The origin of globular cluster systems from cosmological simulations

We investigate the structural, kinematical, and chemical properties of globular cluster systems (GCSs) in galaxies of different Hubble types in a self-consistent manner based on high-resolution cosmological N-body simulations combined with semi-analytic models of galaxy and globular cluster (GC) formation. We focus on correlations between the physical properties of GCSs and those of their host galaxies for about 10^5 simulated galaxies located at the centres of dark matter halos (i.e. we do not consider satellite galaxies in sub-halos). Our principal results, which can be tested against observations, are as follows. The majority (about 90%) of GCs currently in halos are formed in low-mass galaxies at redshifts greater than 3 with mean formation redshifts of z = 5.7 (12.7 Gyrs ago) and 4.3 (12.3 Gyrs ago) for metal-poor GCs (MPC) and metal-rich GCs (MRCs), respectively. About 52 % of galaxies with GCs show clear bimodality in their metallicity distribution functions, though less luminous galaxies with M_B fainter than -17 are much less likely to show bimodality owing to little or no MRCs. The number fraction of MRCs does not depend on Hubble type but is generally smaller for less luminous galaxies. The specific frequencies (S_ N) of GCSs are typically higher in ellipticals (S_ N ~ 4.0) than in spirals (S_ N ~ 1.8), and higher again (S_N ~ 5.0) for galaxies located at the centers of clusters of galaxies. The total number of GCs per unit halo mass does not depend strongly on M_B or Hubble type of the host galaxy. The mean metallicities of MPCs and MRCs depend on M_B such that they are higher in more luminous galaxies, though the dependence is significantly weakerfor MPCs.Comment: 19 pages, 29 figures, accepted in MNRA

Gravitational Wave Physics and Astronomy in the nascent era

The detections of gravitational waves (GW) by the LIGO/Virgo collaborations provide various possibilities for both physics and astronomy. We are quite sure that GW observations will develop a lot, both in precision and in number, thanks to the continuous work on the improvement of detectors, including the expected new detector, KAGRA, and the planned detector, LIGO-India. On this occasion, we review the fundamental outcomes and prospects of gravitational wave physics and astronomy. We survey the development, focusing on representative sources of gravitational waves: binary black holes, binary neutron stars, and supernovae. We also summarize the role of gravitational wave observations as a probe of new physics

DOI:10.1068/htjr081 Surface melting of copper with (100), (110), and (111) orientations in terms of molecular dynamics simulation

Abstract. Surface melting of copper having the (100), (110), and (111) orientations has been investigated with the use of molecular dynamics (MD) simulation. The interaction between copper atoms was expressed by the approximation of second-moment tight-binding scheme potential. The structures of copper were determined at temperatures between 500 and 1390 K by constanttemperature MD, where calculation was conducted on bulk and surface models of copper having the (100), (110), and (111) orientations. The position and velocity of atoms calculated led to the internal energy, the number density of atoms, and the mean square amplitude of thermal vibrations of atoms. The (110), (100), and (111) surface models melted at temperatures of about 1270, 1290, and 1310 K, respectively; these temperatures are lower than the melting point of copper. The surface internal energies for the (110), (100), and (111) surface models, derived as the difference between the internal energies for the bulk and surface models having the same plane orientation, displayed steep increases at temperatures of about 1100, 1200, and 1300 K, respectively. In addition, the distribution of the number density of atoms in the direction normal to the surface indicated the presence of a structurally disordered layer near the surface of each surface model. Lindemann's law on melting has suggested that surface melting occurs in the surface model

DOI:10.1068/htjr085 Relative measurements of thermal conductivity of liquid gallium by the transient hot-wire method

Abstract. Thermal conductivity of liquid gallium as a function of temperature has been determined by the transient hot-wire method with an alumina-coated probe. Theoretical analysis of the temperature increase of the hot wire with coating indicates that the coating layer affects absolute measurements by this method and its presence is prone to yield smaller values of thermal conductivity. Relative measurements were carried out over the temperature range 310 ^ 471 K on liquid mercury and gallium at 310 K as standard samples to establish the correction line. The thermal conductivities obtained for liquid gallium are as follows: 29:3 Wm �1 K �