286 research outputs found
An Objective and Automatic Cluster Finder: An Improvement of the Matched-Filter Method
We describe an objective and automated method for detecting clusters of
galaxies from optical imaging data. This method is a variant of the so-called
`matched-filter' technique pioneered by Postman et al. (1996). With
simultaneous use of positions and apparent magnitudes of galaxies, this method
can, not only find cluster candidates, but also estimate their redshifts and
richnesses as byproducts of detection. We examine errors in the estimation of
cluster's position, redshift, and richness with a number of Monte Carlo
simulations. No systematic discrepancies between the true and estimated values
are seen for either redshift or richness. Spurious detection rate of the method
is about less than 10% of those of conventional ones which use only surface
density of galaxies. A cluster survey in the North Galactic Pole is executed to
verify the performance characteristics of the method with real data. Two known
real clusters are successfully detected. We expect these methods based on
`matched-filter' technique to be essential tools for compiling large and
homogeneous optically-selected cluster catalogs.Comment: 13 pages, 12 PostScript figures, uses LaTeX L-AA, A&AS accepte
A Passivity-Based Distributed Reference Governor for Constrained Robotic Networks
This paper focuses on a passivity-based distributed reference governor (RG)
applied to a pre-stabilized mobile robotic network. The novelty of this paper
lies in the method used to solve the RG problem, where a passivity-based
distributed optimization scheme is proposed. In particular, the gradient
descent method minimizes the global objective function while the dual ascent
method maximizes the Hamiltonian. To make the agents converge to the agreed
optimal solution, a proportional-integral consensus estimator is used. This
paper proves the convergence of the state estimates of the RG to the optimal
solution through passivity arguments, considering the physical system static.
Then, the effectiveness of the scheme considering the dynamics of the physical
system is demonstrated through simulations and experiments.Comment: 8 pages, International Federation of Automatic Conference 2017, 8
figure
Delay Time Distribution Measurement of Type Ia Supernovae by the Subaru/XMM-Newton Deep Survey and Implications for the Progenitor
The delay time distribution (DTD) of type Ia supernovae (SNe Ia) from star
formation is an important clue to reveal the still unknown progenitor system of
SNe Ia. Here we report on a measurement of the SN Ia DTD in a delay time range
of t_Ia = 0.1-8.0 Gyr by using the faint variable objects detected in the
Subaru/XMM-Newton Deep Survey (SXDS) down to i' ~ 25.5. We select 65 SN
candidates showing significant spatial offset from nuclei of the host galaxies
having old stellar population at z ~ 0.4-1.2, out of more than 1,000 SXDS
variable objects. Although spectroscopic type classification is not available
for these, we quantitatively demonstrate that more than ~80% of these should be
SNe Ia. The DTD is derived using the stellar age estimates of the old galaxies
based on 9 band photometries from optical to mid-infrared wavelength. Combined
with the observed SN Ia rate in elliptical galaxies at the local universe, the
DTD in t_Ia ~ 0.1-10 Gyr is well described by a featureless power-law as
f_D(t_Ia) \propto t_Ia^{-1}. The derived DTD is in excellent agreement with the
generic prediction of the double-degenerate scenario, giving a strong support
to this scenario. In the single-degenerate (SD) scenario, although predictions
by simple analytic formulations have broad DTD shapes that are similar to the
observation, DTD shapes calculated by more detailed binary population synthesis
tend to have strong peaks at characteristic time scales, which do not fit the
observation. This result thus indicates either that the SD channel is not the
major contributor to SNe Ia in old stellar population, or that improvement of
binary population synthesis theory is required. Various sources of systematic
uncertainties are examined and tested, but our main conclusions are not
affected significantly.Comment: Matches the final version to be published in PASJ. A very minor bug
in the visibility time calculation has been fixed, resulting in slight
changes in the derived DTD (<~ 10%). Conclusions are not affected at all. The
font error of the labels in Fig 3 also fixe
Proper motions with Subaru II. A sample in the Subaru/XMM-Newton Deep Survey field
We search for stars with proper motions in a set of deep Subaru images,
covering about 0.48 square degrees to a depth of , taken over a
span of five and a half years. We follow the methods described in
\citet{Richmond2009} to reduce and analyze this dataset. We present a sample of
69 stars with motions of high significance, and discuss briefly the populations
from which they are likely drawn. Based on photometry and motions alone, we
expect that 14 of the candidates may be white dwarfs. Our candidate with the
largest proper motion is surprisingly faint and likely to prove interesting:
its colors and motions suggest that it might be an M dwarf moving at over 500
km/sec or an L dwarf in the halo.Comment: 10 pages, 5 figures. Accepted by Publications of the Astronomical
Society of Japan, to appear in volume 62, February 2010. Revised version:
removed PASJ LaTeX tutorial which was mistakenly appended to pape
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