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Leo T is a dwarf galaxy situated in the Leo constellation and discovered in 2006 in the data obtained by Sloan Digital Sky Survey. The galaxy is located at the distance of about 409 kpc from the Sun and moves away from the Sun with the velocity of about 35 km/s. The velocity with respect to the Milky Way is around −60 km/s implying a slow infall onto the Milky Way. Leo T is classified as a transitional object ('T' in the name) between dwarf spheroidal galaxies (dSph) and dwarf irregular galaxies (dIrr). Its half-light radius is about 180 pc.

Leo T is one of the smallest and faintest galaxies in the Local Group—its integrated luminosity is about 40,000 times that of the Sun (absolute visible magnitude of about −7.1). However, its mass is about 8 million solar masses, which means that Leo's mass to light ratio is around 140. A high mass to light ratio implies that Leo T is dominated by dark matter.

Neutral hydrogen and star formation

The stellar population of Leo T consists of both old and young stars. The old stars probably formed from 12 to 6 billion years ago. The metallicity of these old stars is very low at ≈ −2.02 ± 0.54, which means that they contain 100 times less heavy elements than the Sun. The observed old stars are primarily red giants, although a number of horizontal branch stars and red clump stars were also discovered. After a pause star formation activity resumed about 1 billion years ago resulting in a generation of blue young stars. These young stars, which comprise only about 10% of all stellar mass, appear to be more concentrated at the center of Leo T than the old population. Currently there is no star formation in this galaxy.

Leo T contains significant amount of neutral hydrogen (HI) gas with the mass of about 280,000 solar masses, which is three times more than the mass of the stars in this galaxy. As of 2023, it is the least massive galaxy known to contain neutral gas. The gas includes two main components: cool gas in the center of the galaxy with a temperature of about 500 K and warm gas distributed throughout Leo T with a temperature of 6,000 K. The density of this gas is, however, not enough on average for star formation, which indicates that local processes have a role. Still the presence of hydrogen gas implies that in the future the galaxy will begin forming stars again.

Leo T galaxy may have formed when a small dark matter halo started accretion of gas some time after the reionization epoch. Later this gas gave birth to the first generation of old stars.

Notes

1. From another source the absolute magnitude is about −8.0.
2. Other sources report metallicity of about −1.5.

References

1. ^ "NAME Leo T dSph". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2010-03-14.
2. ^ Vaz, Daniel; Brinchmann, Jarle; Zoutendijk, Sebastiaan L.; Boogaard, Leindert A.; Kamann, Sebastian; Read, Justin I.; Roth, Martin M.; Weilbacher, Peter M.; Steinmetz, Matthias (2023). "The MUSE-Faint survey. IV. Dissecting Leo T, a gas-rich relic with recent star formation". Astronomy & Astrophysics. 678: A59. arXiv:2308.16263. Bibcode:2023A&A...678A..59V. doi:10.1051/0004-6361/202346453.
3. ^ Irwin, V.; Belokurov, V.; Evans, N. W.; et al. (2007). "Discovery of an Unusual Dwarf Galaxy in the Outskirts of the Milky Way". The Astrophysical Journal. 656 (1): L13 – L16. arXiv:astro-ph/0701154. Bibcode:2007ApJ...656L..13I. doi:10.1086/512183. S2CID 18742260.
4. ^ Simon, Joshua D.; Geha, Marla (2007). "The Kinematics of the Ultra-faint Milky Way Satellites: Solving the Missing Satellite Problem". The Astrophysical Journal. 670 (1): 313–331. arXiv:0706.0516. Bibcode:2007ApJ...670..313S. doi:10.1086/521816. S2CID 9715950.
5. ^ de Jong, J.T.A.; Harris, J.; Coleman, M.G.; et al. (2008). "The Structural Properties and Star Formation History of Leo T from Deep LBT Photometry". The Astrophysical Journal. 680 (2): 1112–1119. arXiv:0801.4027. Bibcode:2008ApJ...680.1112D. doi:10.1086/587835. S2CID 14357361.
6. Kirby, Evan N.; Simon, Joshua D.; Geha, Marla; et al. (2008). "Uncovering Extremely Metal-Poor Stars in the Milky Way's Ultrafaint Dwarf Spheroidal Satellite Galaxies". The Astrophysical Journal. 685 (1): L43 – L46. arXiv:0807.1925. Bibcode:2008ApJ...685L..43K. doi:10.1086/592432. S2CID 3185311.
7. ^ Ryan-Weber, Emma V.; Begum, Ayesha; Oosterloo, Tom; et al. (2008). "The Local Group dwarf Leo T: HI on the brink of star formation". Mon. Not. R. Astron. Soc. 384 (2): 535–540. arXiv:0711.2979. Bibcode:2008MNRAS.384..535R. doi:10.1111/j.1365-2966.2007.12734.x. S2CID 13855611.
8. Ricotti, Massimo (2009). "Late gas accretion on to primordial minihaloes: a model for Leo T, dark galaxies and extragalactic high-velocity clouds". Mon. Not. R. Astron. Soc. 392 (1): L45 – L49. arXiv:0806.2402. Bibcode:2009MNRAS.392L..45R. doi:10.1111/j.1745-3933.2008.00586.x. S2CID 18393415.

v t e Constellation of Leo
List of stars in Leo Leo in Chinese astronomy
Stars	Bayer α (Regulus) β (Denebola) γ (Algieba) δ (Zosma) ε (Algenubi) ζ (Adhafera) η θ (Chertan) ι κ (Al Minliar al Asad) λ (Alterf) μ (Rasalas) ν ξ ο (Subra) π ρ σ τ υ φ χ ψ ω Flamsteed 3 6 (h) 7 8 9 10 11 12 13 15 (f) 18 19 20 21 22 (g) 23 26 31 (A) 33 34 35 37 39 40 42 43 44 45 46 48 49 50 51 (m) 52 (k) 53 (l) 54 55 56 57 58 (d) 59 (c) 60 (b) 61 (p) 62 (p) 64 65 (p) 66 67 69 (p) 71 72 73 (n) 75 76 79 80 81 82 83 85 86 87 (e) 88 89 90 92 93 95 (o) 6 LMi 18 LMi 49 LMi 52 LMi Variable R AD CN CW DP EE HR 4253 (p) 4459 (Formosa) HD 81040 88133 89307 96063 (Dingolay) 97658 99109 (Shama) 100777 (Sagarmatha) 102272 Other BD+20 2457 Gliese 408 Gliese 436 (Noquisi) GJ 3685 HVS 7 K2-3 K2-18 2MASSI J0937347+293142 2MASS J10475385+2124234 MACS J1149 Lensed Star 1 PSR B0943+10 PSR B0950+08 SDSS J102915+172927
Exoplanets γ Leonis b μ Leonis b υ Leonis b DP Leonis b Gliese 436 b (Awohali) HD 81040 b HD 88133 b HD 89307 b HD 89345 b HD 96063 b (Ramajay) HD 99109 b (Perwana) HD 100777 b (Laligurans) HD 102272 b c K2-18b c
Galaxies	Messier 65 66 95 96 105 NGC 2903 2906 2911 2964 3041 3048 3049 3177 3185 3187 3190 3193 3226 3227 3239 3274 3301 3357 3362 3367 3370 3377 3384 3412 3426 3447 3455 3489 3501 3506 3521 3524 3535 3593 3596 3598 3599 3602 3605 3607 3608 3628 3632 3640 3646 3647 3664 3666 3678 3686 3697 3705 3710 3758 3799 3800 3801 3805 3806 3810 3816 3821 3837 3840 3841 3842 3844 3845 3851 3857 3859 3860 3861 3862 3864 3867 3868 3873 3875 3883 3884 3886 3900 3902 3908 3925 3937 3947 3954 4005 Numbered I II III IV V Other Cosmic Horseshoe IC 2498 IC 2628 IRAS 10565+2448 J1000+1242 Leo P Leo T PSO J172.3556+18.7734 UGC 6614 UGC 6697
Category

v t e Milky Way
Location	Milky Way → Milky Way subgroup → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster → Local Hole → Observable universe → Universe Each arrow (→) may be read as "within" or "part of".
Structure	Galactic Center Sagittarius A Sagittarius A* Fermi bubbles Supermassive black hole Galactic Center filaments Disk Carina–Sagittarius Norma–Cygnus Orion–Cygnus Perseus Scutum–Centaurus Near 3 kpc Arm Far 3 kpc Arm Halo Aquarius Stream Fimbulthul stream Gaia Sausage Helmi stream Magellanic Stream Monoceros Ring Palomar 5 stream Pisces-Eridanus stream Sagittarius Stream Virgo Stream
Satellite galaxies	Magellanic Clouds Large Magellanic Cloud Small Magellanic Cloud Magellanic Bridge Dwarfs Antlia II Boötes I Boötes II Boötes III Canes Venatici I Canes Venatici II Canis Major Carina Coma Berenices Crater 2 Draco Eridanus II Fornax Hercules Leo I Leo II Leo IV Leo V Leo T Phoenix Pisces Overdensity Pisces II Reticulum II Sagittarius Spheroidal Segue 1 Segue 2 Sculptor Sextans Triangulum II Ursa Major I Ursa Major II Ursa Major III Ursa Minor Virgo I Willman 1
Related	Alternate names Andromeda–Milky Way collision Baade's Window In mythology Zone of Avoidance
Astronomy portal Category

Local Group

v t e Milky Way Location Milky Way → Milky Way subgroup → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster → Local Hole → Observable universe → Universe Each arrow (→) may be read as "within" or "part of". Structure Galactic Center Sagittarius A Sagittarius A* Fermi bubbles Supermassive black hole Galactic Center filaments Disk Carina–Sagittarius Norma–Cygnus Orion–Cygnus Perseus Scutum–Centaurus Near 3 kpc Arm Far 3 kpc Arm Halo Aquarius Stream Fimbulthul stream Gaia Sausage Helmi stream Magellanic Stream Monoceros Ring Palomar 5 stream Pisces-Eridanus stream Sagittarius Stream Virgo Stream Satellite galaxies Magellanic Clouds Large Magellanic Cloud Small Magellanic Cloud Magellanic Bridge Dwarfs Antlia II Boötes I Boötes II Boötes III Canes Venatici I Canes Venatici II Canis Major Carina Coma Berenices Crater 2 Draco Eridanus II Fornax Hercules Leo I Leo II Leo IV Leo V Leo T Phoenix Pisces Overdensity Pisces II Reticulum II Sagittarius Spheroidal Segue 1 Segue 2 Sculptor Sextans Triangulum II Ursa Major I Ursa Major II Ursa Major III Ursa Minor Virgo I Willman 1 Related Alternate names Andromeda–Milky Way collision Baade's Window In mythology Zone of Avoidance Astronomy portal Category v t e Andromeda Galaxy Location Andromeda Galaxy → Andromeda subgroup → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster → Local Hole → Observable universe → Universe Each  → may be read as "within" or "part of". Satellite galaxies M32 M110 NGC 185 NGC 147 Andromeda I Andromeda II Andromeda III Andromeda IV* Andromeda V Andromeda VI Andromeda VII Andromeda VIII Andromeda IX Andromeda X Andromeda XI Andromeda XII Andromeda XIII Andromeda XIV Andromeda XV Andromeda XVI Andromeda XVII Andromeda XVIII Andromeda XIX Andromeda XX Andromeda XXI Andromeda XXII Andromeda XXIII Andromeda XXIV Andromeda XXV Andromeda XXVI Andromeda XXVII Andromeda XXVIII Andromeda XXIX Triangulum subgroup* *It is uncertain whether these are companion galaxies of the Andromeda Galaxy Catalogued stars AE Andromedae AF Andromedae M31-RV Other Andromeda–Milky Way collision S Andromedae Mayall II M32p NGC 206 3XMM J004232.1+411314 Category v t e Triangulum Galaxy Location Triangulum Galaxy → Triangulum subgroup → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster → Local Hole → Observable universe → Universe Each arrow (→) may be read as "within" or "part of". H II regions NGC 588 NGC 595 NGC 604 Suspected satellite galaxies Pisces Dwarf Andromeda II Andromeda XXII Other IC 10 IC 1613 Phoenix Dwarf Leo A Tucana Dwarf Cetus Dwarf Pegasus Dwarf Irregular Galaxy Wolf–Lundmark–Melotte Aquarius Dwarf Sagittarius Dwarf Irregular Galaxy

• Dwarf spheroidal galaxies
• Principal Galaxies Catalogue objects
• Leo (constellation)
• Local Group
• Milky Way Subgroup
• Astronomical objects discovered in 2006