The Nucleus of the Sagittarius DSPH Galaxy and M54: A Window on the Process of Galaxy Nucleation

Bellazzini, M.; Ibata, Rodrigo; Chapman, Scott; Mackey, A. D.; Monaco, L.; Irwin, M. J.; Martín, Nicolás F.; Lewis, Geraint F.; Dalessandro, E.

doi:10.1088/0004-6256/136/3/1147

Cited by 231 publications

(298 citation statements)

References 111 publications

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“…It has been suggested that ω Cen may be the remnant of the nucleus of a, now destroyed, dwarf galaxy that had hosted a globular cluster (GC) at its center (Bellazzini et al 2008;Carretta et al 2010). ω Cen would then be a system similar to the GC M 54 plus the nucleus (SgrN) of the Sagittarius dwarf spheroidal galaxy (Sgr dSph) at whose center it lies.…”

Section: Discussionmentioning

confidence: 99%

The lithium content ofω Centauri

Monaco

Bonifacio

Sbordone

et al. 2010

A&A

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Context.A discrepancy has emerged between the cosmic lithium abundance inferred by the WMAP satellite measurement coupled with the prediction of the standard big-bang nucleosynthesis theory, and the constant Li abundance measured in metal-poor halo dwarf stars (the so-called Spite plateau). Several models are being proposed to explain this discrepancy, involving either new physics, in situ depletion, or the efficient depletion of Li in the pristine Galaxy by a generation of massive first stars. The realm of possibilities may be narrowed considerably by observing stellar populations in different galaxies, which have experienced different evolutionary histories. Aims. The ω Centauri stellar system is commonly considered as the remnant of a dwarf galaxy accreted by the Milky Way. We investigate the lithium content of a conspicuous sample of unevolved stars in this object. Methods. We obtained moderate resolution (R = 17 000) spectra for 91 main-sequence/early sub-giant branch (MS/SGB) ω Cen stars using the FLAMES-GIRAFFE/VLT spectrograph. Lithium abundances were derived by matching the equivalent width of the Li i resonance doublet at 6708 Å to the prediction of synthetic spectra computed with different Li abundances. Synthetic spectra were computed using the SYNTHE code along with ATLAS-9 model atmospheres. The stars effective temperatures are derived by fitting the wings of the H α line with synthetic profiles. Results. We obtain a mean content of A(Li) = 2.19 ± 0.14 dex for ω Centauri MS/SGB stars. This is comparable to what is observed in Galactic halo field stars of similar metallicities and temperatures. Conclusions. The Spite plateau seems to be an ubiquitous feature of old, warm metal-poor stars. It exists also in external galaxies, if we accept the current view about the origin of ω Cen. This implies that the mechanism(s) that causes the "cosmological lithium problem" may be the same in the Milky Way and other galaxies.

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Section: Discussionmentioning

confidence: 99%

The lithium content ofω Centauri

Monaco

Bonifacio

Sbordone

et al. 2010

A&A

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“…It is sufficiently massive to contain more than one stellar population, as indicated by helium abundance variations (Norris 2004;Piotto et al 2005) and its peculiar position in the sizeluminosity plane (Mackey & van der Bergh 2005). It has been also argued that ω Cen may not be a genuine globular cluster but the nuclear remnant of a dwarf galaxy that merged in the past with the Milky Way (e.g., Bellazzini et al 2008).…”

Section: Radial Velocity Measurements For ω Centaurimentioning

confidence: 99%

Testing Newtonian gravity in the low acceleration regime with globular clusters: the case ofω Centauri revisited

Scarpa

Falomo

2010

A&A

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Context. Stellar kinematics in the external regions of globular clusters can be used to probe the validity of Newton's law in the low acceleration regimes without the complication of non-baryonic dark matter. Indeed, in contrast to the case of galaxies, in globular clusters a systematic deviation of the velocity dispersion profile from the expected Keplerian falloff would be indicative of a breakdown of Newtonian dynamics rather than the existence of dark matter. Aims. We perform a detailed analysis of the velocity dispersion in the globular cluster ω Centauri to determine whether it decreases monotonically with distance as expected within the framework of Newtonian dynamics, or whether it converges toward a constant value as recent works suggest. Methods. We combine measurements from two previous studies to almost double the data available at large radii, to better constrain the velocity dispersion profile in the low acceleration regime. Results. We found the inner region of ω Centauri is clearly rotating, while the rotational velocity tends to vanish, being consistent with no rotation at all in the external regions. The cluster velocity dispersion at large radii from the center is found to clearly deviate from the Newtonian prediction. Conclusions. We conclude that there are strong similarities between globular clusters and elliptical galaxies, for in both classes of objects the velocity dispersion tends to remain constant at large radii. In the case of galaxies, this is ascribed to the existence of a massive halo of dark matter, which is physically unlikely in the case of globular clusters. This similarity, if confirmed, is best explained by a breakdown of Newtonian dynamics below a critical acceleration.

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“…With the discovery of Sgr dSph, 4 globular clusters (GC) which were before considered belonging to the halo have been recognized as being associated with the Sgr dSph. While three of them (Terzan 7, Terzan 8, and Arp 2) lay at the outskirts of Sgr dSph, the position of the fourth one, M 54, coincides with the center of the dwarf spheroidal (Monaco et al 2005b) although it likely formed elsewhere and fell subsequently into the galaxy core (Bellazzini et al 2008). It became subsequently clear that a number of other globular clusters, currently lying far from Sgr dSph, have kinematical properties compatible with an origin within the Sgr dSph system, and a subsequent stripping (Bellazzini et al 2003), or were actually embedded into the stream material (Martínez-Delgado et al 2002).…”

Section: Introductionmentioning

confidence: 99%

A wide angle view of the Sagittarius dwarf spheroidal galaxy

Giuffrida

Sbordone

Zaggia

et al. 2010

A&A

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Context. The Sagittarius dwarf Spheroidal Galaxy (Sgr dSph) provides us with a unique possibility of studying a dwarf galaxy merging event while still in progress. Moving along a short-period, quasi-polar orbit in the Milky Way Halo, Sgr dSph is being tidally dispersed along a huge stellar stream. Due to its low distance (25 kpc), the main body of Sgr dSph covers a vast area in the sky (roughly 15 × 7 degrees). Available photometric and spectroscopic studies have concentrated either on the central part of the galaxy or on the stellar stream, but the overwhelming majority of the galaxy body has never been probed. Aims. The aim of the present study is twofold. On the one hand, to produce color magnitude diagrams across the extension of Sgr dSph to study its stellar populations, searching for age and/or composition gradients (or lack thereof). On the other hand, to derive spectroscopic low-resolution radial velocities for a subsample of stars to determine membership to Sgr dSph for the purpose of high resolution spectroscopic follow-up. Methods. We used VIMOS@VLT to produce V and I photometry on 7 fields across the Sgr dSph minor and major axis, plus 3 more centered on the associated globular clusters Terzan 7, Terzan 8 and Arp 2. A last field has been centered on M 54, lying in the center of Sgr dSph. VIMOS high resolution spectroscopic mode has then been used to derive radial velocities for a subsample of the observed stars, concentrating on objects having colors and magnitudes compatible with the Sgr dSph red giant branch. Results. We present photometry for 320 000 stars across the main body of Sgr dSph, one of the richest, and safely the most wide-angle sampling ever produced for this fundamental object. We also provide robust memberships for more than one hundred stars, whose high resolution spectroscopic analysis will be the object of forthcoming papers. Sgr dSph appears remarkably uniform among the observed fields. We confirm the presence of a main Sgr dSph population characterized roughly by the same metallicity of 47 Tuc, but we also found the presence of multiple populations on the peripheral fields of the galaxy, with a metallicity spanning from [Fe/H] = -2.3 to a nearly solar value.

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The Nucleus of the Sagittarius DSPH Galaxy and M54: A Window on the Process of Galaxy Nucleation

Cited by 231 publications

References 111 publications

The lithium content ofω Centauri

The lithium content ofω Centauri

Testing Newtonian gravity in the low acceleration regime with globular clusters: the case ofω Centauri revisited

A wide angle view of the Sagittarius dwarf spheroidal galaxy

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