Unusual fossil galaxy discovered 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 the 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 first fossil galaxies in fFollow-up observations by professional astronomers using the Gemini International Observatory, a program of NSF NOIRLab.

An extremely faint unusual dwarf galaxy has been discovered at the edge of the Andromeda Galaxy with the help of several NSF’s 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, Spain, when amateur astronomer Giuseppe Donatello discovered a strange “smudge” in the data in

The Dark Energy Spectroscopic Instrument (DESI) is a new instrument for conducting a spectrographic survey of distant galaxies that has been retrofitted onto the Mayall Telescope on top of Kitt Peak in the Sonoran Desert 55 miles distant from Tucson, Arizona. Its main components are a focal plane containing 5000 fiber-positioning robots and a bank of spectrographs which are fed by the fibers. It enables an experiment to probe the expansion history of the Universe and the mysterious physics of dark energy.

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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.


تم الكشف عن النجوم الباهتة في Pegasus V في متابعة أعمق من قبل علماء الفلك باستخدام تلسكوب Gemini North الأكبر ، الذي يبلغ طوله 8.1 متر مع أداة GMOS ، مما يؤكد أنها مجرة ​​قزمة باهتة للغاية على مشارف مجرة ​​أندروميدا. الجوزاء الشمالية في هاواي هي نصف مرصد الجوزاء الدولي.

أظهرت الملاحظات مع الجوزاء أن المجرة تبدو ناقصة للغاية في العناصر الأثقل مقارنة بالمجرات القزمة المماثلة ، مما يعني أنها قديمة جدًا ومن المحتمل أن تكون أحد أحفورة المجرات الأولى في الكون.

علقت ميشيل كولينز ، عالمة الفلك في جامعة ساري بالمملكة المتحدة والمؤلفة الرئيسية للورقة التي أعلنت عن هذا الاكتشاف: “لقد وجدنا مجرة ​​باهتة للغاية تشكلت نجومها في وقت مبكر جدًا من تاريخ الكون”. “هذا الاكتشاف يمثل المرة الأولى التي يتم فيها العثور على مجرة ​​بهذا الضوء الخافت حول مجرة ​​أندروميدا باستخدام مسح فلكي لم يكن مصممًا خصيصًا لهذه المهمة.”

مجرة القزم الخافت للغاية Pegasus V

تم اكتشاف مجرة ​​قزم خافتة للغاية في الأطراف الخارجية لمجرة أندروميدا بفضل العيون الحادة لعالم فلك هاو يفحص البيانات الأرشيفية من كاميرا الطاقة المظلمة المُصنَّعة من وزارة الطاقة الأمريكية على Víctor M. Blanco بطول 4 أمتار تلسكوب في مرصد Cerro Tololo Inter-American (CTIO) ومعالجته بواسطة مركز علوم المجتمع والبيانات (CSDC). كشفت المتابعة التي قام بها علماء الفلك المحترفون باستخدام مرصد الجوزاء الدولي أن المجرة القزمة – Pegasus V – تحتوي على عدد قليل جدًا من العناصر الأثقل ومن المحتمل أن تكون حفرية من المجرات الأولى. جميع المرافق الثلاثة المعنية هي برامج NOIRLab التابعة لمؤسسة NSF. الائتمان: مرصد الجوزاء الدولي / NOIRLab / NSF / AURA ، إقرار: معالجة الصور: TA Rector (جامعة ألاسكا أنكوراج / NSF’s NOIRLab) ، M. Zamani (NSF’s NOIRLab) و D. de Martin (NSF’s NOIRLab)

تعتبر المجرات الخافتة من أحافير المجرات الأولى التي تشكلت ، وتحتوي بقايا المجرات هذه على أدلة حول تكوين النجوم الأولى. بينما يتوقع علماء الفلك أن الكون يعج بالمجرات الخافتة مثل Pegasus V ،[2] They haven’t yet discovered nearly what their theories predict. If there are really fewer faint galaxies than expected, this means that there is a serious problem with astronomers understanding cosmology and dark matter.

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

“The problem with these very faint galaxies is that they contain too few bright stars that we normally use to identify and measure their distances,” explained Emily Charles, a PhD student at the University of Surrey who was also involved in the study. . “The 8.1-meter Gemini mirror allowed us to find faint old stars, which enabled us to measure the distance to Pegasus V and determine that the number of stars there is very old.”

The strong concentration of ancient stars the team found in Pegasus V indicates that the object is likely a fossil of the first galaxies. When compared to other fainter galaxies around Andromeda, Pegasus V appears uniquely old and lacking in minerals, indicating that its star formation actually stopped very early.

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

“The publicly available Gemini North telescope provides a range of capabilities for community astronomers,” said Martin Steele, Gemini Program Officer at the National Science Foundation. “In this case, Gemini supported this international team to confirm the existence of the dwarf galaxy, physically link it to the Andromeda galaxy, and identify the mineral-deficient nature of its sophisticated star clusters.”

Upcoming astronomical facilities are set to shed more light on faint galaxies. Pegasus V witnessed a time in the history of the universe known as reionization, and other objects dating back to this 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, a program of NSF NOIRLab. The Rubin Observatory will conduct an unprecedented, ten-year survey of the optical sky called the Legacy of Space and Time (LSST) survey.


  1. Ancient DESI imaging surveys were performed to identify dark energy spectroscopic instrumentation (DESI) process targets. These surveys include a unique combination of three projects that have monitored a third of the night sky: The Inherited Dark Energy Camera Survey (DECaLS), observed by the Department of Energy’s built Dark Energy Camera (DECam) on the Víctor M. Blanco 4-meter telescope at the 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 in KPNO. CTIO and KPNO are NSF NOIRLab affiliate programs.
  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 about 18.5 degrees.

more information

This research was presented in a paper titled “Pegasus V – a newly discovered ultra-light dwarf galaxy in the outskirts of Andromeda” to appear in Monthly Notices of the Royal Astronomical Society.

Reference: “Pegasus V – a newly discovered ultra-light dwarf galaxy in the outskirts of Andromeda” By Michelle L.M. Collins, Emily J.E. Charles, David Martinez-Delgado, Matteo Monelli, Nuchin Creme, Giuseppe Donatello, Eric J. Tollerud and Walter Buchen, Agreed, Monthly Notices of the Royal Astronomical Society.
arXiv: 2204.09068

The team consisted 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), Universidad de La Laguna, Fundación G. Galilei – INAF (Telescopio Nazionale Galileo), Spain).

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