The local hole in the galaxy distribution: new optical evidence

Abstract

We present a new CCD survey of bright galaxies predominantly within the Northern and Southern strips of the 2dF Galaxy Redshift Survey (2dFGRS) areas. We use the new CCD data to check the photographic photometry scales of the 2dFGRS 100‐k release, APM Bright Galaxy Catalogue, APM–Stromlo Redshift Survey, Durham–UKST (DUKST) Survey, Millennium Galaxy Catalogue (MGC) and Sloan Digital Sky Survey (SDSS). We find evidence for scale and zero‐point errors in the 2dFGRS 100‐k release Northern field, DUKST and APM data of 0.10, 0.24 and 0.31 mag, respectively; we find excellent agreement with the MGC and SDSS photometry. We use our new CCD data to correct the photographic photometry, we then compare the CCD number counts in both the Northern and Southern survey areas. We find conclusive evidence that the Southern counts with B < 17 mag are down by ≈30 per cent relative to both the Northern counts and to the models of Metcalfe et al. in the same magnitude range. We further compare the number redshift distributions from the B < 17 mag Durham–UKST and B < 19.5 2dFGRS redshift surveys using the corrected photometry. While the Northern n(z) from 2dFGRS appears relatively homogeneous over its whole range, the Southern n(z) shows a 30 per cent deficiency out to z= 0.1; at higher redshifts it agrees much better with the Northern n(z) and the homogeneous model n(z). The Durham–UKST n(z) shows that the Southern ‘hole’ extends over a 20 × 75 deg2 area. The troughs with z < 0.1 in the Durham–UKST n(z) appear deeper than for the fainter 2dFGRS data. This effect appears to be real since the troughs also appear to deepen in the 2dFGRS data when magnitude‐limited at B < 17 mag and so this may be evidence that the local galaxy distribution is biased on ≳50 h−1 Mpc scales which is unexpected in a ΛCDM cosmology. Finally, since the Southern local void may persist over the full area of the APM and APM Bright Galaxy Catalogue with a ≈25 per cent deficiency in the counts below B≈ 17, this would mean that its extent is approximately 300 h−1 Mpc × 300 h−1 Mpc on the sky as well as ≈300 h−1 Mpc in the redshift direction. Such a 25 per cent deficiency extending over ≈107h−3 Mpc3 may imply that the power‐law behaviour of the galaxy correlation function extends to ≈150 h−1 Mpc with no break and shows more excess large‐scale power than detected in the 2dFGRS correlation function or expected in the ΛCDM cosmology.

Persistent fluctuations in the distribution of galaxies from the Two-degree Field Galaxy Redshift Survey

“…On the other hand our results fairly agree with studies of galaxy counts as a function of the apparent magnitude N (m), which indirectly probe radial distance fluctuations. These show large fluctuations around the average behavior: particularly N (m) in the SGC are down by 30% relative to the NGC counts [14]. These behaviors can be now directly related to large scale galaxy structures and particularly to the fact that in the NGC samples there are more structures, and thus an higher amplitude of N (r; R, ∆r) (Fig.2), than in SGC samples.…”

“…However, recently in a CCD survey of bright galaxies within the Northern and Southern strips of the 2dF Galaxy Redshift Survey (2dFGRS) [3] conclusive evidences where found that there are fluctuations of the order ∼ 30% in galaxy counts as a function of apparent magnitude [14] (see also [15,16] for similar observations in other galaxy samples). Further since in the angular region toward the Southern galactic cap (SGC) a deficiency, with respect to the Northern galactic cap (NGC), in the counts below magnitude ∼ 17 (in the B filter) was found, persisting over the full area of the APM and APMBGC catalogs, this would be an evidence that there is a large void of radius of about 150 Mpc/h implying that there are spatial correlations extending to scales larger than the scale detected by the 2dFGRS correlation function [10,11].…”

Observational challenges for the standard FLRW model

“…Shanks presented new evidence that strengthens results that were suspected from faint galaxy number counts in the 1980s and were seriously quantified in the 2000s using the 2 Micron All-sky Survey (2MASS) [82], and by photometric followup of bright galaxies in the Two Degree Field Galaxy Redshift Survey (2dFGRS) [83]. These tentatively identified a 150-300 h −1 Mpc scale underdensity with respect to more distant galaxies, including a celestial North-South asymmetry, dubbing it the "Local Hole".…”

The complex universe: recent observations and theoretical challenges

“…Many authors found that there are fluctuations of the order of ∼ 30% on scales of the order of 200 Mpc in a number of different three dimensional and angular catalogs [38,39,40,41,42,43] implying that there is more excess large-scale power than detected by the standard correlation function analysis [33,34]. As we discuss below, large scale structures and wide fluctuations at scales of the order of 100 Mpc/h or more are at odds both the small value of the characteristic length scale r 0 and with the predictions of the concordance model of galaxy formation [39,40,41].…”