Discovery of a Large and Faint Nebula at the Triangulum Galaxy

Abstract

Abstract We report the discovery of a previously uncatalogued arch-shaped filamentary nebula at the outer part of the Triangulum galaxy (M33) centered at α = 1h34m25s, δ = + 30 ° 20 ′ 17 ″ (ICRS). This discovery stems from meticulous observations employing deep exposures of M33, using both Hα and [O iii] narrow-band filters. The nebula, designated as Roig1 Prades Sky, exhibits an Hα surface brightness of 23.9 mag arcsec − 2 . Its sky projected location is 21′ away from the M33 galactic center toward the southeast direction with an extent of (120 × 440) ± 30 pc. Deep spectroscopic observations are required to unveil its real nature.