PEARLS: A Potentially Isolated Quiescent Dwarf Galaxy with a TRGB Distance of 30 Mpc

TL;DR

This paper reports the discovery of a distant, isolated quiescent dwarf galaxy with a TRGB distance of 30 Mpc, challenging the view that most isolated dwarfs are star-forming and highlighting the potential for JWST to find more such galaxies.

Contribution

It presents the serendipitous discovery and detailed analysis of a quiescent dwarf galaxy at 30 Mpc, providing new insights into dwarf galaxy populations and quenching mechanisms.

Findings

The galaxy is at 30 Mpc distance based on TRGB stars.

It has an extremely low specific star formation rate.

Its velocity suggests it is isolated from massive galaxies.

Abstract

A wealth of observations have long suggested that the vast majority of isolated classical dwarf galaxies ($M_*=10^7$-$10^9$ M$_\odot$) are currently star-forming. However, recent observations of the large abundance of "Ultra-Diffuse Galaxies" beyond the reach of previous large spectroscopic surveys suggest that our understanding of the dwarf galaxy population may be incomplete. Here we report the serendipitous discovery of an isolated quiescent dwarf galaxy in the nearby Universe, which was imaged as part of the PEARLS GTO program. Remarkably, individual red-giant branch stars are visible in this near-IR imaging, suggesting a distance of $30\pm4$ Mpc, and a wealth of archival photometry point to an sSFR of $2\times10^{-11}$ yr$^{-1}$ and SFR of $4\times10^{-4}$ M$_\odot$ yr$^{-1}$. Spectra obtained with the Lowell Discovery Telescope find a recessional velocity consistent with the Hubble Flow and ${>}1500$ km/s separated from the nearest massive galaxy in SDSS, suggesting that this galaxy was either quenched from internal mechanisms or had a very high-velocity ($>1000$ km/s) interaction with a nearby massive galaxy in the past. This analysis highlights the possibility that many nearby quiescent dwarf galaxies are waiting to be discovered and that JWST has the potential to resolve them.