96 research outputs found
MApping the Most Massive Overdensities (MAMMOTH) II -- Discovery of an Extremely Massive Overdensity BOSS1441 at
Cosmological simulations suggest a strong correlation between high
optical-depth Ly absorbers, which arise from the intergalactic medium
(IGM), and 3-D mass overdensities on scales of comoving Mpc.
By examining the absorption spectra of 80,000 QSO sight-lines over a
volume of 0.1 Gpc in the Sloan Digital Sky Survey III (SDSS-III), we have
identified an extreme overdensity, BOSS1441, which contains a rare group of
strong Ly absorbers at . This absorber group is
associated with six QSOs at the same redshift on a 30 comoving Mpc scale. Using
Mayall/MOSAIC narrowband and broadband imaging, we detect Ly emitters
(LAEs) down to , and reveal a large-scale
structure of Ly emitters (LAEs) in this field. Our follow-up Large
Binocular Telescope (LBT) observations have spectroscopically confirmed 19
galaxies in the density peak. We show that BOSS1441 has an LAE overdensity of
on a 15 comoving Mpc scale which could collapse to a massive
cluster with M at . This overdensity is among
the most massive large-scale structures at discovered to date.Comment: 12 pages, 8 figures. submitted to ApJ, Comments are welcom
Constraining Very High Mass Population III Stars through He II Emission in Galaxy BDF-521 at z = 7.01
Numerous theoretical models have long proposed that a strong He II 1640
emission line is the most prominent and unique feature of massive Population
III (Pop III) stars in high redshift galaxies. The He II 1640 line strength can
constrain the mass and IMF of Pop III stars. We use F132N narrowband filter on
the Hubble Space Telescope's (HST) Wide Field Camera 3 (WFC3) to look for
strong He II lambda 1640 emission in the galaxy BDF-521 at z=7.01, one of the
most distant spectroscopically-confirmed galaxies to date. Using deep F132N
narrowband imaging, together with our broadband imaging with F125W and F160W
filters, we do not detect He II emission from this galaxy, but place a 2-sigma
upper limit on the flux of 5.3x10^-19 ergs s^-1 cm^-2. This measurement
corresponds to a 2-sigma upper limit on the Pop III star formation rate
(SFR_PopIII) of ~ 0.2 M_solar yr^-1, assuming a Salpeter IMF with 50< M/M_solar
< 1000. From the high signal-to-noise broadband measurements in F125W and
F160W, we fit the UV continuum for BDF-521. The spectral flux density is ~ 3.6x
10^-11 lambda^-2.32 ergs s^-1 cm^-2 A^-1, which corresponds to an overall
unobscured SFR of ~ 5 M_solar yr^-1. Our upper limit on SFR_PopIII suggests
that massive Pop III stars represent < 4% of the total star formation. Further,
the HST high resolution imaging suggests that BDF-521 is an extremely compact
galaxy, with a half-light radius of 0.6 kpc.Comment: 14 pages, 2 figures, Accepted for Publication in ApJ
Effects of wave parameters on load reduction performance for amphibious aircraft with V-hydrofoil
An investigation of the influence of the hydrofoil on load reduction
performance during an amphibious aircraft landing on still and wavy water is
conducted by solving the Unsteady Reynolds-Averaged Navier-Stokes equations
coupled with the standard turbulence model in this paper. During the
simulations, the numerical wave tank is realized by using the velocity-inlet
boundary wave maker coupled with damping wave elimination technique on the
outlet, while the volume of fluid model is employed to track the water-air
interface. Subsequently, the effects of geometric parameters of hydrofoil have
been first discussed on still water, which indicates the primary factor
influencing the load reduction is the static load coefficient of hydrofoil.
Furthermore, the effects of descent velocity, wave length and wave height on
load reduction are comprehensively investigated. The results show that the
vertical load reduces more than 55 at the early stage of landing on the
still water through assembling the hydrofoil for different descent velocity
cases. Meanwhile, for the amphibious aircraft with high forward velocity, the
bottom of the fuselage will come into close contact with the first wave when
landing on crest position, and then the forebody will impact the next wave
surface with extreme force. In this circumstance, the load reduction rate
decreases to around 30, which will entail a further decline with the
increase of wave length or wave height
Experiment of Carbonate Dissolution: Implication for High Quality Carbonate Reservoir Formation in Deep and Ultradeep Basins
Dust emission in an accretion-rate-limited sample of z>6 quasars
We present Atacama Large Millimeter Array 1mm observations of the rest-frame
far-infrared (FIR) dust continuum in 27 quasars at redshifts 6.0 < z < 6.7. We
detect FIR emission at >3sigma in all quasar host galaxies with flux densities
at ~1900GHz in the rest-frame of 0.12 < S_rest,1900GHz < 5.9mJy, with a median
(mean) flux density of 0.88mJy (1.59mJy). The implied FIR luminosities range
from L_FIR = (0.27-13)x10^12 L_sun, with 74% of our quasar hosts having L_FIR >
10^12 L_sun. The estimated dust masses are M_dust = 10^7-10^9 M_sun. If the
dust is heated only by star formation, then the star formation rates in the
quasar host galaxies are between 50 and 2700 M_sun/yr. In the framework of the
host galaxy-black hole coevolution model a correlation between ongoing black
hole growth and star formation in the quasar host galaxy would be expected.
However, combined with results from the literature to create a
luminosity-limited quasar sample, we do not find a strong correlation between
quasar UV luminosity (a proxy for ongoing black hole growth) and FIR luminosity
(star formation in the host galaxy). The absence of such a correlation in our
data does not necessarily rule out the coevolution model, and could be due to a
variety of effects (including different timescales for black hole accretion and
FIR emission).Comment: 14 pages, 5 figures. Published in ApJ (Venemans et al. 2018, ApJ 866,
159
Effects of KevlarÂź 29 yarn twist on tensile and tribological properties of self-lubricating fabric liner
Yarn twist in textile technology is an important characteristic since it considerably affects the properties of knitted or woven fabrics. Many researchers have investigated the effect of staple-spun yarn twist on the properties of the yarns and fabrics. However, the effects of twist level of KevlarÂź 29 filament yarn on the properties of yarn and its resin-impregnated self-lubricating fabric liner are not fully known yet. In this study, we have investigated the effects of KevlarÂź 29 twist level on the tensile and tribological properties of the fabric liner (KevlarÂź 29/polytetrafluoroethylene fabric-resin composite). Two unexpected findings about the effect of yarn twist have been observed, namely (1) asynchronous twist effect on the yarnâs and the linerâs tensile strength and (2) dissimilar yarn twist effect on the linerâs performance. These findings are mainly attributed to the synergic contributions of the yarn twist and strength and the interaction of the resin with the yarn orientation in the woven fabric structure of the liner
CRISPR/Cas9âmediated restoration of Tamyb10 to create preâharvest sproutingâresistant red wheat
ALMA and HST Kiloparsec-scale Imaging of a Quasar-galaxy Merger at Z â 6.2
We present kiloparsec-scale Atacama Large Millimeter/submillimeter Array (ALMA) and Hubble Space Telescope imaging of the quasar PJ308â21 at z = 6.2342, tracing dust, gas (via the [C II] 158 ÎŒm line), and young stars. At a resolution of ~0.â3 (â1.7 kpc), the system is resolved over >4'' (>20 kpc). In particular, it features a main component, identified to be the quasar host galaxy, centered on the accreting supermassive black hole; and two other extended components are on the west and east side: one redshifted and the other blueshifted relative to the quasar. The [C II] emission of the entire system stretches over >1500 km s^(â1) along the line of sight. All the components of the system are observed in dust, [C II], and rest-frame ultraviolet (UV) emission. The inferred [C II] luminosities [(0.9â4.6)Ă10^9 Lâ]; dust luminosities [(0.15â2.6)Ă10^(12) Lâ]; rest-frame UV luminosities [(6.6â15)Ă10^(10) Lâ], their ratios, and the implied gas/dust masses; and star formation rates [11â290 Mâ yr^(â1)] are typical of high-redshift star-forming galaxies. A toy model of a single satellite galaxy that is tidally stripped by the interaction with the quasar host galaxy can account for the observed velocity and spatial extent of the two extended components. An outflow interpretation of the unique features in PJ308â21 is not supported by the data. PJ308â21 is thus one of the earliest galaxy mergers imaged at cosmic dawn
An ALMA [CII] survey of 27 quasars at z>5.94
We present a survey of the [CII] 158 m line and underlying far-infrared
(FIR) dust continuum emission in a sample of 27 z>6 quasars using the Atacama
Large Millimeter Array (ALMA) at ~1" resolution. The [CII] line was
significantly detected (at >5-sigma) in 23 sources (85%). We find typical line
luminosities of L, and an average line width
of ~385 km/s. The [CII]-to-far-infrared luminosity ratio ([CII]/FIR) in our
sources span one order of magnitude, highlighting a variety of conditions in
the star-forming medium. Four quasar host galaxies are clearly resolved in
their [CII] emission on a few kpc scales. Basic estimates of the dynamical
masses of the host galaxies give masses between and
M, i.e., more than an order of magnitude below what is
expected from local scaling relations, given the available limits on the masses
of the central black holes ( M, assuming
Eddington-limited accretion). In stacked ALMA [CII] spectra of individual
sources in our sample, we find no evidence of a deviation from a single
Gaussian profile. The quasar luminosity does not strongly correlate with either
the [CII] luminosity or equivalent width. This survey (with typical on-source
integration times of 8 min) showcases the unparalleled sensitivity of ALMA at
millimeter wavelengths, and offers a unique reference sample for the study of
the first massive galaxies in the universe.Comment: Accepted for publication in the Astrophysical Journa
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