109 research outputs found
Low Complexity Algorithm for Range-Point Migration-Based Human Body Imaging for Multistatic UWB Radars
High-resolution, short-range sensors that can be applied in optically challenging environments (e.g., in the presence of clouds, fog, and/or dark smog) are in high demand for various applications. Ultrawideband radar is a promising sensor that is suitable for short-range surveillance or watching sensors. Range-point migration (RPM) has been recently established as a promising imaging approach to achieve accurate and real-time 3-D imaging. However, when objects with many scattering points are dealt with, such as a human body, RPM suffers from high computational costs. In this letter, we propose an algorithm with a lower complexity for an RPM-based 3-D imaging method by introducing a sampling-based scattering center extraction with a simplified evaluation function, in which an efficient sample pattern is provided by a golden ratio. The results from a finite-difference time-domain-based numerical test, which introduces a realistic human body object, demonstrate that our proposed method remarkably reduces the computational cost without sacrificing the reconstruction accuracy
The Obscured Fraction of Quasars at Cosmic Noon
Statistical studies of X-ray selected Active Galactic Nuclei (AGN) indicate
that the fraction of obscured AGN increases with increasing redshift, and the
results suggest that a significant part of the accretion growth occurs behind
obscuring material in the early universe. We investigate the obscured fraction
of highly accreting X-ray AGN at around the peak epoch of supermassive black
hole growth utilizing the wide and deep X-ray and optical/IR imaging datasets.
A unique sample of luminous X-ray selected AGNs above was constructed by
matching the XMM-SERVS X-ray point-source catalog with a PSF-convolved
photometric catalog covering from to 4.5 bands.
Photometric redshift, hydrogen column density, and 2-10 keV AGN luminosity of
the X-ray selected AGN candidates were estimated. Using the sample of 306 2-10
keV detected AGN at above redshift 2, we estimate the fraction of AGN with
, assuming parametric X-ray luminosity and
absorption functions. The results suggest that of luminous
quasars () above redshift 2 are obscured.
The fraction indicates an increased contribution of obscured accretion at high
redshift than that in the local universe. We discuss the implications of the
increasing obscured fraction with increasing redshift based on the AGN
obscuration scenarios, which describe obscuration properties in the local
universe. Both the obscured and unobscured AGN show a broad range of SEDs
and morphology, which may reflect the broad variety of host galaxy properties
and physical processes associated with the obscuration.Comment: 25 Pages, 19 Figure, ApJ accepted. Updated version contains
corrections based on comments from the communit
X-Ray bright optically faint active galactic nuclei in the Subaru Hyper Suprime-Cam wide survey
We construct a sample of X-ray bright optically faint active galactic nuclei
by combining Subaru Hyper Suprime-Cam, XMM-Newton, and infrared source
catalogs. 53 X-ray sources satisfying i band magnitude fainter than 23.5 mag
and X-ray counts with EPIC-PN detector larger than 70 are selected from 9.1
deg^2, and their spectral energy distributions (SEDs) and X-ray spectra are
analyzed. 44 objects with an X-ray to i-band flux ratio F_X/F_i>10 are
classified as extreme X-ray-to-optical flux sources. SEDs of 48 among 53 are
represented by templates of type 2 AGNs or starforming galaxies and show
signature of stellar emission from host galaxies in the optical in the source
rest frame. Infrared/optical SEDs indicate significant contribution of emission
from dust to infrared fluxes and that the central AGN is dust obscured.
Photometric redshifts determined from the SEDs are in the range of 0.6-2.5.
X-ray spectra are fitted by an absorbed power law model, and the intrinsic
absorption column densities are modest (best-fit log N_H = 20.5-23.5 cm^-2 in
most cases). The absorption corrected X-ray luminosities are in the range of
6x10^42 - 2x10^45 erg s^-1. 20 objects are classified as type 2 quasars based
on X-ray luminsosity and N_H. The optical faintness is explained by a
combination of redshifts (mostly z>1.0), strong dust extinction, and in part a
large ratio of dust/gas.Comment: 25 pages, 14 figures, 5 tables, accepted for publication in PAS
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