14,489 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
An X-ray study of the SNR G344.7-0.1 and the central object CXOU J170357.8-414302
Aims. We report results of an X-ray study of the supernova remnant (SNR)
G344.7-0.1 and the point-like X-ray source located at the geometrical center of
the SNR radio structure. Methods. The morphology and spectral properties of the
remnant and the central X-ray point-like source were studied using data from
the XMM-Newton and Chandra satellites. Archival radio data and infrared Spitzer
observations at 8 and 24 m were used to compare and study its multi-band
properties at different wavelengths. Results. The XMM-Newton and Chandra
observations reveal that the overall X-ray emission of G344.7-0.1 is extended
and correlates very well with regions of bright radio and infrared emission.
The X-ray spectrum is dominated by prominent atomic emission lines. These
characteristics suggest that the X-ray emission originated in a thin thermal
plasma, whose radiation is represented well by a plane-parallel shock plasma
model (PSHOCK). Our study favors the scenario in which G344.7-0.1 is a 6 x 10^3
year old SNR expanding in a medium with a high density gradient and is most
likely encountering a molecular cloud on the western side. In addition, we
report the discovery of a soft point-like X-ray source located at the
geometrical center of the radio SNR structure. The object presents some
characteristics of the so-called compact central objects (CCO). However, its
neutral hydrogen absorption column (N_{H}) is inconsistent with that of the
SNR. Coincident with the position of the source, we found infrared and optical
objects with typical early-K star characteristics. The X-ray source may be a
foreground star or the CCO associated with the SNR. If this latter possibility
were confirmed, the point-like source would be the farthest CCO detected so far
and the eighth member of the new population of isolated and weakly magnetized
neutron stars.Comment: 9 pages, 8 figures, accepted for publication in Astronomy and
Astrophysics. Higher resolution figures can be seen on A&
In vitro Study of the Survival, Reproduction and Morphology of Daphnia pulicaria irradiated with a Low Energy Laser
Daphnia is a genus of crustaceans that is representative of freshwater communities. The species exhibit a high sensitivity to a wide range of toxic compounds so that they have been used internationally as biomonitors in toxicity tests to evaluate ecosystem conditions such as water quality. It is also a model genus in genetics, epigenetics and reproductive ecology. In this work, we used Daphnia pulicaria as a model to measure the effects of low-energy laser irradiation on survival, reproduction, and morphology variables of parental organisms and their offspring. We used (1) a single clone line of organisms to eliminate interindividual genetic variability; (2) individuals from more than 50 generations after the clone line was established, and offspring from the third brood onwards to dissipate maternal and epigenetic effects, and (3) neonates, those individuals of the species that have less than 48 hours of life, because they are the most sensitive stage to optical stimuli. We analyzed number of deaths, longevity, age at first reproduction, number of offspring per week, number of total offspring during all their life cycle, body size, size of the antennules, and length of the apical spine of the 4th and 5th brood of the irradiated individuals, who were exposed to a blue laser stimulus of 405 nm for 25 minutes with a power of 40 mW at a distance of 50 cm, compared to those of the control (non-irradiated) group
Red quasars not so dusty
Webster et al (1995) claimed that up to 80% of QSOs may be obscured by dust.
They inferred the presence of this dust from the remarkably broad range of B-K
optical-infrared colours of a sample of flat-spectrum PKS radio QSOs. If such
dust is typical of QSOs, it will have rendered invisible most of those which
would otherwise been have detected by optical surveys. We used the William
Herschel Telescope on La Palma to obtain K infrared images of 54 B3 radio
quasars selected at low frequency (mainly steep-spectrum), and we find that
although several have very red optical-infrared colours, most of these can be
attributed to an excess of light in K rather than a dust-induced deficit in B.
We present evidence that some of the infrared excess comes from the light of
stars in the host galaxy (some, as previously suggested, comes from synchrotron
radiation associated with flat-spectrum radio sources). The B-K colours of the
B3 QSOs provide no evidence for a large reddened population. Either the Webster
et al QSOs are atypical in having such large extinctions, or their reddening is
not due to dust; either way, the broad range of their B-K colours does not
provide evidence that a large fraction of QSOs has been missed from optical
surveys.Comment: 16 pages TeX file + 2 PostScript figures. Accepted in MNRA
Clean optical spectrum of the radio jet of 3C 120
We present integral field spectroscopy (IFS) of the central region of 3C 120.
We have modeled the nuclear and host galaxy 3D spectra using techniques
normally applied to imaging, decoupling both components, and obtained a
residual datacube. Using this residual datacube, we detected the extended
emission line region associated with the radio jet. We obtained, for the first
time, a clean spectrum of this region and found compelling evidences of a
jet-cloud interaction. The jet compresses and splits the gas cloud which is
ionized by the AGN and/or by the strong local UV photon field generated by a
shock process. We cannot confirm the detection of an extended emission line
region associated with the counter-jet reported by Axon (1989).Comment: 13 pages, 3 figures, accepted for publishing in Ap
K-band imaging of 52 B3-VLA quasars: Nucleus and host properties
We present K-band imaging and photometry of a sample of 52 radio loud quasars
(RQs) selected from the B3 survey with flux densities above 0.5 Jy at 408 MHz.
The optical completeness of the sample is 90% and the quasars cover the
redshift range 0.4 - 2.3. For ~57% of the sources for which the quality of the
images allowed a detailed morphological study (16/28) resolved extended
emission was detected around the QSO, and its K flux was measured. Interpreting
this ``fuzz'' as starlight emission from the host galaxy, its location on the
K-z plane at z<1 is consistent with radio quasars being hosted by galaxies
similar to radio galaxies (RGs) or giant ellipticals (gEs). At higher redshifts
the detected host galaxies of RQs are more luminous than typical RGs and gEs,
although some weak detections or upper limits are consistent with a similar
fraction of RQs being hosted by galaxies with the expected luminosities for RGs
or gEs. We found a significant correlation between radio power and nuclear
infrared luminosity indicating a direct link between the radio synchrotron
emission and the nuclear emission in K. This correlation is more tight for the
steep-spectrum sources (99.97% significance). In addition, a trend is found
between radio power and infrared luminosity of the host galaxy (or mass), in
the sense that the most powerful quasars inhabit the most luminous galaxies.Comment: tar gzipped file including 1 LaTeX file, 4 latex tables, and 13
PostScript figures. Accepted in AJ (April 1998
Revan-degree indices on random graphs
Given a simple connected non-directed graph , we consider two
families of graph invariants:
(which has gained interest recently) and (that we introduce in this work); where denotes the edge of
connecting the vertices and , is the Revan degree of the
vertex , and is a function of the Revan vertex degrees. Here, with and the maximum and minimum
degrees among the vertices of and is the degree of the vertex .
Particularly, we apply both and R on two models of
random graphs: Erd\"os-R\'enyi graphs and random geometric graphs. By a
thorough computational study we show that \left and
\left, normalized to the order of the graph, scale
with the average Revan degree \left; here \left
denotes the average over an ensemble of random graphs. Moreover, we provide
analytical expressions for several graph invariants of both families in the
dense graph limit.Comment: 16 pages, 10 figure
The origin of the Acheulean: the 1.7 million-year-old site of FLK West, Olduvai Gorge (Tanzania)
The appearance of the Acheulean is one of the hallmarks of human evolution. It represents the
emergence of a complex behavior, expressed in the recurrent manufacture of large-sized tools, with
standardized forms, implying more advance forethought and planning by hominins than those required
by the precedent Oldowan technology. The earliest known evidence of this technology dates back to
c. 1.7 Ma. and is limited to two sites (Kokiselei [Kenya] and Konso [Ethiopia]), both of which lack fauna.
The functionality of these earliest Acheulean assemblages remains unknown. Here we present the
discovery of another early Acheulean site also dating to c. 1.7 Ma from Olduvai Gorge. This site provides
evidence of the earliest steps in developing the Acheulean technology and is the oldest Acheulean site in
which stone tools occur spatially and functionally associated with the exploitation of fauna. Simple and
elaborate large-cutting tools (LCT) and handaxes co-exist at FLK West, showing that complex cognition
was present from the earliest stages of the Acheulean. Here we provide a detailed technological study
and evidence of the use of these tools on the butchery and consumption of fauna, probably by early
Homo erectus sensu lato
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