197 research outputs found
A Thirty-Four Billion Solar Mass Black Hole in SMSS J2157-3602, the Most Luminous Known Quasar
From near-infrared spectroscopic measurements of the MgII emission line
doublet, we estimate the black hole (BH) mass of the quasar, SMSS
J215728.21-360215.1, as being (3.4 +/- 0.6) x 10^10 M_sun and refine the
redshift of the quasar to be z=4.692. SMSS J2157 is the most luminous known
quasar, with a 3000A luminosity of (4.7 +/- 0.5) x 10^47 erg/s and an estimated
bolometric luminosity of 1.6 x 10^48 erg/s, yet its Eddington ratio is only
~0.4. Thus, the high luminosity of this quasar is a consequence of its
extremely large BH -- one of the most massive BHs at z > 4.Comment: 7 pages, 3 figures. Accepted for publication in MNRA
Titanium-Aluminium Oxide Coating on Aluminized Steel
In this study, a plasma electrolytic oxidation (PEO) process was used to form titanium-aluminium oxide coating on aluminized steel. The present work was mainly to study the effects of treatment time of PEO process on properties of the titanium coating. A potentiodynamic polarization corrosion test was employed to investigate the corrosion resistance of the coating. The friction coefficient and wear resistance of the coating were studied by using pin-on-disc test. The thermal transfer behaviours of uncoated and PEO-coated aluminized steels were also studied. It could be seen that treatment time of PEO process significantly influenced the properties of the titanium oxide coating. Samples with a longer treatment time had a better performance for corrosion and wear protection. This paper demonstrated different treatment time could alter the surface behaviour of the coating material
Discovery of Eight z ~ 6 Quasars in the Sloan Digital Sky Survey Overlap Regions
We present the discovery of eight quasars at z~6 identified in the Sloan
Digital Sky Survey (SDSS) overlap regions. Individual SDSS imaging runs have
some overlap with each other, leading to repeat observations over an area
spanning >4000 deg^2 (more than 1/4 of the total footprint). These overlap
regions provide a unique dataset that allows us to select high-redshift quasars
more than 0.5 mag fainter in the z band than those found with the SDSS
single-epoch data. Our quasar candidates were first selected as i-band dropout
objects in the SDSS imaging database. We then carried out a series of follow-up
observations in the optical and near-IR to improve photometry, remove
contaminants, and identify quasars. The eight quasars reported here were
discovered in a pilot study utilizing the overlap regions at high galactic
latitude (|b|>30 deg). These quasars span a redshift range of 5.86<z<6.06 and a
flux range of 19.3<z_AB<20.6 mag. Five of them are fainter than z_AB=20 mag,
the typical magnitude limit of z~6 quasars used for the SDSS single-epoch
images. In addition, we recover eight previously known quasars at z~6 that are
located in the overlap regions. These results validate our procedure for
selecting quasar candidates from the overlap regions and confirming them with
follow-up observations, and provide guidance to a future systematic survey over
all SDSS imaging regions with repeat observations.Comment: AJ in press (8 pages
Thermoplasmatales and Methanogens: Potential Association with the Crenarchaeol Production in Chinese Soils
Crenarchaeol is a unique isoprenoid glycerol dibiphytanyl glycerol tetraether (iGDGT) lipid, which is only identified in cultures of ammonia-oxidizing Thaumarchaeota. However, the taxonomic origins of crenarchaeol have been debated recently. The archaeal populations, other than Thaumarchaeota, may have associations with the production of crenarchaeol in ecosystems characterized by non-thaumarchaeotal microorganisms. To this end, we investigated 47 surface soils from upland and wetland soils and rice fields and another three surface sediments from river banks. The goal was to examine the archaeal community compositions in comparison with patterns of iGDGTs in four fractional forms (intact polar-, core-, monoglycosidic- and diglycosidic-lipid fractions) along gradients of environments. The DistLM analysis identified that Group I.1b Thaumarchaeota were mainly responsible for changes in crenarchaeol in the overall soil samples; however, Thermoplasmatales may also contribute to it. This is further supported by the comparison of crenarchaeol between samples characterized by methanogens, Thermoplasmatales or Group I.1b Thaumarchaeota, which suggests that the former two may contribute to the crenarchaeol pool. Last, when samples containing enhanced abundance of Thermoplasmatales and methanogens were considered, crenarchaeol was observed to correlate positively with Thermoplasmatales and archaeol, respectively. Collectively, our data suggest that the crenarchaeol production is mainly derived from Thaumarchaeota and partly associated with uncultured representatives of Thermoplasmatales and archaeol-producing methanogens in soil environments that may be in favor of their growth. Our finding supports the notion that Thaumarchaeota may not be the sole source of crenarchaeol in the natural environment, which may have implication for the evolution of lipid synthesis among different types of archaea
Black Hole Mass Estimates and Rapid Growth of Supermassive Black Holes in Luminous 3.5 Quasars
We present new near-infrared (IR) observations of the H
and MgII lines for 32 luminous quasars with using the
Palomar Hale 200 inch telescope and the Large Binocular Telescope. We find that
the MgII Full Width at Half Maximum (FWHM) is well correlated with the H
FWHM, confirming itself as a good substitute for the H FWHM in the black
hole mass estimates. The continuum luminosity at 5100 \AA\ well correlates with
the continuum luminosity at 3000 \AA\ and the broad emission line luminosities
(H and MgII). With simultaneous near-IR spectroscopy of the H and
MgII lines to exclude the influences of flux variability, we are able to
evaluate the reliability of estimating black hole masses based on the MgII line
for high redshift quasars. With the reliable H line based black hole
mass and Eddington ratio estimates, we find that the quasars in our
sample have black hole masses , with a median of and are accreting at Eddington ratios between 0.30 and 3.05, with a
median of . Assuming a duty cycle of 1 and a seed black hole mass of
, we show that the quasars in this sample can grow
to their estimated black hole masses within the age of the Universe at their
redshifts.Comment: 38 pages, 6 figures, accepted for publication in Ap
Exploratory chandra observation of the ultraluminous quasar SDSS J010013.02+280225.8 at redshift 6.30
We report exploratory Chandra observations of the ultraluminous quasar SDSS J010013.02+280225.8 at redshift 6.30. The quasar is clearly detected by Chandra with a possible component of extended emission.Y.-L.A. thanks the support from NSFC grant Nos. 11273060,
11333008, and State Key Development Program for Basic
Research of China (Nos. 2013CB834900 and 2015CB857000).
F.W. and X.-B.W. thank the support from the NSFC grants
No.11373008 and 11533001, the Strategic Priority Research
Program “The Emergence of Cosmological Structures” of the
Chinese Academy of Sciences, grant No. XDB09000000, and
the National Key Basic Research Program of China
2014CB845700
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