Vertical Structure of Local Disk Galaxies revealed by DESI Imaging Data

TL;DR

This study analyzes the vertical structure of 79 local disk galaxies using DESI imaging, revealing that most are thin with minimal flaring, and finds a correlation between scale height and stellar mass.

Contribution

It provides the first homogeneous measurement of vertical disk structure in a large sample of nearby galaxies, supporting the Milky Way's thin disk as typical.

Findings

Galactic disks are generally thin with negligible flaring.

Median scale heights at one effective radius are around 0.22 kpc.

A positive correlation exists between scale height and stellar mass.

Abstract

The vertical structure of galactic disks is an important probe of disk assembly history. We investigate a sample of 79 local disk galaxies within 50 Mpc using data from the DESI Legacy Imaging Surveys. Vertical luminosity profiles as a function of radius in the g, r, and z bands are extracted and fitted with a single-component sech^2 model to determine the scale height and its radial variation (flaring). Our results show that local galactic disks are generally thin with negligible flaring. The median scale heights at one effective radius are 0.21, 0.22, and 0.22 kpc in the g, r, and z bands, respectively, while the corresponding median radial gradients are -0.006, 0.003, and 0.001. These values are consistent with those of the geometric thin disk of the Milky Way, represented by metal-rich, low-[alpha/Fe] populations, supporting the conclusion of weak flaring. We also find a clear positive correlation between scale height and stellar mass, extending down to 10^7 solar masses. These results provide a homogeneous benchmark for the vertical structure of nearby disk galaxies and support the cosmological representativeness of the Milky Way thin disk.