Andromeda II

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Galaxy
Andromeda II
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AladinLite
Constellation Andromeda
Position
equinox :  J2000.0 , epoch : J2000.0
Right ascension 01 h 16 m 29.8 s
declination + 33 ° 25 ′ 09 ″
Appearance
Morphological type dSph  
Brightness  (visual) 13.5 likes
Angular expansion 3 ′., 6 × 2 ′, 52
Physical data
Radial velocity (−188 ± 3) km / s  
distance (2,220,000 ± 70,000) Lj /
(680,000 ± 20,000) pc
Metallicity [Fe / H] −1.47 ± 0.19
history
discovery Sidney van den Bergh
Discovery date 1970
Catalog names
PGC  4601 • IRAS  F01133 + 3305 • And II, Andromeda II Dwarf Spheroidal,

Andromeda II for short also And II is a spheroidal dwarf galaxy (dSph) in the constellation of Andromeda . The galaxy is about 2.22 million light years from our solar system. Andromeda II is a member of the Local Group and is a satellite of the Andromeda Galaxy M31, but is also very close to the triangular nebula M33, so it could be a satellite of one or the other parent galaxy.

And II was discovered by Sidney van den Bergh in 1970 during a survey with photographic plates taken with the 1.2 m Oschin Schmidt telescope of the Palomar observatory in 1970 and 1971 together with Andromeda I , Andromeda III , and the probable background galaxy Andromeda IV .

properties

Using the Keck telescope , Côté et al. 1999 Create spectra of 7 single stars within Andromeda II . An average radial velocity of v r = (−188 ± 3)  k m / s and a velocity dispersion of (9.2 ± 2.6) km / s could be determined from these data .
This resulted in a mass-luminosity ratio of M / L v = 21 compared to the sun , which equates to a significant amount of dark matter . In 1999, Côté, Oke, & Cohen were able to use the Keck telescope to find 42 spectra of red giants in this dwarf galaxy. From this an average metallicity of [Fe / H] = −1.47 ± 0.19 and a metallicity dispersion of 0.35 ± 0.10 could be derived.

Also in 1999, investigations of the color-brightness diagram of And II by Da Costa et al. Showed that most of the stars there were between 6 and 9 billion years old. Nevertheless, observations of RR Lyrae stars and blue stars on the horizontal branch showed the existence of a population older than 10 billion years.

And II differs from Andromeda I in that there is no radial gradient in the morphology in the horizontal branch. The dispersion of the metal abundances is significantly greater here than in And I . This implies a fundamentally different development of these two satellites of the Andromeda Nebula. It also raises the question of whether there is a connection between the radial gradient of the horizontal branch and the metallic dispersion in spheroidal dwarf galaxies.

additional

Individual evidence

  1. ↑ a b c d e f NASA / IPAC Extragalactic Database . In: Results for Andromeda I . Retrieved January 21, 2008.
  2. ↑ ID Karachentsev, VE Karachentseva, WK Hutch Meier, DI Makarov: A Catalog of Neighboring Galaxies . In: Astronomical Journal . 127, No. 4, 2004, pp. 2031-2068. bibcode : 2004AJ .... 127.2031K . doi : 10.1086 / 382905 .
  3. ^ A b c Sidney Van den Bergh: Updated Information on the Local Group . In: The Publications of the Astronomical Society of the Pacific . 112, No. 770, April 2000, p. 533. arxiv : astro-ph / 0001040 . bibcode : 2000PASP..112..529V . doi : 10.1086 / 316548 .
  4. ↑ SIMBAD Astronomical Database . In: Results for Andromeda II . Retrieved November 29, 2006.
  5. ↑ McConnachie, AW; Irwin, MJ; Ferguson, AMN; Ibata, RA; Lewis, GF; Tanvir, N .: Distances and metallicities for 17 Local Group galaxies . In: Monthly Notices of the Royal Astronomical Society . 356, No. 4, 2005, pp. 979-997. arxiv : astro-ph / 0410489 . bibcode : 2005MNRAS.356..979M . doi : 10.1111 / j.1365-2966.2004.08514.x .
  6. ^ Sidney Van den Bergh: Search for Faint Companions to M31 . In: Astrophysical Journal . 171, January 1972, p. L31. bibcode : 1972ApJ ... 171L..31V . doi : 10.1086 / 180861 .

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