Is there a preferred direction in the Universe P. Jain, IIT Kanpur There appear to be several indications of the existence...
On distance scales of less than 100 Mpc the Universe is not homogeneous and isotropic The Virgo cluster sits at the center...
CFA Survey 1986
CFA Survey 1986
CMBR WMAP released very high resolution data in march 2003 Total number of pixels = 512 x 512 x 12 The data is available a...
CMBR Probe WMAP
K band  23 GHz Ka band  33 GHz Q band  41 GHz V band  61 GHz W band  94 GHz WMAP multi-frequency maps
 
 
 T  Temperature Fluctuations about the mean Two Point Correlation Function Statistical isotropy implies
If we assume that   T (and a lm ) are Gaussian random variables (with 0 mean)   then all the statistical information is c...
TT Cross Power Spectrum
The power is low at small l (quadrupole l=2) The probability for such a low quadrupole to occur by a random fluctuation is...
Quadrupole Octopole Cleaned Map Oliveira-Costa  et al  2003 All the hot and cold spots of the Quadrupole and Octopole lie ...
Extraction of Preferred Axis Imagine   T as a wave function   Maximize the angular momentum dispersion  Oliveira-Costa ...
Extraction of Preferred Axis k = 1 …3,  m = - l  …  l Preferred frame e k   is obtained by Singular Value Decomposition e...
<ul><li>The preferred axis for both  </li></ul><ul><li>Quadrupole  </li></ul><ul><li>and  </li></ul><ul><li>Octopole  </li...
Hence WMAP data suggests the existence of a preferred direction (pointing towards Virgo) We (Ralston and Jain, 2003) show ...
CMBR Dipole The dipole is assumed to arise due to the local (peculiar) motion of the milky way, arising due to local in-ho...
Physical Explanations Many explanations have been proposed for the anomalous behavior of the low order harmonics  <ul><li>...
Anisotropy in Radio Polarizations <ul><li>Offset angle  </li></ul><ul><li>   RM)    </li></ul><...
 
Likelihood Analysis   The Anisotropy is significant at 1% in full (332 sources) data set  and  0.06% after making a cut...
Distribution of RM The cut eliminates the data near the central peak
The radio dipole axis also points towards Virgo Jain and Ralston, 1999
Anisotropy in Extragalactic Radio Polarizations beta = polarization offset angle Using the cut |RM - <RM>| > 6 rad/m 2
Anisotropy in Extragalactic Radio Polarizations Using the cut |RM - <RM>| > 6 rad/m 2 Galactic Coordinates
Equatorial Coordinates Anisotropy in Extragalactic Radio Polarizations A generalized (RM dependent) statistic indicates th...
Possible Explanation An anisotropically distributed background pseudoscalar field    of sufficiently large strength can e...
Hutsem é kers   Effect Optical Polarizations of QSOs appear to be  locally aligned with one another.  (Hutsem é kers, 1998...
Hutsem é kers   Effect Equatorial Coordinates 1<z<2.3
Statistical Analysis <ul><li>A measure of alignment is obtained by comparing polarization angles in a local neighborhood  ...
Statistic <ul><li>Maximizing d i (  ) with respect to    gives a measure of alignment D i   and  the mean angle    </li...
Alignment Results We find a strong signal of redshift dependent alignment in a data sample of 213 quasars <ul><li>Low pola...
Significance Level
Significance Level
Significance Level Large redshifts (z > 1) show alignment over the entire sky
Alignment Statistic (z > 1)
Alignment Results Strongest correlation is seen at low polarizations ( p < 2%) at  distance scales of order Gpc Large reds...
Possible Explanation Optical Alignment can also be explained by a pseudoscalar field.  As the EM wave passes through large...
Preferred Axis Two point correlation Define the correlation tensor Define where is the matrix of sky locations S is a unit...
Preferred Axis Optical axis is the eigenvector of S with maximum eigenvalue
Alignment Statistic Preferred axis points towards (or opposite) to Virgo Degree of Polarization < 2%
Prob. for pairwise coincidences Ralston and Jain, 2003 0.008 radio 0.026 0.059 octo 0.004 0.023 0.015 quad 0.024 0.042 0.0...
Concluding Remarks There appears to be considerable evidence that there is a preferred direction in the Universe pointing ...
Anisotropy in Extragalactic Radio Polarizations sin(2  ) < 0  + sin(2  ) > 0   Using the cut |RM - <RM>| > 6 rad/m 2
Significance Level of Radio Anisotropy
Radiation propagating over cosmological distances also probes isotropy of the Universe <ul><li>CMBR </li></ul><ul><li>Radi...
The 3-dim space appears the same in all directions and at all locations One way to test for isotropy and homogeneity is by...
APM Survey 100 degrees by 50 degrees around the South Galactic Pole   Intensities scaled to the number of galaxies   blue,...
 
The APM survey has about 5 million galaxies It gives an accurate measure of the angular two point correlation function to ...
 
 
 
 
 
 
Upcoming SlideShare
Loading in...5
×

Universe

316

Published on

Universe

Is there a preferred direction in the Universe ... On distance scales of less than 100 Mpc the Universe is not homogeneous

Published in: Education, Technology, Spiritual
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total Views
316
On Slideshare
0
From Embeds
0
Number of Embeds
1
Actions
Shares
0
Downloads
3
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Universe

  1. 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) <ul><li>Optical polarizations from distant AGNs </li></ul><ul><li>Radio polarizations from distant AGNs </li></ul><ul><li>Low order multipoles of CMBR </li></ul>
  2. 2. On distance scales of less than 100 Mpc the Universe is not homogeneous and isotropic The Virgo cluster sits at the center of this disc like structure Most galaxies in our vicinity lie in a plane (the supergalactic plane) which is approximately perpendicular to the galactic plane. On larger distance scales the universe appears isotropic
  3. 3. CFA Survey 1986
  4. 4. CFA Survey 1986
  5. 5. CMBR 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 What does CMBR imply about the isotropy of the universe?
  6. 6. CMBR Probe WMAP
  7. 7. K band 23 GHz Ka band 33 GHz Q band 41 GHz V band 61 GHz W band 94 GHz WMAP multi-frequency maps
  8. 10.  T  Temperature Fluctuations about the mean Two Point Correlation Function Statistical isotropy implies
  9. 11. If we assume that  T (and a lm ) are Gaussian random variables (with 0 mean) then all the statistical information is contained in the two point correlation function or
  10. 12. TT Cross Power Spectrum
  11. 13. The power is low at small l (quadrupole l=2) 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
  12. 14. Quadrupole Octopole Cleaned Map Oliveira-Costa et al 2003 All the hot and cold spots of the Quadrupole and Octopole lie in a plane, inclined at approx 30 o to galactic plane
  13. 15. Extraction of Preferred Axis Imagine  T as a wave function  Maximize the angular momentum dispersion  Oliveira-Costa et al 2003
  14. 16. Extraction of Preferred Axis k = 1 …3, m = - l … l Preferred frame e k  is obtained by Singular Value Decomposition e  represent 3 orthogonal axes in space The preferred axes is the one with largest eigenvalue   Ralston, Jain 2003 Alternatively Define
  15. 17. <ul><li>The preferred axis for both </li></ul><ul><li>Quadrupole </li></ul><ul><li>and </li></ul><ul><li>Octopole </li></ul><ul><li>points roughly in the direction </li></ul><ul><li>(l,b)  (-110 o ,60 o ) in Virgo Constellation </li></ul>
  16. 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 <ul><li>CMBR dipole </li></ul><ul><li>Anisotropy in radio polarizations from distant AGNs </li></ul><ul><li>Two point correlations in optical polarizations from AGNs </li></ul>Also point in this direction
  17. 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
  18. 20. Physical Explanations Many explanations have been proposed for the anomalous behavior of the low order harmonics <ul><li>Non trivial topology </li></ul><ul><li>(Luminet, Weeks, Riazuelo, Leboucq </li></ul><ul><li>and Uzan, 2003) </li></ul><ul><li>Anisotropic Universe </li></ul><ul><li>(Berera, Buniy and Kephart, 2003) </li></ul><ul><li>Sunyaev Zeldovich effect due to local supercluster </li></ul><ul><li>(Abramo and Sodre, 2003) </li></ul>
  19. 21. Anisotropy in Radio Polarizations <ul><li>Offset angle  </li></ul><ul><li>   RM)   </li></ul><ul><ul><li>RM : Faraday Rotation Measure </li></ul></ul><ul><ul><li> = IPA (Polarization at source) </li></ul></ul> shows a Dipole ANISOTROPY Radio Polarizations from distant AGNs show a dipole anisotropy Birch 1982 Jain, Ralston, 1999 Jain, Sarala, 2003
  20. 23. 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)  RM - <RM>| > 6 rad/m <RM> = 6 rad/m    = polarization offset angle
  21. 24. Distribution of RM The cut eliminates the data near the central peak
  22. 25. The radio dipole axis also points towards Virgo Jain and Ralston, 1999
  23. 26. Anisotropy in Extragalactic Radio Polarizations beta = polarization offset angle Using the cut |RM - <RM>| > 6 rad/m 2
  24. 27. Anisotropy in Extragalactic Radio Polarizations Using the cut |RM - <RM>| > 6 rad/m 2 Galactic Coordinates
  25. 28. Equatorial Coordinates Anisotropy in Extragalactic Radio Polarizations A generalized (RM dependent) statistic indicates that the entire data set shows dipole anisotropy
  26. 29. Possible Explanation An anisotropically distributed background pseudoscalar field  of sufficiently large strength can explain the observations To account for the RM dependence <ul><li>Rotation in polarization =g  (   </li></ul><ul><li> change in the pseudoscalar field along the path </li></ul>Pseudoscalar field at source g  < 10 -11 GeV -1
  27. 30. Hutsem é kers Effect Optical Polarizations of QSOs appear to be locally aligned with one another. (Hutsem é kers, 1998) A very strong alignment is seen in the direction of Virgo cluster 1<z<2.3
  28. 31. Hutsem é kers Effect Equatorial Coordinates 1<z<2.3
  29. 32. Statistical Analysis <ul><li>A measure of alignment is obtained by comparing polarization angles in a local neighborhood </li></ul>The polarizations at different angular positions are compared by making a parallel transport along the great circle joining the two points
  30. 33. Statistic <ul><li>Maximizing d i (  ) with respect to  gives a measure of alignment D i and the mean angle  </li></ul> k , k=1…n v are the polarizations of the n v nearest neighbours of the source i  k  i = contribution due to parallel transport Statistic Jain, Narain and Sarala, 2003
  31. 34. Alignment Results We find a strong signal of redshift dependent alignment in a data sample of 213 quasars <ul><li>Low polarization sample (p < 2%) </li></ul><ul><li>High redshift sample (z > 1) </li></ul>The strongest signal is seen in
  32. 35. Significance Level
  33. 36. Significance Level
  34. 37. Significance Level Large redshifts (z > 1) show alignment over the entire sky
  35. 38. Alignment Statistic (z > 1)
  36. 39. Alignment Results Strongest correlation is seen at low polarizations ( p < 2%) at distance scales of order Gpc Large redshifts z > 1 show alignment over the entire sky Jain, Narain and Sarala, 2003
  37. 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
  38. 41. Preferred Axis Two point correlation Define the correlation tensor Define where is the matrix of sky locations S is a unit matrix for an isotropic uncorrelated sample
  39. 42. Preferred Axis Optical axis is the eigenvector of S with maximum eigenvalue
  40. 43. Alignment Statistic Preferred axis points towards (or opposite) to Virgo Degree of Polarization < 2%
  41. 44. Prob. for pairwise coincidences Ralston and Jain, 2003 0.008 radio 0.026 0.059 octo 0.004 0.023 0.015 quad 0.024 0.042 0.061 0.020 dipole optical radio octo quad dipole
  42. 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. However it is not possible to attribute optical alignment to a local effect Future observations will hopefully clarify the situation Radio anisotropy may also arise due to some local unknown effect
  43. 46. Anisotropy in Extragalactic Radio Polarizations sin(2  ) < 0 + sin(2  ) > 0  Using the cut |RM - <RM>| > 6 rad/m 2
  44. 47. Significance Level of Radio Anisotropy
  45. 48. Radiation propagating over cosmological distances also probes isotropy of the Universe <ul><li>CMBR </li></ul><ul><li>Radiation from distant AGNs </li></ul>
  46. 49. 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 On Large scale it is assumed that Universe is Isotropic and Homogeneous
  47. 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
  48. 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  CDM model with    Dodelson (2003) Maddox et al (1990)
  1. A particular slide catching your eye?

    Clipping is a handy way to collect important slides you want to go back to later.

×