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NGC 147 (also known as DDO3 or Caldwell 17) is a dwarf spheroidal galaxy about 2.58 Mly away in the constellation Cassiopeia. NGC 147 is a member of the Local group of galaxies and a satellite galaxy of the Andromeda Galaxy (M31). It forms a physical pair with the nearby galaxy NGC 185,[5] another remote satellite of M31. It was discovered by John Herschel in September 1829. Visually it is both fainter and slightly larger than NGC 185 (and therefore has a considerably lower surface brightness). This means that NGC 147 is more difficult to see than NGC 185, which is visible in small telescopes. In the Webb Society Deep-Sky Observer's Handbook,[6] the visual appearance of NGC 147 is described as follows:

Large, quite faint, irregularly round; it brightens in the middle to a stellar nucleus.

NGC 147
2MASS image of NGC 147
Observation data (J2000 epoch)
ConstellationCassiopeia
Right ascension00h 33m 12.1s[1]
Declination+48° 30′ 32″[1]
Redshift-193 ± 3 km/s[1]
Distance2.53 ± 0.11 Mly (780 ± 30 kpc)[2][3][4][a]
Apparent magnitude (V)10.5[1]
Characteristics
TypedSph/dE5[1]
Apparent size (V)13′.2 × 7′.8[1]
Notable featuressatellite galaxy of M31
Other designations
PGC 2004,[1] UGC 326,[1] DDO 3,[1] LEDA 2004, Caldwell 17

The membership of NGC 147 in the Local Group was confirmed by Walter Baade in 1944 when he was able to resolve the galaxy into individual stars with the 100-inch (2.5 m) telescope at Mount Wilson near Los Angeles.


Characteristics


A survey of the brightest asymptotic giant branch (AGB) stars in the area of radius 2′ from the center of NGC 147 shows that the last significant star-forming activity in NGC 147 occurred around 3 Gyr ago.[7] NGC 147 contains a large population of older stars which show a spread in metallicity and age. The metallicity spread suggests that NGC 147 has had chemical enrichment. However, H I has not been observed and the interstellar medium (ISM) mass upper limit is much lower than expected had the material which is emitted from evolving stars been kept in the galaxy. This implies depletion of the ISM.[7]


Distance measurements


At least two techniques have been used to measure distances to NGC 147. The surface brightness fluctuations distance measurement technique estimates distances to spiral galaxies based on the graininess of the appearance of their bulges. The distance measured to NGC 147 using this technique is 2.67 ± 0.18 Mly (870 ± 60 kpc).[2] However, NGC 147 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 147 using this technique is 2.21 ± 0.09 Mly (680 ± 30 kpc).[3] Averaged together, these distance measurements give a distance estimate of 2.53 ± 0.11 Mly (780 ± 30 kpc).[a]


See also



Notes


  1. ^ average(870 ± 60, 680 ± 30) = ((870 + 680) / 2) ± ((602 + 302)0.5 / 2) = 780 ± 30

References


  1. "NASA/IPAC Extragalactic Database". Results for NGC 147. Retrieved 2006-12-07.
  2. 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.
  3. McConnachie, A. W.; Irwin, M. J.; Ferguson, A. M. N.; Ibata, R. A.; et al. (2005). "Distances and metallicities for 17 Local Group galaxies". Monthly Notices of the Royal Astronomical Society. 356 (4): 979–997. arXiv:astro-ph/0410489. Bibcode:2005MNRAS.356..979M. doi:10.1111/j.1365-2966.2004.08514.x.
  4. 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.
  5. "NGC 147". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2006-12-07.
  6. Jones, K. G. (1981). Webb Society Deep-Sky Observer's Handbook. Enslow Publishers. ISBN 978-0-89490-134-8.
  7. Davidge, T. J. (2005). "The Evolved Stellar Content of NGC 147, NGC 185, and NGC 205". The Astronomical Journal. 130 (5): 2087–2103. arXiv:astro-ph/0509612. Bibcode:2005AJ....130.2087D. doi:10.1086/491706. S2CID 17456987.


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На других языках

[de] NGC 147

NGC 147 ist eine elliptische Zwerggalaxie vom Hubble-Typ dE5 im Sternbild Kassiopeia am Nordsternhimmel. Die Galaxie ist schätzungsweise 300.000 Lichtjahre von Andromeda entfernt (etwa die gleiche Entfernung wie zwischen der Milchstraße und der Großen Magellanschen Wolke) und hat eine Größe von etwa 8000 Lichtjahren entlang der größten Abmessung. Sie ist eine Begleitgalaxie der Andromeda-Galaxie und bildet zusammen mit NGC 185 gravitativ gebundenes Galaxienpaar.
- [en] NGC 147

[es] NGC 147

NGC 147 es una galaxia enana esferoidal a unos 2,53 millones de años luz de la Tierra en la constelación de Casiopea. Es una galaxia satélite de la galaxia de Andrómeda (M31) y por tanto forma parte del Grupo Local. Forma un sistema doble con la cercana NGC 185, también satélite de M31. Visualmente es más tenue (magnitud visual 10,5) pero algo más grande que NGC 185, aunque ambas galaxias se pueden observar con pequeños telescopios. Fue descubierta por John Herschel en 1829.

[ru] NGC 147

NGC 147 (другие обозначения — DDO 3, UGC 326, MCG 8-2-5, ZWG 550.6, PGC 2004) — карликовая сфероидальная галактика в созвездии Кассиопеи, находящаяся на расстоянии 2,2 миллиона световых лет[4]. Является членом Местной группы и спутником Туманности Андромеды (M31). Гравитационно связана с галактикой NGC 185, другим карликовым спутником M31. Относительно яркий объект, может наблюдаться в любительские телескопы.


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