Triangulum IV: A Possible Ultra-Diffuse Satellite of M33

TL;DR

This paper reports the discovery of Triangulum IV, a faint, ultra-diffuse dwarf galaxy likely orbiting M33, highlighting the potential for many more such satellites to be detected with deep imaging.

Contribution

The study presents the first detection of Triangulum IV as a probable satellite of M33 using deep Subaru/HSC imaging, revealing ultra-diffuse properties.

Findings

Tri IV is at 932 kpc, near M33 within its virial radius.

Tri IV has a surface brightness of 29.72 mag/arcsec^2.

Tri IV's half-light radius is approximately 1749 pc.

Abstract

We report the detection of a dwarf satellite candidate (Triangulum IV: Tri IV) of the Triangulum galaxy (M33) using the deep imaging of Subaru/Hyper Suprime-Cam (HSC). From the apparent magnitude of the horizontal branch in Tri IV, the heliocentric distance of Tri IV is estimated to be $932^{+49}_{-43}$ kpc, indicating that Tri IV is located at the distance of $75^{+48}_{-40}$ kpc from the M33 center. This means that Tri IV is the probable satellite of M33, because its distance from M33 is within the virial radius of M33. We also estimate its surface brightness of $\mu_{\it V} = 29.72^{+0.10}_{-0.10}$ mag arcsec$^{-2}$, and half-light radius of $r_h = 1749^{+523}_{-425}$ pc, suggesting that Tri IV is an ultra-diffuse galaxy or dynamically heated galaxy. The surface brightness of Tri IV is too low to be detected in the previous survey, so this detection suggests that much fainter satellites may be present in the outskirts of M33.