The age of the main population of the Sagittarius dwarf spheroidal
 galaxy

Bellazzini, M.; Correnti, Matteo; Ferraro, F. R.; Monaco, L.; Montegriffo, P.

doi:10.1051/0004-6361:200500223

Cited by 63 publications

(77 citation statements)

References 25 publications

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“…It appears to have been essentially level from the formation of those clusters until at least the formation of Whiting 1 ≈ 3 Gyr later. This is consistent with the recent conclusion of Bellazzini et al (2006) that the stellar population in the core of Sgr has [Fe/H] ≈ −0.6 and age ≈8 Gyr. Observations of the red giants clearly indicate that [Fe/H] eventually rose to a higher value (≈0) than found in any of the known Sgr clusters (e.g., Bonifacio et al 2004;McWilliam & SmeckerHane 2005;Monaco et al 2005).…”

Section: Whiting 1 and The Star Cluster Family Of The Sgr Dsphsupporting

confidence: 93%

Whiting 1: the youngest globular cluster associated with the Sagittarius dwarf spheroidal galaxy

Carraro¹,

Zinn²,

Bidin³

2007

A&A

120

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Context. Recently, Carraro (2005) drew attention to the remarkable star cluster Whiting 1 by showing that it lies about 40 kpc from the Sun and is therefore unquestionably a member of the Galactic halo (b = −60.6 deg). Its Color Magnitude Diagram (CMD) indicated that Whiting 1 is very young (∼5 Gyr) for a globular cluster. It is very likely that Whiting 1 originated in a dwarf galaxy that has since been disrupted by the Milky Way. Aims. The main goals of this investigation were to constrain better the age, metallicity, and distance of Whiting 1 and to assess whether it belongs to a stellar stream from the Sagittarius dwarf spheroidal galaxy (Sgr dSph). Methods. Deep CCD photometry in the BVI pass-bands obtained with the VLT is used to improve the quality of the CMD and to determine the cluster's luminosity function and surface density profile. High-resolution spectrograms obtained with Magellan are used to measure the cluster's radial velocity and to place limits on its possible metallicity. The measurements of distance and radial velocity are used to test the cluster's membership in the stellar streams from the Sgr dSph. Results. From our CMD of Whiting 1, we derive new estimates for the cluster's age (6.5 +1.0 −0.5 Gyr), metallicity (Z = 0.004 ± 0.001, [Fe/H] = -0.65), and distance (29.4 +1.8 −2.0 kpc). From echelle spectrograms of three stars, we obtain -130.6 ± 1.8 km s −1 for the cluster's radial velocity and show from measurements of two infra-red CaII lines that the [Fe/H] of the cluster probably lies in the range -1.1 to -0.4. Both the luminosity function and the surface density profile suggest that the cluster has undergone tidal stripping by the Milky Way. We demonstrate that the position of Whiting 1 on the sky, its distance from the Sun, and its radial velocity are identical to within the errors of both the theoretical predictions of the trailing stream of stars from the Sgr dSph galaxy and the previous observations of the M giant stars that delineate the streams. Conclusions. With the addition of Whiting 1, there is now strong evidence that 6 globular clusters formed within the Sgr dSph. Whiting 1 is particularly interesting because it is the youngest and among the most metal rich. The relatively young age of Whiting 1 demonstrates that this dwarf galaxy was able to form star clusters for a period of at least 6 Gyr, and the age and metallicity of Whiting 1 are consistent with the age-metallicity relationship in the main body of the Sgr dSph. The presence now of Whiting 1 in the Galactic halo provides additional support for the view that the young halo clusters originated in dwarf galaxies that have been accreted by the Milky Way.

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Section: Whiting 1 and The Star Cluster Family Of The Sgr Dsphsupporting

confidence: 93%

Whiting 1: the youngest globular cluster associated with the Sagittarius dwarf spheroidal galaxy

Carraro¹,

Zinn²,

Bidin³

2007

A&A

120

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“…There is no obvious East-West distance gradient among these variables. The square near the center represents the 1 • × 1 • area observed by Bellazzini et al (2006) where they established that the bulk of the stars are older than 5 Gyr.…”

Section: Pl Relation and Distancesmentioning

confidence: 99%

“…Similarly, Giuffrida et al (2010) have detected several populations of different metallicities and presumably ages in a few fields in Sgr. According to Bellazzini et al (2006) the mean age of the population in the central region of Sgr is larger than 5 Gyr with a best estimate of 8 ± 1.5 Gyr. Sagittarius also has an impressive number of RR Lyrae stars (Kunder & Chaboyer 2009) indicating the presence of a much older population.…”

Section: Period Distributionsmentioning

confidence: 99%

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The variability of carbon stars in the Sagittarius dwarf spheroidal galaxy

Battinelli

Demers

2013

A&A

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Context. Stars have been forming in massive dwarf spheroidal galaxies continuously for several Gyr. The detection of AGB carbon stars indicates that an intermediate-age population is present. Sagittarius, the most massive, contains some 100 carbon stars. Most of them are probably variable. Aims. Using photometric monitoring we intend to detect long period variables among Sagittarius carbon stars. We should be able to identify mira variables, semi-regular and irregular variables, and to determine their period and age group. Methods. We have obtained K and J images over four semesters. These images are centered on a sample of 27 photometrically identified C stars to follow their variation and determine their periodicity. Results. We have established the period of 14 program stars and have identified 13 miras among them. From their periods we determined that most of them are in the 3−5 Gyr age group. Conclusions. The known miras, distributed over a wide area within Sagittarius dwarf spheroidal galaxy (Sgr), belong to populations of various ages and, most probably, various metallicities.

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“…M 54 and the surrounding area have been examined photometrically (e.g. Marconi et al 1998;Bellazzini et al 1999a,b;Layden & Sarajedini 2000;Monaco et al 2004;Bellazzini et al 2006a;Siegel et al 2007) as well as by means of high resolution spectroscopy (Bonifacio et al 2000aTautvaišienė et al 2004;Zaggia et al 2004;Sbordone et al 2005;Caffau et al 2005;Monaco et al 2005a;McWilliam & Smecker-Hane 2005;Sbordone et al 2007;Mottini et al 2008). While ground based photometry suggests for the Sgr dSph main body population a mean metallicity of [Fe/H] ∼ -1, spectroscopy shows a surprising abundance spread in the main body, with a significant population around [Fe/H] = 0, a mean value around [Fe/H] = -0.5 and a weak metal poor tail possibly extending below [Fe/H] = -2.5.…”

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 age of the main population of the Sagittarius dwarf spheroidal galaxy

Cited by 63 publications

References 25 publications

Whiting 1: the youngest globular cluster associated with the Sagittarius dwarf spheroidal galaxy

Whiting 1: the youngest globular cluster associated with the Sagittarius dwarf spheroidal galaxy

The variability of carbon stars in the Sagittarius dwarf spheroidal galaxy

A wide angle view of the Sagittarius dwarf spheroidal galaxy

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