11,703 research outputs found
Photometric properties and luminosity function of nearby massive early-type galaxies
We perform photometric analyses for a bright early-type galaxy (ETG) sample
with 2949 galaxies ( mag) in the redshift range of 0.05 to
0.15, drawn from the SDSS DR7 with morphological classification from Galaxy Zoo
1. We measure the Petrosian and isophotal magnitudes, as well as the
corresponding half-light radius for each galaxy. We find that for brightest
galaxies ( mag), our Petrosian magnitudes, and isophotal
magnitudes to 25 and 1\% of the sky brightness are on
average 0.16 mag, 0.20 mag, and 0.26 mag brighter than the SDSS Petrosian
values, respectively. In the first case the underestimations are caused by
overestimations in the sky background by the SDSS PHOTO algorithm, while the
latter two are also due to deeper photometry. Similarly, the typical half-light
radii () measured by the SDSS algorithm are smaller than our
measurements. As a result, the bright-end of the -band luminosity function
is found to decline more slowly than previous works. Our measured luminosity
densities at the bright end are more than one order of magnitude higher than
those of Blanton et al. (2003), and the stellar mass densities at and are a few tenths
and a factor of few higher than those of Bernardi et al. (2010). These results
may significantly alleviate the tension in the assembly of massive galaxies
between observations and predictions of the hierarchical structure formation
model.Comment: 43 pages, 14 figures, version accepted for publication in the
Astrophysical Journa
Microlensing of Sub-parsec Massive Binary Black Holes in Lensed QSOs: Light Curves and Size-Wavelength Relation
Sub-parsec binary massive black holes (BBHs) are long anticipated to exist in
many QSOs but remain observationally elusive. In this paper, we propose a novel
method to probe sub-parsec BBHs through microlensing of lensed QSOs. If a QSO
hosts a sub-parsec BBH in its center, it is expected that the BBH is surrounded
by a circum-binary disk, each component of the BBH is surrounded by a small
accretion disk, and a gap is opened by the secondary component in between the
circum-binary disk and the two small disks. Assuming such a BBH structure, we
generate mock microlensing light curves for some QSO systems that host BBHs
with typical physical parameters. We show that microlensing light curves of a
BBH QSO system at the infrared-optical-UV bands can be significantly different
from those of corresponding QSO system with a single massive black hole (MBH),
mainly because of the existence of the gap and the rotation of the BBH (and its
associated small disks) around the center of mass. We estimate the half-light
radii of the emission region at different wavelengths from mock light curves
and find that the obtained half-light radius vs. wavelength relations of BBH
QSO systems can be much flatter than those of single MBH QSO systems at a
wavelength range determined by the BBH parameters, such as the total mass, mass
ratio, separation, accretion rates, etc. The difference is primarily due to the
existence of the gap. Such unique features on the light curves and half-light
radius-wavelength relations of BBH QSO systems can be used to select and probe
sub-parsec BBHs in a large number of lensed QSOs to be discovered by current
and future surveys, including the Panoramic Survey Telescope and Rapid Response
System (Pan-STARRS), the Large Synoptic Survey telescope (LSST) and Euclid.Comment: 18 pages, 17 figures, accepted for publication in the Astrophysical
Journa
Observation of Andreev Surface Bound States in the 3-K phase Region of Sr_2RuO_4
The tunneling spectrum of the superconducting phase with T_c ~ 3.0 K has been
measured in the Ru-embedded region of Sr_2RuO_4 using cleaved junctions. A
sharp zero-bias conductance peak (ZBCP) has been observed below 3 K. All
characteristics of this ZBCP suggest that it originates from Andreev surface
bound states, indicating that the pairing in the 3-K phase is also non-s-wave.
Below the bulk T_c of Sr_2RuO_4 (~1.5 K), a bell-shaped ZBCP was found. This
supports that there is a phase transition in the 3-K phase region near the bulk
T_c.Comment: 4 pages, to appear in Phys. Rev. Lett. 87 (2001
Numerical simulation of a metro vehicle running over rail with fastening system failure using finite element method
In this paper, the dynamic responses of a moving vehicle traversing over railway track with fastening system failure were investigated using a vehicle/track coupling system model. In this model, the moving vehicle is developed by multi-body dynamics, and the direct fixation track is modeled by finite element method, where the rail is treated as an Euler-Bernoulli beam supported by fastening systems. An invalidation factor is used to determine the failure of the fastening system. The Hertzian spring is adapted to model the wheel/rail contact force between the moving wheel set and the rail. The proposed vehicle/track system model is verified with some field testing results in Zhengzhou subway. To solve the vehicle/track system model with nonlinear contact force, an iterative procedure is proposed. The effects of fastening system failure on the responses of the vehicle and track are investigated. It indicates that the wheel/rail contact force varies abruptly when the vehicle passing over the fastening system failure zone, which result in track deterioration
Emergence of intrinsic superconductivity below 1.178 K in the topologically non-trivial semimetal state of CaSn3
Topological materials which are also superconducting are of great current
interest, since they may exhibit a non-trivial topologically-mediated
superconducting phase. Although there have been many reports of pressure-tuned
or chemical-doping-induced superconductivity in a variety of topological
materials, there have been few examples of intrinsic, ambient pressure
superconductivity in a topological system having a stoichiometric composition.
Here, we report that the pure intermetallic CaSn3 not only exhibits topological
fermion properties but also has a superconducting phase at 1.178 K under
ambient pressure. The topological fermion properties, including the nearly zero
quasi-particle mass and the non-trivial Berry phase accumulated in cyclotron
motions, were revealed from the de Haas-van Alphen (dHvA) quantum oscillation
studies of this material. Although CaSn3 was previously reported to be
superconducting at 4.2K, our studies show that the superconductivity at 4.2K is
extrinsic and caused by Sn on the degraded surface, whereas its intrinsic bulk
superconducting transition occurs at 1.178 K. These findings make CaSn3 a
promising candidate for exploring new exotic states arising from the interplay
between non-trivial band topology and superconductivity, e.g. topological
superconductivityComment: 20 pages,4 figure
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