arXiv:0912.5330v1 [astro-ph.CO] 29 Dec 2009
Anisotropy of the Space Orientation of Radio Sources. I: The Catalog
V. R. Amirkhanyan1
1Sternberg Astronomical Institute, Universitetskii pr. 13, Moscow, 119992 Russia
(Received January 21, 2009; Revised May 20, 2009)
A catalog of extended extragalactic radio sources consisting of 10461 objects is compiled based
on the list of radio sources of the FIRST survey. A total of 1801 objects are identified with galaxies
and quasars of the SDSS survey and the Veron-Veron catalog. The distribution of position angles of
the axes of radio sources from the catalog is determined, and the probability that this distribution
is equiprobable is shown to be less than 10−7. This result implies that at Z equal to or smaller than
0.5, the spatial orientation of the axes of radio sources is anisotropic at a statistically significant
The uniform morphology of galaxies make them
excellent test bodies for the investigations of the
structure of space. The British astronomer Brown
was the first to study the orientation of galaxies in
1930s . Brown , Nilson , Lauberts , and
Karachentsev et al.  compiled extensive catalogs
providing the galaxy parameters that are of most
importance to such studies: position angles and ax-
ial ratios.Reinhardt , Nilson , Lauberts ,
Mandzhos , and Parnovsky et al.  analyzed
these catalogs and showed convincingly that the spa-
tial orientation of galaxies is anisotropic on the scale
lengths of at least 200 Mpc. Extended extragalac-
tic radio sources can be seen to exhibit equally uni-
form and anisotropic structure. Radio sources are
very appealing objects for such studies, because they
should eventually allow to either prove or refute the
results based on an independent sample of galaxies
and increase substantially the volume of the space
domain studied. Amirkhanyan  tried to use such
radio sources as indicators of anisotropy, but failed
to reach a conclusive result because of a rather small
size of the available homogeneous sample, which con-
sisted of 298 radio sources of the MG catalog. It is
evident that to obtain a statistically significant re-
sult, a catalog of extended radio sources is required,
comparable in size with galaxy catalogs. However,
no such catalogs are available to date. Therefore, we
decided, with the ultimate aim of analyzing the spa-
tial orientation of radio sources, to compile such a
catalog based on the list of objects of the FIRST sur-
vey . This catalog cannot be used directly since
it provides no information about the multiplicity of
radio sources. The catalog gives the parameters of
individual components without indicating eventual
associations between them.
2.1.Rules of Selection
For the task to succeed, minimizing the number
of false objects is more important than finding all
the true radio sources. Hence, the selection rules
embedded into the first01 program that produces
the catalog, focused on the former rather than the
latter goal. The rules are as follows:
(1) each radio source must consist of at least three
(2) the integrated flux from each component must
be greater than or equal to 2.5 mJy;
(3) the root mean square distance of the compo-
nents from the axis of the radio source drawn opti-
mally across the coordinates of the components must
not exceed 0.12 Θ, where Θ is the separation be-
tween the most distant components.
We use the cluster analysis methods to gener-
ate the list of components that make up the radio
source. Under these conditions, if we assume that
all the 440046 objects of the FIRST survey with
integrated fluxes equal to or greater than 2.5 mJy
are mutually unassociated, we should find no more
than three false radio sources with three compo-
nents. The probability of finding a false object with
four or more components is negligible. Another pos-
sible source of false objects are very extended radio
sources, where the separation between the groups of
components exceeds the clusterization radius of 60′′.
In this case, the program may mistake a group of
components, if it meets the above rules of selection,
for an independent radio source. Such objects are
rare and most of them do not satisfy the rules of se-
lection. The program yielded a catalog consisting of
10461 radio sources. Figure 1 shows examples of ob-
jects combined and their radio images in the FIRST
survey. We performed such visual control for sev-
eral tens of radio sources and it revealed no errors
whatsoever. The program simultaneously identified
the radio sources combined with objects of the SDSS
survey  and the Veron-Veron Catalog . If the
separation between the average coordinates of the
The author is grateful to I. D. Karachentsev for
fruitful discussion of this work.
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