Colour dependence of the distribution of IRAS galaxies revealed by multifractal measures

Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, PR China School of Physics & Astronomy, Nottingham University, Nottingham NG7 2RD, UK e-mail: Jun.Pan@nottingham.ac.uk

Received: 6 December 2005
Accepted: 6 May 2006

Abstract

Multifractal measures are applied to three IRAS galaxy subsamples selected by colour from the PSCz catalogue. As shown by a generalised dimension spectrum, hot IRAS galaxies are found to be less clustered than cold galaxies, but the difference is very small. An alternative tool, the conditional multifractal dimension spectrum reveals an apparent peculiarity of the distribution of hot galaxies, especially at high orders. The conditional multifractal measure basically measures the environment of selected galaxies. A detailed analysis of the distribution of galaxies with their number of neighbours shows that cold galaxies are more likely to be in over-dense regions than hot galaxies. Further studies suggest that since the colour of IRAS galaxies is a good trace of star formation rate, it is possible that we have statistical evidence here for enhanced star formation rate due to galaxy interactions.