benign diseases.Conclusion: The results of the present study suggest that the expression of survivin is strongly selective for cancer cells and may be useful for identifying and quantifying human breast cancer

    Observational signatures of forming young massive clusters: continuum emission from dense HII regions

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    Young massive clusters (YMCs) are the most massive star clusters forming in nearby galaxies and are thought to be a young analogue to the globular clusters. Understanding the formation process of YMCs leads to looking into very efficient star formation in high-redshift galaxies suggested by recent JWST observations. We investigate possible observational signatures of their formation stage, particularly when the mass of a cluster is increasing via accretion from a natal molecular cloud. To this end, we study the broad-band continuum emission from ionized gas and dust enshrouding YMCs, whose formation is followed by recent radiation-hydrodynamics simulations. We perform post-process radiative transfer calculations using simulation snapshots and find characteristic spectral features at radio and far-infrared frequencies. We show that a striking feature is long-lasting, strong free-free emission from a \sim 10pc-scale HII region with a large emission measure of 107cm6 pc\gtrsim 10^7 \mathrm{cm}^{-6} \ \mathrm{pc}, corresponding to the mean electron density of 103 cm3\gtrsim 10^3~\mathrm{cm}^{-3}. There is a turnover feature below \sim 10 GHz, a signature of the optically-thick free-free emission, often found in Galactic ultra-compact HII regions. These features come from the peculiar YMC formation process, where the cluster's gravity effectively traps photoionized gas for a long duration and enables continuous star formation within the cluster. Such large and dense HII regions show distinct distribution on the density-size diagram, apart from the standard sequence of Galactic HII regions. This is consistent with the observational trend inferred for extragalactic HII regions associated with YMCs.Comment: 12 pages, 10 figures, accepted for publication in MNRA