291 research outputs found
High-Resolution Spectroscopy from 3050 to 10000 A of the HDF-S QSO J2233-606 with UVES at the ESO VLT
We report on high-resolution observations () of the Hubble
Deep Field South QSO J2233-606 obtained with the VLT UV-Visual Echelle
Spectrograph (UVES). We present spectral data for the wavelength region \AA. The ratio of the final spectrum is about 50 per
resolution element at 4000 \AA, 90 at 5000 \AA, 80 at 6000 \AA, 40 at 8000 \AA.
Redshifts, column densities and Doppler widths of the absorption features have
been determined with Voigt-profile fitting. A total of 621 lines have been
measured. In particular 270 Ly-alpha lines, 41 Ly-beta and 24 systems
containing metal lines have been identified. Together with other data in the
literature, the present spectrum confirms that the evolution of the number
density of Ly-alpha lines with \huno has an upturn at .Comment: 34 pages Latex, with 3 PostScript figures. Astronomical Journal, in
press. A few revised upper limit
Measuring the Cosmological Geometry from the Lyman Alpha Forest along Parallel Lines of Sight
We discuss the feasibility of measuring the cosmological metric using the
redshift space correlation function of the Lya forest in multiple lines of
sight, as a function of angular and velocity separation. The geometric
parameter that is measured is f(z) = H(z) D(z)/c, where H(z) is the Hubble
constant and D(z) the angular diameter distance at redshift z. The correlation
function is computed in linear theory. We describe a method to measure it from
observations with the Gaussianization procedure of Croft et al (1998) to map
the Lya forest transmitted flux to an approximation of the linear density
field. The effect of peculiar velocities on the shape of the recovered power
spectrum is pointed out. We estimate the error in recovering the f(z) factor
from observations due to the variance in the Lya absorbers. We show that ~ 20
pairs of quasars (separations < 3') are needed to distinguish a flat \Omega_0=1
universe from a universe with \Omega_0=0.2, \Omega_\Lambda=0.8. A second
parameter that is obtained from the correlation function of the Lya forest is
\beta \simeq \Omega(z)^{0.6}/b (affecting the magnitude of the peculiar
velocities), where b is a linear theory bias of the Lya forest. The statistical
error of f(z) is reduced if b can be determined independently from numerical
simulations, reducing the number of quasar pairs needed for constraining
cosmology to approximately six. On small scales, where the correlation function
is higher, f(z) should be measurable with fewer quasars, but non-linear effects
must then be taken into account. The anisotropy of the non-linear redshift
space correlation function as a function of scale should also provide a precise
quantitative test of the gravitational instability theory of the Lya forest.Comment: submitted to Ap
Historical trade-offs of livestockâs environmental impacts
Human demand for animal products has risen markedly over the past 50 years with important environmental impacts. Dairy and cattle production have disproportionately contributed to greenhouse gas (GHG) emissions and land use, while crop demands of more intensive systems have increased fertilizer use and competition for available crop calories. At the same time, chicken and pig production has grown more rapidly than for ruminants, indicating a change in the environmental burden per animal calorie (EBC) with time. How EBCs have changed and to what extent resource use efficiency (RUE), the composition of animal production and the trade of feed have played a role in these changes have not been examined to date. We employ a calorie-based perspective, distinguishing animal calorie production between calories produced from feedcrop sourcesâdirectly competing with humans for available caloriesâand those from non-feed sourcesâplant biomass unavailable for direct human consumption. Combining this information with data on agricultural resource use, we calculate EBCs in terms of land, GHG emissions and nitrogen. We find that EBCs have changed substantially for land (â62%), GHGs (â46%) and nitrogen (+188%). Changes in RUE (e.g., selective breeding, increased grain-feeding) have been the primary contributor to these EBC trends, but shifts in the composition of livestock production were responsible for 12%â41% of the total EBC changes. In addition, the virtual trade of land for feed has more than tripled in the past 25 years with 77% of countries currently relying on virtual land imports to support domestic livestock production. Our findings indicate that important tradeoffs have occurred as a result of livestock intensification, with more efficient land use and emission rates exchanged for greater nitrogen use and increased competition between feed and food. This study provides an integrated evaluation of livestock's impact on food security and the environment
Large-Scale Correlations in the Lyman-alpha Forest at z = 3-4
We present a study of the spatial coherence of the intergalactic medium
toward two pairs of high-redshift quasars with moderate angular separations
observed with Keck/ESI, Q1422+2309A/Q1424+2255 (z_em = 3.63, theta = 39") and
Q1439-0034A/B (z_em = 4.25, theta = 33"). The crosscorrelation of transmitted
flux in the Lyman-alpha forest shows a 5-7 sigma peak at zero velocity lag for
both pairs. This strongly suggests that at least some of the absorbing
structures span the 230-300/h_70 proper kpc transverse separation between
sightlines. We also statistically examine the similarity between paired spectra
as a function of transmitted flux, a measure which may be useful for comparison
with numerical simulations. In investigating the dependence of the correlation
functions on spectral characteristics, we find that photon noise has little
impact for S/N >~ 10 per resolution element. However, the agreement between the
autocorrelation along the line sight and the crosscorrelation between
sightlines, a potential test of cosmological geometry, depends significantly on
instrumental resolution. Finally, we present an inventory of metal lines. These
include a a pair of strong C IV systems at z ~ 3.4 appearing only toward
Q1439B, and a Mg II + Fe II system present toward Q1439 A and B at z = 1.68.Comment: 33 pages, 13 figures, submitted to Ap
Ecohydrology of groundwater-dependent ecosystems: a stochastic framework for plant transpiration
Groundwater-dependent ecosystems are found in areas with a shallow water table, where the groundwater plays a key role on the ecosystem functions. In these areas, the water table depth, the capillary fluxes, and the soil moisture content exert a major control on most ecohydrologic processes, such as infiltration, surface runoff, aquifer recharge, land-atmosphere feedbacks, vegetation dynamics, nutrient cycling, and pollutant transport. Understanding and modeling the soil water balance and its relationships with climate, soil, and vegetation is therefore a crucial aspect for geosciences such as hydrology and ecology. The ecohydrology of groundwater-dependent ecosystems can be described with a modeling framework based on a stochastic process-based water balance. The model is driven by a compound marked Poisson noise representing the rainfall events and, under some simplifying, yet realistic, assumptions, it includes rainfall infiltration, root water uptake, capillary flux, and subsurface flow to/from an external water body. The framework provides the long-term probability distribution of water table depth and of soil moisture vertical profiles, enabling a quantitative study of the local hydrology with a limited number of parameters. We here apply this framework to investigate plant transpiration and root water uptake. The probability distributions of water uptake are derived from those of the soil water content and are investigated for different scenarios of climate, soil, and vegetation. The results of this approach allow for interesting speculations about the groundwater contribution to root uptake, the soil water available for plant transpiration, and the optimal strategies of root growth and plant competition. This information is useful to assess the impact of climate changes, vegetation modification, and water management operation
Ecohydrology of groundwater-dependent ecosystems: a stochastic framework for plant transpiration
Groundwater-dependent ecosystems are found in areas with a shallow water table, where the groundwater plays
a key role on the ecosystem functions. In these areas, the water table depth, the capillary fluxes, and the soil
moisture content exert a major control on most ecohydrologic processes, such as infiltration, surface runoff,
aquifer recharge, land-atmosphere feedbacks, vegetation dynamics, nutrient cycling, and pollutant transport.
Understanding and modeling the soil water balance and its relationships with climate, soil, and vegetation is
therefore a crucial aspect for geosciences such as hydrology and ecology.
The ecohydrology of groundwater-dependent ecosystems can be described with a modeling framework
based on a stochastic process-based water balance. The model is driven by a compound marked Poisson noise
representing the rainfall events and, under some simplifying, yet realistic, assumptions, it includes rainfall
infiltration, root water uptake, capillary flux, and subsurface flow to/from an external water body. The framework
provides the long-term probability distribution of water table depth and of soil moisture vertical profiles, enabling
a quantitative study of the local hydrology with a limited number of parameters.
We here apply this framework to investigate plant transpiration and root water uptake. The probability distributions
of water uptake are derived from those of the soil water content and are investigated for different
scenarios of climate, soil, and vegetation. The results of this approach allow for interesting speculations about
the groundwater contribution to root uptake, the soil water available for plant transpiration, and the optimal
strategies of root growth and plant competition. This information is useful to assess the impact of climate changes,
vegetation modification, and water management operation
Photometric redshifts and selection of high redshift galaxies in the NTT and Hubble Deep Fields
We present and compare in this paper new photometric redshift catalogs of the
galaxies in three public fields: the NTT Deep Field, the HDF-N and the HDF-S.
Photometric redshifts have been obtained for thewhole sample, by adopting a
minimization technique on a spectral library drawn from the Bruzual
and Charlot synthesis models, with the addition of dust and intergalactic
absorption. The accuracy, determined from 125 galaxies with known spectroscopic
redshifts, is in the redshift intervals . The global redshift distribution of I-selected galaxies shows a
distinct peak at intermediate redshifts, z~0.6 at I_{AB}<26 and z~0.8 at
I_{AB}<27.5 followed by a tail extending to z~6. We also present for the first
time the redshift distribution of the total IR-selected sample to faint limits
( and ). It is found that the number density of galaxies
at 1.25<z<1.5 is ~ 0.1 /arcmin^22 at J<=21 and ~1./arcmin^2} at J<22, and drops
to 0.3/arcmin^2 (at J<22) at 1.5<z<2. The HDFs data sets are used to compare
the different results from color selection criteria and photometric redshifts
in detecting galaxies in the redshift range 3.5<z<4.5 Photometric redshifts
predict a number of high z candidates in both the HDF-N and HDF-S that is
nearly 2 times larger than color selection criteria, and it is shown that this
is primarily due to the inclusion of dusty models that were discarded in the
original color selection criteria by Madau et al 1998. In several cases, the
selection of these objects is made possible by the constraints from the IR
bands. Finally, it is shown that galactic M stars may mimic z>5 candidates in
the HDF filter set and that the 4 brightest candidates at in the HDF-S
are indeed most likely M stars. (ABRIDGED)Comment: Version accepted on July, 20, 2000. To appear on Astronomical
Journal, Nov 2000. The data and photometric redshift catalogs presented here
are available on line at http://www.mporzio.astro.it/HIGH
What Produced the Ultraluminous Supernova Remnant in NGC 6946?
The ultraluminous supernova remnant (SNR) in NGC 6946 is the brightest known
SNR in X-rays, ~1000 times brighter than Cas A. To probe the nature of this
remnant and its progenitor, we have obtained high-dispersion optical echelle
spectra. The echelle spectra detect H-alpha, [N II], and [O III] lines, and
resolve these lines into a narrow (FWHM ~20--40 km/s) component from un-shocked
material and a broad (FWHM ~250 km/s) component from shocked material. Both
narrow and broad components have unusually high [N II]/H-alpha ratios, ~1.
Using the echelle observation, archival HST images, and archival ROSAT X-ray
observations, we conclude that the SNR was produced by a normal supernova,
whose progenitor was a massive star, either a WN star or a luminous blue
variable. The high luminosity of the remnant is caused by the supernova ejecta
expanding into a dense, nitrogen-rich circumstellar nebula created by the
progenitor.Comment: 20 pages, 5 figures. To be published in The Astronomical Journal,
March 200
Toward a Measurement of the Cosmological Geometry at z~2: Predicting Lyman-alpha Forest Correlation in Three Dimensions, and the Potential of Future Data Sets
The correlation between Lyman-alpha absorption in the spectra of quasar pairs
can be used to measure the transverse distance scale at z~2, which is sensitive
to the cosmological constant (Omega_Lambda) or other forms of vacuum energy.
Using Hydro-PM simulations, I compute the three-dimensional power spectrum of
the Lyman-alpha forest flux, P_F(k,mu), from which the redshift-space
anisotropy of the correlation can be obtained. I find that box size ~40 Mpc/h
and resolution ~40 Kpc/h are necessary for convergence of the calculations to
<5% on all relevant scales, although somewhat poorer resolution can be used for
large scales. I compute directly the linear theory bias parameters of the
Lyman-alpha forest, potentially allowing simulation results to be extended to
arbitrarily large scales. I investigate the dependence of P_F(k,mu) on the
primordial power spectrum, the temperature-density relation of the gas, and the
mean flux decrement, finding that the redshift-space anisotropy is relatively
insensitive to these parameters. A table of results is provided for different
parameter variations. I investigate the constraint that can be obtained on
Omega_Lambda using quasars from a large survey. Assuming 13 (theta/1')^2 pairs
at separation <theta, and including separations <10', a measurement to <5% can
be made if simulations can predict the redshift-space anisotropy with <5%
accuracy, or to <10% if the anisotropy must be measured from the data. The
Sloan Digital Sky Survey (SDSS) will obtain spectra for a factor ~5 fewer pairs
than this, so followup observations of fainter pair candidates will be
necessary. I discuss the requirements on spectral resolution and
signal-to-noise ratio (SDSS-quality spectra are sufficient).Comment: Submitted to ApJ, 47 page
UVES observations of QSO 0000-2620: oxygen and zinc abundances in the Damped Ly-alpha galaxy at z_abs=3.3901
Observations of the QSO 0000-2620 with UVES spectrograph at the 8.2m ESO
KUEYEN telescope are used for abundance analysis of the damped Ly-alpha system
at z_{abs}=3.3901. Several Oxygen lines are identified in the Ly_alpha forest
and a measure for the oxygen abundance is obtained at [O/H]=-1.85 +/- 0.1 by
means of the unsaturated OI 925 A and OI 950 A lines. This represents the most
accurate O measurement in a damped Ly_alpha galaxy so far. We have also
detected ZnII 2026 A and CrII 2056, 2062 A redshifted at about 8900 A and found
abundances [Zn/H] = -2.07 +/- 0.1 and [Cr/H]=-1.99 +/- 0.1. Furthermore,
previous measurements of Fe, Si, Ni and N have been refined yielding
[Fe/H]=-2.04 +/- 0.1, [Si/H]=-1.90 +/- 0.1, [Ni/H]=-2.27 +/- 0.1, and
[N/H]=-2.68 +/- 0.1. The abundance of the non-refractory element zinc is the
lowest among the damped Ly-alpha systems showing that the associated
intervening galaxy is indeed in the early stages of its chemical evolution. The
fact that the Zn abundance is identical to that of the refractory elements Fe
and Cr suggests that dust grains have not formed yet. In this Damped Ly-alpha
system the observed [O,S,Si/Zn,Fe,Cr] ratios, in whatever combination are
taken, are close to solar (i.e 0.1-0.2 dex) and do not show the
[alpha-element/Fe] enhancement observed in Milky Way stars of comparable
metallicity. The observed behavior supports a galaxy evolution model
characterized by either episodic or low star formation rate rather than a
Milky-Way-type evolutionary model.Comment: Accepted by Ap
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