A Nearby Analog of z~2 Compact Quiescent Galaxies with a Rotating Disk

TL;DR

This paper presents NGC 5845 as a nearby analog to high-redshift compact quiescent galaxies, revealing a rotating disk structure that offers insights into their formation and evolution.

Contribution

It identifies and characterizes a local galaxy analog with similar properties to z~2 compact quiescent galaxies, including a prominent rotating disk, enabling detailed study.

Findings

NGC 5845 has a size and mass similar to high-redshift compact galaxies.

The galaxy features a significant rotating disk extending beyond one-third of its effective radius.

It supports the idea that some high-redshift compact galaxies have prominent disks and positive mass-to-light ratio gradients.

Abstract

Recent studies have identified a population of compact quiescent galaxies at z\sim2. These galaxies are very rare today and establishing the existence of a nearby analog could allow us to study its structure in greater detail than is possible at high redshift. Here we present such a local analog, NGC 5845, which has a dynamical mass of M_dyn = 4.3\pm0.6\times10^10 M_sun and an effective radius of only r_e = 0.45\pm0.05kpc. We study the structure and kinematics with HST/WFPC2 data and previously published spatially resolved kinematics. We find that NGC 5845 is similar to compact quiescent galaxies at z\sim2 in terms of size versus dynamical mass (r_e-M_dyn), effective velocity dispersion versus size (sigma_e-r_e), and effective velocity dispersion versus dynamical mass (sigma_e-M_dyn). The galaxy has a prominent rotating disk evident in both the photometry and the kinematics: it extends to well beyond \geq1/3 effective radius and contribute to \geq1/4 of the total light of the galaxy. Our results lend support to the idea that a fraction of z\sim2 compact galaxies have prominent disks and positive mass-to-light ratio gradients, although we caution that NGC 5845 may have had a different formation history than the more massive compact quiescent galaxies at z\sim2.