Bulges and discs of spiral galaxies: edge-on perspective

TL;DR

This study analyzes the structural properties of edge-on spiral galaxies, revealing differences between pseudobulges and classical bulges and their implications for galaxy formation and evolution.

Contribution

It provides a comprehensive analysis of bulge and disc parameters in a large sample of edge-on spirals, highlighting distinctions between pseudobulges and classical bulges.

Findings

Pseudobulges have triaxial, nearly prolate shapes.

Classical bulges are oblate spheroids with moderate flattening.

The Photometric Plane shows curvature at small Sersic index n.

Abstract

We present a sample of edge-on spiral galaxies both of early and late types.The sample consists of 175 galaxies in the Ks-filter, 169 galaxies in the H-filter and 165 galaxies in the J-filter. Bulge and disc decompositions of each galaxy image, taken from the Two Micron All Sky Survey (2MASS), were performed. We discuss several scaling relations for bulges and discs which indicate a tight link between their formation and evolution. We show that galaxies with bulges fitted by the Sersic index n<2 (pseudobulges) have quite different distributions of their structural parameters than galaxies with n>=2 bulges (classical bulges). First of all, the distribution of the apparent bulge axis ratio q_b for the subsample with n<2 can be attributed to triaxial, nearly prolate bulges, while n>=2 bulges seem to be oblate spheroids with moderate flattening. Secondly, the Photometric Plane of the sample bulges is not flat and has a prominent curvature towards small values of n. Thirdly, despite of the existence of a clear relation between the flattening of stellar discs h/z_0 and the relative mass of a spherical component, the distributions over both parameters are quite different for galaxies possesing bulges and pseudobulges.