A Deep Triangulum Galaxy Surrounded by IFN

Last fall 2023 I captured several tens of hours of images on the Triangulum galaxy, Messier 33, that I processed this January 2025 from scratch. I used the popular broadband approach (LRGB), but also gathered more than 100 hours in narrow band filters, Ha and [OIII], in order to see the star forming regions and rich nebulae in this neighbouring galaxy. The resulting image shown above contains more than 150 hours of exposure captured from my backyard, located in Prades, a Bortle 4 dark sky in the south of Barcelona. It shows an LRGB image of the Triangulum Galaxy (M33) surrounded by intricate details of the IFN combined with Ha emissions, galactic cirri, present in this deep field. Several distant galaxies can be found all across the field.

The goal was also to seek for new nebulae that may have been hidden in other works. I was inspired by the work “Discovery of Extensive [OIII] Emission Near M31” published that same year (January 2023) by Marcel Drechsler, Xavier Strottner, Yann Sainty and Robert A. Fesen. Their discovery also became Image of the Year at the Royal Observatory Greenwich “Andromeda Unexpected“.

That work made me think about the possible existence of similar structures around the M33 galaxy. In the effort of seeking this hypothetical structure I spent more than 80h in the [OIII] filter, a rare approach for such a galaxy (normally photographed using LRGB and Ha filters). After several weeks of acquiring data (September and October 2023) I did not find such a structure, but I was able to discover a large and faint nebula that had previously been unrevealed. I named it in the honor of my grandfather.

I worked with professional astronomers in order to confirm the discovery: Dr. Raúl Infante (Centro de Estudios de Física del Cosmos de Aragón) and Judith Ardèvol (Universitat de Barcelona). We all three have worked hard to confirm the discovery that was published in the Research Notes of the American Astronomical Society. The name of the nebula is Roig1 Prades Sky.

https://iopscience.iop.org/article/10.3847/2515-5172/ad12d1

This is my personal tribute to my grandfather, Jaume Roig, who introduced me to astronomy when I was a little child some 35 years ago in the 80’s. And also a tribute to Prades and its dark sky, the village I love and live with my wife Georgina Serven. We two work at Parc Astronòmic Muntanyes de Prades, a project that works for the protection of the dark sky, for the diffusion of astronomy and the promotion of astronomy research.

Roig1 Prades Sky coordinates (can be found in Aladin Sky Atlas):

Center (RA, hms): 01h 34m 25s
Center (Dec, dms): +30° 20′ 17″

New confirmations of the discovery (2024):

Yann Sainty, October 2024: https://app.astrobin.com/i/hktrku

Bray Falls et al., November 2024 : https://app.astrobin.com/i/ey9s59

The image covers an area of 2º23′ x 1º34′.

Thanks for taking your time on this site.