Leo I (dwarf galaxy)

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Leo I
Ugc5470.jpg
Leo I appears as a faint patch to the right of the bright star, Regulus.
Observation data (J2000 epoch)
Constellation Leo
Right ascension 10h 08m 27.4s [1]
Declination +12° 18′ 27″ [1]
Redshift 285 ± 2 km/s [1]
Distance 820 ± 70 kly (250 ± 20 kpc) [2] [3]
Apparent magnitude  (V)11.2 [1]
Absolute magnitude  (V)−12.0 [4]
Characteristics
Type E;dSph [1]
Mass (2.0 ± 1.0) × 107  M☉
Size2000 ly [5]
Apparent size  (V)9.8′ × 7.4′ [1]
Notable features Milky Way satellite
Other designations
UGC 5470, [1] PGC 29488, [1] DDO 74, [1] A1006, [1] Harrington-Wilson #1, [1] Regulus Dwarf [1]

Leo I is a dwarf spheroidal galaxy in the constellation Leo. At about 820,000 light-years distant, it is a member of the Local Group of galaxies and is thought to be one of the most distant satellites of the Milky Way galaxy. It was discovered in 1950 by Albert George Wilson on photographic plates of the National Geographic Society – Palomar Observatory Sky Survey, which were taken with the 48-inch Schmidt camera at Palomar Observatory. [6] [7]

Contents

Visibility

Leo I is located only 12 arc minutes from Regulus, the brightest star in the constellation. For that reason, the galaxy is sometimes called the Regulus Dwarf. Scattered light from the star makes studying the galaxy more difficult, and it was not until the 1990s that it was detected visually. [6] [7]

The proximity of Regulus and the low surface brightness make it a real challenge to observe. Medium-sized amateur telescopes (15 cm or more) and a dark sky appear to be required for a sighting. But some reports of April 2013 tell that one observer with an 11 cm mini Dobson and even a refractor as small as 7 cm f/10 has sighted Leo I under very dark sky conditions. [8]

Mass

The measurement of radial velocities of some bright red giants in Leo I have made possible to measure its mass. It was found to be at least (2.0 ± 1.0) × 107 M☉. The results are not conclusive, and do not exclude or confirm the existence of a large dark matter halo around the galaxy. However, it seems to be certain that the galaxy does not rotate. [7]

A kinematic study of Leo I could not place much constraints on dark matter, but suggested the presence of a black hole of three million solar masses in the center of the galaxy. This would be significant, as it would be the first time this has been done with a dwarf spheroidal galaxy. [9] A black hole of three million solar masses is comparable to the mass of the Milky Way's black hole, Sagittarius A*. [5] However, another study could not confirm this, suggesting at most an intermediate-mass black hole of a few 105 solar masses. [10]

It has been suggested that Leo I is a tidal debris stream in the outer halo of the Milky Way. This hypothesis has not been confirmed, however. [7]

Star formation

Typical to a dwarf galaxy, the metallicity of Leo I is very low, only one percent that of the Sun. Gallart et al. (1999) deduce from Hubble Space Telescope observations that the galaxy experienced a major increase (accounting for 70% to 80% of its population) in its star formation rate between 6 Ga and 2 Ga (billion years ago). There is no significant evidence of any stars that are more than 10 Ga old. About 1 Ga ago, star formation in Leo I appears to have dropped suddenly to an almost negligible rate, roughly coinciding with its latest periastron passage of the Milky Way. Ram pressure stripping would have removed its gas, decreasing its star formation rate. [4] Some low-level activity may have continued until 200-500 Ma. Therefore, it is thought to be the youngest dwarf spheroidal satellite galaxy of the Milky Way. In addition, the galaxy may be embedded in a cloud of ionized gas with a mass similar to that of the whole galaxy. [7] [11]

Related Research Articles

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A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards its center. It can contain anywhere from tens of thousands to many millions of member stars, all orbiting in a stable, compact formation. Globular clusters are similar in form to dwarf spheroidal galaxies, and the distinction between the two is not always clear. Their name is derived from Latin globulus. Globular clusters are occasionally known simply as "globulars".

<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">Triangulum Galaxy</span> Spiral galaxy in the constellation Triangulum

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<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 through 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">NGC 404</span> Galaxy in the constellation Andromeda

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<span class="mw-page-title-main">Dwarf galaxy</span> Small galaxy composed of up to several billion stars

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<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">Andromeda I</span> Dwarf galaxy in the constellation Andromeda

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

The Sculptor Dwarf Galaxy is a dwarf spheroidal galaxy that is a satellite of the Milky Way. The galaxy lies within the constellation Sculptor. It was discovered in 1937 by American astronomer Harlow Shapley using the 24-inch Bruce refractor at Boyden Observatory. The galaxy is located about 290,000 light-years away from the Solar System. The Sculptor Dwarf contains only 4 percent of the carbon and other heavy elements in our own galaxy, the Milky Way, making it similar to primitive galaxies seen at the edge of the universe.

<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">Carina Dwarf Spheroidal Galaxy</span> Dwarf galaxy in the constellation Carina

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

The Draco Dwarf is a spheroidal galaxy which was discovered by Albert George Wilson of Lowell Observatory in 1954 on photographic plates of the National Geographic Society's Palomar Observatory Sky Survey (POSS). It is part of the Local Group and a satellite galaxy of the Milky Way galaxy. The Draco Dwarf is situated in the direction of the Draco Constellation at 34.6° above the galactic plane.

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

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<span class="mw-page-title-main">Leo II (dwarf galaxy)</span> Dwarf Spheroidal galaxy in the constellation Leo

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<span class="mw-page-title-main">Palomar 12</span> Globular cluster in the constellation Capricornus

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<span class="mw-page-title-main">Hercules (dwarf galaxy)</span> Dwarf spheroidal galaxy in the constellation Hercules

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References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 "NASA/IPAC Extragalactic Database". Results for Leo I. Retrieved 2006-11-29.
  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 Ruiz-Lara, T.; Gallart, C.; Monelli, M.; Fritz, T. K.; Battaglia, G.; Cassisi, S.; Aznar, M Luis; Russo Cabrera, A. V.; Rodríguez-Martín, I.; Salazar-González, J. J. (2021). "Dissecting the stellar content of Leo I: A dwarf irregular caught in transition". Monthly Notices of the Royal Astronomical Society. 501 (3): 3962–3980. arXiv: 2012.07863 . doi: 10.1093/mnras/staa3871 .
  5. 1 2 Pultarova, Tereza (2021-12-03). "Giant black hole inside a tiny satellite galaxy of our Milky Way defies explanation". Space.com. Retrieved 2021-12-03.
  6. 1 2 "Leo I". SEDS Messier Database. Retrieved 2006-05-15.
  7. 1 2 3 4 5 Van den Bergh, Sidney (2000). Galaxies of the Local Group (1st ed.). Cambridge University Press. pp. 243–245. ISBN   0-521-65181-6.
  8. ↑ "Faint Fuzzy Observations". Archived from the original on 2014-03-24. Retrieved 2014-03-24.
  9. ↑ Bustamante-Rosell, M. J.; Noyola, Eva; Gebhardt, Karl; Fabricius, Maximilian H.; Mazzalay, Ximena; Thomas, Jens; Zeimann, Greg (2021). "Dynamical Analysis of the Dark Matter and Central Black Hole Mass in the Dwarf Spheroidal Leo I". The Astrophysical Journal. 921 (2): 107. arXiv: 2111.04770 . Bibcode:2021ApJ...921..107B. doi: 10.3847/1538-4357/ac0c79 . S2CID   243798608.
  10. ↑ Pascale, R.; Nipoti, C.; Calura, F.; Della Croce, A. (2024). "The central black hole in the dwarf spheroidal galaxy Leo I: Not supermassive, at most an intermediate-mass candidate". Astronomy & Astrophysics. 684: L19. arXiv: 2403.14784 . Bibcode:2024A&A...684L..19P. doi:10.1051/0004-6361/202449620.
  11. ↑ van den Bergh, Sidney (April 2000). "Updated Information on the Local Group". The Publications of the Astronomical Society of the Pacific. 1sss. 112 (770): 529–536. arXiv: astro-ph/0001040 . Bibcode:2000PASP..112..529V. doi:10.1086/316548. S2CID   1805423.
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