Reticulum II explained

Reticulum II
Epoch:J2000
Dist Ly:31.6kpc[1]
Appmag V:17.4
Size V:3.37′ × 3.64′
Notes:Enriched in r-process elements
Constellation Name:Reticulum
Names:Reticulum II, Reticulum 2

Reticulum II (or Reticulum 2) is a dwarf galaxy in the Local Group. Reticulum II was discovered in 2015 by analysing images from the Dark Energy Survey. It is a satellite of the Magellanic Clouds and was probably captured relatively recently.[2] Like other dwarf spheroidal galaxies, its stellar population is old: the galaxy was quenched before 11.5 billion years ago.[2]

Reticulum II is elongated, having an major/minor axis ratio of 0.6. The size is given by a half-light radius of 15 parsecs (pc). This is too large for it to be a globular cluster. The absolute magnitude (MV) of the galaxy is -2.7. The distance from Earth is about 30 kpc.[1] The galaxy contains some blue horizontal branch stars. Other features visible are a main sequence, and a main sequence turn off, and a red giant branch.[3] [4] It has an unusual enhancement of r-process elements, meaning that gold and europium are enriched in the brightest stars in the galaxy.[5] About 72% of its stars are enriched in r-process elements.[1] The implication of the unusual enrichment in elements heavier than zinc, is that the r-process is very rare, and only happened once in this galaxy, possibly by the collision of two neutron stars.[6]

Gamma rays mostly with energies between 2 and 10 GeV have been detected by the Fermi satellite.[7] The radiation from Reticulum II is more significant than that of other dwarf galaxy emissions.[8] However this finding has been contested.[9]

Notes and References

  1. 2212.00810 . 10.3847/1538-4357/aca9d1 . Timing the r-process Enrichment of the Ultra-faint Dwarf Galaxy Reticulum II . 2023 . Simon . Joshua D. . Brown . Thomas M. . Mutlu-Pakdil . Burçin . Ji . Alexander P. . Drlica-Wagner . Alex . Avila . Roberto J. . Martínez-Vázquez . Clara E. . Li . Ting S. . Balbinot . Eduardo . Bechtol . Keith . Frebel . Anna . Geha . Marla . Marla Geha . Hansen . Terese T. . James . David J. . Pace . Andrew B. . Aguena . M. . Alves . O. . Andrade-Oliveira . F. . Annis . J. . Bacon . D. . Bertin . E. . Brooks . D. . Burke . D. L. . Rosell . A. Carnero . Kind . M. Carrasco . Carretero . J. . Costanzi . M. . Da Costa . L. N. . De Vicente . J. . Desai . S. . The Astrophysical Journal . 944 . 1 . 43 . 2023ApJ...944...43S . 254221028 . 1 . free .
  2. 10.3847/2041-8213/ac2aa3. Star Formation Histories of Ultra-faint Dwarf Galaxies: Environmental Differences between Magellanic and Non-Magellanic Satellites?. 2021. Sacchi. Elena. Richstein. Hannah. Kallivayalil. Nitya. Van Der Marel. Roeland. Libralato. Mattia. Zivick. Paul. Besla. Gurtina. Brown. Thomas M.. Choi. Yumi. Deason. Alis. Fritz. Tobias. Geha. Marla. Marla Geha . Guhathakurta. Puragra. Jeon. Myoungwon. Kirby. Evan. Majewski. Steven R.. Patel. Ekta. Simon. Joshua D.. Tony Sohn. Sangmo. Tollerud. Erik. Wetzel. Andrew. The Astrophysical Journal Letters. 920. 1. L19. 2108.04271. 2021ApJ...920L..19S. 236965965 . free .
  3. Beasts of the Southern Wild. Discovery of a large number of Ultra Faint satellites in the vicinity of the Magellanic Clouds . Sergey E. Koposov . Vasily Belokurov . Gabriel Torrealba . N. Wyn Evans . 10 March 2015 . 1503.02079 . The Astrophysical Journal . 2015ApJ...805..130K . 10.1088/0004-637X/805/2/130 . 805 . 2 . 130. 118267222 .
  4. Eight New Milky Way Companions Discovered in First-Year Dark Energy Survey Data . DES Collaboration . 10 March 2015 . 1503.02584 . The Astrophysical Journal . 2015ApJ...807...50B . 10.1088/0004-637X/807/1/50 . 807 . 1 . 50. 12011753 .
  5. Web site: Ji. Alex. The Origin of the Cosmos' Heaviest Elements. Phys.org. 24 March 2016. 22 March 2016.
  6. Ji. Alexander P.. Frebel. Anna. Chiti. Anirudh. Simon. Joshua D.. R-process enrichment from a single event in an ancient dwarf galaxy. Nature. 21 March 2016. 10.1038/nature17425. 1512.01558 . 2016Natur.531..610J. 531. 7596 . 610–613. 27001693. 205248401 .
  7. Hooper. Dan. Linden. Tim. On The gamma-ray emission from Reticulum II and other dwarf galaxies. Journal of Cosmology and Astroparticle Physics. 3 September 2015. 2015. 9. 016. 10.1088/1475-7516/2015/09/016. 1503.06209. 2015JCAP...09..016H . 118482641 .
  8. Geringer-Sameth. Alex. Walker. Matthew G.. Koushiappas. Savvas M.. Koposov. Sergey E.. Belokurov. Vasily. Torrealba. Gabriel. Evans. N. Wyn. Indication of Gamma-Ray Emission from the Newly Discovered Dwarf Galaxy Reticulum II. Physical Review Letters. 17 August 2015. 115. 8. 10.1103/PhysRevLett.115.081101. 2015PhRvL.115h1101G. 26340176. 081101. 1503.02320 . 16494335 .
  9. News: Overbye. Dennis. Gamma Rays May Be Clue on Dark Matter. 20 October 2016. The New York Times. 10 March 2015.

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