Photometric scaling relations for bulges of galaxies

¹ GEPI, Observatoire de Paris-Meudon, 92195 Meudon, France e-mail: Chazhiyat.Ravikumar@obspm.fr
² School of Studies in Physics, Pt. Ravishankar Shukla University, Raipur, India e-mail: sudhan@iucaa.ernet.in
³ Inter University Centre for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, Pune 411007, India e-mail: akk@iucaa.ernet.in
⁴ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore MD 21218, USA e-mail: mobasher@stsci.edu
⁵ Department of Physics, Cochin University of Science and Technology, Kochi 682022, India e-mail: vck@cusat.ac.in

Received: 1 June 2005
Accepted: 7 September 2005

Abstract

We describe the photometric parameters of the bulges of galaxies of different Hubble types including ellipticals, lenticulars, early and late type spirals and early type dwarf galaxies. Analyzing the distributions of various photometric parameters and two- and three-dimensional correlations between them, we find that there is a difference in the correlations exhibited by bright () and faint bulges, irrespective of their Hubble type. Importantly, the bright bulges, which include typically E/S0 galaxies and bulges of early type spirals, are tightly distributed around a common photometric plane (PP), while their fainter counterparts, mainly bulges of late type spirals and dwarf galaxies show significant deviation from the planar distribution. We show that the specific entropy, determined from the bulge structural parameters, systematically increases as we move from late to early Hubble types. We interpret this as evidence for hierarchical merging and passive evolution scenarios for bright and faint bulges respectively.