The local hole in the galaxy distribution: evidence from 2MASS

Abstract

Using the bright galaxy counts from the 2 Micron All‐sky Survey (2MASS) second incremental release, two techniques for probing large‐scale structure at distances of ∼150 h−1 Mpc are investigated. First, we study the counts from two sets of six 5°×∼80° strips in the two galactic caps. In the six southern strips a deficit of ∼30 per cent was found relative to a predicted homogeneous distribution at Ks∼ 11. These strips were also in good agreement with a model incorporating the radial density function of the southern 2dF Galaxy Redshift Survey (2dFGRS), which shows a deep underdensity between ∼90 and 180 h−1 Mpc. These results indicate a very large ‘local hole’ in the Southern Galactic Cap (SGC) to ≳150 h−1 Mpc with a linear size across the sky of ∼200 h−1 Mpc, but with a significantly lower mean underdensity of ∼30 per cent compared with that suggested by the bright APM SGC counts. The counts in the northern set of strips are low overall but indicate a more varied pattern. When all the available 2MASS data with |b| > 30° were aggregated, they indicated underdensities of ∼18 and ∼30 per cent at Ks∼ 11 for the northern and southern areas, respectively. Our second method uses the ratio of the counts between 11.38 < Ks < 12.38 and 12.88 < Ks < 13.38 to the ratio of the corresponding counts of the homogeneous model binned in 25 deg2 areas; the counts from these areas provide a smoothed map over the sky of the slope in the counts between Ks= 11.38 and 13.38. Visually, the resulting map shows the expected complex form of the cosmic web and picks out known rich clusters, demonstrating the usefulness of this ‘slope statistic’ as a probe of large‐scale structure at distances of ≲150 h−1 Mpc. Most interestingly, the map also shows large regions, ∼100° across, of steep counts in both hemispheres. Thus, the present 2MASS data suggest the presence of a potentially huge contiguous void stretching from south to north. Not only would this delineate further the limits for the cosmological principle but it would also show the possible presence of significant power on scales of ≳300 h−1 Mpc in the galaxy power spectrum.

Breaking the self-averaging properties of spatial galaxy fluctuations in the Sloan Digital Sky Survey – Data release six

“…Our results are compatible with a series of analyses of galaxy number counts in different catalogs, e.g., APM (Shanks 1990;Maddox et al 1990), 2dFGRS (Busswell et al 2003), 2MASS (Frith et al 2003), and a sample of galaxies in the H band (Frith et al 2006). In all those surveys count fluctuations not normalized to the sample average have been considered, and it was concluded that there are local fluctuations of ∼30% extending over scales of ∼200 Mpc/h, which are at odds with ΛCDM predictions.…”

“…Furthermore a deficiency of bright galaxies around the south galactic pole was first examined by Shanks (1990) and then by Maddox et al (1990) which observed a large deficit in the number counts (50% at B = 16, 30% at B = 17) over a 4000 deg 2 solid angle. More recently in a CCD survey of bright galaxies within the Northern and Southern strips of the 2dFGRS conclusive evidence was found that there are fluctuations of about 30% in galaxy counts as a function of apparent magnitude (Busswell et al 2003). In addition Frith et al (2003), using the bright galaxy counts from the 2 Micron All Sky Survey, found results indicating a very large "local hole" in the Southern Galactic Cap (SGC) to >150 Mpc/h with a linear size across the sky of ∼200 Mpc/h, suggesting the presence of a potentially huge contiguous void stretching from south to north, and indicating the possible presence of significant correlations on scales of the order of 300 Mpc/h.…”

“…More recently in a CCD survey of bright galaxies within the Northern and Southern strips of the 2dFGRS conclusive evidence was found that there are fluctuations of about 30% in galaxy counts as a function of apparent magnitude (Busswell et al 2003). In addition Frith et al (2003), using the bright galaxy counts from the 2 Micron All Sky Survey, found results indicating a very large "local hole" in the Southern Galactic Cap (SGC) to >150 Mpc/h with a linear size across the sky of ∼200 Mpc/h, suggesting the presence of a potentially huge contiguous void stretching from south to north, and indicating the possible presence of significant correlations on scales of the order of 300 Mpc/h. Similarly, by studying H-band number counts over 0.30 deg 2 to H = 19, as well as H < 14 counts from 2MASS, concluded that these counts represent a 4.0 sigma fluctuation implying a local hole which extends over the entire local galaxy distribution and being at odds with ΛCDM predictions Frith et al (2006).…”

“…For instance, by studying the redshift distribution in the Durham/UKST Galaxy Redshift Survey, fluctuations were found in the observed radial density function of 50% occurring on ∼50 Mpc/h scales (Ratcliffe et al 1998;Busswell et al 2003). In a similar way in the 2dFGRS two clear "holes" in the galaxy distribution were detected in the ranges 0.03 < z < 0.055, with an under-density of ∼40%, and 0.06 < z < 0.1 where the density deficiency is about ∼25% (Busswell et al 2003).…”

At what particle energy do extragalactic cosmic rays start to predominate?

“…For example, there is evidence for 'huge regions of underdensity in both hemispheres' [15] and there is a 30% reduction to z = 0.1 (≈440 Mpc) in the Southern Hemisphere. The net result for the range of distances corresponding to the ankle (≈840 Mpc for log E = 19) is that we estimate a standard deviation in log E of about 0.3.…”