Angular two point correlation function of NVSS catalog

Is the large angle correlation cosmic ?

Songchen

Motivation

Two-point angular correlation function from the Planck smica map (Copi, Craig J. et al. 2013)

NVSS catalog

National Radio Astronomy Observatory (NRAO) Very Large Array(VLA) Sky Survey

VLA manly has 4 configurations (A,B,C,D) NVSS catalog use D́ ́and D́nC ́Frequency : 1.4 GHz Sky coverage : dec > -40° Number of sources : nearly 2×106

Contaminations

Contaminations

Contaminations

The ways to correct

Contamination Methods

Bright sources Mask out with 0.6 degree radius/ pixels

Foreground Cut galactic plane with |b| < X°

Strip effect a. Use only high flux threshold (S > 10mJy)

b. Normalize the number density to the strip mean

The ways to correct

Contamination Methods

Bright sources Mask out with 0.6 degree radius/ pixels

Foreground Cut galactic plane with |b| < X°

Strip effect a. Use only high flux threshold (S > 10mJy)

b. Normalize the number density to the strip mean

Caution !?

What other people found

C.Blake, P.G. Ferreira and J.Borrill 2004

What other people found

J.Xia, M. Viel, C.Baccigalupi,G. Zotti and S.Matarrese 2010

What other people found

Dipole measurements

M. Rubart and D.J. Schwarz 2013

C. Blake and J. Wall 2002 High flux threshold (> 15mJy) : The dipole model is a good fit Low flux threshold : Dipole direction move to high declination

To subtract dipole correctly, we choose : S > 15mJy Or S > 25mJy

Our New Mask + Healpix

Estimator

Angular two point correlation function based on Land & Szalay estimator:

Error:

Considering dipole subtraction,

What we found

What we found

Our Mask

Mask

1. Neighborhood of bright sources deviate from Poisson distribution

2. High noise pixels

Mask

1. Neighborhood of bright sources deviate from Poisson distribution

2. High noise pixels

Condon 1998 Theoretical rms noise level at the center of an NVSS snapshot image

Large scale correlation

Zoom In

Angular Power Spectrum

S> 15mJy Our Mask

Suspicion

Conclusion

The large scale correlation signal (l=4) is approximately 1

magnitude bigger than the Lambda CDM prediction

We highly suspect that this signal is caused by the survey noise, instead of large scale structures

The predicted large scale correlation signal is at 10-6 level. To detect it , one needs at least 107 sources.

Thank you for your attention !

Mask

Mask

Mask