Discovery of an unusual fossil galaxy on the outskirts of Andromeda

The Gemini North telescope reveals traces of the oldest galaxies.

An extremely faint dwarf galaxy has been discovered on the outer edges of the Andromeda Galaxy thanks to the discerning eyes of an amateur astronomer examining archival data processed by NSF’s NOIRLab Science and Data Center. The dwarf galaxy – Pegasus V – has been revealed to contain very few heavier elements and is likely to be one of the earliest fossil galaxies in fTracking observations by professional astronomers using the Gemini International Observatory, an NSF NOIRLab program.

An extremely faint unusual dwarf galaxy has been discovered at the edge of the Andromeda Galaxy with the help of several NSF NOIRLab facilities. The galaxy, called Pegasus V, was first discovered as part of a systematic search for Andromeda dwarfs coordinated by David Martinez-Delgado of the Instituto de Astrofísica de Andalucía in Spain, when amateur astronomer Giuseppe Donatello discovered a strange “dot” in the data of[{” attribute=””>DESI صورة استطلاعات التصوير القديمة.” width=”777″ height=”396″ srcset=”” sizes=”” ezimgfmt=”rs rscb1 src ng ngcb1 srcset” loading=”eager” importance=”high”/>

تم التقاط الصورة بكاميرا الطاقة المظلمة المصنّعة من وزارة الطاقة الأمريكية على تلسكوب Víctor M. Blanco الذي يبلغ ارتفاعه 4 أمتار في مرصد Cerro Tololo Inter-American (CTIO). تمت معالجة البيانات من خلال خط أنابيب المجتمع الذي يديره مركز علوم المجتمع والبيانات (CSDC) التابع لـ NOIRLab.

The faint stars of Pegasus V have been detected during closer tracking by astronomers using the largest Gemini North Telescope, an 8.1-meter telescope with the GMOS instrument, confirming that it is a very faint dwarf galaxy on the outskirts of the Andromeda Galaxy. Gemini North in Hawaii is half of the Gemini International Observatory.

Observations with Gemini have shown that the galaxy appears to be extremely deficient in heavier elements compared to similar dwarf galaxies, meaning it is very old and probably one of the earliest fossil galaxies in the universe.

“We found a very faint galaxy whose stars formed very early in the history of the universe,” commented Michelle Collins, an astronomer at the University of Surrey, UK and lead author of the paper. announcing the discovery. “This discovery represents the first time a galaxy with this faint light has been found around the Andromeda Galaxy using an astronomical survey that was not specifically designed for this task.”

The very faint dwarf galaxy Pegasus V

An extremely faint dwarf galaxy has been discovered on the outer edges of the Andromeda Galaxy thanks to the keen eyes of an amateur astronomer examining archival data from the US Department of Energy’s Dark Energy Camera on the Víctor Telescope M. Blanco of 4 meters at Cerro Inter -American Observatory of Tololo (CTIO) and processed by the Community and Data Science Center (CSDC). Tracking by professional astronomers using the international Gemini Observatory has revealed that the dwarf galaxy – Pegasus V – contains very few heavier elements and is likely a fossil of early galaxies. All three facilities involved are NSF NOIRLab programs. Credit: Gemini International Observatory/NOIRLab/NSF/AURA, Acknowledgments: Image processing: TA Rector (University of Alaska Anchorage/NSF NOIRLab), M. Zamani (NSF NOIRLab) and D. de Martin (NSF NOIRLab)

Dark galaxies are among the fossils of the earliest galaxies that formed, and these galactic remnants contain clues to the formation of the first stars. As astronomers speculate that the universe is filled with faint galaxies like Pegasus V,[2] They still haven’t figured out roughly what their theories predict. If there are really fewer faint galaxies than expected, it means there is a serious problem with astronomers understanding cosmology and black matter.

Discovering examples of these faint galaxies is therefore an important undertaking, but also a difficult one. Part of the challenge is that these faint galaxies are extremely difficult to see, appearing as a few scattered stars hidden in huge images of the sky.

“The problem with these very faint galaxies is that they contain so few bright stars that we normally use them to identify and measure their distances,” explained Emily Charles, a PhD student at the University of Surrey who also took part in the study. ‘study. . “Gemini’s 8.1-meter mirror allowed us to find faint ancient stars, allowing us to measure the distance to Pegasus V and determine that the number of stars there are very ancient.”

The high concentration of ancient stars found by the team in Pegasus V indicates that the object is likely a fossil of early galaxies. Compared to other fainter galaxies around Andromeda, Pegasus V appears unusually old and devoid of minerals, indicating that its star formation actually stopped very early.

“We hope that further study of the chemical properties of Pegasus V will provide clues to the earliest periods of star formation in the universe,” Collins concluded. “This tiny fossil galaxy from the early universe could help us understand how galaxies formed and whether our understanding of dark matter is correct.”

“The publicly accessible Gemini North Telescope offers a range of resources for astronomers in the community,” said Martin Steele, Gemini Program Manager at the National Science Foundation. “In this case, Gemini supported this international team to confirm the existence of the dwarf galaxy by physically linking it to the Andromeda Galaxy and identifying the mineral-deficient nature of its sophisticated star clusters.”

Upcoming astronomical facilities should shed more light on faint galaxies. Pegasus V witnessed a moment in the history of the universe known as reionization, and more objects from that time will soon be observed. NASA’s James Webb Space Telescope. Astronomers also hope to discover other faint galaxies in the future using the Vera C. Rubin Observatory, an NSF NOIRLab program. The Rubin Observatory will conduct an unprecedented ten-year survey of the optical sky called the Legacy of Space and Time (LSST) survey.


  1. Surveys of old DESI images were taken to identify targets for the Dark Energy Spectroscopic Instrumentation (DESI) process. These surveys include a unique combination of three projects that have monitored one-third of the night sky: The Inherited Dark Energy Camera Survey (DECaLS), observed by the Dark Energy Camera (DECam) built by the Department of Energy on the Víctor M. Blanco 4-meter telescope at Cerro Tololo Pan American Observatory (CTIO) in Chile; Mayall z-band Legacy Survey (MzLS), by the Mosaic3 camera on the Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory (KPNO); The Beijing-Arizona Sky Survey (BASS) with the 90 Prime camera on the 2.3-meter Bock Telescope, which is owned and operated by the University of Arizona and located at KPNO. CTIO and KPNO are affiliate programs of NSF NOIRLab.
  2. Pegasus V is so named because it is the fifth dwarf galaxy discovered in the constellation Pegasus. The distance between Pegasus V and the Andromeda Galaxy in the sky is approximately 18.5 degrees.

More information

This research is presented in a paper titled “Pegasus V – a newly discovered ultralight dwarf galaxy on the outskirts of Andromeda” to be published in Royal Astronomical Society Monthly Notices.

Reference: “Pegasus V – a newly discovered ultralight dwarf galaxy on the outskirts of Andromeda” By Michelle LM Collins, Emily JE Charles, David Martinez-Delgado, Matteo Monelli, Nuchin Creme, Giuseppe Donatello, Eric J. Tollerud and Walter Buchen, okay, Royal Astronomical Society Monthly Notices.
arXiv: 2204.09068

The team was composed of Michel LM Collins (Department of Physics, University of Surrey, UK), Emily GE Charles (Department of Physics, University of Surrey, UK), David Martinez-Delgado (Instituto Astrophysica of Andalusia, Spain), Matteo Monelli (Instituto). de Astrofísica de Canarias (IAC) and Universidad de La Laguna, Spain), Noushin Karim (Department of Physics, University of Surrey, UK), Giuseppe Donatiello (UAI – Unione Astrofili Italiani, Italy), Erik J. Tollerud (Space Telescope Science Institute, USA), Walter Boschin (Instituto de Astrofísica de Canarias (IAC), University of La Laguna, G. Galilei Foundation – INAF (Telescopio Nazionale Galileo), Spain).

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