1,718 research outputs found
Optical and radio properties of giant radio quasars: Central black hole characteristics
We analysed the optical and radio properties of lobe-dominated giant-sized (>
0.72 Mpc) radio quasars and compared the results with those derived for a
sample of smaller radio sources to determine whether the large size of some
extragalactic radio sources is related to the properties of their nuclei. We
compiled the largest (to date) sample of giant radio quasars, including 24 new
and 21 previously-known objects, and calculated a number of important
parameters of their nuclei such as the black hole mass and the accretion rate.
We conclude that giant radio quasars have properties similar to those of
smaller size and that giant quasars do not have more powerful central engines
than other radio quasars. The results obtained are consistent with evolutionary
models of extragalactic radio sources which predict that giant radio quasars
could be more evolved (aged) sources compared to smaller radio quasars. In
addition we found out that the environment may play only a minor role in
formation of large-scale radio structures.Comment: 19 pages, 17 figures, submitted to MNRA
GB2 0909+353: One of the Largest Double Radio Source
The evidence are given that the radio source GB2 0909+353 (GB2 catalogue:
Machalski 1978; ICRS 2000.0 coordinates: 09 12 51.7, +35 10 10) is likely one
of the largest classical doubles known, though its optical identification is
not certain. Our deep VLA observations at 5 GHz did not reveal a radio core
brighter than 0.5 mJy/beam at this frequency. Thus a distance to the source is
evaluated using photometric -- redshift estimates of the faint galaxies in the
optical field. The equipartition magnetic field and energy density in the
source is calculated and compared with corresponding parameters of other
`giant' radio sources known, showing extremely low values of both physical
parameters of the source investigated. On the other hand, the age of
relativistic electrons, and the advance speed of the `hot spot' in the source
are typical for much smaller and brighter 3CR sources.Comment: 10 pages with 3 Postscript figures, accepted to Acta Astronomic
J1145-0033 - the most distant giant radio source?
We present J1145-0033, a candidate for the most distant (z=2.055)
lobe-dominated giant radio quasar, with a projected linear size of 1.34 Mpc.
This quasar has both FR II -- type radio morphology and broad absorption lines
in its optical spectrum. Some physical characteristics (e.g. black hole mass,
accretion rate, equipartition magnetic field, energy density and particle
density of ambient medium) based on the optical and radio data are provided. We
have also found that the quasar has a relatively large central black hole mass
and a very small accretion rate in comparison with similar objects.Comment: 12 pages, 4 Postscript figure
Giant Radio Sources in View of the Dynamical Evolution of FRII-type Population
The time evolution of giant (D>1 Mpc) lobe-dominated galaxies is analysed on
the basis of dynamical evolution of the entire FRII-type population.Comment: 4 pages, 2 Postscript figures, uses baltlat1.sty To be published in
"Radio astronomy at 70: from Karl Jansky to microjansky", JENAM-2003
Symposium, eds. L.Gurvits and S.Frey, (Baltic Astronomy
Giant Radio Sources in View of the Dynamical Evolution of FRII-type Population. I. The Observational Data, and Basic Physical Parameters of Sources Derived from the Analytical Model
The time evolution of giant lobe-dominated radio galaxies (with projected
linear size D>1 Mpc if H_{0}=50 km/s/Mpc and q_{0}=0.5 is analysed on the basis
of dynamical evolution of the entire FRII-type population. Two basic physical
parameters, namely the jet power Q_{0} and central density of the galaxy
nucleus rho0 are derived for a sample of giants with synchrotron ages reliably
determined, and compared with the relevant parameters in a comparison sample of
normal-size sources consisting of 3C, B2, and other sources. Having the
apparent radio luminosity P and linear size D of each sample source, Q_{0} and
rho_{0} are obtained by fitting the dynamical model of Kaiser et al. (1997). We
find that: (i) there is not a unique factor governing the source size; they are
old sources with temperate jet power (Q_{0}) evolved in a relatively
low-density environment (rho_{0}). The size is dependent, in order of
decreasing partial correlation coefficients, on age; then on Q_{0}; next on
rho_{0}. (ii) A self-similar expansion of the sources' cocoon seems to be
feasible if the power supplied by the jets is a few orders of magnitude above
the minimum-energy value. In other cases the expansion can only initially be
self-similar; a departure from self-similarity for large and old sources is
justified by observational data of giant sources. (iii) An apparent increase of
the lowest internal pressure value observed within the largest sources' cocoon
with redshift is obscured by the intrinsic dependence of their size on age and
the age on redshift, which hinders us from making definite conclusions about a
cosmological evolution of intergalactic medium (IGM) pressure.Comment: 36 pages, 8 figures, 7 table
1.4-GHz observations of extended giant radio galaxies
This paper presents 1.4-GHz radio continuum observations of 15 very extended
radio galaxies. These sources are so large that most interferometers lose
partly their structure and total flux density. Therefore, single-dish
detections are required to fill in the central (u,v) gap of interferometric
data and obtain reliable spectral index patterns across the structures, and
thus also an integrated radio continuum spectrum. We have obtained such 1.4-GHz
maps with the 100-m Effelsberg telescope and combined them with the
corresponding maps available from the NVSS. The aggregated data allow us to
produce high-quality images, which can be used to obtain physical parameters of
the mapped sources. The combined images reveal in many cases extended low
surface-brightness cocoons.Comment: 39 pages, 19 figures, 3 tables. Published in Ac
Large-Scale Radio Structure in the Universe: Giant Radio Galaxies
Giant radio galaxies (GRGs), with linear sizes larger than 1 Mpc (H0=50
km/s/Mpc), represent the biggest single objects in the Universe. GRGs are rare
among the entire population of radio galaxies (RGs) and their physical
evolution is not well understood though for many years they have been of
special interest for several reasons. The lobes of radio sources can compress
cold gas clumps and trigger star or even dwarf galaxy formation, they can also
transport gas from a host galaxy to large distances and seed the IGM with
magnetic fields. Since GRGs have about 10 to 100 times larger sizes than normal
RGs, their influence on the ambient medium is correspondingly wider and is
pronounced on scales comparable to those of clusters of galaxies or larger.
Therefore `giants' could play an important role in the process of large-scale
structure formation in the Universe. Recently, thanks to the new all sky radio
surveys, significant progress in searching for new GRGs has been made.Comment: To appear in Multiwavelength AGN Surveys, ed. R. Maiolino and R.
Mujica, Singapore: World Scientific, 2004, 2 page
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