Do bulges of early- and late-type spirals have different morphology?

¹ School of Physics & Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK
² CRAL, Observatoire de Lyon, 69561 St-Genis Laval Cedex, France

Corresponding author: K. Fathi, ppxkf@nottingham.ac.uk

Received: 7 October 2002
Accepted: 12 May 2003

Abstract

We study HST/NICMOS H-band images of bulges of two equal-sized samples of early- () and late-type spiral (mainly Sbc-Sc) galaxies matched in outer disk axis ratio. We find that bulges of late-type spirals are more elongated than their counterparts in early-type spirals. Using a KS-test we find that the two distributions are different at the 98.4% confidence level. We conclude that the two data sets are different, i.e. late-type galaxies have a broader ellipticity distribution and contain more elongated features in the inner regions. We discuss the possibility that these would correspond to bars at a later evolutionary stage, i.e. secularly evolved bars. Consequent implications are raised, and we discuss relevant questions regarding the formation and structure of bulges. Are bulges of early-type and late-type spirals different? Are their formation scenarios different? Can we talk about bulges in the same way for different types of galaxies?