Why are classical bulges more common in S0 galaxies than in spiral galaxies?

TL;DR

This study investigates why classical bulges are more prevalent in S0 galaxies than in spirals, finding that internal quenching processes likely transform classical bulge spirals into S0s.

Contribution

It provides a comparative analysis of bulge types in S0 and spiral galaxies, highlighting the role of internal quenching in morphological transformation.

Findings

Higher fraction of classical bulges in S0s at fixed stellar mass.

Classical bulge spirals are more likely to be quenched and become S0s.

Pseudobulge spirals are mostly star-forming.

Abstract

In this paper, we try to understand why the classical bulge fraction observed in S0 galaxies is significantly higher than that in spiral galaxies. We carry out a comparative study of the bulge and global properties of a sample of spiral and S0 galaxies in a fixed environment. Our sample is flux limited and contains 262 spiral and 155 S0 galaxies drawn from the Sloan Digital Sky Survey. We have classified bulges into classical and pseudobulge categories based on their position on the Kormendy diagram. Dividing our sample into bins of galaxy stellar mass, we find that the fraction of S0 galaxies hosting a classical bulge is significantly higher than the classical bulge fraction seen in spirals even at fixed stellar mass. We have compared the bulge and the global properties of spirals and S0 galaxies in our sample and find indications that spiral galaxies which host a classical bulge, preferentially get converted into S0 population as compared to pseudobulge hosting spirals. By studying the star formation properties of our galaxies in the NUV-r color-mass diagram, we find that the pseudobulge hosting spirals are mostly star forming while the majority of classical bulge host spirals are in the green valley or in the passive sequence. We suggest that some internal process, such as AGN feedback or morphological quenching due to the massive bulge, quenches these classical bulge hosting spirals and transforms them into S0 galaxies, thus resulting in the observed predominance of the classical bulge in S0 galaxies.