2,769 research outputs found
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
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
Neural-network selection of high-redshift radio quasars, and the luminosity function at z~4
We obtain a sample of 87 radio-loud QSOs in the redshift range 3.6<z<4.4 by
cross-correlating sources in the FIRST radio survey S{1.4GHz} > 1 mJy with
star-like objects having r <20.2 in SDSS Data Release 7. Of these 87 QSOs, 80
are spectroscopically classified in previous work (mainly SDSS), and form the
training set for a search for additional such sources. We apply our selection
to 2,916 FIRST-DR7 pairs and find 15 likely candidates. Seven of these are
confirmed as high-redshift quasars, bringing the total to 87. The candidates
were selected using a neural-network, which yields 97% completeness (fraction
of actual high-z QSOs selected as such) and an efficiency (fraction of
candidates which are high-z QSOs) in the range of 47 to 60%. We use this sample
to estimate the binned optical luminosity function of radio-loud QSOs at , and also the LF of the total QSO population and its comoving density. Our
results suggest that the radio-loud fraction (RLF) at high z is similar to that
at low-z and that other authors may be underestimating the fraction at high-z.
Finally, we determine the slope of the optical luminosity function and obtain
results consistent with previous studies of radio-loud QSOs and of the whole
population of QSOs. The evolution of the luminosity function with redshift was
for many years interpreted as a flattening of the bright end slope, but has
recently been re-interpreted as strong evolution of the break luminosity for
high-z QSOs, and our results, for the radio-loud population, are consistent
with this.Comment: 20 pages. Accepted for publication in MNRAS on 3 March 201
Population dynamics of Meloidogyne incognita on cucumber grafted onto the Cucurbita hybrid RS841 or ungrafted and yield losses under protected cultivation
The influence of the squash hybrid RS841 rootstock (Cucurbita maxima x C. moschata) on population dynamics of Meloidogyne incognita and yield of cucumber cv. Dasher II was assessed during 2013 and 2014 in a plastic greenhouse. In addition, the relationship between ecophysiological parameters (plant water status, gas exchange, and leaf reflectance) and Pi and cucumber yield were also estimated in 2013. Nematode densities were determined at the beginning (Pi) and at the end (Pf) of each crop, and the relationship between these parameters was used to estimate the maximum multiplication rate (a), the maximum population density (M) and the equilibrium density (E) per grafted and ungrafted cucumber and cropping season. Moreover, the relationship between the multiplication rate (Pf/Pi) and Pi was compared between grafted and ungrafted cucumber per cropping season. Finally, the relative yield of grafted or ungrafted cucumber was plotted against Pi to determine the tolerance limit (T) and the minimum relative yield (m) by the Seinhorst damage function model. Values of a, M and E in grafted cucumber were higher than in ungrafted one irrespective of the cropping season. These results were supported by comparing the relationship between Pf/Pi and Pi between grafted and ungrafted cucumber. The relationship between Pi and yield fitted the Seinhorst damage function. The values of T and m did not differ between grafted and ungrafted each year. Predawn water potential, net photosynthetic rate, and leaf chlorophyll index decreased with increasing Pi. In addition, relative yield was related to variation in net photosynthetic rate and the leaf chlorophyll index. Under the conditions of this study, RS841 rootstock was neither resistant nor tolerant to M. incognita.Postprint (published version
Use of neural networks for the identification of new z>=3.6 QSOs from FIRST-SDSS DR5
We aim to obtain a complete sample of redshift > 3.6 radio QSOs from FIRST
sources having star-like counterparts in the SDSS DR5 photometric survey
(r<=20.2). We found that simple supervised neural networks, trained on sources
with SDSS spectra, and using optical photometry and radio data, are very
effective for identifying high-z QSOs without spectra. The technique yields a
completeness of 96 per cent and an efficiency of 62 per cent. Applying the
trained networks to 4415 sources without DR5 spectra we found 58 z>=3.6 QSO
candidates. We obtained spectra of 27 of them, and 17 are confirmed as high-z
QSOs. Spectra of 13 additional candidates from the literature and from SDSS DR6
revealed 7 more z>=3.6 QSOs, giving and overall efficiency of 60 per cent. None
of the non-candidates with spectra from NED or DR6 is a z>=3.6 QSO,
consistently with a high completeness. The initial sample of z>=3.6 QSOs is
increased from 52 to 76, i.e. by a factor 1.46. From the new identifications
and candidates we estimate an incompleteness of SDSS for the spectroscopic
classification of FIRST 3.6<=z<=4.6 QSOs of 15 percent for r<=20.2.Comment: 16 pages, 9 figures accepted for publication in MNRA
Structural Disorder, Octahedral Coordination, and 2-Dimensional Ferromagnetism in Anhydrous Alums
The crystal structures of the triangular lattice, layered anhydrous alums
KCr(SO4)2, RbCr(SO4)2 and KAl(SO4)2 are characterized by X-ray and neutron
powder diffraction at temperatures between 1.4 and 773 K. The compounds all
crystallize in the space group P-3, with octahedral coordination of the
trivalent cations. In all cases, small amounts of disorder in the stacking of
the triangular layers of corner sharing MO6 octahedra and SO4 tetrahedra is
seen, with the MO6-SO4 network rotated in opposite directions between layers.
The electron diffraction study of KCr(SO4)2 supports this model, which on
average can be taken to imply trigonal prismatic coordination for the M3+ ions;
as was previously reported for the prototype anhydrous alum KAl(SO4)2. The
temperature dependent magnetic susceptibilities for ACr(SO4)2 (A = K,Rb,Cs)
indicate the presence of predominantly ferromagnetic interactions. Low
temperature powder neutron diffraction reveals that the magnetic ordering is
ferromagnetic in-plane, with antiferromagnetic ordering between planes below 3
K.Comment: Accepted to the Journal of Solid State Chemistr
XMM-Newton and Deep Optical Observations of the OTELO fields: the Groth-Westphal Strip
OTELO (OSIRIS Tunable Emission Line Object Survey) will be carried out with
the OSIRIS instrument at the 10 m GTC telescope at La Palma, and is aimed to be
the deepest and richest survey of emission line objects to date. The deep
narrow-band optical data from OSIRIS will be complemented by means of
additional observations that include: (i) an exploratory broad-band survey that
is already being carried out in the optical domain, (ii) FIR and sub-mm
observations to be carried with the Herschel space telescope and the GTM, and
(iii) deep X-Ray observations from XMM-Newton and Chandra.Here we present a
preliminary analysis of public EPIC data of one of the OTELO targets,the
Groth-Westphal strip, gathered from the XMM-Newton Science Archive (XSA). EPIC
images are combined with optical BVRI data from our broadband survey carried
out with the 4.2m WHT at La Palma. Distance-independent diagnostics (involving
X/O ratio, hardness ratios, B/T ratio) are tested.Comment: 2 pages, 2 figures, uses graphicx package. To appear in proceedings
of "The X-Ray Universe 2005", San Lorenzo del Escorial, Spain, September
26-30, 200
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