Anisotropy in the all-sky distribution of galaxy morphological types
  We present the first study of the isotropy of the distribution of
morphological types of galaxies in the Local Universe out to around 200 Mpc
using more than 60,000 galaxies from the HyperLeda database. We divide the sky
into two opposite hemispheres and compare the abundance distribution of the
morphological types, $T$, using the Kolmogorov-Smirnov (KS) test. This is
repeated for different directions in the sky and the KS statistic as a function
of sky coordinates is obtained. For three samples of galaxies within around
100, 150, and 200 Mpc, we find a significant hemispherical asymmetry with a
vanishingly small chance of occurring in an isotropic distribution.
Astonishingly, regardless of this extreme significance, the hemispherical
asymmetry is aligned with the Celestial Equator at the 97.1-99.8% and with the
Ecliptic at the 94.6-97.6% confidence levels, estimated using a Monte Carlo
analysis. Shifting $T$ values randomly within their uncertainties has a
negligible effect on this result. When a magnitude limit of $B\leq 15$ mag is
applied, the sample within 100 Mpc shows no significant anisotropy after random
shifting of $T$. However, the direction of the asymmetry in the samples within
150 and 200 Mpc and $B\leq 15$ mag is found to be within an angular separation
of 32 degrees from $(l,b)=(123.7, 24.6)$ with 97.2% and 99.9% confidence
levels, respectively. This direction is only 2.6 degrees away from the
Celestial North Pole. Unless the Local Universe has a significant anisotropic
distribution of galaxy types aligned with the orientation or the orbit of the
Earth (which would be a challenge for the Cosmological Principle), our results
show that there seems to be a systematic bias in the classification of galaxy
morphological types between the data from the Northern and the Southern
Equatorial sky. Further studies are absolutely needed to find out the exact
source of this anisotropy.
