48,270 research outputs found
PRIORITIES IN THE CHANGING WORLD OF AGRICULTURE
Agricultural and Food Policy,
R-Band Imaging of Fields Around 1<z<2 Radiogalaxies
We have taken deep -band images of fields around five radiogalaxies:
0956+47, 1217+36, 3C256, 3C324 and 3C294 with . 0956+47 is found to
show a double nucleus. Our data on 1217+36 suggest the revision of its
classification as a radiogalaxy. We found a statistically significant excess of
bright () galaxies on scales of 2 arcmin around the radiogalaxies
(which have ) in our sample. The excess has been determined
empirically to be at level. It is remarkable that this excess
is not present for galaxies within the same area, suggesting that
the excess is not physically associated to the galaxies but due to intervening
groups and then related to gravitational lensing.Comment: 20 pages, uuencoded compressed PostScript including tables. Figures
available upon request. To appear in the March 1995 issue of The Astronomical
Journa
Compact modes in quasi one dimensional coupled magnetic oscillators
In this work we study analytically and numerically the spectrum and
localization properties of three quasi-one-dimensional (ribbons) split-ring
resonator arrays which possess magnetic flatbands, namely, the stub, Lieb and
kagome lattices, and how their spectra is affected by the presence of
perturbations that break the delicate geometrical interference needed for a
magnetic flatband to exist. We find that the Stub and Lieb ribbons are stable
against the three types of perturbations considered here, while the kagome
ribbon is, in general, unstable. When losses are incorporated, all flatbands
remain dispersionless but become complex, with the kagome ribbon exhibiting the
highest loss rate.Comment: 11 pages, 15 figure
Cluster of galaxies around seven radio-loud QSOs at 1<z<1.6: K-band images
We have conducted a NIR study of the environments of seven radio-loud quasars
at redshifts 1<z<1.6. In present paper we describe deep band images
obtained for the fields of ~6X6 arcmin around the quasars with 3
limiting magnitudes of K~20.5. These fields were previously studied using deep
B and R band images (Sanchez & Gonzalez-Serrano 1999). Using together optical
and NIR data, it has been found a significant excess of galaxies which
optical-NIR colours, luminosity, spatial scale, and number of galaxies are
compatible with clusters at the redshift of the quasar.
We have selected a sample of cluster candidates analyzing the R-K vs. K
diagram. A ~25% of the candidates present red optical-NIR colours and an
ultraviolet excess. This population has been also found in clusters around
quasars at the same redshifts (Tanaka et al. 2000; Haines et al. 2001). These
galaxies seem to follow a mixed evolution: a main passive evolution plus late
starformation processes. The quasars do not inhabit the core of the clusters,
being found in the outer regions. This result agrees with the hypothesis that
the origin/feeding mechanism of the nuclear activity were merging processes.
The quasars inhabit the region were a collision is most probably to produce a
merger.Comment: 15 pages. A&A, accepted for publishin
Are optically-selected QSO catalogs biased ?
A thorough study of QSO-galaxy correlations has been done on a region close
to the North Galactic Pole using a complete subsample of the optically selected
CFHT/MMT QSO survey and the galaxy catalog of Odewahn and Aldering (1995).
Although a positive correlation between bright QSOs and galaxies is expected
because of the magnification bias effect, none is detected. On the contrary,
there is a significant (>99.6%) anticorrelation between z<1.6 QSOs and red
galaxies on rather large angular distances. This anticorrelation is much less
pronounced for high redshift z>1.6 QSOs, which seems to exclude dust as a cause
of the QSO underdensity. This result suggests that the selection process
employed in the CFHT/MMT QSO survey is losing up to 50% of low redshift z<1.6
QSOs in regions of high galaxy density. The incompleteness in the whole z<1.6
QSO sample may reach 10% and have important consequences in the estimation of
QSO evolution and the QSO autocorrelation function.Comment: 17 pages LaTeX (aasms4), plus 6 EPS figures. To be published in the
Astronomical Journa
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