226 research outputs found
The Nature and Origin of Low-Redshift O VI Absorbers
The O VI ion observed in quasar absorption line spectra is the most
accessible tracer of the cosmic metal distribution in the low redshift (z<0.5)
intergalactic medium (IGM). We explore the nature and origin of O VI absorbers
using cosmological hydrodynamic simulations including galactic outflows. We
consider the effects of ionization background variations, non-equilibrium
ionization and cooling, uniform metallicity, and small-scale (sub-resolution)
turbulence. Our main results are 1) IGM O VI is predominantly photo-ionized
with T= 10^(4.2+/-0.2) K. A key reason for this is that O VI absorbers
preferentially trace over-enriched regions of the IGM at a given density, which
enhances metal-line cooling such that absorbers can cool within a Hubble time.
As such, O VI is not a good tracer of the WHIM. 2) The predicted O VI
properties fit observables only if sub-resolution turbulence is added. The
required turbulence increases with O VI absorber strength such that stronger
absorbers arise from more recent outflows with turbulence dissipating on the
order of a Hubble time. The amount of turbulence is consistent with other
examples of turbulence observed in the IGM and galactic halos. 3) Metals traced
by O VI and H I do not trace exactly the same baryons, but reside in the same
large-scale structure. Observed alignment statistics are reproduced in our
simulations. 4) Photo-ionized O VI traces gas in a variety of environments, and
is not directly associated with the nearest galaxy, though is typically nearest
to ~0.1L* galaxies. Weaker O VI components trace some of the oldest cosmic
metals. 5) Very strong absorbers are more likely to be collisionally ionized,
tracing more recent enrichment (<2 Gyr) within or near galactic halos.Comment: 33 pages, 18 figures, accepted to MNRAS. Two new figures adde
nifH pyrosequencing reveals the potential for location-specific soil chemistry to influence N2-fixing community dynamics
A dataset of 87 020 nifH reads and 16 782 unique nifH protein sequences obtained over 2 years from four locations across a gradient of agricultural soil types in Argentina were analysed to provide a detailed and comprehensive picture of the diversity, abundance and responses of the N2-fixing community in relation to differences in soil chemistry and agricultural practices. Phylogenetic analysis revealed an expected high proportion of Alphaproteobacteria, Betaproteobacteria and Deltaproteobacteria, mainly relatives to Bradyrhizobium and Methylosinus/Methylocystis, but a surprising paucity of Gammaproteobacteria. Analysis of variance and stepwise regression modelling suggested location and treatment-specific influences of soil type on diazotrophic community composition and organic carbon concentrations on nifH diversity. nifH gene abundance, determined by quantitative real-time polymerase chain reaction, was higher in agricultural soils than in non-agricultural soils, and was influenced by soil chemistry under intensive crop rotation but not under monoculture. At some locations, sustainable increased crop yields might be possible through the management of soil chemistry to improve the abundance and diversity of N2-fixing bacteriaFil: Collavino, Mónica Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Nordeste. Instituto de Botánica del Nordeste (i); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Instituto de Biotecnología y Biología Molecular; ArgentinaFil: Tripp, H. James. University of California. Department of Ocean Sciences; Estados UnidosFil: Frank, Ildiko E.. University of California. Department of Ocean Sciences; Estados UnidosFil: Vidoz, María Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Nordeste. Instituto de Botánica del Nordeste (i); ArgentinaFil: Calderoli, Priscila Anabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Instituto de Biotecnología y Biología Molecular; ArgentinaFil: Donato, Mariano Humberto. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Laboratorio de Sistemática y Biología Evolutiva; ArgentinaFil: Zehr, Jonathan P.. University of California. Department of Ocean Sciences; Estados UnidosFil: Aguilar, Orlando Mario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Instituto de Biotecnología y Biología Molecular; Argentin
Cepheid Calibration of the Peak Brightness of SNe Ia. X. SN 1991T in NGC 4527
Repeated imaging observations have been made of NGC 4527 with the Hubble
Space Telescope between April and June 1999, over an interval of 69 days.
Images were obtained on 12 epochs in the F555W band and on five epochs in the
F814W band. The galaxy hosted the type Ia supernova SN1991T, which showed
relatively unusual behavior by having both an abnormal spectrum near light
maximum, and a slower declining light curve than the proto-typical Branch
normal SNe Ia.
A total of 86 variables that are putative Cepheids have been found, with
periods ranging from 7.4 days to over 70 days. From photometry with the DoPHOT
program, the de-reddened distance modulus is determined to be (m-M)_0 = 30.67
+/- 0.12 (internal uncertainty) using a subset of the Cepheid data whose
reddening and error parameters are secure. A parallel analysis of the Cepheids
using photometry with ROMAFOT yields (m -M)_0 =30.82 +/- 0.11. The final
adopted modulus is (m -M)_0 =30.74 +/- 0.12 +/- 0.12 (d=14.1 +/- 0.8 +/- 0.8
Mpc).
The photometric data for SN1991T are used in combination with the Cepheid
distance to NGC 4527 to obtain the absolute magnitude for this supernova of
M_V^0(max) = -19.85 +/- 0.29. The relatively large uncertainty is a result of
the range in estimates of the reddening to the supernova. Thus SN1991T is seen
to be only moderately brighter (by ~ 0.3 mag) than the mean for
spectroscopically normal supernovae, although magnitude differences of up to
0.6 mag cannot be ruled out.Comment: 46 pages, LATEX using aaspp4.sty, including 9 embedded tables, 19
figures (gif and jpg files), a full-resolution version (ps files) is
available at http://www.astro.unibas.ch/forschung/ll/cepheid.shtml, accepted
for publication in the Astrophysical Journa
Star Formation Feedback and Metal Enrichment History Of The Intergalactic Medium
Using hydrodynamic simulations we compute the metal enrichment history of the
intergalactic medium (IGM). We show that galactic superwind (GSW) feedback can
transport metals to the IGM and that the properties of simulated metal
absorbers match observations. The distance of influence of GSW is typically
limited to >0.5Mpc and within regions of overdensity >10. Most CIV and OVI
absorbers are located within shocked regions of elevated temperature
(T>2x10^4K), overdensity (>10), and metallicity ([-2.5,-0.5]). OVI absorbers
have typically higher metallicity, lower density and higher temperature than
CIV absorbers. For OVI absorbers collisional ionization dominates over the
entire redshift range z=0-6, whereas for CIV absorbers the transition occurs at
moderate redshift z~3 from collisionally dominated to photoionization
dominated. We find that the observed column density distributions for CIV and
OVI in the range log N cm^2=12-15 are reasonably reproduced by the simulations.
The evolution of mass densities contained in CIV and OVI lines, Omega_CIV and
Omega_OVI, is also in good agreement with observations, which shows a near
constancy at low redshifts and an exponential drop beyond redshift z=3-4. For
both CIV and OVI, most absorbers are transient and the amount of metals probed
by CIV and OVI lines of column log N cm^2=12-15 is only ~2% of total metal
density at any epoch. While gravitational shocks from large-scale structure
formation dominate the energy budget (80-90%) for turning about 50% of IGM to
the warm-hot intergalactic medium (WHIM) by z=0, GSW feedback shocks are
energetically dominant over gravitational shocks at z > 1-2. Most of the
so-called "missing metals" at z=2-3 are hidden in a warm-hot (T=10^{4.5-7}K)
gaseous phase, heated up by GSW feedback shocks. Their mass distribution is
broadly peaked at in the IGM, outside virialized halos.Comment: 52 pages, 26 figures, published in the Astrophysical Journal, 2011,
ApJ, 731, 1
Petroleomic analysis of the treatment of naphthenic organics in oil sands process-affected water with buoyant photocatalysts
The final publication is available at Elsevier via https://dx.doi.org/10.1016/j.watres.2018.05.011 © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/The persistence of toxicity associated with the soluble naphthenic organic compounds (NOCs) of oil sands process-affected water (OSPW) implies that a treatment solution may be necessary to enable safe return of this water to the environment. Due to recent advances in high-resolution mass spectrometry (HRMS), the majority of the toxicity of OSPW is currently understood to derive from a subset of toxic classes, comprising only a minority of the total NOCs. Herein, oxidative treatment of OSPW with buoyant photocatalysts was evaluated under a petroleomics paradigm: chemical changes across acid-, base- and neutral-extractable organic fractions were tracked throughout the treatment with both positive and negative ion mode electrospray ionization (ESI) Orbitrap MS. Elimination of detected OS+ and NO+ classes of concern in the earliest stages of the treatment, along with preferential degradation of high carbon-numbered O2− acids, suggest that photocatalysis may detoxify OSPW with higher efficiency than previously thought. Application of petroleomic level analysis offers unprecedented insights into the treatment of petroleum impacted water, allowing reaction trends to be followed across multiple fractions and thousands of compounds simultaneously.Natural Sciences and Engineering Research Council of CanadaNSERC Vanier Canada Graduate ScholarshipOntario Graduate Scholarshi
A Population of X-ray Weak Quasars: PHL 1811 Analogs at High Redshift
We report the results from Chandra and XMM-Newton observations of a sample of
10 type 1 quasars selected to have unusual UV emission-line properties (weak
and blueshifted high-ionization lines; strong UV Fe emission) similar to those
of PHL 1811, a confirmed intrinsically X-ray weak quasar. These quasars were
identified by the Sloan Digital Sky Survey at high redshift (z~2.2); eight are
radio quiet while two are radio intermediate. All of the radio-quiet PHL 1811
analogs are notably X-ray weak by a mean factor of ~13. These sources lack
broad absorption lines and have blue UV/optical continua, suggesting they are
intrinsically X-ray weak. However, their average X-ray spectrum appears to be
harder than those of typical quasars, which may indicate the presence of heavy
intrinsic X-ray absorption. Our radio-quiet PHL 1811 analogs support a
connection between an X-ray weak spectral energy distribution and PHL 1811-like
UV emission lines; this connection provides an economical way to identify X-ray
weak type 1 quasars. The fraction of radio-quiet PHL 1811 analogs in the
radio-quiet quasar population is estimated to be < 1.2%. We have investigated
correlations between relative X-ray brightness and UV emission-line properties
for a sample combining radio-quiet PHL 1811 analogs, PHL 1811, and typical type
1 quasars. These correlation analyses suggest that PHL 1811 analogs may have
extreme wind-dominated broad emission-line regions. Observationally,
radio-quiet PHL 1811 analogs appear to be a subset (~30%) of radio-quiet
weak-line quasars. The existence of a subset of quasars in which
high-ionization "shielding gas" covers most of the BELR, but little more than
the BELR, could potentially unify the PHL 1811 analogs and WLQs. The two
radio-intermediate PHL 1811 analogs are X-ray bright. One of them appears to
have jet-dominated X-ray emission, while the nature of the other remains
unclear.Comment: ApJ accepted; 25 pages, 11 figures and 8 table
Reconstructing the Cosmic Velocity and Tidal Fields with Galaxy Groups Selected from the Sloan Digital Sky Survey
[abridge]Cosmic velocity and tidal fields are important for the understanding
of the cosmic web and the environments of galaxies, and can also be used to
constrain cosmology. In this paper, we reconstruct these two fields in SDSS
volume from dark matter halos represented by galaxy groups. Detailed mock
catalogues are used to test the reliability of our method against uncertainties
arising from redshift distortions, survey boundaries, and false identifications
of groups by our group finder. We find that both the velocity and tidal fields,
smoothed on a scale of ~2Mpc/h, can be reliably reconstructed in the inner
region (~66%) of the survey volume. The reconstructed tidal field is used to
split the cosmic web into clusters, filaments, sheets, and voids, depending on
the sign of the eigenvalues of tidal tensor. The reconstructed velocity field
nicely shows how the flows are diverging from the centers of voids, and
converging onto clusters, while sheets and filaments have flows that are
convergent along one and two directions, respectively. We use the reconstructed
velocity field and the Zel'dovich approximation to predict the mass density
field in the SDSS volume as function of redshift, and find that the mass
distribution closely follows the galaxy distribution even on small scales. We
find a large-scale bulk flow of about 117km/s in a very large volume,
equivalent to a sphere with a radius of ~170Mpc/h, which seems to be produced
by the massive structures associated with the SDSS Great Wall. Finally, we
discuss potential applications of our reconstruction to study the environmental
effects of galaxy formation, to generate initial conditions for simulations of
the local Universe, and to constrain cosmological models. The velocity, tidal
and density fields in the SDSS volume, specified on a Cartesian grid with a
spatial resolution of ~700kpc/h, are available from the authors upon request.Comment: 35 pages, 13 figures, accepted for publication in MNRA
nifH pyrosequencing reveals the potential for location-specific soil chemistry to influence N₂-fixing community dynamics
A dataset of 87 020 nifH reads and 16 782 unique nifH protein sequences obtained over 2 years from four locations across a gradient of agricultural soil types in Argentina were analysed to provide a detailed and comprehensive picture of the diversity, abundance and responses of the N₂-fixing community in relation to differences in soil chemistry and agricultural practices. Phylogenetic analysis revealed an expected high proportion of Alphaproteobacteria, Betaproteobacteria and Deltaproteobacteria, mainly relatives to Bradyrhizobium and Methylosinus/Methylocystis, but a surprising paucity of Gammaproteobacteria. Analysis of variance and stepwise regression modelling suggested location and treatment-specific influences of soil type on diazotrophic community composition and organic carbon concentrations on nifH diversity. nifH gene abundance, determined by quantitative real-time polymerase chain reaction, was higher in agricultural soils than in non-agricultural soils, and was influenced by soil chemistry under intensive crop rotation but not under monoculture. At some locations, sustainable increased crop yields might be possible through the management of soil chemistry to improve the abundance and diversity of N₂-fixing bacteria.Facultad de Ciencias ExactasInstituto de Biotecnologia y Biologia MolecularFacultad de Ciencias Naturales y MuseoLaboratorio de Sistemática y Biología Evolutiv
Proceedings of the international workshop on Ribosomal RNA technology, April 7–9, 2008, Bremen, Germany
Author Posting. © The Author(s), 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Systematic and Applied Microbiology 31 (2008): 258-268, doi:10.1016/j.syapm.2008.08.004.Thirty years have passed since Carl Woese proposed three primary domains of life based on the phylogenetic analysis of ribosomal RNA genes. Adopted by researchers worldwide, ribosomal RNA has become the “gold-standard” for molecular taxonomy, biodiversity analysis and the identification of microorganisms. The more than 700,000 rRNA sequences in public databases constitute an unprecedented hallmark of the richness of microbial biodiversity on earth. The International Workshop on Ribosomal RNA Technology convened on April 7-9, 2008 in Bremen, Germany (http://www.arb-silva.de/rrna-workshop) to summarize the current status of the field and strategize on the best ways of proceeding on both biological and technological fronts. In five sessions, 26 leading international speakers and ~120 participants representing diverse disciplines discussed new technological approaches to address three basic ecological questions: “Who is out there?” “How many are there?” and “What are they doing?”The workshop was a joint collaborative effort of the Max Planck Institute in Bremen and the Ribocon GmbH Bremen, the Technical University Munich, the International Census of Marine Microbes (ICoMM) and the European Census of Marine Life (EuroCoML). The workshop was further sponsored by the Operon and BioCat biotechnology companies
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