Properties of Disks and Bulges of Spiral and Lenticular Galaxies in the Sloan Digital Sky Survey

TL;DR

This study analyzes the properties of bulges and disks in spiral and lenticular galaxies from SDSS, revealing systematic bulge property changes along the morphological sequence and near-universality of disk properties.

Contribution

It provides a large, homogeneous analysis of galaxy components, confirming trends in bulge properties and clarifying the origins of the bulge-to-total luminosity ratio.

Findings

Bulge properties vary systematically with galaxy type.

Disk properties are nearly universal across disk galaxy types.

Bulge-to-total ratio changes are mainly due to bulges, not disks.

Abstract

A bulge-disk decomposition is made for 737 spiral and lenticular galaxies drawn from a SDSS galaxy sample for which morphological types are estimated. We carry out the bulge-disk decomposition using the growth curve fitting method. It is found that bulge properties, effective radius, effective surface brightness, and also absolute magnitude, change systematically with the morphological sequence; from early to late types, the size becomes somewhat larger, and surface brightness and luminosity fainter. In contrast disks are nearly universal, their properties remaining similar among disk galaxies irrespective of detailed morphologies from S0 to Sc. While these tendencies were often discussed in previous studies, the present study confirms them based on a large homogeneous magnitude-limited field galaxy sample with morphological types estimated. The systematic change of bulge-to-total luminosity ratio, $B/T$, along the morphological sequence is therefore not caused by disks but mostly by bulges. It is also shown that elliptical galaxies and bulges of spiral galaxies are unlikely to be in a single sequence. We infer the stellar mass density (in units of the critical mass density) to be $\Omega=$0.0021 for spheroids, i.e., elliptical galaxies plus bulges of spiral galaxies, and $\Omega=$0.00081 for disks.