1,611 research outputs found
Superconductivity of the Ternary Boride Li_2Pd_3B Probed by ^{11}B NMR
We report a ^{11}B NMR measurement on the recently discovered superconductor
Li_2Pd_3B. The nuclear spin lattice relaxation rate 1/T_1 shows a well-defined
coherence peak just below T_c (H=1.46 T)=5.7 K, and the spin susceptibility
measured by the Knight shift also decreases below T_c. These results indicate
that the superconductivity is of conventional nature, with an isotropic gap.
Our results also suggest that the -electrons of boron and the d-electrons of
palladium that hybridize with boron -electrons are primarily responsible for
the superconductivity.Comment: 4 pages, 5 figure
SDSS J131339.98+515128.3: A new gravitationally lensed quasar selected based on near-infrared excess
We report the discovery of a new gravitationally lensed quasar, SDSS
J131339.98+515128.3, at a redshift of 1.875 with an image separation of 1.24".
The lensing galaxy is clearly detected in visible-light follow-up observations.
We also identify three absorption-line doublets in the spectra of the lensed
quasar images, from which we measure the lens redshift to be 0.194. Like
several other known lenses, the lensed quasar images have different continuum
slopes. This difference is probably the result of reddening and microlensing in
the lensing galaxy. The lensed quasar was selected by correlating Sloan Digital
Sky Survey (SDSS) spectroscopic quasars with Two Micron All Sky Survey (2MASS)
sources and choosing quasars that show near-infrared (IR) excess. The near-IR
excess can originate, for example, from the contribution of the lensing galaxy
at near-IR wavelengths. We show that the near-IR excess technique is indeed an
efficient method to identify lensed systems from a large sample of quasars.Comment: Accepted to MNRAS, 8 pages, 7 figure
Discovery of Multiply Imaged Galaxies behind the Cluster and Lensed Quasar SDSS J1004+4112
We have identified three multiply imaged galaxies in Hubble Space Telescope
images of the redshift z=0.68 cluster responsible for the large-separation
quadruply lensed quasar, SDSS J1004+4112. Spectroscopic redshifts have been
secured for two of these systems using the Keck I 10m telescope. The most
distant lensed galaxy, at z=3.332, forms at least four images, and an Einstein
ring encompassing 3.1 times more area than the Einstein ring of the lensed QSO
images at z=1.74, due to the greater source distance. For a second multiply
imaged galaxy, we identify Ly_alpha emission at a redshift of z=2.74. The
cluster mass profile can be constrained from near the center of the brightest
cluster galaxy, where we observe both a radial arc and the fifth image of the
lensed quasar, to the Einstein radius of the highest redshift galaxy, ~110 kpc.
Our preliminary modeling indicates that the mass approximates an elliptical
body, with an average projected logarithmic gradient of ~-0.5. The system is
potentially useful for a direct measurement of world models in a previously
untested redshift range.Comment: 5 pages, 3 figures. Accepted by ApJL. High resolution version of the
paper can be found at: http://wise-obs.tau.ac.il/~kerens/papers.htm
The Sloan Digital Sky Survey Quasar Lens Search. V. Final Catalog from the Seventh Data Release
We present the final statistical sample of lensed quasars from the Sloan
Digital Sky Survey (SDSS) Quasar Lens Search (SQLS). The well-defined
statistical lens sample consists of 26 lensed quasars brighter than i=19.1 and
in the redshift range of 0.6<z<2.2 selected from 50,836 spectroscopically
confirmed quasars in the SDSS Data Release 7 (DR7), where we restrict the image
separation range to 1"<\theta<20" and the i-band magnitude differences in two
image lenses to be smaller than 1.25 mag. The SDSS DR7 quasar catalog also
contains 36 additional lenses identified with various techniques. In addition
to these lensed quasars, we have identified 81 pairs of quasars from follow-up
spectroscopy, 26 of which are physically associated binary quasars. The
statistical lens sample covers a wide range of image separations, redshifts,
and magnitudes, and therefore is suitable for systematic studies of
cosmological parameters and surveys of the structure and evolution of galaxies
and quasars.Comment: 42 pages, 2 figures, 6 tables, accepted for publication in AJ; see
http://www-utap.phys.s.u-tokyo.ac.jp/~sdss/sqls/ for supplemental informatio
Adaptive optics observations of the gravitationally lensed quasar SDSS J1405+0959
We present the result of Subaru Telescope multi-band adaptive optics
observations of the complex gravitationally lensed quasar SDSS J1405+0959,
which is produced by two lensing galaxies. These observations reveal
dramatically enhanced morphological detail, leading to the discovery of an
additional object 0. 26'' from the secondary lensing galaxy, as well as three
collinear clumps located in between the two lensing galaxies. The new object is
likely to be the third quasar image, although the possibility that it is a
galaxy cannot be entirely excluded. If confirmed via future observations, it
would be the first three image lensed quasar produced by two galaxy lenses. In
either case, we show based on gravitational lensing models and photometric
redshift that the collinear clumps represent merging images of a portion of the
quasar host galaxy, with a magnification factor of 15 - 20, depending on the
model.Comment: 12 pages, 8 figures, 7 tables. Submitted to MNRA
The Sloan Digital Sky Survey Quasar Lens Search. VI. Constraints on Dark Energy and the Evolution of Massive Galaxies
We present a statistical analysis of the final lens sample from the Sloan
Digital Sky Survey Quasar Lens Search (SQLS). The number distribution of a
complete subsample of 19 lensed quasars selected from 50,836 source quasars is
compared with theoretical expectations, with particular attention to the
selection function. Assuming that the velocity function of galaxies does not
evolve with redshift, the SQLS sample constrains the cosmological constant to
\Omega_\Lambda=0.79^{+0.06}_{-0.07}(stat.)^{+0.06}_{-0.06}(syst.) for a flat
universe. The dark energy equation of state is found to be consistent with w=-1
when the SQLS is combined with constraints from baryon acoustic oscillation
(BAO) measurements or results from the Wilkinson Microwave Anisotropy Probe
(WMAP). We also obtain simultaneous constraints on cosmological parameters and
redshift evolution of the galaxy velocity function, finding no evidence for
redshift evolution at z<1 in any combinations of constraints. For instance,
number density evolution quantified as \nu_n=d\ln\phi_*/d\ln(1+z) and the
velocity dispersion evolution \nu_\sigma=d\ln\sigma_*/d\ln(1+z) are constrained
to \nu_n=1.06^{+1.36}_{-1.39}(stat.)^{+0.33}_{-0.64}(syst.) and
\nu_\sigma=-0.05^{+0.19}_{-0.16}(stat.)^{+0.03}_{-0.03}(syst.) respectively
when the SQLS result is combined with BAO and WMAP for flat models with a
cosmological constant. We find that a significant amount of dark energy is
preferred even after fully marginalizing over the galaxy evolution parameters.
Thus the statistics of lensed quasars robustly confirm the accelerated cosmic
expansion.Comment: 44 pages, 12 figures, 4 tables, accepted for publication in A
The quasar-galaxy cross SDSS J1320+1644: A probable large-separation lensed quasar
We report the discovery of a pair of quasars at , with a separation
of 8\farcs585\pm0\farcs002. Subaru Telescope infrared imaging reveals the
presence of an elliptical and a disk-like galaxy located almost symmetrically
between the quasars, creating a cross-like configuration. Based on absorption
lines in the quasar spectra and the colors of the galaxies, we estimate that
both galaxies are located at redshift . This, as well as the
similarity of the quasar spectra, suggests that the system is a single quasar
multiply imaged by a galaxy group or cluster acting as a gravitational lens,
although the possibility of a binary quasar cannot be fully excluded. We show
that the gravitational lensing hypothesis implies these galaxies are not
isolated, but must be embedded in a dark matter halo of virial mass assuming an NFW model with a
concentration parameter of , or a singular isothermal sphere profile
with a velocity dispersion of km s. We place constraints on
the location of the dark matter halo, as well as the velocity dispersions of
the galaxies. In addition, we discuss the influence of differential reddening,
microlensing and intrinsic variability on the quasar spectra and broadband
photometry.Comment: Published in The Astrophysical Journa
The Rewards of Patience: An 822 Day Time Delay in the Gravitational Lens SDSS J1004+4112
We present 107 new epochs of optical monitoring data for the four brightest
images of the gravitational lens SDSS J1004+4112 observed between October 2006
and June 2007. Combining this data with the previously obtained light curves,
we determine the time delays between images A, B and C. We confirm our previous
measurement finding that A leads B by dt_BA=40.6+-1.8 days, and find that image
C leads image A by dt_CA=821.6+-2.1 days. The lower limit on the remaining
delay is that image D lags image A by dt_AD>1250 days. Based on the
microlensing of images A and B we estimate that the accretion disk size at a
rest wavelength of 2300 angstrom is 10^{14.8+-0.3} cm for a disk inclination of
cos{i}=1/2, which is consistent with the microlensing disk size-black hole mass
correlation function given our estimate of the black hole mass from the MgII
line width of logM_BH/M_sun=8.44+-0.14. The long delays allow us to fill in the
seasonal gaps and assemble a continuous, densely sampled light curve spanning
5.7 years whose variability implies a structure function with a logarithmic
slope of gamma = 0.35+-0.02. As C is the leading image, sharp features in the C
light curve can be intensively studied 2.3 years later in the A/B pair,
potentially allowing detailed reverberation mapping studies of a quasar at
minimal cost.Comment: Submitted to ApJ, 12 pages, 3 figure
Strong lensing in the Einstein-Straus solution
We analyse strong lensing in the Einstein-Straus solution with positive
cosmological constant. For concreteness we compare the theory to the light
deflection of the lensed quasar SDSS J1004+4112.Comment: 14 pages, 3 figures, 5 tables. To the memory of J\"urgen Ehlers v2
contains a note added during publication in GRG and less typo
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