111 research outputs found
Radio AGN Selection and Characterization in Three Deep-Drilling Fields of the Vera C. Rubin Observatory Legacy Survey of Space and Time
The Australia Telescope Large Area Survey (ATLAS) and the VLA survey in the
XMM-LSS/VIDEO deep field provide deep ( Jybeam) and
high-resolution ( 4.5--8 arcsec) radio coverage of the three XMM-SERVS
fields (W-CDF-S, ELAIS-S1, and XMM-LSS). These data cover a total sky area of
11.3 deg and contain radio components. Furthermore, about
3~deg of the XMM-LSS field also has deeper MIGHTEE data that achieve a
median RMS of 5.6 Jy beam and detect more than 20000 radio
sources. We analyze all these radio data and find source counterparts at other
wavebands utilizing deep optical and IR surveys. The nature of these radio
sources is studied using radio-band properties (spectral slope and morphology),
and the IR-radio correlation. %and spectral energy distribution. Radio AGNs are
selected and compared with those selected using other methods (e.g. X-ray). We
found 1656 new AGNs that were not selected using X-ray and/or MIR methods. We
constrain the FIR-to-UV SEDs of radio AGNs using {\sc cigale} and investigate
the dependence of radio AGN fraction upon galaxy stellar mass and
star-formation rate.Comment: 25 pages, 21+3 figures, 8+1 tables, MNRAS accepted (final version).
The catalogues are available from
https://personal.psu.edu/wnb3/xmmservs/zhu2023-tables-2023-04-12.tar.zi
Piercing Through Highly Obscured and Compton-thick AGNs in the Chandra Deep Fields: I. X-ray Spectral and Long-term Variability Analyses
We present a detailed X-ray spectral analysis of 1152 AGNs selected in the
Chandra Deep Fields (CDFs), in order to identify highly obscured AGNs (). By fitting spectra with physical models, 436 (38%)
sources with are confirmed to be highly
obscured, including 102 Compton-thick (CT) candidates. We propose a new
hardness-ratio measure of the obscuration level which can be used to select
highly obscured AGN candidates. The completeness and accuracy of applying this
method to our AGNs are 88% and 80%, respectively. The observed logN-logS
relation favors cosmic X-ray background models that predict moderate (i.e.,
between optimistic and pessimistic) CT number counts. 19% (6/31) of our highly
obscured AGNs that have optical classifications are labeled as broad-line AGNs,
suggesting that, at least for part of the AGN population, the heavy X-ray
obscuration is largely a line-of-sight effect, i.e., some high-column-density
clouds on various scales (but not necessarily a dust-enshrouded torus) along
our sightline may obscure the compact X-ray emitter. After correcting for
several observational biases, we obtain the intrinsic NH distribution and its
evolution. The CT-to-highly-obscured fraction is roughly 52% and is consistent
with no evident redshift evolution. We also perform long-term (~17 years in the
observed frame) variability analyses for 31 sources with the largest number of
counts available. Among them, 17 sources show flux variabilities: 31% (5/17)
are caused by the change of NH, 53% (9/17) are caused by the intrinsic
luminosity variability, 6% (1/17) are driven by both effects, and 2 are not
classified due to large spectral fitting errors.Comment: 32 pages, 21 figures, 9 tables, accepted for publication in Ap
Cuprous oxide/Titanium dioxide nanotube-array with coaxial heterogeneous structure synthesized by multiple-cycle chemical adsorption plus reduction method
We report the formation and characterization of Cuprous oxide/Titanium dioxide (Cu2O/TiO2) nanotube-array coaxial heterogeneous structure, which is supposed to have potential applications in photo-induced water decomposition and organic pollutant degradation. Such structure is formed by coating nano-particles of Cu2O onto titanium dioxide nanotube-array walls via multiple-cycle chemical adsorption plus reduction method (MC-CAR). The practical deposition technique employs a soaking step to separate the adsorption and reduction processes, thus enhancing the controllability of deposition rate and preventing the clogging of nanotube pores. The size of Cu2O nano-particles is adjusted by changing the glucose concentration in the reaction solutions. As a result, compact nano-particle film with sufficiently small crystal sizes is uniformly covered on the tube walls, resulting in the formation of coaxial heterogeneous structure. The detailed synthesis process and the surface morphology, structure, photoelectric properties, and hydrogen evolution ability of the Cu2O/TiO2 nanotube-array with coaxial heterogeneous structure are systematically investigated. The resulting film shows a stable hydrogen production rate of 3.1 mLcm-2h-1, which can be targeted for energy application in relation with solar energy driven production of hydrogen from water
Identification and Characterization of a Large Sample of Distant Active Dwarf Galaxies in XMM-SERVS
Active dwarf galaxies are important because they contribute to the evolution
of dwarf galaxies and can reveal their hosted massive black holes. However, the
sample size of such sources beyond the local universe is still highly limited.
In this work, we search for active dwarf galaxies in the recently completed
XMM-Spitzer Extragalactic Representative Volume Survey (XMM-SERVS). XMM-SERVS
is currently the largest medium-depth X-ray survey covering 13
in three extragalactic fields, which all have well-characterized
multi-wavelength information. After considering several factors that may lead
to misidentifications, we identify 73 active dwarf galaxies at , which
constitutes the currently largest X-ray-selected sample beyond the local
universe. Our sources are generally less obscured than predictions based on the
massive-AGN (active galactic nucleus) X-ray luminosity function and have a low
radio-excess fraction. We find that our sources reside in similar environments
to inactive dwarf galaxies. We further quantify the accretion distribution of
the dwarf-galaxy population after considering various selection effects and
find that it decreases with X-ray luminosity, but redshift evolution cannot be
statistically confirmed. Depending upon how we define an AGN, the active
fraction may or may not show a strong dependence on stellar mass. Their
Eddington ratios and X-ray bolometric corrections significantly deviate from
the expected relation, which is likely caused by several large underlying
systematic biases when estimating the relevant parameters for dwarf galaxies.
Throughout this work, we also highlight problems in reliably measuring
photometric redshifts and overcoming strong selection effects for distant
active dwarf galaxies.Comment: 34 pages, 21 figures, 6 tables, accepted for publication in Ap
The Most Obscured AGNs in the XMM-SERVS Fields
We perform X-ray spectral analyses to derive characteristics (e.g., column
density, X-ray luminosity) of 10,200 active galactic nuclei (AGNs) in
the XMM-Spitzer Extragalactic Representative Volume Survey (XMM-SERVS), which
was designed to investigate the growth of supermassive black holes across a
wide dynamic range of cosmic environments. Using physical torus models (e.g.,
Borus02) and a Bayesian approach, we uncover 22 representative Compton-thick
(CT; ) AGN candidates with good
signal-to-noise ratios as well as a large sample of 136 heavily obscured AGNs.
We also find an increasing CT fraction (\fct ) from low () to high
() redshift. Our CT candidates tend to show hard X-ray spectral shapes
and dust extinction in their SED fits, which may shed light on the connection
between AGN obscuration and host-galaxy evolution.Comment: 12 pages, 9 figures, accepted for publication in Ap
The Most Obscured AGNs in the XMM-SERVS Fields
We perform X-ray spectral analyses to derive the characteristics (e.g., column density, X-ray luminosity) of ≈10,200 active galactic nuclei (AGNs) in the XMM-Spitzer Extragalactic Representative Volume Survey, which was designed to investigate the growth of supermassive black holes across a wide dynamic range of cosmic environments. Using physical torus models (e.g., Borus02) and a Bayesian approach, we uncover 22 representative Compton-thick (CT; NH > 1.5 × 1024 cm−2) AGN candidates with good signal-to-noise ratios as well as a large sample of 136 heavily obscured AGNs. We also find an increasing CT fraction (fCT) from low (z 0.75) redshift. Our CT candidates tend to show hard X-ray spectral shapes and dust extinction in their spectral energy distribution fits, which may shed light on the connection between AGN obscuration and host-galaxy evolution
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