On the limits of measuring the bulge and disk properties of local and high-redshift massive galaxies

TL;DR

This study assesses the accuracy of measuring bulge and disk properties in massive galaxies at high redshift, finding robust size measurements but limited detail recovery for bulges with low bulge-to-total ratios.

Contribution

It provides the most comprehensive simulations to date on two-component galaxy decomposition at high redshift, evaluating the robustness of bulge and disk property measurements.

Findings

Galaxy sizes can be reliably measured with a single Sersic fit.

Bulge-to-total ratio can be accurately determined for B/T > 0.2.

Disk properties are measured with high accuracy regardless of B/T.

Abstract

A considerable fraction of the massive quiescent galaxies at \emph{z} $\approx$ 2, which are known to be much more compact than galaxies of comparable mass today, appear to have a disk. How well can we measure the bulge and disk properties of these systems? We simulate two-component model galaxies in order to systematically quantify the effects of non-homology in structures and the methods employed. We employ empirical scaling relations to produce realistic-looking local galaxies with a uniform and wide range of bulge-to-total ratios ($B/T$), and then rescale them to mimic the signal-to-noise ratios and sizes of observed galaxies at \emph{z} $\approx$ 2. This provides the most complete set of simulations to date for which we can examine the robustness of two-component decomposition of compact disk galaxies at different $B/T$. We confirm that the size of these massive, compact galaxies can be measured robustly using a single S\'{e}rsic fit. We can measure $B/T$ accurately without imposing any constraints on the light profile shape of the bulge, but, due to the small angular sizes of bulges at high redshift, their detailed properties can only be recovered for galaxies with $B/T$ \gax\ 0.2. The disk component, by contrast, can be measured with little difficulty.