NGC 185

NGC 185 (also known as Caldwell 18) is a dwarf spheroidal galaxy located 2.08 million light-years from Earth, appearing in the constellation Cassiopeia. It is a member of the Local Group, and is a satellite of the Andromeda Galaxy (M31).[6] NGC 185 was discovered by William Herschel on November 30, 1787, and he cataloged it "H II.707".[6] John Herschel observed the object again in 1833 when he cataloged it as "h 35", and then in 1864 when he cataloged it as "GC 90" within his General Catalogue of Nebulae and Clusters.[6] NGC 185 was first photographed between 1898 and 1900 by James Edward Keeler with the Crossley Reflector of Lick Observatory.[6] Unlike most dwarf elliptical galaxies, NGC 185 contains young stellar clusters, and star formation proceeded at a low rate until the recent past. NGC 185 has an active galactic nucleus (AGN) and is usually classified as a type 2 Seyfert galaxy,[7] though its status as a Seyfert is questioned.[8] It is possibly the closest Seyfert galaxy to Earth, and is the only known Seyfert in the Local Group.

NGC 185
NGC 185 as taken at the James Gregory Telescope
Observation data (J2000.0[1] epoch)
ConstellationCassiopeia
Right ascension00h 38m 57.970s[1]
Declination+48° 20′ 14.56″[1]
Redshift-202 ± 3 km/s[2]
Distance2.05 ± 0.13 Mly (630 ± 40 kpc)[3][4][5][a]
Apparent magnitude (V)10.1[2]
Characteristics
TypedSph/dE3,[2] Sy2 [1]
Apparent size (V)11′.7 × 10′.0[2]
Notable featuressatellite galaxy of the
Andromeda Galaxy
Other designations
UGC 396,[2] PGC 2329,[2] LEDA 2329,[1] Caldwell 18

Distance measurements

At least two techniques have been used to measure distances to NGC 185. The surface brightness fluctuations distance measurement technique estimates distances to galaxies based on the graininess of their appearance. The distance measured to NGC 185 using this technique is 2.08 ± 0.15 Mly (640 ± 50 kpc).[3] However, NGC 185 is close enough that the tip of the red giant branch (TRGB) method may be used to estimate its distance. The estimated distance to NGC 185 using this technique is 2.02 ± 0.2 Mly (620 ± 60 kpc).[4][5]

Star formation

Martínez-Delgado, Aparicio, & Gallart (1999) looked into the star formation history of NGC 185 and found that the majority of star formation in NGC 185 happened at early times.[8] In the last ~1 Gyr, stars have formed only near the center of this galaxy. Walter Baade discovered young blue objects within this galaxy in 1951, but these have turned out to be star clusters and not individual stars. A supernova remnant near the center was also discovered by Martínez-Delgado et al.[9]

See also

References
  1. "NGC 185". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2014-05-05.
  2. "NASA/IPAC Extragalactic Database". Results for NGC 185. Retrieved 2006-11-29.
  3. J. L. Tonry; A. Dressler; J. P. Blakeslee; E. A. Ajhar; et al. (2001). "The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances". Astrophysical Journal. 546 (2): 681–693. arXiv:astro-ph/0011223. Bibcode:2001ApJ...546..681T. doi:10.1086/318301. S2CID 17628238.
  4. I. D. Karachentsev; V. E. Karachentseva; W. K. Huchtmeier; D. I. Makarov (2004). "A Catalog of Neighboring Galaxies". Astronomical Journal. 127 (4): 2031–2068. Bibcode:2004AJ....127.2031K. doi:10.1086/382905.
  5. 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.
  6. "SEDS — NGC 185".
  7. Ho, Luis C.; Filippenko, Alexei V.; Sargent, Wallace L. W. (October 1997). "A Search for 'Dwarf' Seyfert Nuclei. III. Spectroscopic Parameters and Properties of the Host Galaxies". The Astrophysical Journal Supplement Series. 112 (2): 315–390. arXiv:astro-ph/9704107. Bibcode:1997ApJS..112..315H. doi:10.1086/313041. S2CID 17086638.
  8. Martins, Lucimara P.; Lanfranchi, Gustavo; Goncalves, Denise R.; Magrini, Laura; Teodorescu, Ana M.; Quireza, Cintia (February 2012). "The ionization mechanism of NGC 185: How to fake a Seyfert galaxy?". Monthly Notices of the Royal Astronomical Society. 419 (4): 3159–3166. arXiv:1110.5891. Bibcode:2012MNRAS.419.3159M. doi:10.1111/j.1365-2966.2011.19954.x. S2CID 119188037.
  9. van den Bergh, Sidney (April 2000). "Updated Information on the Local Group". The Publications of the Astronomical Society of the Pacific. 112 (770): 529–536. arXiv:astro-ph/0001040. Bibcode:2000PASP..112..529V. doi:10.1086/316548. S2CID 1805423.


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