2,932 research outputs found
The Polarized Spectrum of Apm 08279+5255
We report the discovery of significant linear polarization (p > 1%) in the
hyperluminous z=3.87 BALQSO APM~08279+5255. The polarization spectrum is
complex, with properties similar to those of other, lower redshift but more
highly polarized BALQSOs. The resonance emission lines are unpolarized while
the absorption troughs show polarization similar to or higher than the
continuum. In particular, an apparent increase of polarization in the trough
covering 1000-1030 angstroms (rest) supports the interpretation of this feature
as a broad absorption component associated with OVI/Ly_beta local to the QSO,
as opposed to an intervening damped Ly_alpha absorption system.
The elevated polarization in some of the absorption features implies that we
view the scattered (polarized) spectrum through a sightline with less absorbing
material than the direct spectrum. Therefore, the complex structure of the
polarization spectrum in this brilliant lensed BALQSO suggests that it will be
an important laboratory for studying the structure of QSOs at high redshift.Comment: 8 pages, 1 figure. Accepted for publication in The Astrophysical
Journal Letter
Effect of phytase on phytate P utilization by turkeys
An in vitro method was developed for poultry to predict inorganic phosphorus release from maize-soya bean feeds containing supplemental phytase (E.C. 3.1.3.8), and to quantify the effect of acid phosphatase (E.C. 3.1,3.2.), fungal protease (E.C. 3.4.23.6) and Aspergillus niger cellulase (E.C. 3.2.1.4.) on phytate dephosphorylation. Pepsin and pancreatin digestion periods were preceded by a 30 min preincubation at pH 5.25 to simulate digestion in the crop of poultry. Pancreatin digestion was carried out in dialysis tubings, with a ratio of about 1:25 (v/v) between the digesta and dialyzing medium, to simulate gradient absorption from the duodenum. The feed/water ratio was kept within physiological limits and a constant feed weight to digestive enzymes was maintained. There was a linear response to increasing dosages of phytase up to 1000 FTU/kg feed, and to increasing phosphate concentration in feeds. In vivo validation was performed with growing turkeys (1-3 wk) fed diets containing 12 g/kg of calcium; 0, 500, 1000 FTU/kg of phytase in a factorial arrangement with 0, 1, 2, 3 g/kg of supplemental phosphate (from KH2PO4). After a simple transformation (variable/in vitro phosphorus = f (in vitro phosphorus)) amounts of phosphorus hydrolyzed from feed samples by in vitro digestions correlated with the 3 week body weight gains (R= 0.986 P [less than] 0.0001), toe ash (R=0.952 P [less than] 0.0001), feed intake (R=0.994 P [less than] 0.0001) and feed efficiency (R=0.992 P [less than] 0.0001). The dephosphorylating ability of phytase in vitro was significantly enhanced (P [less than] 0.05) by the addition of acid phosphatase. Fungal acid protease and Aspergillus niger cellulase also enhanced the dephosphorylation process in vitro.Project # G-2029-01 Agreement # 14-08-0001-G-2029-0
Partial covering of emission regions of Q 0528-250 by intervening H clouds
We present an analysis of the molecular hydrogen absorption system at z = 2.811 in the spectrum of the blazar Q0528-250. We demonstrate that the
molecular cloud does not cover the background source completely. The partial
coverage reveals itself as a residual flux in the bottom of saturated H_2
absorption lines. This amounts to about (2.220.54)% of the continuum and
does not depend on the wavelength. This value is small and it explains why this
effect has not been detected in previous studies of this quasar spectrum.
However, it is robustly detected and significantly higher than the zero flux
level in the bottom of saturated lines of the Ly-alpha forest,
(-0.210.22)%. The presence of the residual flux could be caused by
unresolved quasar multicomponents, by light scattered by dust, and/or by
jet-cloud interaction. The H absorption system is very well described by a
two-component model without inclusion of additional components when we take
partial coverage into account. The derived total column densities in the H
absorption components A and B are logN(H)[cm] = 18.100.02 and
17.820.02, respectively. HD molecules are present only in component B.
Given the column density, logN(HD)= 13.330.02, we find
N(HD)/2N(H)=(1.480.10)x10, significantly lower than previous
estimations. We argue that it is crucial to take into account partial coverage
effects for any analysis of H bearing absorption systems, in particular
when studying the physical state of high-redshift interstellar medium.Comment: Accepted for MNRA
Neutral chlorine and molecular hydrogen at high redshift
Chlorine and molecular hydrogen are known to be tightly linked together in
the cold phase of the local interstellar medium through rapid chemical
reactions. We present here the first systematic study of this relation at high
redshifts using H-bearing damped Ly systems (DLAs) detected along
quasar lines of sight. Using high-resolution spectroscopic data from VLT/UVES
and Keck/HIRES, we report the detection of ClI in 9 DLAs (including 5 new
detections) out of 18 high- DLAs with Hcm
(including a new H detection at towards J21000641) and
present upper limits for the remaining 9 systems. We find a 5
correlation between (ClI) and (H) with only 0.2dex
dispersion over the range 18.1log(H)20.1, thus probing
column densities 10 times lower those seen towards nearby stars, roughly
following the relation (ClIH.
This relation between column densities is surprisingly the same at low and high
redshift suggesting that the physical and chemical conditions are similar for a
given H (or ClI) column density. In turn, the N({Cl\,I})/N({\rm
H_2}) ratio is found to be uncorrelated with the overall metallicity in the
DLA. Our results confirm that neutral chlorine is an excellent tracer of
molecule-rich gas and show that the molecular fraction or/and metallicity in
the H-bearing component of DLA could possibly be much higher than the
line-of-sight average values usually measured in DLAs.Comment: 5 pages, 3 figures, Accepted for publication in A&A Letter
HD Molecular Lines in an Absorption System at Redshift z = 2.3377
We have analyzed the spectrum of the quasar PKS 1232+082 obtained by
Petitjean et al. (2000). HD molecular lines are identified in an absorption
system at the redshift z=2.3377. The column density of HD molecules in the
system is estimated, N(HD)=(1-4)x10^{14} cm^{-2}. The temperature of excitation
of the first rotational level J=1 relative to the ground state J=0 is
T_ex=70+-7 K. This is, to our knowledge, the first detection of HD molecules at
high redshift.Comment: 7 pages, 1 figure, accepted for publication in "Astronomy Letters
Sparsity and Incoherence in Compressive Sampling
We consider the problem of reconstructing a sparse signal from a
limited number of linear measurements. Given randomly selected samples of
, where is an orthonormal matrix, we show that minimization
recovers exactly when the number of measurements exceeds where is the number of
nonzero components in , and is the largest entry in properly
normalized: . The smaller ,
the fewer samples needed.
The result holds for ``most'' sparse signals supported on a fixed (but
arbitrary) set . Given , if the sign of for each nonzero entry on
and the observed values of are drawn at random, the signal is
recovered with overwhelming probability. Moreover, there is a sense in which
this is nearly optimal since any method succeeding with the same probability
would require just about this many samples
Promovendo a formação agroflorestal na região Pan-Amazônica: curso internacional de capacitação em tecnologias agroflorestais.
CO-dark molecular gas at high redshift: very large H content and high pressure in a low metallicity damped Lyman-alpha system
We present a detailed analysis of a H-rich, extremely strong intervening
Damped Ly- Absorption system (DLA) at towards the
quasar J0843+0221, observed with the Ultraviolet and Visual Echelle
Spectrograph on the Very Large Telescope. The total column density of molecular
(resp. atomic) hydrogen is (H)= (resp. (HI)=), making it to be the first case in quasar absorption
lines studies with H column density as high as what is seen in
CO-selected clouds in the Milky-Way.
We find that this system has one of the lowest metallicity detected among
H-bearing DLAs, with . This can be the
reason for the marked differences compared to systems with similar H column
densities in the local Universe: the kinetic temperature, 120~K,
derived from the H rotational levels is at least twice higher than
expected; there is little dust extinction with A; no
CO molecules are detected, putting a constraint on the factor
cm/(km/s\,K), in the very low metallicity
gas. Low CO and high H contents indicate that this system represents
"CO-dark/faint" gas.
We investigate the physical conditions in the H-bearing gas using the
fine-structure levels of CI, CII, SiII and the rotational levels of
HD and H. We find the number density to be about cm, implying a high thermal pressure of cmK. We further identify a trend of increasing pressure with
increasing total hydrogen column density. This independently supports the
suggestion that extremely strong DLAs (with N(H) ) probe
high-z galaxies at low impact parameters.Comment: 21 pages, 21 figures. Accepted for publication in MNRA
A clumpy and anisotropic galaxy halo at z=1 from gravitational-arc tomography
Every star-forming galaxy has a halo of metal-enriched gas extending out to
at least 100 kpc, as revealed by the absorption lines this gas imprints on the
spectra of background quasars. However, quasars are sparse and typically probe
only one narrow pencil beam through the intervening galaxy. Close quasar pairs
and gravitationally lensed quasars have been used to circumvent this inherently
one-dimensional technique, but these objects are rare and the structure of the
circum-galactic medium remains poorly constrained. As a result, our
understanding of the physical processes that drive the re-cycling of baryons
across the lifetime of a galaxy is limited. Here we report integral-field
(tomographic) spectroscopy of an extended background source -a bright giant
gravitational arc. We can thus coherently map the spatial and kinematic
distribution of Mg II absorption -a standard tracer of enriched gas- in an
intervening galaxy system at redshift 0.98 (i.e., ~8 Gyr ago). Our
gravitational-arc tomography unveils a clumpy medium in which the
absorption-strength decreases with increasing impact parameter, in good
agreement with the statistics towards quasars; furthermore, we find strong
evidence that the gas is not distributed isotropically. Interestingly, we
detect little kinematic variation over a projected area of ~600 kpc squared,
with all line-of-sight velocities confined to within a few tens of km/s of each
other. These results suggest that the detected absorption originates from
entrained recycled material, rather than in a galactic outflow.Comment: Published online in Nature on 31 January 201
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