4,239 research outputs found
JHK Imaging and Photometry of Low z QSOs and Radio Galaxy
We describe J,H,K deep imaging of 90 arcmin fields around 4 QSOs and one
Radio galaxy at redshifts in the range 0.06 to 0.30, and show their images,
luminosity profiles, and NIR 2-colour diagrams of objects. We find that the QSO
hosts are all resolved, and compare them with previous CCD images. The host
galaxy colours are consistent with old and young stellar populations at the QSO
redshift. The colours of nearby galaxies suggest that all the AGN live in
groups of generally smaller companion galaxies, mostly with evolved populations
at the same redshift. The two radio-loud objects live in richer cluster
environments than the others. Gissel population models indicate reddening in
the galaxies, star-forming regions, and possibly a systematic H-K offset. The
QSO luminosity profiles are complex and reveal some of their tidal disturbance
and star-formation history.Comment: 22 pages of text (latex), 2 tables )latex), and 15 figures
(postscript). Accepted for publication in AJ, February 1997. Also available
at http://www.dao.nrc.ca/DAO/SCIENCE/science.htm
Amplifier provides dual outputs from a single source with complete isolation
Amplifier provides two amplified outputs from a single input signal with complete transformer isolation. It uses modulation techniques to obtain the separated output
Geometrically nonlinear Cosserat elasticity in the plane: applications to chirality
Modelling two-dimensional chiral materials is a challenging problem in
continuum mechanics because three-dimensional theories reduced to isotropic
two-dimensional problems become non-chiral. Various approaches have been
suggested to overcome this problem. We propose a new approach to this problem
by formulating an intrinsically two-dimensional model which does not require
references to a higher dimensional one. We are able to model planar chiral
materials starting from a geometrically non-linear Cosserat type elasticity
theory. Our results are in agreement with previously derived equations of
motion but can contain additional terms due to our non-linear approach. Plane
wave solutions are briefly discussed within this model.Comment: 22 pages, 1 figure; v2 updated versio
Evolution of luminous IRAS galaxies: Radio imaging
In a recent study of IRAS galaxies' optical morphologies, we found that luminous IR sources lie in the IR color-luminosity plane in groups which separate out by optical spectroscopic type and also by degree of tidal disturbance. We found that the most luminous steep-IR-spectrum sources are generally galaxies in the initial stages of a major tidal interaction. Galaxies with active nuclei were generally found to have flatter IR spectra, to cover a range of IR luminosity, and to be in the later stages of a tidal interaction. We proposed a sequence of events by which luminous IR sources evolve: they start as interacting or merging galaxies, some develop active nuclei, and most undergo extensive star-formation in their central regions. Another way to study these objects and their individual evolution is to study their radio morphologies. Radio emission may arise at a detectable level from supernovae in star-forming regions and/or the appearance of an active nucleus can be accompanied by a nuclear radio source (which may develop extended structure). Therefore, the compact radio structure may trace the evolution of the inner regions of IRAS-luminous sources. If the radio sources are triggered by the interactions, we would expect to find the radio morphology related to the optical 'interactivity' of the systems. Here, we explore using the radio emission of IRAS galaxies as a possible tracer of galaxy evolution. We present and discuss observations of the compact radio morphology of 111 luminous IRAS-selected active galaxies covering a wide range of IR and optical properties
A Supernova Factory in the Merger System Arp 299
We have imaged the nearby galaxy merger Arp 299 at arcsecond and
milliarcsecond resolution, using both the Very Large Array and the Very Long
Baseline Array. The large-scale radio emission from the merger contains 5
bright, compact radio sources embedded in diffuse emission, with diameters less
than 200 pc. Supernova rates of 0.1 to 1 per year are required to produce the
VLA-detected radio emission in these sources. Two of the compact VLA radio
sources, designated Source A and Source D, also have been detected and imaged
at milliarcsecond scales. Source A, which is associated with the nucleus of one
of the merging galaxies, contains five milliarcsecond-scale sources, each with
a radio power between 100 and 1000 times that of the Galactic supernova remnant
Cassiopeia A. Four of these have flat or inverted spectra and appear to be
young supernovae. Three of the VLBI-scale sources are located within 10 pc
(projected) of one another, and two are separated by less than 3 pc, indicating
that they all may be within the same super starcluster or complex of such
clusters. The brightest VLBI-scale source, A0, has an extremely inverted
pectrum, with alpha larger than +2 at gigahertz frequencies. It seems to be the
youngest supernova, which has not yet broken out of its circumstellar shell.
The milliarcsecond radio sources within Source A appear to constitute a
upernova factory, confirming the presence of an extreme starburst that peaked
at least a few million years ago.Comment: Accepted for the Astrophysical Journal, 22 pages, 10 figure
Band gaps in the relaxed linear micromorphic continuum
In this note we show that the relaxed linear micromorphic model recently
proposed by the authors can be suitably used to describe the presence of
band-gaps in metamaterials with microstructures in which strong contrasts of
the mechanical properties are present (e.g. phononic crystals and lattice
structures). This relaxed micromorphic model only has 6 constitutive parameters
instead of 18 parameters needed in Mindlin- and Eringen-type classical
micromorphic models. We show that the onset of band-gaps is related to a unique
constitutive parameter, the Cosserat couple modulus which starts to
account for band-gaps when reaching a suitable threshold value. The limited
number of parameters of our model, as well as the specific effect of some of
them on wave propagation can be seen as an important step towards indirect
measurement campaigns
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