A new measurement of the baryonic fraction using the sparse NGC 3258 group of galaxies

New X-ray observations of the sparse NGC 3258 group of galaxies made by the ASCA satellite with good spectral and spatial resolution has revealed that this group has a gravitational potential deep enough to prohibit significant mass removal from the system. The baryonic fraction within 240 kpc is found to be 0.065 +0.051/-0.020 for h_{50}=1, where h_{50}=H_0/50 km/s/Mpc, in good agreement with the universal value of 0.05 +/-0.01 predicted by standard Big Bang nucleosynthesis for a Universe with Omega_0=1 and h_{50}=1. Since the deep potential of the NGC 3258 group ensures that all pristine intragroup gas has been retained, the baryonic fraction of the NGC 3258 group is indicative of the universal value. Consequently it seems premature to rule out a critical Universe.Comment: 19 pages Latex, using aasms4.sty, paper also available at http://www.dsri.dk/~kristian To appear in Astrophysical Journal Letter

Variation of Inner Radius of Dust Torus in NGC4151

The long-term optical and near infrared monitoring observations for a type 1 act ive galactic nucleus NGC 4151 were carried out for six years from 2001 to 2006 b y using the MAGNUM telescope, and delayed response of flux variations in the $K(2.2\mu m)$ band to those in the $V(0.55\mu m)$ band was clearly detected. Based on cross correlation analysis, we precisely measured a lag time $\Delta t$ for eight separate periods, and we found that $\Delta t$ is not constant changing be tween 30 and 70 days during the monitoring period. Since $\Delta t$ is the ligh t travel time from the central energy source out to the surrounding dust torus, this is the first convincing evidence that the inner radius of dust torus did ch ange in an individual AGN. In order to relate such a change of $\Delta t$ with a change of AGN luminosity $L$, we presented a method of taking an average of th e observed $V$-band fluxes that corresponds to the measured value of $\Delta t$, and we found that the time-changing track of NGC 4151 in the $\Delta t$ versus $L$ diagram during the monitoring period deviates from the relation of $\Delta t \propto L^{0.5}$ expected from dust reverberation. This result, combined with t he elapsed time from period to period for which $\Delta t$ was measured, indicat es that the timescale of dust formation is about one year, which should be taken into account as a new constraint in future studies of dust evolution in AGNs.Comment: 5 pages, 3 figures, To appear in the ApJ Lette

Equilibrium Properties of Mouse-Torpedo Acetylcholine Receptor Hybrids Expressed in Xenopus Oocytes

This study used messenger RNA encoding each subunit (α, β, γ and δ) of the nicotinic acetylcholine (ACh) receptor from mouse BC3H-1 cells and from Torpedo electric organ. The mRNA was synthesized in vitro by transcription with SP6 polymerase from cDNA clones. All 16 possible combinations that include one mRNA for each of α, β, γ and δ were injected into oocytes. After allowing 2-8 d for translation and assembly, we assayed each oocyte for (a) receptor assembly, measured by the binding of [^125]α-bungarotoxin to the oocyte surface, and (b) ACh-induced conductance, measured under voltage clamp at various membrane potentials. All combinations yielded detectable assembly (30-fold range among different combinations) and ACh-induced conductances (>1,000-fold range at 1 µM). On double-logarithmic coordinates, the dose-response relations all had a slope near 2 for low concentrations of ACh. Data were corrected for variations in efficiency of translation among identically injected oocytes by expressing ACh-induced conductance per femtomole of α-bungarotoxin-binding sites. Five combinations were tested for d-tubocurarine inhibition by the dose-ratio method; the apparent dissociation constant ranged from 0.08 to 0.27 µM. Matched responses and geometric means are used for describing the effects of changing a particular subunit (mouse vs. Torpedo) while maintaining the identity of the other subunits. A dramatic subunit-specific effect is that of the β subunit on voltage sensitivity of the response: g_ACh(-90 mV)/g_Ach(+30 mV) is always at least 1, but this ratio increases by an average of 3.5-fold if β_M replaces β_T. Also, combinations including γ_T or δ_M usually produce greater receptor assembly than combinations including the homologous subunit from the other species. Finally, E_ACh is defined as the concentration of ACh inducing 1 µS/fmol at -60 mV; E_ACh is consistently lower for α_m. We conclude that receptor assembly, voltage sensitivity, and E_ACh are governed by different properties

Determining Ω\Omega from cluster correlation function

It is shown how data on the cluster correlation function can be used in order to reconstruct the density of the pregalactic density field on the cluster mass scale. The method is applied to the data on the cluster correlation amplitude -- richness dependence. The spectrum of the recovered density field has the same shape as the density field derived from data on the galaxy correlation function which is measured as function of linear scales. Matching the two amplitudes relates the mass to the comoving scale it contains and thereby leads to a direct determination of $\Omega$. The resultant density parameter turns out to be $\Omega$=0.25.Comment: to appear in Physics Reports, "Dark Matter 98", vol.30

The Interpretation of Near-Infrared Star Counts at the South Galactic Pole

We present new deep $K'$ counts of stars at the South Galactic Pole (SGP) taken with the NAOJ PICNIC camera to $K'=17.25$. Star-galaxy separation to $K'=17.5$ was accomplished effectively using image profiles because the pixel size we used is 0.509 arcsec. We interpret these counts using the SKY (Cohen 1994) model of the Galactic point source sky and determine the relative normalization of halo-to-disk populations, and the location of the Sun relative to the Galactic plane, within the context of this model. The observed star counts constrain these parameters to be: halo/disk $\sim$ 1/900 and z$_\odot$=16.5$\pm$2.5 pc. These values have been used to correct our SGP galaxy counts for contamination by the point source Galactic foreground.Comment: accepted for publication in AJ, 15 pages with 2 figure

Spin-Glass-like Transition and Hall Resistivity of Y2-xBixIr2O7

Various physical properties of the pyrochlore oxide Y2-xBixIr2O7 have been studied. The magnetizations M measured under the conditions of the zero-field-cooling(ZFC) and the field-cooling(FC) have different values below the temperature T=TG. The anomalous T-dependence of the electrical resistivities r and the thermoelectric powers S observed at around TG indicates that the behavior of the magnetization is due to the transition to the state with the spin freezing. In this spin-frozen state, the Hall resistivities rH measured with the ZFC and FC conditions are found to have different values, too, in the low temperature phase (T<TG). Possible mechanisms which induce such the hysteretic behavior are discussed.Comment: 9 pages, 7 figures, J. Phys. Soc. Jpn. 72 (2003) No.

Kinematics of Metal-Poor Stars in the Galaxy. II. Proper Motions for a Large Non-Kinematically Selected Sample

We present a revised catalog of 2106 Galactic stars, selected without kinematic bias, and with available radial velocities, distance estimates, and metal abundances in the range 0.0 <= [Fe/H] <= -4.0. This update of the Beers and Sommer-Larsen (1995) catalog includes newly-derived homogeneous photometric distance estimates, revised radial velocities for a number of stars with recently obtained high-resolution spectra, and refined metallicities for stars originally identified in the HK objective-prism survey (which account for nearly half of the catalog) based on a recent re-calibration. A subset of 1258 stars in this catalog have available proper motions, based on measurements obtained with the Hipparcos astrometry satellite, or taken from the updated Astrographic Catalogue (AC 2000; second epoch positions from either the Hubble Space Telescope Guide Star Catalog or the Tycho Catalogue), the Yale/San Juan Southern Proper Motion (SPM) Catalog 2.0, and the Lick Northern Proper Motion (NPM1) Catalog. Our present catalog includes 388 RR Lyrae variables (182 of which are newly added), 38 variables of other types, and 1680 non-variables, with distances in the range 0.1 to 40 kpc.Comment: 31 pages, including 8 figures, to appear in AJ (June 2000), full paper with all figures embedded available at http://pluto.mtk.nao.ac.jp/people/chiba/preprint/halo4

Spectrophotometric Redshifts. A New Approach to the Reduction of Noisy Spectra and its Application to GRB090423

We have developed a new method, close in philosophy to the photometric redshift technique, which can be applied to spectral data of very low signal-to-noise ratio. Using it we intend to measure redshifts while minimising the dangers posed by the usual extraction techniques. GRB afterglows have generally very simple optical spectra over which the separate effects of absorption and reddening in the GRB host, the intergalactic medium, and our own Galaxy are superimposed. We model all these effects over a series of template afterglow spectra to produce a set of clean spectra that reproduce what would reach our telescope. We also model carefully the effects of the telescope-spectrograph combination and the properties of noise in the data, which are then applied on the template spectra. The final templates are compared to the two-dimensional spectral data, and the basic parameters (redshift, spectral index, Hydrogen absorption column) are estimated using statistical tools. We show how our method works by applying it to our data of the NIR afterglow of GRB090423. At z ~ 8.2, this was the most distant object ever observed. We use the spectrum taken by our team with the Telescopio Nazionale Galileo to derive the GRB redshift and its intrinsic neutral Hydrogen column density. Our best fit yields z=8.4^+0.05/-0.03 and N(HI)<5x10^20 cm^-2, but with a highly non-Gaussian uncertainty including the redshift range z [6.7, 8.5] at the 2-sigma confidence level. Our method will be useful to maximise the recovered information from low-quality spectra, particularly when the set of possible spectra is limited or easily parameterisable while at the same time ensuring an adequate confidence analysis.Comment: 6 pages, 6 figures. Accepted for publication in Astronomy and Astrophysic

On the Thermal Instability in a Contracting Gas Cloud and Formation of a Bound Cluster

We perform linear analysis of thermal instability in a contracting large cloud filled with warm HI gas and investigate the effect of metallicity and radiation flux. When the cloud reaches critical density n_f, the cloud fragments into cool, dense condensations because of thermal instability. For a lower metallicity gas cloud, the value of n_f is high. Collision between condensations will produce self-gravitating clumps and stars thereafter. From the result of calculation, we suggest that high star formation efficiency and bound cluster formation are realized in low-metallicity and/or strong-radiation environments.Comment: 7 pages, including 7 figures, LaTeX2e(emulateapj5.sty) To appear in ApJ, Jun 10, 200

JHK' Imaging Photometry of Seyfert 1 AGNs and Quasars I: Multi-Aperture Photometry

Near-infrared $JHK'$ imaging photometry was obtained of 331 AGNs consisting mainly of Seyfert 1 AGNs and quasars (QSOs). This sample was selected to cover a range of radio emission strength, redshift from $z=0$ to 1, and absolute $B$-magnitude from $M_B=-29$ mag to -18 mag. Among low-$z$ AGNs with $z<0.3$, Seyfert $1-1.5$ AGNs are distributed over a region from a location typical of ``galaxies'' to a location typical of ``QSOs'' in the two-color $J-H$ to $H-K'$ diagram, but Seyfert $1.8-2$ AGNs are distributed around the location of ``galaxies''. Moreover, bright AGNs with respect to absolute $B$-magnitude are distributed near the location of ``QSOs'', while faint AGNs are near the location of ``galaxies''. The distribution of such low-$z$ AGNs in this diagram was found to have little dependence on their 6 cm radio flux. The near-infrared colors of the AGNs observed with an aperture of 7 pixels ($7.49''$) are more QSO-like than those observed with larger apertures up to 15 pixels ($16.1''$). This aperture effect may be explained by contamination from the light of host galaxies within larger apertures. This effect is more prominent for less luminous AGNs