Redshift Drift in LTB Void Universes

We study the redshift drift, i.e., the time derivative of the cosmological redshift in the Lema\^itre-Tolman-Bondi (LTB) solution in which the observer is assumed to be located at the symmetry center. This solution has often been studied as an anti-Copernican universe model to explain the acceleration of cosmic volume expansion without introducing the concept of dark energy. One of decisive differences between LTB universe models and Copernican universe models with dark energy is believed to be the redshift drift. The redshift drift is negative in all known LTB universe models, whereas it is positive in the redshift domain $z \lesssim 2$ in Copernican models with dark energy. However, there have been no detailed studies on this subject. In the present paper, we prove that the redshift drift of an off-center source is always negative in the case of LTB void models. We also show that the redshift drift can be positive with an extremely large hump-type inhomogeneity. Our results suggest that we can determine whether we live near the center of a large void without dark energy by observing the redshift drift.Comment: 16 pages, 2 figure

On the evolution and environmental dependence of the star formation rate versus stellar mass relation since z ˜ 2.

This paper discusses the evolution of the correlation between galaxy star formation rates (SFRs) and stellar mass (M*) over the last ∼10 Gyr, particularly focusing on its environmental dependence. We first present the mid-infrared (MIR) properties of the Hα-selected galaxies in a rich cluster Cl 0939+4713 at z = 0.4. We use wide-field Spitzer/MIPS 24 μm data to show that the optically red Hα emitters, which are most prevalent in group-scale environments, tend to have higher SFRs and higher dust extinction than the majority population of blue Hα sources. With an MIR stacking analysis, we find that the median SFR of Hα emitters is higher in higher density environment at z = 0.4. We also find that star-forming galaxies in high-density environment tend to have higher specific SFR (SSFR), although the trend is much less significant compared to that of SFR. This increase of SSFR in high-density environment is not visible when we consider the SFR derived from Hα alone, suggesting that the dust attenuation in galaxies depends on environment; galaxies in high-density environment tend to be dustier (by up to ∼0.5 mag), probably reflecting a higher fraction of nucleated, dusty starbursts in higher density environments at z = 0.4. We then discuss the environmental dependence of the SFR–M* relation for star-forming galaxies since z ∼ 2, by compiling our comparable, narrow-band-selected, large Hα emitter samples in both distant cluster environments and field environments. We find that the SSFR of Hα-selected galaxies (at the fixed mass of log (M*/M⊙) = 10) rapidly evolves as (1 + z)3, but the SFR–M* relation is independent of the environment since z ∼ 2, as far as we rely on the Hα-based SFRs (with M*-dependent extinction correction). Even if we consider the possible environmental variation in the dust attenuation, we conclude that the difference in the SFR–M* relation between cluster and field star-forming galaxies is always small (≲0.2 dex level) at any time in the history of the Universe since z ∼ 2

Border of Spacetime

It is still uncertain whether the cosmic censorship conjecture is true or not. To get a new insight into this issue, we propose the concept of the border of spacetime as a generalization of the spacetime singularity and discuss its visibility. The visible border, corresponding to the naked singularity, is not only relevant to mathematical completeness of general relativity but also a window into new physics in strongly curved spacetimes, which is in principle observable.Comment: 4 pages, 1 figure, accepted for publication in Physical Review D, typos correcte

3D Relativistic Magnetohydrodynamic Simulations of Magnetized Spine-Sheath Relativistic Jets

Numerical simulations of weakly magnetized and strongly magnetized relativistic jets embedded in a weakly magnetized and strongly magnetized stationary or weakly relativistic (v = c/2) sheath have been performed. A magnetic field parallel to the flow is used in these simulations performed by the new GRMHD numerical code RAISHIN used in its RMHD configuration. In the numerical simulations the Lorentz factor $\gamma = 2.5$ jet is precessed to break the initial equilibrium configuration. In the simulations sound speeds are $\lesssim c/\sqrt 3$ in the weakly magnetized simulations and $\lesssim 0.3c$ in the strongly magnetized simulations. The Alfven wave speed is $\lesssim 0.07c$ in the weakly magnetized simulations and $\lesssim 0.56c$ in the strongly magnetized simulations. The results of the numerical simulations are compared to theoretical predictions from a normal mode analysis of the linearized relativistic magnetohydrodynamic (RMHD) equations capable of describing a uniform axially magnetized cylindrical relativistic jet embedded in a uniform axially magnetized relativistically moving sheath. The theoretical dispersion relation allows investigation of effects associated with maximum possible sound speeds, Alfven wave speeds near light speed and relativistic sheath speeds. The prediction of increased stability of the weakly magnetized system resulting from c/2 sheath speeds and the stabilization of the strongly magnetized system resulting from c/2 sheath speeds is verified by the numerical simulation results.Comment: 31 pages, 8 figures, accepted for publicatin in ApJ. A paper with high resolution figures available at http://gammaray.nsstc.nasa.gov/~mizuno/research_new.htm

An integrable semi-discretization of the Camassa-Holm equation and its determinant solution

An integrable semi-discretization of the Camassa-Holm equation is presented. The keys of its construction are bilinear forms and determinant structure of solutions of the CH equation. Determinant formulas of $N$-soliton solutions of the continuous and semi-discrete Camassa-Holm equations are presented. Based on determinant formulas, we can generate multi-soliton, multi-cuspon and multi-soliton-cuspon solutions. Numerical computations using the integrable semi-discrete Camassa-Holm equation are performed. It is shown that the integrable semi-discrete Camassa-Holm equation gives very accurate numerical results even in the cases of cuspon-cuspon and soliton-cuspon interactions. The numerical computation for an initial value condition, which is not an exact solution, is also presented

Submillimeter Array Observation of the Proto-Planetary Nebula CRL 618 in the CO J=6-5 Line

We report on the results of a Submillimeter Array interferometric observation of the proto-planetary nebula CRL 618 in the 12CO J=6-5 line. With the new capability of SMA enabling us to use two receivers at a time, we also observed simultaneously in the 12CO J=2-1 and 13CO J=2-1 lines. The 12CO J=6-5 and 13CO J=2-1 lines were first interferometrically observed toward CRL 618. The flux of the high velocity component of the 12CO J=6-5 line is almost fully recovered, while roughly 80% of the flux of the low velocity component is resolved out. The low recovery rate suggests that the emission region of the low velocity component of the 12CO J=6-5 line is largely extended. Continuum emission is detected both at 230 and 690 GHz. The flux of the 690 GHz continuum emission seems to be partially resolved out, suggesting dust emission partly contaminates the 690 GHz continuum flux. The cavity structure, which has been confirmed in a previous observation in the 12CO J=2-1 line, is not clearly detected in the 12CO J=6-5 line, and only the south wall of the cavity is detected. This result suggests that the physical condition of the molecular envelope of CRL 618 is not exactly axial symmetric.Comment: 24 pages, 9 figures, 1 table, accepted for publication in AJ. Full resolution version available at http://www.asiaa.sinica.edu.tw/~junichi/paper

Implant isolation of ZnO

We study ion-irradiation-induced electrical isolation in n-type single-crystal ZnO epilayers. Emphasis is given to improving the thermal stability of isolation and obtaining a better understanding of the isolation mechanism. Results show that an increase in the dose of 2 MeV ¹⁶Oions (up to ∼2 orders of magnitude above the threshold isolation dose) and irradiation temperature (up to 350 °C) has a relatively minor effect on the thermal stability of electrical isolation, which is limited to temperatures of ∼300–400 °C. An analysis of the temperature dependence of sheet resistance suggests that effective levels associated with irradiation-produced defects are rather shallow (<50 meV). For the case of implantation with keV Cr, Fe, or Niions, the evolution of sheet resistance with annealing temperature is consistent with defect-induced isolation, with a relatively minor effect of Cr, Fe, or Ni impurities on the thermal stability of isolation. Results also reveal a negligible ion-beam flux effect in the case of irradiation with 2 MeV 16Oions, supporting high diffusivity of ion-beam-generated defects during ion irradiation and a very fast stabilization of collision cascade processes in ZnO. Based on these results, the mechanism for electrical isolation in ZnO by ion bombardment is discussed

On the tau-functions of the Degasperis-Procesi equation

The DP equation is investigated from the point of view of determinant-pfaffian identities. The reciprocal link between the Degasperis-Procesi (DP) equation and the pseudo 3-reduction of the $C_{\infty}$ two-dimensional Toda system is used to construct the N-soliton solution of the DP equation. The N-soliton solution of the DP equation is presented in the form of pfaffian through a hodograph (reciprocal) transformation. The bilinear equations, the identities between determinants and pfaffians, and the $\tau$-functions of the DP equation are obtained from the pseudo 3-reduction of the $C_{\infty}$ two-dimensional Toda system.Comment: 27 pages, 4 figures, Journal of Physics A: Mathematical and Theoretical, to be publishe

Discrete Integrable Systems and Hodograph Transformations Arising from Motions of Discrete Plane Curves

We consider integrable discretizations of some soliton equations associated with the motions of plane curves: the Wadati-Konno-Ichikawa elastic beam equation, the complex Dym equation, and the short pulse equation. They are related to the modified KdV or the sine-Gordon equations by the hodograph transformations. Based on the observation that the hodograph transformations are regarded as the Euler-Lagrange transformations of the curve motions, we construct the discrete analogues of the hodograph transformations, which yield integrable discretizations of those soliton equations.Comment: 19 page

The History of the Mysterious Eclipses of KH 15D II. Asiago, Kiso, Kitt Peak, Mt. Wilson, Palomar, Tautenburg and Rozhen Observatories, 1954-97

The unusual pre-main-sequence binary star named KH 15D undergoes remarkably deep and long-lasting periodic eclipses. Some clues about the reason for these eclipses have come from the observed evolution of the system's light curve over the last century. Here we present UBVRI photometry of KH 15D based on photographic plates from various observatories, ranging in time from 1954 to 1997. The system has been variable at the ~1 mag level since at least 1965. There is no evidence for color variations, with a typical limit of Delta(B-V) < 0.2 mag. We confirm some previously published results that were based on a smaller sample of plates: from approximately 1965 to 1990, the total flux was modulated with the 48-day orbital period of the binary, but the maximum flux was larger, the fractional variations were smaller, and the phase of minimum flux was shifted by almost a half-cycle relative to the modern light curve. All these results are consistent with the recently proposed theory that KH 15D is being occulted by an inclined, precessing, circumbinary ring.Comment: 10 pages, 3 figures, 3 tables, accepted for publication in Astronomical Journa