2,140 research outputs found
Hydrological studies in experimental and representative basins in Brazil: the experience of the REHIDRO network.
Effects of the environment on galaxies in the Catalogue of Isolated Galaxies: physical satellites and large scale structure
We aim to identify and quantify the effects of the satellite distribution
around a sample of galaxies in the Catalogue of Isolated Galaxies (CIG), as
well as the effects of the Large Scale Structure (LSS) using the SDSS-DR9. To
recover the physically bound galaxies we focus on the satellites which are
within the escape speed of each CIG galaxy. We also propose a more conservative
method using the stacked Gaussian distribution of the velocity difference of
the neighbours. The tidal strengths affecting the primary galaxy are estimated
to quantify the effects of the local and LSS environments. We also define the
projected number density parameter at the 5 nearest neighbour to
characterise the LSS around the CIG galaxies. Out of the 386 CIG galaxies
considered in this study, at least 340 (88\% of the sample) have no physically
linked satellite. Out of the 386 CIG galaxies, 327 (85\% of the sample) have no
physical companion within a projected distance of 0.3 Mpc. The CIG galaxies are
distributed following the LSS of the local Universe, although presenting a
large heterogeneity in their degree of connection with it. A clear segregation
appears between early-type CIG galaxies with companions and isolated late-type
CIG galaxies. Isolated galaxies are in general bluer, with likely younger
stellar populations and rather high star formation with respect to older,
redder CIG galaxies with companions. Reciprocally, the satellites are redder
and with an older stellar populations around massive early-type CIG galaxies,
while they have a younger stellar content around massive late-type CIG
galaxies. This suggests that the CIG is composed of a heterogeneous population
of galaxies, sampling from old to more recent, dynamical systems of galaxies.Comment: 19 pages, 10 figures, 1 table, accepted for publication in Astronomy
& Astrophysic
Sensitive VLBI Continuum and H I Absorption Observations of NGC 7674: First Scientific Observations with the Combined Array VLBA, VLA & Arecibo
We present phase-referenced VLBI observations of the radio continuum emission
from, and the H I 21 cm absorption toward, the Luminous Infrared Galaxy NGC
7674. The observations were carried out at 1380 MHz using the VLBA, the phased
VLA, and theArecibo radio telescope. These observations constitute the first
scientific use of the Arecibo telescope in a VLBI observation with the VLBA.
The high- and low-resolution radio continuum images reveal several new
continuum structures in the nuclear region of this galaxy. At ~100 mas
resolution, we distinguish six continuum structures extending over 1.4 arcsec,
with a total flux density of 138 mJy. Only three of these structures were known
previously. All these structures seem to be related to AGN activity. At the
full resolution of the array, we only detect two of the six continuum
structures. Both are composed of several compact components with brightness
temperatures on the order of K. While it is possible that one of these
compact structures could host an AGN, they could also be shock-like features
formed by the interaction of the jet with compact interstellar clouds in the
nuclear region of this galaxy. Complex H I absorption is detected with our VLBI
array at both high and low angular resolution. Assuming that the widest H I
feature is associated with a rotating H I disk or torus feeding a central AGN,
we estimate an enclosed dynamical mass of ~7 x 10^7 M_sun, comparable to the
value derived from the hidden broad H emission in this galaxy. The
narrower H I lines could represent clumpy neutral hydrogen structures in the H
I torus. The detection of H I absorption toward some of the continuum
components, and its absence toward others, suggest an inclined H I disk or
torus in the central region of NGC 7674.Comment: 37 pages, 11 figures. ApJ accepted. To appear in the Nov. 10, 2003
issue of ApJ. Please use the PDF version if the postscript doesn't show the
figure
The charge-dyon bound system in the spherical quantum well
The spherical wave functions of charge-dyon bounded system in a rectangular
spherical quantum dot of infinitely and finite height are calculated. The
transcendent equations, defining the energy spectra of the systems are
obtained. The dependence of the energy levels from the wall sizes is found.Comment: 8 pages, 5 figure
Circumnuclear stellar population, morphology and environment of Seyfert 2 galaxies: an evolutionary scenario
We investigate the relation between the characteristics of the circumnuclear
stellar population and both the galaxy morphology and the presence of close
companions for a sample of 35 Seyfert 2 nuclei. Fifteen galaxies present
unambiguous signatures of recent episodes of star formation within 300
pc from the nucleus. When we relate this property with the Hubble type of the
host galaxy, we find that the incidence of recent circumnuclear star formation
increases along the Hubble sequence, and seems to be larger than in non-Seyfert
galaxies for the early Hubble types S0 and Sa, but similar to that in
non-Seyfert galaxies for later Hubble types. Both in early-type and late-type
Seyferts, the presence of recent star-formation is related to the galaxy
morphology in the inner few kiloparsecs, as observed in HST images through the
filter F606W by Malkan et al., who has assigned a late ``inner Hubble type'' to
most Seyfert 2s with recent nuclear star-formation. This new classification is
due to the presence of dust lanes and spiral structures in the inner region.
The presence of recent star formation in Seyfert 2 nuclei is also related to
interactions: among the 13 galaxies of the sample with close companions or in
mergers, 9 have recent star formation in the nucleus. These correlations
between the presence of companions, inner morphology and the incidence of
recent star formation suggest an evolutionary scenario in which the interaction
is responsible for sending gas inwards which both feeds the AGN and triggers
star-formation. The starburst then fades with time and the composite Seyfert 2
+ Starburst nucleus evolves to a ``pure'' Seyfert 2 nucleus with an old stellar
population.Comment: 12 pages, 6 figures, 2 table
Genetic perturbation of IFN-α transcriptional modulators in human endothelial cells uncovers pivotal regulators of angiogenesis
The HI content of the Eridanus group of galaxies
The HI content of galaxies in the Eridanus group is studied using the GMRT
observations and the HIPASS data. A significant HI deficiency up to a factor of
2-3 is observed in galaxies in the high galaxy density regions. The HI
deficiency in galaxies is observed to be directly correlated with the local
projected galaxy density, and inversely correlated with the line-of-sight
radial velocity. Furthermore, galaxies with larger optical diameters are
predominantly in the lower galaxy density regions. It is suggested that the HI
deficiency in Eridanus is due to tidal interactions. In some galaxies,
evidences of tidal interactions are seen. An important implication is that
significant evolution of galaxies can take place in the group environment. In
the hierarchical way of formation of clusters via mergers of groups, a fraction
of the observed HI deficiency in clusters could have originated in groups. The
co-existence of S0's and severely HI deficient galaxies in the Eridanus group
suggests that galaxy harassment is likely to be an effective mechanism for
transforming spirals to S0's.Comment: 21 pages; Accepted for publication in Journal of Astroph. & Astron.
March, 200
An aquarium hobbist poisoning: Identification of new palytoxins in Palythoa cf. toxica and complete detoxification of the aquarium water by activated carbon
Palytoxin (PLTX) is a lethal natural toxin often found in Palythoa zoantharians that, together with its congeners, may induce adverse effects in humans after inhalation of toxic aerosols both in open-air and domestic environments, namely in the vicinity of public and private aquaria. In this study, we describe a poisoning of an aquarium hobbyist who was hospitalized after handling a PLTXs-containing zoantharian hexacoral. Furthermore, we provide evidence for water detoxification. The zoantharian was morphologically and genetically identified as Palythoa cf. toxica (Cnidaria: Anthozoa). Palytoxin itself and two new PLTX congeners, a hydroxyPLTX and a deoxyPLTX, were detected and structurally identified by liquid chromatography high resolution multiple stage mass spectrometry (LC-HRMSn, n = 1, 2). Total and individual toxins were quantified by LC-HRMS and sandwich ELISA both in the zoantharian (93.4 and 96.80 \u3bcg/g, respectively) and in the transport water (48.3 and 42.56 \u3bcg/mL, respectively), with an excellent mean bias of 1.3% between the techniques. Activated carbon adsorbed 99.7% of PLTXs contained in the seawater and this represents a good strategy for preventing aquarium hobbyist poisonings
HI Observations of the Stephan's Quintet
Using the VLA, we have made spectral-line and continuum observations of the
neutral hydrogen in the direction of the compact group of galaxies Stephan's
Quintet. The high-velocity clouds between 5600 and 6600 km/s, the disk of the
foreground galaxy, NGC 7320, at 800 km/s, the extended continuum ridge near the
center of the group, and 3 faint dwarf-like galaxies in the surrounding field
were imaged with C, CS, and D arrays. Four of the HI clouds previously detected
are confirmed. The two largest HI features are coincident with and concentrated
mainly along separate large tidal tails that extend eastward. The most diffuse
of the four clouds is resolved into two clumps, one coincide with tidal
features south of NGC 7318a and the other devoid of any detectable stellar or
Halfa sources. The two compact clouds, along the same line of sight, have peak
emission at luminous infrared and bright Halfa sources probably indicative of
star-forming activity. The total amount of HI detected at high redshifts is ~
10**10Msol. As in previous HI studies of the group, no detectable emission was
measured at the positions of any high-redshift galaxies so that any HI still
bound to their disks must be less than 2.4 x 10**7Msol.Comment: Accepted for publication in AJ and tentatively scheduled for the May
2002 issue. High-resolution ps figures are available at:
http://www.iaa.es/~lourdes/bw/bw-paper.tar.g
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