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| Sextans (dwarf galaxy) | |
|---|---|
| Name | Sextans dSph |
| Type | Dwarf spheroidal galaxy |
| Epoch | J2000 |
| Distance | 86 kly |
| Appmag v | 10.4 |
| Size v | 30′ |
| Constellation name | Sextans |
| Notes | Satellite of the Milky Way |
Sextans (dwarf galaxy) Sextans is a dwarf spheroidal galaxy discovered as a low surface brightness satellite of the Milky Way. It was identified in wide-field surveys and subsequently studied with instruments on observatories such as the Palomar Observatory and the Anglo-Australian Telescope. Sextans is notable for its diffuse morphology, old stellar population, and large mass-to-light ratio that implicates substantial dark matter dominance.
Sextans was discovered in 1990 during searches for faint companions around the Milky Way using photographic plates and follow-up CCD imaging at facilities including Palomar Observatory, Kitt Peak National Observatory, European Southern Observatory telescopes, and programs led by teams from institutions such as the Carnegie Institution for Science and the Max Planck Society. It was classified as a dwarf spheroidal (dSph) on the basis of its low surface brightness, lack of obvious gas emission compared with dwarf irregulars like IC 1613 or WLM (galaxy), and its stellar morphology similar to systems such as Draco (dwarf galaxy), Ursa Minor Dwarf, and Sculptor (galaxy). Follow-up spectroscopic campaigns at the Keck Observatory and the Very Large Telescope refined the membership and confirmed the classification used in catalogs maintained by organizations including the NASA/IPAC Extragalactic Database and the European Space Agency.
Sextans appears as a faint, extended object in surveys conducted by projects like the Sloan Digital Sky Survey, the Two Micron All Sky Survey, and targeted imaging from the Hubble Space Telescope. Its half-light radius and structural parameters were measured using data from institutions such as Massachusetts Institute of Technology teams and survey consortia including the National Optical Astronomy Observatory. Photometry indicates a low integrated luminosity, similar to ultra-faint dwarfs discovered by collaborations involving European Southern Observatory and Harvard-Smithsonian Center for Astrophysics researchers. Surface brightness profiles derived with instruments on the Subaru Telescope and analysis methods developed at Princeton University place Sextans among the most diffuse Milky Way companions, comparable in extent to Fornax (dwarf galaxy) but with lower central density.
Stellar color–magnitude diagrams obtained with the Hubble Space Telescope and ground-based facilities run by teams from University of Cambridge and University of Tokyo reveal an old, metal-poor population dominated by red giant branch and horizontal branch stars. Isochrone fitting using models from groups at Padova Observatory and the Geneva Observatory indicates most stars formed over 10 billion years ago, similar to ancient populations in Sculptor (galaxy) and Draco (dwarf galaxy). Deep photometry by collaborations including researchers from Space Telescope Science Institute and University of California, Berkeley found sparse evidence for intermediate-age populations, contrasting with prolonged star formation witnessed in systems like Carina (dwarf galaxy). Studies led by scientists at Yale University and University of Chicago constrained the early star formation epoch and subsequent quenching, consistent with environmental effects documented for satellites of the Milky Way.
Radial velocity surveys using spectrographs at Keck Observatory, Very Large Telescope, and Magellan Telescopes measured stellar line-of-sight velocities for member stars, performed by teams from University of Washington and University of California, Santa Cruz. The measured velocity dispersion, analyzed with dynamical mass estimators developed at University of Cambridge and Harvard University, implies a high mass-to-light ratio, indicating dominance by dark matter as proposed in models from the Cold Dark Matter paradigm and explored by researchers at Institute for Advanced Study. Mass modeling incorporating Bayesian methods from groups at Rutgers University and University of Oxford suggests Sextans retains an extended dark matter halo similar to predictions from cosmological simulations by the Millennium Simulation consortium and studies from the Max Planck Institute for Astrophysics.
High-resolution spectroscopy of Sextans red giants using instruments at Keck Observatory and Very Large Telescope provided elemental abundances analyzed by teams from Carnegie Institution for Science and Observatoire de Paris. The galaxy exhibits low overall metallicity ([Fe/H]) with a broad spread comparable to measurements in Bootes I and Segue 1 reported by researchers at University of Cambridge and Harvard-Smithsonian Center for Astrophysics. Detailed abundance patterns for alpha-elements and neutron-capture elements were interpreted using nucleosynthesis yields from studies at Max Planck Institute for Astronomy and Lawrence Berkeley National Laboratory, indicating early contributions from core-collapse supernovae and stochastic enrichment consistent with low star formation efficiency modeled at University of Illinois.
Proper motion constraints from the Gaia mission and orbit modeling by teams at European Space Agency and University of Leiden place Sextans on an extended orbit around the Milky Way with pericentric passages that may have induced tidal effects akin to those invoked for Sagittarius Dwarf Spheroidal Galaxy. Simulations run on supercomputers at Princeton University and the National Center for Supercomputing Applications explored interactions between Sextans, the Milky Way, and other satellites such as Large Magellanic Cloud and Small Magellanic Cloud, with tidal stripping scenarios compared to observed structural anomalies discussed in papers from University of Cambridge and University of Edinburgh.
Sextans lacks massive globular clusters like those orbiting Fornax (dwarf galaxy); surveys by teams at Space Telescope Science Institute and University of Oxford found no confirmed cluster systems, though searches continue using facilities at Subaru Telescope and Gemini Observatory. Variable star studies conducted by researchers from University of California, Los Angeles and the Carnegie Institution for Science identified RR Lyrae variables that trace the ancient population, similar to variables cataloged in Sculptor (galaxy) and analyzed by collaborations including Max Planck Institute for Astronomy. The RR Lyrae census informed distance estimates coordinated with the Hubble Space Telescope distance ladder efforts led by Space Telescope Science Institute astronomers.