Thickness of Stellar Disks in Early-type Galaxies

TL;DR

This paper introduces a new photometric method to measure the relative thickness of stellar disks in early-type galaxies, applied to SDSS data, revealing differences related to surface-brightness profiles and galaxy features.

Contribution

The paper develops and verifies a novel method for deriving galactic disk thickness from 2D surface brightness data, applied to a sample of 45 galaxies.

Findings

Disks of lenticular and early-type spirals have similar thicknesses.

Presence of a bar marginally increases disk thickness.

Thicker disks are associated with single-exponential profiles, thinner with Type III profiles.

Abstract

We suggest and verify a new photometric method enabling derivation of relative thickness of a galactic disk from two-dimensional surface-brightness distribution of the galaxy in the plane of the sky. The method is applied to images of 45 early-type (S0-Sb) galaxies with known radial exponential or double-exponential (with a flatter outer profile) surface-brightness distributions. The data in the r-band have been retrieved from the SDSS archive. Statistics of the estimated relative thicknesses of the stellar disks of early-type disk galaxies shows the following features. The disks of lenticular and early-type spiral galaxies have similar thicknesses. The presence of a bar results in only a slight marginal increase of the thickness. However, we have found a substantial difference between the thicknesses of the disks with a single-scaled exponential brightness profile and the disks that represent the inner segments of the Type III (antitruncated) profiles. The disks are significantly thicker in the former subsample than in the latter one. This may provide evidence for a surface-brightness distribution of a single-scaled exponential disk to be formed due to viscosity effects acting over the entire period of star formation in the disk.