78 research outputs found
Star Formation in QSO Host Galaxies
Many of the conditions that are necessary for starbursts appear to be
important in the triggering of QSOs. However, it is still debatable whether
starbursts are ubiquitously present in galaxies harboring QSOs. In this paper
we review our current knowledge from observations of the role of starbursts in
different types of QSOs. Post-starburst stellar populations are potentially
present in the majority of QSO hosts. QSOs with far-infrared colors similar to
those of ultraluminous infrared galaxies invariably reside in merging galaxies
that have interaction-induced starbursts of a few hundred Myr or less. Similar,
but dramatically more luminous post-starburst populations are found in the
recently discovered class of QSOs known as post-starburst QSOs, or Q+A's. Both
of these classes, however, comprise only a small fraction (10-15%) of the total
QSO population. The so-called "red" QSOs generally suffer from strong
extinction at optical wavelengths, making them ideal candidates for the study
of hosts. Their stellar populations typically show a post-starburst component
as well, though with a larger range of ages. Finally, optical "classical" QSO
hosts show traces of major star formation episodes (typically involving >10% of
the mass of the stellar component) in the more distant past (1-2 Gyr). These
starbursts appear to be linked to past merger events. It remains to be
determined whether these mergers were also responsible for triggering the QSO
activity that we observe today.Comment: 8 pages, 5 figures, invited review for "QSO Host Galaxies: Evolution
and Environment", held at the Lorentz Center, Universiteit Leiden, August,
200
21-cm synthesis observations of VIRGOHI 21 - a possible dark galaxy in the Virgo Cluster
Many observations indicate that dark matter dominates the extra-galactic
Universe, yet no totally dark structure of galactic proportions has ever been
convincingly identified. Previously we have suggested that VIRGOHI 21, a 21-cm
source we found in the Virgo Cluster using Jodrell Bank, was a possible dark
galaxy because of its broad line-width (~200 km/s) unaccompanied by any visible
gravitational source to account for it. We have now imaged VIRGOHI 21 in the
neutral-hydrogen line and find what could be a dark, edge-on, spinning disk
with the mass and diameter of a typical spiral galaxy. Moreover, VIRGOHI 21 has
unquestionably been involved in an interaction with NGC 4254, a luminous spiral
with an odd one-armed morphology, but lacking the massive interactor normally
linked with such a feature. Numerical models of NGC 4254 call for a close
interaction ~10^8 years ago with a perturber of ~10^11 solar masses. This we
take as additional evidence for the massive nature of VIRGOHI 21 as there does
not appear to be any other viable candidate. We have also used the Hubble Space
Telescope to search for stars associated with the HI and find none down to an I
band surface brightness limit of 31.1 +/- 0.2 mag/sq. arcsec.Comment: 8 pages, accepted to ApJ, uses emulateapj.cls. Mpeg animation (Fig.
2) available at ftp://ftp.naic.edu/pub/publications/minchin/video2.mp
The FIRST-2MASS Red Quasar Survey II: An anomalously high fraction of LoBALs in searches for dust-reddened quasars
We present results on a survey to find extremely dust-reddened Type-1
Quasars. Combining the FIRST radio survey, the 2MASS Infrared Survey and the
Sloan Digital Sky Survey, we have selected a candidate list of 122 potential
red quasars. With more than 80% spectroscopically identified objects, well over
50% are classified as dust-reddened Type 1 quasars, whose reddenings (E(B-V))
range from approximately 0.1 to 1.5 magnitudes. They lie well off the color
selection windows usually used to detect quasars and many fall within the
stellar locus, which would have made it impossible to find these objects with
traditional color selection techniques. The reddenings found are much more
consistent with obscuration happening in the host galaxy rather than stemming
from the dust torus. We find an unusually high fraction of Broad Absorption
Line (BAL) quasars at high redshift, all but one of them belonging to the Low
Ionization BAL (LoBAL) class and many also showing absorption the metastable
FeII line (FeLoBAL). The discovery of further examples of dust-reddened LoBAL
quasars provides more support for the hypothesis that BAL quasars (at least
LoBAL quasars) represent an early stage in the lifetime of the quasar. The fact
that we see such a high fraction of BALs could indicate that the quasar is in a
young phase in which quasar feedback from the BAL winds is suppressing star
formation in the host galaxy.Comment: 17 pages, 7 figures, accepted for publication in Ap
Scientific Opportunities for Monitoring at Environmental Remediation Sites (SOMERS): Integrated Systems-Based Approaches to Monitoring
Through an inter-disciplinary effort, DOE is addressing a need to advance monitoring approaches from sole reliance on cost- and labor-intensive point-source monitoring to integrated systems-based approaches such as flux-based approaches and the use of early indicator parameters. Key objectives include identifying current scientific, technical and implementation opportunities and challenges, prioritizing science and technology strategies to meet current needs within the DOE complex for the most challenging environments, and developing an integrated and risk-informed monitoring framework
Biological flora of Central Europe: Cyperus esculentus L
This paper presents information on all aspects of the biology of Cyperus esculentus L. (yellow nutsedge) and deals with its taxonomy, morphology, genetic diversity, distribution, habitat requirements, ecology and life cycle, with special emphasis on uses and cultivation, history of introduction, impact and management in Europe. C. esculentus is a tuber geophyte and most likely originates from the Mediterranean and Southwest Asia. It is a variable plant and four wild-type varieties are presently recognized, in addition
to a cultivated form. C. esculentus reproduces primarily by its underground tubers, although abundant seeds are produced. In temperate climates, tubers usually sprout in late spring and the plant withers at the beginning of the winter. C. esculentus is only cultivated in the València region in Spain. Invasion foci emerged across Europe at the beginning of the 1980s and at present, C. esculentus is most abundant on arable land and in ruderal habitats, followed by riverine vegetation. In heavily infested regions of Europe, C. esculentus causes substantial yield losses in field crops and although different management strategies are available, C. esculentus remains difficult to control.Follak, S.; Belz, R.; Bohren, C.; Castro, OD.; Guacchio, ED.; Pascual-Seva, N.; Schwarz, M.... (2016). Biological flora of Central Europe: Cyperus esculentus L. Perspectives in Plant Ecology, Evolution and Systematics. 23:33-51. doi:10.1016/j.ppees.2016.09.003S33512
Multifaceted highly targeted sequential multidrug treatment of early ambulatory high-risk SARS-CoV-2 infection (COVID-19)
The SARS-CoV-2 virus spreading across the world has led to surges of COVID-19 illness, hospitalizations, and
death. The complex and multifaceted pathophysiology of life-threatening COVID-19 illness including viral mediated
organ damage, cytokine storm, and thrombosis warrants early interventions to address all components of the devastating
illness. In countries where therapeutic nihilism is prevalent, patients endure escalating symptoms and without
early treatment can succumb to delayed in-hospital
care and death. Prompt early initiation of sequenced multidrug
therapy (SMDT) is a widely and currently available
solution to stem the tide of hospitalizations and death. A
multipronged therapeutic approach includes 1) adjuvant
nutraceuticals, 2) combination intracellular anti-infective
therapy, 3) inhaled/oral corticosteroids, 4) antiplatelet
agents/anticoagulants, 5) supportive care including supplemental
oxygen, monitoring, and telemedicine. Randomized
trials of individual, novel oral therapies have not
delivered tools for physicians to combat the pandemic in
practice. No single therapeutic option thus far has been
entirely effective and therefore a combination is required
at this time. An urgent immediate pivot from single drug to
SMDT regimens should be employed as a critical strategy
to deal with the large numbers of acute COVID-19 patients
with the aim of reducing the intensity and duration
of symptoms and avoiding hospitalization and death
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