Surrey astronomers help discover one of the faintest galaxies around Andromeda
One of the faintest galaxies ever discovered orbiting the Andromeda Galaxy has been identified by an international team of astronomers, with researchers at the University of Surrey helping to discover a rare 'cosmic fossil' that could provide new clues about how the first galaxies formed.
Stacked GTC OSIRIS+ image of And XXXVI. And XXVI is clearly evident in-between two bright foreground stars. In the inset we show a negative colour zoom-in on And XXVI
In a study published in Astronomy & Astrophysics, the Surrey team worked with lead astronomers from the Instituto de Astrofísica de Andalucía (IAA-CSIC) to confirm the existence of what they have named Andromeda XXXVI (And XXXVI) – an ultra-faint dwarf galaxy believed to be around 12.5 billion years old.
Ultra-faint dwarf galaxies are among the smallest and dimmest galaxies known. Formed during the earliest stages of the Universe, they are considered fossil records of the first galaxies to emerge after the Big Bang. Each discovery provides a unique window into early galaxy formation and a way to test dark matter models.
The Andromeda Galaxy, located around 2.5 million light-years from Earth, is the Milky Way's nearest large galactic neighbour. Although current theoretical predictions suggest it could host as many as 90 satellite galaxies, only around 40 have so far been identified, with just 15 classified as ultra-faint.
Our study suggests that And XXXVI is an extremely old galaxy, around 12.5 billion years old, and remarkably poor in heavy elements. However, observations with space telescopes such as Hubble will be needed to determine its distance, age and chemical composition with greater precision.Joanna Sakowska, researcher at IAA-CSIC and lead author of the study
“What is already clear is that And XXXVI is one of the faintest satellite galaxies discovered around Andromeda to date. Each new discovery, such as Andromeda XXXVI, is important because it suggests that we may still be seeing only the tip of the iceberg of a much larger population of extremely faint galaxies.
The extremely low brightness of And XXXVI meant researchers were able to identify only 46 stars belonging to the galaxy, making it exceptionally difficult to determine its distance using the usual methods. The team obtained much deeper images using the Gran Telescopio Canarias and OSIRIS+ instrument before comparing the stars with theoretical stellar evolution models, known as isochrones. These observations strongly suggested that And XXXVI lies at approximately the same distance as Andromeda and is one of its satellite galaxies.
Researchers at Surrey then led the analysis of the galaxy's structural properties and brightness, measuring its size, shape and luminosity to help characterise the newly discovered system.
Location of And XXXVI (marked in red) within the Pan-Andromeda Archaeological Survey (PAndAS) around M31. We additionally mark Peg V and Psc VII, which are previous discoveries by the team.
Andromeda XXXVI was first spotted by astrophotographer and amateur astronomer Giuseppe Donatiello while examining publicly available images from the Pan-Andromeda Archaeological Survey. His findings were then shared with professional astronomers for further investigation.
Dr David Martínez-Delgado, an ARAID researcher at CEFCA and co-author of the study, said the discovery marks the fourth dwarf galaxy uncovered through the project in the Andromeda region over the past decade, highlighting the valuable contribution amateur astronomers can make when they have access to public data from major sky surveys.
Our list of possible candidates for these ‘lost galaxies’ already exceeds a dozen, and we are eager to obtain observing time on telescopes with apertures between eight and 10 meters to confirm them.Dr David Martínez-Delgado, an ARAID researcher at CEFCA and co-author of the study
As astronomers continue searching the skies for similar objects, discoveries such as Andromeda XXXVI suggest many more ultra-faint galaxies may still be waiting to be found, offering fresh insights into the earliest chapters of the Universe’s history.
[ENDS]
Notes to editors
- Professor Michelle Collins is available for interview; please contact mediarelations@surrey.ac.uk to arrange. Images are available upon request.
- Read the full paper ‘Andromeda XXXVI: discovery of a new ultra-faint dwarf galaxy towards M31’ here.
- Find out more here: https://www.iaa.csic.es/noticia/andromeda-xxxvi-galaxias-enanas-mas-debiles-identificadas-andromeda/
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