Is There a Violation of the Copernican Principle in Radio Sky

Cosmic Microwave Background Radiation (CMBR) observations from the WMAP satellite have shown some unexpected anisotropies, which surprisingly seem to be aligned with the ecliptic1,2. This alignment has been dubbed the “axis of evil” with very damaging implications for the standard model of cosmology3. The latest data from the Planck satellite have confirmed the presence of these anisotropies4. Here we report even larger anisotropies in the sky distributions of powerful extended quasars and some other sub-classes of radio galaxies in the 3CRR catalogue, one of the oldest and most intensively studies sample of strong radio sources5
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    a  r   X   i  v  :   1   3   0   5 .   4   1   3   4  v   1   [  a  s   t  r  o  -  p   h .   C   O   ]   1   7   M  a  y   2   0   1   3 Is there a violation of the Copernican principle in radio sky? Ashok K. Singal Astronomy and Astrophysics Division, Physical Research Laboratory,Navrangpura, Ahmedabad - 380 009, India  ∗ Cosmic Microwave Background Radiation (CMBR) observations from theWMAP satellite have shown some unexpected anisotropies, which surprisinglyseem to be aligned with the ecliptic 1,2 . This alignment has been dubbed the “axisof evil” with very damaging implications for the standard model of cosmology 3 .The latest data from the Planck satellite have confirmed the presence of theseanisotropies 4 . Here we report even larger anisotropies in the sky distributionsof powerful extended quasars and some other sub-classes of radio galaxies inthe 3CRR catalogue, one of the oldest and most intensively studies sample of strong radio sources 5,6,7 . The anisotropies lie about a plane passing throughthe two equinoxes and the north celestial pole (NCP). We can rule out at a 99 . 995%  confidence level the hypothesis that these asymmetries are merely dueto statistical fluctuations. Further, even the distribution of observed radio sizesof quasars and radio galaxies show large systematic differences between thesetwo sky regions. The redshift distribution appear to be very similar in bothregions of sky for all sources, which rules out any local effects to be the causeof these anomalies. Two pertinent questions then arise. First, why should therebe such large anisotropies present in the sky distribution of some of the mostdistant discrete sources implying inhomogeneities in the universe at very largescales (covering a fraction of the universe)? What is intriguing even furtheris why such anisotropies should lie about a great circle decided purely by theorientation of earth’s rotation axis and/or the axis of its revolution around thesun? It looks as if these axes have a preferential placement in the larger schemeof things, implying an apparent breakdown of the Copernican principle or itsmore generalization, cosmological principle, upon which all modern cosmologicaltheories are based upon. Copernican principle states that earth does not have any eminent or privileged position  2in the universe and therefore an observer’s choice of srcin and/or orientation of his/hercoordinate system should have no bearing on the appearance of the distant universe. Itsnatural generalization is the cosmological principle that the universe on a sufficiently largescale should appear homogeneous and isotropic, with no preferred directions, to all ob-servers. However to us on earth the universe does show heterogeneous structures up tothe scale of superclusters of galaxies and somewhat beyond, but it is assumed that it willall appear homogeneous and isotropic when observed on still larger scales, perhaps beyonda couple of hundreds of megaparsecs. Radio galaxies and quasars, the most distant dis-crete objects (at distances of many gigaparsecs or further) seen in the universe should tracethe distribution of matter in the universe at that large scale and should therefore appearisotropically distributed from any vantage point in the universe including that on earth.One of the earliest and best studied source of radio galaxies and quasars is the 3CRR (3rdCambridge twice revised) catalogue 5,6,7 , which is radio complete in the sense that all ra-dio sources brighter than a certain sensitive limit are included and also it has completeoptical identification content with detailed optical spectra to classify radio sources in toradio galaxies and quasars. The catalogue with the latest updates is downloadable from  .The radio galaxies are broadly divided into two classes, Fanaroff-Riley type I and II (FRIand FRII), based on their radio morphologies 8 . When compared to FRIs, the FRII types arealmost always found amongst the more powerful radio galaxies. Included among quasars arewhat are termed as weak quasars (WQ) or broad line radio galaxies (BLRGs), with broademission lines seen in polarized optical emission, or/and compact optical nuclei detected ininfrared or X-rays. FRII type radio galaxies are further sub-divided by their optical spectrainto low excitation galaxies (LEGs) and high excitation galaxies (HEGs). The conventionalwisdom 9 is that steep spectrum ( α >  0 . 5) HEGs and quasars belong to the same parentpopulation, excluding of course a small number of compact steep spectrum sources (CSSS,with angular size  < ∼  2 arcsec). In this unification scheme, the observed numbers and sizes of quasars are expected to be about a factor of two lower as compared to those of HEGs.It was while investigating the unification scheme that we noted that the relative numberof quasars and HEGs varies heavily within the 3CRR sample if we compared it in twoadjacent and contiguous regions of the sky. A close investigation showed that HEGs, whichare the largest number of the 3CRR constituents, are quite uniformly distributed over the  3 FIG. 1: The sky distribution of HEGs (empty circles), quasars (solid dots) and FRI type sources(plus signs) from the 3CRR sample shown in the sinusoidal (equal-area) projection. Region Iextends in right ascension from 0 to 12 hour and region II from 12 to 24 hour. The dotted b=0curve shows the path of the galactic plane, and B=0 shows the Supergalactic plane.TABLE I: Counts of radio sources in two regions of the sky.RA(hours) N(HEG) N(Q) N(LEG) N(FRI)00 − 24 65 48 17 2300 − 12 32 33 11 612 − 24 33 15 6 17 observed sky, however quasars are quite unevenly distributed. To a first order, the maximumdifference seems to occur when sky is divided into 0-12 hour (say, Region I) and 12-24 hour(Region II) in right ascension (RA). This division amounts to passing a great circle betweenthe equinoxes (intersection points of the equatorial plane and the ecliptic) and the NCP.While slightly more than two thirds of the quasars in the catalogue lie in region I, theremainder of them appear in region II. Probability of such an anomaly occurring (at ∼ 2 . 6 σ level) in a binomial distribution due to statistical fluctuations is less than one percent 10 .Figure 1 shows the distribution of 3CRR sources in the sinusoidal (equal area) projectionin sky, where we readily see the uneven distribution of quasars between regions I and II.The zone of avoidance (  ± 10 ◦ ) about the galactic plane (b=0) is almost evenly distributedbetween the two regions, with only a marginal excess in region I. If anything, due to this thenumber of quasars should only be lower in region I, opposite to what actually seen. Also a  4 FIG. 2: Histogram of the redshift distributions of the 3CR sample in regions I and II of the sky (a)for HEGs (b) for quasars. In the lower panels, the region under the overlaid dark line representsweak quasars (WQs) or BLRGs. N(HEG) and N(Q) give the number of high excitation galaxiesand quasars respectively, in each plot. number of quasars which seem to lie in the supergalactic plane (B=0) at ra ∼ 0-03 hour areactually at high redshifts, the lowest being at z=0.425. Therefore being at least hundredtimes more distant than the local virgo-supercluster, they are in no way physically relatedto it or other local objects. We also note from Figure 1 (and Table 1) that even FRI typeshave a highly asymmetric number ratio of about 1 to 3 in the two regions, but in oppositesense to that of quasars. Similarly LEGs also have a number ratio of about 2 to 1 in regionsI and II (Table 1). It is to be noted that all of these asymmetries have independent binomialprobabilities if these are due to a random statistical fluctuation, and then their combinedprobability of occurrence due to being simply a statistical fluctuation is only about 5 × 10 − 5 .These results are robust. There is little likelihood that these anomaly could be the resultof, e.g., some missing sources in the 3CRR catalogue, as this is one of the most thoroughlystudied radio complete sample of sources, in the sense that all source above the sensitivity
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