Terzan 7

Terzan 7

Terzan7 by Hubble Space Telescope; 3.5′ view
Credit: NASA, ESA, and A. Sarajedini (University of Florida). Acknowledgement: Gilles Chapdelaine
Observation data (J2000 epoch)
Constellation Sagittarius
Right ascension 19h 17m 43.92s[1]
Declination −34° 39′ 27.8″[1]
Distance 75.7 kly (23.2 kpc)[2]
Apparent magnitude (V) 12.0[2]
Apparent dimensions (V) 7′.3[2]
Physical characteristics
Radius 160 ly[a]
VHB 17.76[3]
Estimated age 7.5 Gyr[4]
Notable features young extragalactic globular
Other designations Ter 7,[4] GCl 109.1[5]

Terzan 7 is a sparse and young globular cluster that is believed to have originated in the Sagittarius Dwarf Spheroidal Galaxy (Sag DEG) and is physically associated with it. It is relatively metal rich with [Fe/H = -0.6[6] and an estimated age of 7.5 Gyr.[4] Terzan 7 has low levels of nickel ([Ni/Fe]=-0.2) which supports its membership in the Sag DEG system since it has a similar chemical signature.[7] It has a rich population of blue stragglers that are strongly concentrated toward the center of Terzan 7.[8] It has an average luminosity distribution of Mv = -5.05.[9] It has a half-light radius (Rh) = 6.5pc.[10]

History

Terzan 7 was the brightest[11] of six globulars discovered by the French[11] astronomer Agop Terzan in 1968.[12]

Young globular

Nearly all globular clusters of the Milky Way's galactic halo formed at the same time (12-15 Gyr). Even the far situated NGC 2419 (~100 kpc from galactic center) has a similar age. This trend also applies to the age of globulars found in the Large Magellanic Cloud and Fornax Dwarf (~140 kpc from galactic center). However, a few globulars seem to be significantly younger than the rest; these include Palomar 1, Palomar 3, Palomar 4, Palomar 12, Palomar 14, Ruprecht 106, IC 4499, Arp 2, Eridanus, Fornax 4, and Terzan 7. In particular, the ones associated with the Sag DEG appear to have formed more recently. The data suggests that all the present outer halo globulars may have originally formed in dwarf spheroidals.[10]

Hierarchical galaxy formation

Alternatively, a hierarchical galaxy formation model is hypothesized under which a portion, possibly large, of the Milky Way's globular clusters would have originated in the accretion of other dwarf spheroidals like Sag DEG. The best candidate for this idea is Palomar 12.[6][13]

Notes

  1. ^ 75.7 kly × tan( 7′.3 / 2 ) = 160 ly. radius

References

  1. 1 2 Goldsbury, Ryan; et al. (December 2010), "The ACS Survey of Galactic Globular Clusters. X. New Determinations of Centers for 65 Clusters", The Astronomical Journal 140 (6): 1830–1837, arXiv:1008.2755, Bibcode:2010AJ....140.1830G, doi:10.1088/0004-6256/140/6/1830.
  2. 1 2 3 Terzan 7 @ seds
  3. ↑ Wilson, Barbara (July 2, 1995), Obscure Globulars
  4. 1 2 3 Geisler, Doug; Wallerstein, George; Smith, Verne V.; Casetti-Dinescu, Dana I. (September 2007), "Chemical Abundances and Kinematics in Globular Clusters and Local Group Dwarf Galaxies and Their Implications for Formation Theories of the Galactic Halo", The Publications of the Astronomical Society of the Pacific 119 (859): 939–961, arXiv:0708.0570, Bibcode:2007PASP..119..939G, doi:10.1086/521990
  5. ↑ "SIMBAD Astronomical Object Database". Results for Terzan 7. Retrieved 2008-01-27.
  6. 1 2 Sbordone, L.; Bonifacio, P.; Marconi, G.; Buonanno, R.; Zaggia, S. (July 3, 2005), "Family ties: Abundances in Terzan 7, a Sgr dSph globular cluster", Astronomy and Astrophysics 437 (3): 905–910, arXiv:astro-ph/0505307, Bibcode:2005A&A...437..905S, doi:10.1051/0004-6361:20042315
  7. ↑ Sbordone, L.; Bonifacio, P.; Marconi, G.; Buonanno, R. (2004), "Chemical abundances in Terzan 7", Memorie della Societa Astronomica Italiana 75: 396, Bibcode:2004MmSAI..75..396S
  8. ↑ Held, Enrico V.; Rosenberg, Alfred; Saviane, Ivo; Momany, Yazan (March 12–16, 2001), written at Pucon, Chile, Geisler, D.; Grebel, E.K.; Minniti, D., eds., "The Globular Cluster Terzan 7 in the Sagittarius Dwarf Spheroidal Galaxy", Publications of the Astronomical Society of the Pacific (San Francisco, published 2002): 165, Bibcode:2002IAUS..207..165H
  9. ↑ van den Bergh, Sidney (July 2007), "The Luminosity Distribution of Globular Clusters in Dwarf Galaxies", The Astronomical Journal 134 (1): 344–345, arXiv:0704.2226, Bibcode:2007AJ....134..344V, doi:10.1086/518868
  10. 1 2 van den Bergh, Sidney (February 2000), "Young Globular Clusters and Dwarf Spheroidals", The Astrophysical Journal 530 (2): 777–782, arXiv:astro-ph/9910243, Bibcode:2000ApJ...530..777V, doi:10.1086/308413
  11. 1 2 Gottlieb, Steve (August 1, 2000), Sky and Telescope 100 (2): 112, ISSN 0037-6604 Missing or empty |title= (help)
  12. ↑ Terzan, Agop (1968), "Six nouveaux amas stellaires (Terzan 3-8) dans la region DU centre de la Voie lactee et les constellations DU Scorpion et DU Sagittaire", C.R. Acad. Sci. 267 (Ser. B): 1245–1248, Bibcode:1968CRASB.267.1245T
  13. ↑ Briley, Michael M.; Martell, S.; Smith, G. H. (December 2007), "The Homogeneity of Light Elements in the Sagittarius Elliptical Dwarf Galaxy Globular Clusters Terzan 7 and Arp 2", American Astronomical Society, AAS Meeting #211, #58.31, Bibcode:2007AAS...211.5831B

Coordinates: 19h 17m 43.5s, −34° 39′ 27″

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