| NGC 147 | |
|---|---|
 Hubble Space Telescope image of 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] |
| Apparent magnitude (V) | 10.5[1] |
| Characteristics | |
| Type | dSph/dE5[1] |
| Apparent size (V) | 13.2′ × 7.8′[1] |
| Notable features | satellite galaxy of M31 |
| Other designations | |
| PGC 2004,[1] UGC 326,[1] DDO 3,[1] LEDA 2004, Caldwell 17 | |
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.
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.
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Tycho in 60 Seconds (Standard Definition)
Transcription
Tycho in 60 Seconds Narrator (April Hobart, CXC): Over four hundred years ago, the Danish astronomer Tycho Brahe studied the explosion of a star that later became known as Tycho's supernova. A look at Tycho in X-rays by NASA's Chandra X-ray Observatory shows that the supernova remnant contains an expanding bubble of superheated debris, which sits within an even more rapidly moving shell of extremely high-energy electrons. A very long Chandra observation of Tycho totaling about a million seconds of time, has uncovered new and unexpected structures in this aftermath of the star’s explosion. A series of stripes in the remnant provides novel evidence for particles that have been accelerated to extremely high energies. This is an important clue to better understanding the object that Tycho Brahe first saw back in 1572.
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
- ^ average(870 ± 60, 680 ± 30) = ((870 + 680) / 2) ± ((602 + 302)0.5 / 2) = 780 ± 30
References
- ^ a b c d e f g h i "NASA/IPAC Extragalactic Database". Results for NGC 147. Retrieved 2006-12-07.
- ^ a b 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.
- ^ a b 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.
- ^ 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.
- ^ "NGC 147". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2006-12-07.
- ^ Jones, K. G. (1981). Webb Society Deep-Sky Observer's Handbook. Enslow Publishers. ISBN 978-0-89490-134-8.
- ^ 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. arXiv:astro-ph/0509612. Bibcode:2005AJ....130.2087D. doi:10.1086/491706. S2CID 17456987.
External links
- SEDS – NGC 147
- NGC 147 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images
| 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". |  |
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*It is uncertain whether these are companion galaxies of the Andromeda Galaxy | |
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This page was last edited on 28 June 2023, at 21:11