Andromeda I

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Andromeda I
Andromeda I Hubble WikiSky.jpg
Andromeda I by the HST
Observation data (J2000 epoch)
Constellation Andromeda
Right ascension 00h 45m 39.8s [1]
Declination +38° 02′ 28″ [1]
Redshift -368 ± 11 km/s [1]
Distance 2.40 ± 0.08 Mly (735 ± 23 kpc) [2] [3] [4]
Apparent magnitude  (V)13.6 [1]
Characteristics
Type dSph
Apparent size  (V)2.5′ × 2.5′ [1]
Notable features satellite galaxy of M31
Other designations
And I, [2] Anon 0043+37, [1] PGC 2666 [1]

Andromeda I is a dwarf spheroidal galaxy (dSph) [5] about 2.40 [4] million light-years away in the constellation Andromeda. Andromeda I is part of the local group of galaxies and a satellite galaxy of the Andromeda Galaxy (M31). It is roughly 3.5 degrees south and slightly east of M31. [6] As of 2005, it is the closest known dSph companion to M31 [7] at an estimated projected distance of ~40 [4] kpc or ~150,000 [6] light-years.

Contents

Andromeda I was discovered by Sidney van den Bergh [8] in 1970 with the Mount Palomar Observatory 48-inch telescope. [5] Further study of Andromeda I was done by the WFPC2 camera of the Hubble Space Telescope. This found that the horizontal branch stars, like other dwarf spheroidal galaxies were predominantly red. [9] From this, and the abundance of blue horizontal branch stars, along with 99 RR Lyrae stars detected in 2005, [7] lead to the conclusion there was an extended epoch of star formation. The estimated age is approximately 10 Gyr. The Hubble telescope also found a globular cluster in Andromeda I, being the least luminous galaxy where such a cluster was found. [10]

See also

Related Research Articles

<span class="mw-page-title-main">Local Group</span> Group of galaxies that includes the Milky Way

The Local Group is the galaxy group that includes the Milky Way, where Earth is located. It has a total diameter of roughly 3 megaparsecs (10 million light-years; 9×1019 kilometres), and a total mass of the order of 2×1012 solar masses (4×1042 kg). It consists of two collections of galaxies in a "dumbbell" shape; the Milky Way and its satellites form one lobe, and the Andromeda Galaxy and its satellites constitute the other. The two collections are separated by about 800 kiloparsecs (3×10^6 ly; 2×1019 km) and are moving toward one another with a velocity of 123 km/s. The group itself is a part of the larger Virgo Supercluster, which may be a part of the Laniakea Supercluster. The exact number of galaxies in the Local Group is unknown as some are occluded by the Milky Way; however, at least 80 members are known, most of which are dwarf galaxies.

<span class="mw-page-title-main">Andromeda Galaxy</span> Barred spiral galaxy in the Local Group

The Andromeda Galaxy is a barred spiral galaxy and is the nearest major galaxy to the Milky Way. It was originally named the Andromeda Nebula and is cataloged as Messier 31, M31, and NGC 224. Andromeda has a D25 isophotal diameter of about 46.56 kiloparsecs (152,000 light-years) and is approximately 765 kpc (2.5 million light-years) from Earth. The galaxy's name stems from the area of Earth's sky in which it appears, the constellation of Andromeda, which itself is named after the princess who was the wife of Perseus in Greek mythology.

<span class="mw-page-title-main">Sagittarius Dwarf Spheroidal Galaxy</span> Satellite galaxy of the Milky Way

The Sagittarius Dwarf Spheroidal Galaxy (Sgr dSph), also known as the Sagittarius Dwarf Elliptical Galaxy, is an elliptical loop-shaped satellite galaxy of the Milky Way. It contains four globular clusters in its main body, with the brightest of them—NGC 6715 (M54)—being known well before the discovery of the galaxy itself in 1994. Sgr dSph is roughly 10,000 light-years in diameter, and is currently about 70,000 light-years from Earth, travelling in a polar orbit at a distance of about 50,000 light-years from the core of the Milky Way. In its looping, spiraling path, it has passed through the plane of the Milky Way several times in the past. In 2018 the Gaia project of the European Space Agency showed that Sgr dSph had caused perturbations in a set of stars near the Milky Way's core, causing unexpected rippling movements of the stars triggered when it moved past the Milky Way between 300 and 900 million years ago.

<span class="mw-page-title-main">Pegasus Dwarf Spheroidal Galaxy</span> Dwarf spheroidal galaxy in the constellation Pegasus

The Pegasus Dwarf Spheroidal is a dwarf spheroidal galaxy about 2.7 million light-years away in the constellation Pegasus. The Pegasus Dwarf is a member of the Local Group and a satellite galaxy of the Andromeda Galaxy (M31).

<span class="mw-page-title-main">Pegasus Dwarf Irregular Galaxy</span> Dwarf irregular galaxy in the constellation of Pegasus

The Pegasus Dwarf Irregular Galaxy is a dwarf irregular galaxy in the direction of the constellation Pegasus. It was discovered by A. G. Wilson in the 1950s. The Pegasus Dwarf is a companion of the Andromeda Galaxy in the Local Group.

<span class="mw-page-title-main">Dwarf spheroidal galaxy</span> Low-luminosity galaxy of old stars & little dust

A dwarf spheroidal galaxy (dSph) is a term in astronomy applied to small, low-luminosity galaxies with very little dust and an older stellar population. They are found in the Local Group as companions to the Milky Way and as systems that are companions to the Andromeda Galaxy (M31). While similar to dwarf elliptical galaxies in appearance and properties such as little to no gas or dust or recent star formation, they are approximately spheroidal in shape and generally have lower luminosity.

<span class="mw-page-title-main">NGC 147</span> Galaxy in the constellation Cassiopeia

NGC 147 is a dwarf spheroidal galaxy about 2.58 Mly away in the constellation Cassiopeia. NGC 147 is a member of the Local group of galaxies and a satellite galaxy of the Andromeda Galaxy (M31). It forms a physical pair with the nearby galaxy NGC 185, another remote satellite of M31. It was discovered by John Herschel in September 1829. Visually it is both fainter and slightly larger than NGC 185. This means that NGC 147 is more difficult to see than NGC 185, which is visible in small telescopes. In the Webb Society Deep-Sky Observer's Handbook, the visual appearance of NGC 147 is described as follows:

Large, quite faint, irregularly round; it brightens in the middle to a stellar nucleus.

<span class="mw-page-title-main">Tucana Dwarf</span> Dwarf galaxy in the constellation Tucana

The Tucana Dwarf Galaxy is a dwarf galaxy in the constellation Tucana. It was discovered in 1990 by R.J. Lavery of Mount Stromlo Observatory. It is composed of very old stars and is very isolated from other galaxies. Its location on the opposite side of the Milky Way from other Local Group galaxies makes it an important object for study.

<span class="mw-page-title-main">Ursa Minor Dwarf</span> Dwarf spheroidal galaxy

The Ursa Minor Dwarf is a dwarf spheroidal galaxy, discovered by A.G. Wilson of the Lowell Observatory, in the United States, during the Palomar Sky Survey in 1955. It appears in the Ursa Minor constellation, and is a satellite galaxy of the Milky Way. The galaxy consists mainly of older stars and seems to house little to no ongoing star formation. Its centre is around 225,000 light years distant from Earth.

<span class="mw-page-title-main">Fornax Dwarf</span> Dwarf galaxy in the constellation Fornax

The Fornax Dwarf Spheroidal is a dwarf elliptical galaxy in the constellation Fornax that was discovered in 1938 by Harlow Shapley. He discovered it while he was in South Africa on photographic plates taken by the 24 inch (61 cm) Bruce refractor at Boyden Observatory, shortly after he discovered the Sculptor Dwarf Galaxy.

<span class="mw-page-title-main">Andromeda II</span> Dwarf spheroidal galaxy in the constellation Andromeda

Andromeda II is a dwarf spheroidal galaxy about 2.22 Mly away in the constellation Pisces. While part of the Local Group, it is not quite clear if it is a satellite of the Andromeda Galaxy or the Triangulum Galaxy.

Andromeda III is a dwarf spheroidal galaxy about 2.44 million light-years away in the constellation Andromeda. It is part of the Local Group and is a satellite galaxy of the Andromeda Galaxy (M31). The galaxy was discovered by Sidney van den Bergh on photographic plates taken in 1970 and 1971.

<span class="mw-page-title-main">Andromeda IV</span> Isolated irregular dwarf galaxy in the constellation of Andromeda

Andromeda IV is an isolated irregular dwarf galaxy. The moderate surface brightness, a very blue color, low current star formation rate and low metallicity are consistent with it being a small (background) dwarf irregular galaxy, perhaps similar to Local Group dwarfs such as IC 1613 and Sextans A. Arguments based on the observed radial velocity and the tentative detection of the RGB tip suggest that it lies well outside the confines of the Local Group.

Andromeda V is a dwarf spheroidal galaxy about 2.52 Mly away in the constellation Andromeda.

<span class="mw-page-title-main">Cassiopeia Dwarf</span> Galaxy in the constellation Cassiopeia

The Cassiopeia Dwarf (also known as Andromeda VII) is a dwarf spheroidal galaxy about 2.45 Mly away in the constellation Cassiopeia. The Cassiopeia Dwarf is part of the Local Group and a satellite galaxy of the Andromeda Galaxy (M31). In the sky, it appears behind the Milky Way's galactic plane, and so it is reddened by 0.194 magnitudes. With a luminosity of 1.8×107 L☉ and a stellar mass of 19.73×106 M☉, it is the brightest and most massive of the Andromeda Galaxy's dwarf spheroidal galaxy satellites. It also has the highest metallicity out of all of them.

Andromeda XXII is a low surface brightness dwarf spheroidal galaxy about 940–1,033 kiloparsecs away from the Sun in the constellation Pisces, of the Local Group.

<span class="mw-page-title-main">Andromeda XVIII</span> Galaxy in constellation Andromeda

Andromeda XVIII, discovered in 2008, is a dwarf spheroidal galaxy, which is a satellite of the Andromeda Galaxy (M31). It is one of the 14 known dwarf galaxies orbiting M31. It was announced in 2010 that the orbiting galaxies lie close to a plane running through M31's center.

References

  1. 1 2 3 4 5 6 7 "NASA/IPAC Extragalactic Database". Results for Andromeda I. Retrieved 2008-01-21.
  2. 1 2 I. D. Karachentsev; V. E. Karachentseva; W. K. Hutchmeier; D. I. Makarov (2004), "A Catalog of Neighboring Galaxies", Astronomical Journal, 127 (4): 2031–2068, Bibcode:2004AJ....127.2031K, doi: 10.1086/382905
  3. ↑ Karachentsev, I. D.; Kashibadze, O. G. (2006), "Masses of the local group and of the M81 group estimated from distortions in the local velocity field", Astrophysics, 49 (1): 3–18, Bibcode:2006Ap.....49....3K, doi:10.1007/s10511-006-0002-6, S2CID   120973010
  4. 1 2 3 McConnachie, A. W.; Irwin, M. J.; Ferguson, A. M. N.; Ibata, R. A.; et al. (May 2004), "Determining the location of the tip of the red giant branch in old stellar populations: M33, Andromeda I and II", Monthly Notices of the Royal Astronomical Society , 350 (1): 250, arXiv: astro-ph/0401453 , Bibcode:2004MNRAS.350..243M, doi: 10.1111/j.1365-2966.2004.07637.x , S2CID   18742035
  5. 1 2 van den Bergh, Sydney (January 1972), "Search for Faint Companions to M31", Astrophysical Journal, 171: L31, Bibcode:1972ApJ...171L..31V, doi: 10.1086/180861
  6. 1 2 Andromeda I, Students for the Exploration and Development of Space (SEDS), July 25, 2001
  7. 1 2 Pritzl, Barton J.; Armandroff, Taft E.; Jacoby, George H.; Da Costa, G. S. (May 2005), "The Dwarf Spheroidal Companions to M31: Variable Stars in Andromeda I and Andromeda III", The Astronomical Journal, 129 (5): 2232–2256, arXiv: astro-ph/0501083 , Bibcode:2005AJ....129.2232P, doi:10.1086/428372, S2CID   9749493
  8. ↑ McConnachie, A. W.; Irwin, M. J.; Ferguson, A. M. N.; Ibata, R. A.; et al. (2005), "Distances and metallicities for 17 Local Group galaxies", Monthly Notices of the Royal Astronomical Society, 356 (4): 979–997, arXiv: astro-ph/0410489 , Bibcode:2005MNRAS.356..979M, doi: 10.1111/j.1365-2966.2004.08514.x .
  9. ↑ Da Costa, G. S.; Armandroff, T. E.; Caldwell, Nelson; Seitzer, Patrick (December 1996), "The Dwarf Spheroidal Companions to M31: WFPC2 Observations of Andromeda I", Astronomical Journal, 112: 2576, arXiv: astro-ph/9610083 , Bibcode:1996AJ....112.2576D, doi:10.1086/118204, S2CID   119431084
  10. ↑ Grebel, E. K.; Dolphin, A. E.; Guhathakurta, P. (September 18–23, 2000). "Discovery of a Globular Cluster in M31's Dwarf Spheroidal Companion Andromeda I". Abstracts of Contributed Talks and Posters presented at the Annual Scientific Meeting of the Astronomische Gesellschaft. Astronomische Gesellschaft Abstract Series. Vol. 17. Bremen. Bibcode:2000AGM....17..P61G.{{cite book}}: |journal= ignored (help)CS1 maint: location missing publisher (link)
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