NGC 147

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NGC 147
Observation data: J2000 epoch
Constellation: Cassiopeia
Right ascension: 00h 33m 12.1s[1]
Declination: +48° 30′ 32″[1]
Redshift: -193 ± 3 km/s[1]
Distance: 2.53 ± 0.11 Mly (780 ± 30 kpc)[2][3][4][a]
Type: dSph/dE5[1]
Apparent dimensions (V): 13′.2 × 7′.8[1]
Apparent magnitude (V): 10.5[1]
Notable features: satellite galaxy of M31
Other designations
PGC 2004,[1] UGC 326,[1] DDO 3[1]
See also: Galaxy, List of galaxies


NGC 147 is a Dwarf spheroidal galaxy about 2.58 Mly away in the constellation Cassiopeia. NGC 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, but both galaxies are visible in small telescopes.

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 telescope at Mount Wilson near Los Angeles.

Contents

[edit] 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 start-forming activity in NGC 147 occurred around 3 Gyr ago.[6] 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 seen 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.[6]

[edit] 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]

[edit] See also


[edit] External links

[edit] Notes

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

[edit] References

  1. ^ a b c d e f g h i NASA/IPAC Extragalactic Database. Results for NGC 147. Retrieved on December 7, 2006.
  2. ^ a b J. L. Tonry, A. Dressler, J. P. Blakeslee, E. A. Ajhar, A. B. Fletcher, G. A. Luppino, M. R. Metzger, C. B. Moore (2001). "The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances". Astrophysical Journal 546 (2): 681-693. 
  3. ^ a b McConnachie, A. W.; Irwin, M. J.; Ferguson, A. M. N.; Ibata, R. A.; Lewis, G. F.; Tanvir, N. (2005). "Distances and metallicities for 17 Local Group galaxies". Monthly Notices of the Royal Astronomical Society 356 (4): 979-997. 
  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. 
  5. ^ SIMBAD Astronomical Database. Results for NGC 147. Retrieved on December 7, 2006.
  6. ^ a b Davidge, T. J. (2005). "The Evolved Stellar Content of NGC 147, NGC 185, and NGC 205". The Astronomical Journal 130 (5): 2087-2103. 
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