Studies of IRAS Sources at High Galactic Latitudes - I. Source Counts
at |b| >=60 degrees and Evidence of a North-South Anisotropy of
Cosmological Significance
- M. Rowan-Robinson and
D. W. Walker
- Theoretical Astronomy Unit
- Queen Mary College
- Mile End Road
- London E1 4NS
- U. K.
- T. Chester
- Jet Propulsion Laboratory
- Pasadena CA 91109
- U. S. A.
- T. Soifer
- California Institute of Technology
- Pasadena CA 91125
- U. S. A.
- J. Fairclough
- Rutherford Appleton Laboratory
- Didcot OX11 0QX
- U. K.
Abstract
Source counts and identifications of IRAS sources at |b| > 60 degrees
are discussed. It is shown that emission from interstellar dust on the IRAS
point-source angular scale at 100 microns is localized to a few small areas
of the galactic polar caps. At 12 and 25 microns the sky is dominated by
stars, and at 60 and 100 microns by galaxies, at these latitudes. As
expected the 12 and 25 micron source densities are lower than for the
mini-survey area. The 100 micron survey at |b| > 60 degrees reaches
significantly deeper in flux than the mini-survey did, because of the
reduced effect of emission from interstellar dust.
After exclusion of the Virgo cluster and of regions affected by emission
from interstellar dust, comparison of the 60 and 100 micron source counts
at b > 60 degrees and b < -60 degrees shows that the source density
is 20 per cent higher in the north than in the south. This anisotropy
is significant at the 4 sigma level. We argue that this is not due to
any known instrumental effects and that it represents a cosmologically
significant anisotropy in the galaxy distribution. The scale of the
inhomogeneity responsible for the anisotropy appears to be of the order
of at least 100(50/H) Mpc. Existing optical counts of galaxies are
consistent with the reality of this anisotropy, about half of which can be
attributed to sources located within previously catalogued clusters of
galaxies.
M. Rowan-Robinson, D. W. Walker, T. Chester, B. T. Soifer, and J. Fairclough,
Studies of IRAS Sources at High Galactic Latitudes - I. Source Counts
at |b| >=60 degrees and Evidence of a North-South Anisotropy of
Cosmological Significance,
Monthly Notices of the Royal Astronomical Society, Vol. 219, pages 273-283, 1986.