An Optimal Strategy for Accurate Bulge-to-disk Decomposition of Disk Galaxies

TL;DR

This paper develops an optimal 2D bulge-to-disk decomposition strategy for disk galaxies, emphasizing the importance of accounting for secondary morphological features to improve the accuracy of bulge parameter measurements.

Contribution

It introduces a detailed 2D multi-component decomposition method using GALFIT, demonstrating how to incorporate secondary features for more accurate bulge measurements.

Findings

Proper modeling of lenses and rings improves bulge parameter accuracy.

Outer features like spiral arms have negligible impact on bulge measurements.

The proposed strategy enhances bulge parameter estimation for large galaxy samples.

Abstract

The development of two-dimensional (2D) bulge-to-disk decomposition techniques has shown their advantages over traditional one-dimensional (1D) techniques, especially for galaxies with non-axisymmetric features. However, the full potential of 2D techniques has yet to be fully exploited. Secondary morphological features in nearby disk galaxies, such as bars, lenses, rings, disk breaks, and spiral arms, are seldom accounted for in 2D image decompositions, even though some image-fitting codes, such as GALFIT, are capable of handling them. We present detailed, 2D multi-model and multi-component decomposition of high-quality $R$-band images of a representative sample of nearby disk galaxies selected from the Carnegie-Irvine Galaxy Survey, using the latest version of GALFIT. The sample consists of five barred and five unbarred galaxies, spanning Hubble types from S0 to Sc. Traditional 1D decomposition is also presented for comparison. In detailed case studies of the 10 galaxies, we successfully model the secondary morphological features. Through a comparison of best-fit parameters obtained from different input surface brightness models, we identify morphological features that significantly impact bulge measurements. We show that nuclear and inner lenses/rings and disk breaks must be properly taken into account to obtain accurate bulge parameters, whereas outer lenses/rings and spiral arms have a negligible effect. We provide an optimal strategy to measure bulge parameters of typical disk galaxies, as well as prescriptions to estimate realistic uncertainties of them, which will benefit subsequent decomposition of a larger galaxy sample.