Is there a preferred direction in the Universe

1
Is there a preferred direction in the Universe
P. Jain, IIT Kanpur
There appear to be several indications of the
existence of a preferred direction in the
Universe (or a breakdown of isotropy)

• Optical polarizations from distant AGNs
• Radio polarizations from distant AGNs
• Low order multipoles of CMBR

2
On distance scales of less than 100 Mpc the
Universe is not homogeneous and isotropic
Most galaxies in our vicinity lie in a plane (the
supergalactic plane) which is approximately
perpendicular to the galactic plane.
The Virgo cluster sits at the center of this disc
like structure
On larger distance scales the universe appears
isotropic
3
CFA Survey 1986
4
CFA Survey 1986
5
CMBR
What does CMBR imply about the isotropy of the
universe?
WMAP released very high resolution data in march
2003
Total number of pixels 512 x 512 x 12 The data
is available at 5 frequencies
There is considerable contamination from
foreground emissions which complicate the
interpretation of data
6
CMBR Probe WMAP
7
WMAP multi-frequency maps
Ka band 33 GHz
K band 23 GHz
Q band 41 GHz
V band 61 GHz
W band 94 GHz
8
(No Transcript)
9
(No Transcript)
10
DT(q,f) Temperature Fluctuations about the mean
Two Point Correlation Function
Statistical isotropy implies
11
If we assume that DT (and alm) are Gaussian
random variables (with 0 mean) then all the
statistical information is contained in the two
point correlation function
or
12
TT Cross Power Spectrum
13
The power is low at small l (quadrupole l2)
The probability for such a low quadrupole to
occur by a random fluctuation is 5
Oliveira-Costa et al 2003
The Octopole is not small but very planar
Surprisingly the Octopole and Quadrupole appear
to be aligned with one another with the chance
probability 1/62
14
Cleaned Map
Quadrupole
Octopole
All the hot and cold spots of the Quadrupole and
Octopole lie in a plane, inclined at approx 30o
to galactic plane
Oliveira-Costa et al 2003
15
Extraction of Preferred Axis
Imagine dT as a wave function y
Maximize the angular momentum dispersion
?
Oliveira-Costa et al 2003
16
Extraction of Preferred Axis
Alternatively Define
k 1 3, m -l l
Preferred frame eka is obtained by Singular Value
Decomposition
ea represent 3 orthogonal axes in space
The preferred axes is the one with largest
eigenvalue La
Ralston, Jain 2003
17

• The preferred axis for both
• Quadrupole
• and
• Octopole
• points roughly in the direction
• (l,b) ? (-110o,60o) in Virgo Constellation

18
Hence WMAP data suggests the existence of a
preferred direction (pointing towards Virgo)
We (Ralston and Jain, 2003) show that there is
considerable more evidence for this preferred
direction

• CMBR dipole

• Anisotropy in radio polarizations from distant
  AGNs

• Two point correlations in optical polarizations
  from AGNs

Also point in this direction
19
CMBR Dipole
The dipole is assumed to arise due to the local
(peculiar) motion of the milky way, arising due
to local in-homogeneities
The observed dipole also points in the direction
of Virgo
20
Physical Explanations
Many explanations have been proposed for the
anomalous behavior of the low order harmonics

• Non trivial topology
• (Luminet, Weeks, Riazuelo, Leboucq
• and Uzan, 2003)
• Anisotropic Universe
• (Berera, Buniy and
  Kephart, 2003)
• Sunyaev Zeldovich effect due to local
  supercluster
• (Abramo and Sodre, 2003)

21
Anisotropy in Radio Polarizations
Radio Polarizations from distant AGNs show a
dipole anisotropy

• Offset angle b c - y
• q(l2 ) c (RM) l2
• RM Faraday Rotation Measure
• c IPA (Polarization at source)

b shows a Dipole ANISOTROPY
Birch 1982 Jain, Ralston, 1999 Jain, Sarala, 2003
22
(No Transcript)
23
b polarization offset angle
Likelihood Analysis ? The Anisotropy
is significant at 1 in full (332 sources) data
set and 0.06 after making a cut in RM (265
sources)
2
RM - ltRMgt gt 6 rad/m
2
ltRMgt 6 rad/m
24
Distribution of RM
The cut eliminates the data near the central peak
25
The radio dipole axis also points towards Virgo
Jain and Ralston, 1999
26
Anisotropy in Extragalactic Radio Polarizations
beta polarization offset angle
Using the cut RM - ltRMgt gt 6 rad/m2
27
Anisotropy in Extragalactic Radio Polarizations
Using the cut RM - ltRMgt gt 6 rad/m2
Galactic Coordinates
28
Anisotropy in Extragalactic Radio Polarizations
A generalized (RM dependent) statistic indicates
that the entire data set shows dipole anisotropy
Equatorial Coordinates
29
Possible Explanation

An anisotropically distributed background
pseudoscalar field f of sufficiently large
strength can explain the observations
Pseudoscalar field at source
To account for the RM dependence

• Rotation in polarization gfgg (D f)
• f change in the pseudoscalar field along the
  path

gfgg lt 10 -11 GeV-1
30
Hutsemékers Effect
Optical Polarizations of QSOs appear to be
locally aligned with one another. (Hutsemékers,
1998)
1ltzlt2.3
A very strong alignment is seen in the direction
of Virgo cluster
31
Hutsemékers Effect
1ltzlt2.3
Equatorial Coordinates
32
Statistical Analysis

• A measure of alignment is obtained by comparing
  polarization angles in a local neighborhood

The polarizations at different angular positions
are compared by making a parallel transport along
the great circle joining the two points
33
Statistic
qk, k1nv are the polarizations of the nv
nearest neighbours of the source i
D k?i contribution due to parallel transport

• Maximizing di(q) with respect to q gives a
  measure of alignment Di and the mean
  angle q

Statistic
Jain, Narain and Sarala, 2003
34
Alignment Results
We find a strong signal of redshift dependent
alignment in a data sample of 213 quasars
The strongest signal is seen in

• Low polarization sample (p lt 2)
• High redshift sample (z gt 1)

35
Significance Level
36
Significance Level
37
Significance Level
Large redshifts (z gt 1) show alignment over the
entire sky
38
Alignment Statistic (z gt 1)
39
Alignment Results
Strongest correlation is seen at low
polarizations ( p lt 2) at distance scales of
order Gpc
Large redshifts z gt 1 show alignment over the
entire sky
Jain, Narain and Sarala, 2003
40
Possible Explanation
Optical Alignment can also be explained by a
pseudoscalar field. As the EM wave passes
through large scale magnetic field, photons
(polarized parallel to transverse magnetic field)
decay into pseudoscalars
The wave gets polarized perpendicular to the
transverse magnetic field
But we require magnetic field on cosmologically
large distance scales
Jain, Panda and Sarala, 2002
41
Preferred Axis
Two point correlation
Define the correlation tensor
Define
where
S is a unit matrix for an isotropic uncorrelated
sample
is the matrix of sky locations
42
Preferred Axis
Optical axis is the eigenvector of S with maximum
eigenvalue
43
Alignment Statistic
Preferred axis points towards (or opposite) to
Virgo
Degree of Polarization lt 2
44
Prob. for pairwise coincidences
dipole quad octo radio optical
dipole 0.020 0.061 0.042 0.024
quad 0.015 0.023 0.004
octo 0.059 0.026
radio 0.008
Ralston and Jain, 2003
45
Concluding Remarks
There appears to be considerable evidence that
there is a preferred direction in the Universe
pointing towards Virgo
However the CMBR observations may also be
explained in terms of some local distortion of
microwave photons due to supercluster. The
physical mechanism responsible for this is not
known so far.
Radio anisotropy may also arise due to some local
unknown effect
However it is not possible to attribute optical
alignment to a local effect
Future observations will hopefully clarify the
situation
46
Anisotropy in Extragalactic Radio Polarizations
sin(2b) lt 0
sin(2b) gt 0 ?
Using the cut RM - ltRMgt gt 6 rad/m2
47
Significance Level of Radio Anisotropy
48
Radiation propagating over cosmological distances
also probes isotropy of the Universe

• CMBR
• Radiation from distant AGNs

49
On Large scale it is assumed that Universe is
Isotropic and Homogeneous
The 3-dim space appears the same in all
directions and at all locations One way to test
for isotropy and homogeneity is by observing the
density of matter (galaxies) in different
directions and positions
Angular correlation function
or 3-D correlation function
50
APM Survey 100 degrees by 50 degrees around the
South Galactic Pole Intensities scaled to the
number of galaxies blue, green and red for
bright, medium and faint galaxies
51
(No Transcript)
52
The APM survey has about 5 million galaxies It
gives an accurate measure of the angular two
point correlation function to about 10
degrees The results agree reasonably well with
the LCDM model with
WL 0.7
Dodelson (2003) Maddox et al (1990)
53
(No Transcript)
54
(No Transcript)
55
(No Transcript)
56
(No Transcript)
57
(No Transcript)
58
(No Transcript)