THE NUCLEUS OF THE SAGITTARIUS DSPH GALAXY AND M54: A WINDOW ON THE PROCESS OF GALAXY NUCLEATION

By M. Bellazzini, R. Ibata, S. Chapman, A. Mackey, L. Monaco, M. Irwin, N. Martin, Geraint F. Lewis, E. Dalessandro. 2008

183 citations recorded by the source corpus.

We present the results of a thorough study of the nucleus of the Sgr dwarf spheroidal galaxy (Sgr dSph) and of the bright globular cluster M54 (NGC 6715) that resides within the same nucleus (Sgr,N). We have obtained accurate radial velocities and metallicity estimates for 1152 candidate red giant branch stars of Sgr and M54 lying within ∼9′ from the center of the galaxy, from Keck/DEIMOS and VLT/FLAMES spectra of the infrared Ca ii triplet. Using both velocity and metallicity information we selected two samples of 425 and 321 very likely members of M54 and of Sgr,N, respectively. The two considered systems display significantly different velocity dispersion profiles. M54 has a steeply decreasing profile from r = 0′, where σ ≃ 14.2 km s−1, to r ≃ 3.′5 where it reaches σ ≃ 5.3 km s−1, then it appears to rise again to σ ≃ 10 km s−1 at r ∼ 7′. In contrast Sgr,N has a uniformly flat profile at σ ≃ 9.6 km s−1 over the whole 0′ ⩽ r ⩽ 9′ range. Using data from the literature we show that the velocity dispersion of Sgr remains constant at least out to r ∼ 100′ and there is no sign of the transition between the outer flat-luminosity-profile core and the inner nucleus in the velocity profile. These results, together with a re-analysis of the surface brightness profile of Sgr,N and a suite of dedicated N-body simulations, provide very strong support for the hypothesis that the nucleus of Sgr formed independently of M54, which probably plunged to its present position, coincident with Sgr,N, because of significant decay of the original orbit due to dynamical friction.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/145df8f1b10e313b014800bce0340ae0c934f77d

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In Astronomy and Astrophysics

1. E. Carretta
2. R. Gratton
3. A. Bragaglia
4. F. D’Antona
5. G. Piotto
6. A. Milone
7. S. Lucatello
8. P. Ventura

In Instrumentation

1. E. Carretta
2. R. Gratton
3. A. Bragaglia
4. F. D’Antona
5. S. Lucatello
6. P. Ventura
7. C. Sneden
8. G. Piotto

Citations in the corpus

• The two metallicity groups of the globular cluster M 22: a chemical perspective (2011, background): “…established, the Galactic Bulge cluster Ter 5 (Ferraro et al. 2009), M54, the central star cluster of the Sagittarius dwarf (Sarajedini & Layden 1995, Bellazzini et al. 2008, Carretta et al. 2010a), the outer halo cluster NGC 2419 (Cohen et al. 2010), and perhaps NGC 1851 (Carretta et al. 2010b).”
• Intrinsic iron spread and a new metallicity scale for globular clusters (2009, background): “…of several bursts of star formation, with corresponding peaks in the metal abundance (see Gratton et al. 2004 for a comprehensive discussion) and a spread in metallicity seems to be confirmed in M 22 (Marino et al. 2009) as well as in M 54 (Bellazzini et al. 2008; Carretta et al., in preparation).”
• ASSESSING THE MILKY WAY SATELLITES ASSOCIATED WITH THE SAGITTARIUS DWARF SPHEROIDAL GALAXY (2010, background): “…would chance to match Sgr so well), its velocity dispersion and luminosity profile indicate that it formed independently of the Sgr core and later sank to its present position via dynamical friction (Bellazzini et al. 2008, see also Majewski et al. 2003; Monaco et al. 2005; Siegel et al. 2007).”
• Properties of stellar generations in globular clusters and relations with global parameters (2010, background): “…galaxies that can be studied in close detail (such as M 54 for the Sagittarius galaxy) essentially share the full pattern of properties with GCs (see e.g. Bellazzini et al. 2008b; Georgiev et al. 2009; Carretta et al. 2010), although they may have wide spreads in Fe abundances, not observed in GCs.”
• Abundance patterns of multiple populations in globular clusters: a chemical evolution model based on yields from AGB ejecta (2010, result): “…et al. 2009, and references therein) and more recently it has been confirmed in other massive clusters like M22 (Marino et al. 2009; Da Costa et al. 2009, and references therein), M54 (Sarajedini & Layden 1995; Bellazzini et al. 2008, and references therein), and Terzan 5 (Ferraro et al. 2009).”
• Multiple populations in globular clusters (2012, methodology): “(2007): the globular clusters must have been initially a large factor (10-100) more massive than today and almost all the first generation stars must have been preferentially lost.”
• N-body modelling of globular clusters: masses, mass-to-light ratios and intermediate-mass black holes (2016, unknown): “As discussed by Bellazzini et al. (2008), this is most likely due to the fact that the sample includes stars from the Sagittarius dwarf galaxy, which follow a different kinematical profile and whose relative contribution increases in the outermost cluster parts.”
• Detailed abundances of a large sample of giant stars in M 54 and in the Sagittarius nucleus (2010, background): “NGC 6715 (M 54) is a massive globular cluster (GC) immersed in the nucleus of the Sgr (SgrN), a dwarf galaxy currently disrupting within our Galaxy (see Ibata et al. 1994; Bellazzini et al. 2008, from now B08, and references therein).”
• Accreted versus in situ Milky Way globular clusters (2010, background): “They are Terzan 7, Terzan 8, Arp 2, Pal 12, NGC 4147 and NGC 6715 (M54), with the latter being the probable remnant nucleus (see also Bellazzini et al. 2008).”