Leo IV ( eng. Leo IV ) is a dwarf spheroidal galaxy located in the constellation Leo and discovered in 2006 during data processing of the Sloan digital sky survey [3] . The galaxy is at a distance of about 160 kpc from the Sun and moves from the Sun at a speed of about 130 km / s [3] [5] . It has an approximately spherical shape with a radius of about 130 pc and is classified as a dwarf spheroidal galaxy (dSph) [4] .
| Leo IV [1] | |
|---|---|
| Galaxy | |
 Leo IV is one of a series of ultraweak dwarf galaxies found around the Milky Way [2] | |
| Research history | |
| opening date | 2006 |
| Designations | Leo IV |
| Observational data ( Epoch J2000.0 ) | |
| Constellation | a lion |
| Right ascension | |
| Declination | |
| Visible magnitude m V | 11.2 |
| Specifications | |
| Type of | dSph [3] |
| Enters into | |
| Radial velocity | |
| Distance | 520 +49 −45 thousand sv. years (160 +15 −14 kpc ) [3] 154 ± 4 kpc [4] |
| Absolute magnitude (V) | |
| Radius | 130 pc |
| Properties | subgroup of the Milky Way |
Leo IV is one of the smallest and dims of the Milky Way — its integral luminosity is only 15,000 times greater than that of the Sun ( apparent magnitude −5.5 m ± 0.3 m ), which is much lower than the luminosity of a typical globular cluster. . [4] However, its mass is about 1.5 million solar masses , which means that the mass ratio of Leo IV to luminosity is about 150 M / L ☉ . The large mass-to-luminosity ratio means that dark matter dominates Leo IV [5] .
The stellar population of Leo IV consists mainly of old stars, more than 12 billion years old [4] . The metallicity of these old stars is also very low: [Fe / H] ≈ -2.58 ± 0.75 , which means that they contain 400 times less heavy elements than the Sun [6] . The observed stars are mostly red giants, although the stars of the horizontal branch , including three variable stars of the type RR Lyra , were also discovered [4] [note 1] . The stars of Leo IV were probably among the first stars that formed in the universe. However, a detailed study of the stellar population showed the presence of a small number of much younger stars with an age of about 2 billion years or less. This discovery points to a complex history of the formation of stars in this galaxy [4] . There is currently no star formation in Leo IV. Measurements have so far failed to detect neutral hydrogen in it — the upper limit on the mass of HI is only 600 solar masses [7] .
The Bowl-Lev Group
In 2008, another galaxy was discovered in the vicinity of Leo IV, which was named Leo V. It is located 20 kpc farther from the Milky Way than the first, and 3 degrees ( ~ 10 kpc ) from it. It was immediately suggested that these two galaxies may be physically related to each other [8] [9] . Later it was discovered that Leo IV lies on one big circle with four other satellites of the Milky Way: two Bowl 2 and Leo V galaxies belonging to the same class of ultra-dim dwarfs; the classical Lev II dwarf galaxy and the peculiar Bowl Cluster [10] [11] [note 2] . The pole of this large circle (α; δ) = (83.2 °; −11.8 °) is close to the pole of the large circle, along which the Magellanic Stream is directed. The dependence of heliocentric distances and radial velocities on declination also supports the hypothesis that these five objects (the Bowl-Lev group) are in the same orbit and are related by common origin [10] .
Notes
- ↑ The distance to Leo IV, measured by variable stars of the RR Lyrae type , is 154 ± 4 kpc [4] .
- ↑ The peculiar globular cluster of the Bowl , also known as Laevens 1 , is the most distant globular satellite companion of the Milky Way known for 2016 (distance 145 kpc from the Sun, determined by another method gives 170 kpc ) [11] . It is also one of the largest globular clusters.
Links
- ↑ SIMBAD Astronomical Database . Results for Leo IV Dwarf Galaxy . The appeal date is January 31, 2010. Archived May 30, 2013.
- ↑ Hubble Unmasks Ghost Galaxies . The appeal date is July 11, 2012.
- ↑ 1 2 3 4 Belokurov V. et al. Quats of the New Milky Way Companions (English) // The Astrophysical Journal: journal. - 2007. - Vol. 654 , no. 2 - P. 897 . - DOI : 10.1086 / 509718 . - . - arXiv : astro-ph / 0608448 .
- ↑ 1 2 3 4 5 6 7 Sand, David J .; Seth, Anil; Olszewski, Edward W. et al. A Deeper Look at Leo IV: Star Formation History and Extended Structure (Eng.) // The Astrophysical Journal: journal. - 2010. - Vol. 718 . P. 530-542 . - DOI : 10.1088 / 0004-637X / 718/1/530 . - . - arXiv : 0911.5352 .
- 2 1 2 Simon JD, Geha M. The Kinematics of the Ultra ‐ faint Milky Way Satellites: Solving the Missing Satellite Problem (Eng.) // The Astrophysical Journal: journal. - 2007. - Vol. 670 . - P. 313 . - DOI : 10.1086 / 521816 . - . - arXiv : 0706.0516 .
- ↑ Kirby EN, Simon JD, Geha M., Guhathakurta P., Frebel A. Uncovering Extremely Metal-Poor Stars and Dwarf Spheroidal Satellite Galaxies (English) // The Astrophysical Journal: journal. - 2008. - Vol. 685 . - P. L43 . - DOI : 10.1086 / 592432 . - . - arXiv : 0807.1925 .
- Ce Grcevich J., Putman ME HI in Local Group Dwarf Galaxies and Stripping by the Galactic Halo (Eng.) // The Astrophysical Journal: journal. - 2009. - Vol. 696 . - P. 385 . - DOI : 10.1088 / 0004-637X / 696/1/385 . - . - arXiv : 0901.4975 .
- ↑ Belokurov V., Walker MG, Evans NW et al. Leo V: A companion of the Milky Way galaxy (Eng.) // The Astrophysical Journal: journal. - 2008. - Vol. 686 , no. 2 - P. L83 — L86 . - DOI : 10.1086 / 592962 . - . - arXiv : 0807.2831 .
- J de Jong JTA, Martin NF, Rix HW, Smith KW, Jin S., MacCiò AV (English) // The Astrophysical Journal: journal. - 2010. - Vol. 710 , no. 2 - P. 1664 . - DOI : 10.1088 / 0004-637X / 710/2/1664 . - . - arXiv : 0912.3251 .
- ↑ 1 2 Torrealba G., Koposov SE, Belokurov V., Irwin M. The feeble giant. Milk Way Dwarf galaxy in the constellation of Crater // Monthly Notices of the Royal Astronomical Society. - 2016. - P. stw733. - ISSN 0035-8711 . - DOI : 10.1093 / mnras / stw733 . - . - arXiv : 1601.07178 .
- ↑ 1 2 Belokurov V., Irwin MJ, Koposov SE, Evans NW, Gonzalez-Solares E., Metcalfe N., Shanks T. ATLAS lifts the Cup: Discovery of the Milky Way in Crater // Monthly Notices of the Royal Astronomical Society. - 2014. - Vol. 441. - p. 2124-2133. - ISSN 0035-8711 . - DOI : 10.1093 / mnras / stu626 . - . - arXiv : 1403.3406 .