Study inspects the ultra-thin galaxy UGC 11859

Using the Gran Telescopio Canarias (GTC), astronomers have conducted optical imaging observations on a unique and isolated ultra-thin galaxy called UGC 11859. The findings of this observational campaign, published on July 12 in The Astrophysical Journal, provide significant insights into the structure and properties of UGC 11859.

Located approximately 167.5 million light years away, UGC 11859 is an isolated edge-on ultra-thin galaxy. Despite being isolated, the galaxy exhibits a relatively high asymmetry index in the neutral atomic hydrogen (HI) profile, indicating possible invisible interactions with the low surface brightness medium.

Edge-on isolated galaxies like UGC 11859 are excellent subjects for studying the three-dimensional structures of galaxies, including warps and flares, and investigating potential causes of these distortions. This prompted a team of astronomers led by Luis Ossa-Fuentes from the University of Valparaíso in Chile to observe UGC 11859 using GTC’s OSIRIS camera with the aim of identifying distortions.

“The observations were made using the OSIRIS camera with SDSS g and r wavelength filters to optimize atmospheric and filter system transmission. The field of view was sufficient to simultaneously map the stellar disk and its potential low surface brightness external structures,” explained the researchers.

The observations revealed a significant gravitational distortion in the disk of UGC 11859. The images, captured in g and r bands, depict a warp on one side of the stellar disk that appears at a radius where the surface brightness is low.

The galactic plane on both sides of the center of UGC 11859 shows an increasing scale height as the galactocentric radius increases, suggesting the presence of a flare in the stellar distribution. Additionally, the radial surface brightness profile of the disk exhibits a clear break and a sharp decline at a galactocentric radius of approximately 78,000 light years, indicating an edge-on truncation.

The astronomers noted that the existence of a warp, flare, and surface brightness profile break in the outer disk of UGC 11859 raises the question of whether these phenomena are related.

“The presence of this flare supports the suggestion that edge-on disk truncations can be produced by the combination of a flare with the down-bending profile of a conventional Type II disk,” concluded the authors of the paper.

The study also identified a potential small satellite galaxy beyond the warped side of UGC 11859’s disk within a small angular distance. This faint satellite has been designated as GTC-1, and further spectroscopic observations are needed to confirm its association with UGC 11859.

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