A NEARBY ANALOG OF z ∼ 2 COMPACT QUIESCENT GALAXIES WITH A ROTATING DISK

Recent studies have identified a population of compact quiescent galaxies at z ∼ 2. 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 Mdyn = 4.3 ± 0.6 × 1010 M☉ and an effective radius of only re 0.45 ± 0.05 kpc. 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 ∼ 2 in terms of size versus dynamical mass (re–Mdyn), effective velocity dispersion versus size (σe–re), and effective velocity dispersion versus dynamical mass (σe–Mdyn). The galaxy has a prominent rotating disk evident in both the photometry and the kinematics: it extends to well beyond ∼> 1/3 effective radius and contribute to ∼> 1/4 of the total light of the galaxy. Our results lend support to the idea that a fraction of z ∼ 2 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 ∼ 2.