Leo IV dwarf galaxy

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Galaxy
Leo IV dwarf galaxy
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Leo IV is one of more than a dozen Ultra Faint Dwarf galaxies in the direct vicinity of the Milky Way [2]
Leo IV is one of more than a dozen Ultra Faint Dwarf galaxies in the direct vicinity of the Milky Way
AladinLite
Constellation lion
Position
equinox :  J2000.0 , epoch : J2000.0
Right ascension 11 h 32 m 57 s
declination −00 ° 32 ′ 00 ″
Appearance
Morphological type dSph  
Brightness  (visual) 15.9 ± 0.5 mag
Angular expansion 5.7 ′
Physical data
Affiliation Local group  
Redshift (1.63 ± 0.30)  ·  10 −4  
Radial velocity 130 km / s  
distance (520,000 ± 49,000) ly /
(160,000 ± 15,000) pc
history
Discovery date 2006
Catalog names
Leo IV

The Leo IV dwarf galaxy , also briefly Leo IV , is a spheroidal dwarf galaxy (dSph) in the constellation of the lion and was in 2006 after analysis of the data of the survey of the Sloan Digital Sky Survey discovered. The galaxy is about 160 kpc from our solar system and is moving away from it at a speed of approximately 130 km / s .

According to the classification, Leo IV has a rounded shape and a half-light radius of 130 pc (other sources also mention 160 pc).

properties

Leo IV is one of the smallest and faintest satellites in our Milky Way . The integral luminosity is about 15,000 L ☉ with an absolute brightness of M V = (-5.5 ± 0.3) mag , which is less than that of a typical globular cluster .

Nevertheless, the mass of the galaxy with about 1.5 million M ☉ so high that a mass-luminosity ratio results be 150. This implies a not atypical dominance by dark matter for this dwarf galaxy as well.

The population of stars of Leo IV consists mainly of older stars that more than 12 billion originated years. This makes them one of the very first stars to have formed in the universe . The metallicity of these old stars is correspondingly low with a value [Fe / H] ≈ −2.58 ± 0.75 . This means that the frequency of heavier elements is around 400 times less than that of our sun . Red giant stars in particular were observed, although some horizontal branch stars were also discovered, including three variable RR Lyrae stars (the distance determined by the RR Lyrae stars is (154 ± 4) kpc ). Detailed studies of the star population show a small number of significantly younger stars for Leo IV with an age of 2 billion years and less. This suggests a complex history of star formation for this galaxy. At the moment, however, no current star formation can be determined in Leo IV . None of the measurement results also indicate the presence of neutral hydrogen , the maximum upper limit for this is a maximum of 600 M ☉ .

In 2008 , another galaxy named Leo V was discovered in close proximity to Leo IV . It is 20 kpc further from the Milky Way than Leo IV and 3 degrees (~ 10 kpc) from it. Evidence is growing that the two galaxies may also be physically connected.

Individual evidence

  1. ↑ a b c Leo IV Dwarf Galaxy at SIMBAD
  2. ↑ Hubble Unmasks Ghost Galaxies . In: ESA / Hubble Press Release . Retrieved July 11, 2012. 
  3. ↑ a b c d e V. Belokurov, DB Zucker, NW Evans, JT Kleyna, S. Koposov, ST Hodgkin, MJ Irwin, G. Gilmore, MI Wilkinson, M. Fellhauer, DM Bramich, PC Hewett, S. Vidrih, JTA De Jong, JA Smith, H-W. Rix, EF Bell, RFG Wyse, HJ Newberg, PA Mayeur, B. Yanny, CM Rockosi, OY Gnedin, DP Schneider, TC Beers, JC Barentine, H. Brewington, J. Brinkmann, M. Harvanek, SJ Kleinman, J. Krzesinski, D. Long, A. Nitta, SA Snedden: Cats and Dogs, Hair and a Hero: A Quintet of New Milky Way Companions . In: The Astrophysical Journal . tape 654 , no. 2 , 2007, p. 897 , doi : 10.1086 / 509718 .
  4. ↑ a b c d e f g David J. Sand, Anil Seth, Edward W. Olszewski, et al .: A Deeper Look at Leo IV: Star Formation History and Extended Structure . In: The Astrophysical Journal . 718, 2010, pp. 530-42. arxiv : 0911.5352 . bibcode : 2010ApJ ... 718..530S . doi : 10.1088 / 0004-637X / 718/1/530 .
  5. ↑ a b J. D. Simon, Geha, M .: The Kinematics of the Ultra ‐ faint Milky Way Satellites: Solving the Missing Satellite Problem. In: The Astrophysical Journal. 670, 2007, p. 313, doi: 10.1086 / 521816 .
  6. ↑ EN Kirby, JD Simon, Geha, M., Guhathakurta, P., Frebel, A .: Uncovering Extremely Metal-Poor Stars in the Milky Way's Ultrafaint Dwarf Spheroidal Satellite Galaxies. In: The Astrophysical Journal. 685, 2008: L43. doi: 10.1086 / 592432 .
  7. ↑ J. Grcevich, ME Putman: HI in Local Group Dwarf Galaxies and stripping by the Galactic halo. In: The Astrophysical Journal. 696, 2009, p. 385. doi: 10.1088 / 0004-637X / 696/1/385 .
  8. ↑ V. Belokurov, MG Walker, NW Evans, et al .: Leo V: A companion of a companion of the Milky Way galaxy . In: The Astrophysical Journal . 686, No. 2, 2008, pp. L83-L86. arxiv : 0807.2831 . bibcode : 2008ApJ ... 686L..83B . doi : 10.1086 / 592962 .