Photometry of the Globular Cluster M54 and the Sagittarius Dwarf Galaxy: The Age-Metallicity Relation

Layden, Andrew C.; Sarajedini, Ata

doi:10.1086/301293

Cited by 237 publications

(329 citation statements)

References 58 publications

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“…The metal-poor clusters in Sgr appear to be approximately coeval with the oldest Galactic globular clusters (e.g., Layden & Sarajedini 2000), which according to recent studies (e.g., Salaris & Weiss 2002) have ages of 12 to 13 Gyr. The identification of Whiting 1 with Sgr suggests that this galaxy was able to form star clusters for ≈6 Gyr.…”

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

confidence: 76%

“…M 54, which lies at the center of the main body, is very luminous and has an age similar to the ages of the oldest globular clusters in the Galactic halo. It is unusual for a globular cluster in having an internal metallicity spread, and several authors (e.g., Layden & Sarajedini 2000) have suggested that M 54 is actually the nucleus of the galaxy, which if correct would make Sgr a nucleated dwarf elliptical galaxy. Two of the other star clusters, Ter 8 and Arp 2, are metalpoor and old globular clusters, whereas Ter 7 is both metal-rich and young for a globular cluster (Buonanno et al 1995).…”

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

confidence: 99%

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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 Dsphmentioning

confidence: 76%

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

confidence: 99%

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

Carraro¹,

Zinn²,

Bidin³

2007

A&A

120

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“…The period of the dwarf's orbit is less than 1 Gyr, and its extended structure suggests that it is currently being torn apart by the tidal forces of the Milky Way. Although the Sgr dSph does not currently contain neutral hydrogen (Koribalski, Johnston, & Otrupcek 1994), it surely did within the past few Gyr, considering that star formation was occurring within 0.5-3 Gyr ago (Layden & Sarajedini 2000). If the dwarf once had extended neutral hydrogen gas, it is likely to have been the first thing stripped from it, and any remnant would be at large radii from the dwarf's current position.…”

Section: Alternative Explanationsmentioning

confidence: 99%

The Magellanic Stream, High‐Velocity Clouds, and the Sculptor Group

Putman

Staveley‐Smith

Freeman

et al. 2003

ApJ

286

401

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The Magellanic Stream is a 100 Â 10 filament of gas that lies within the Galactic halo and contains $2 Â 10 8 M of neutral hydrogen. In this paper we present data from the H i Parkes All Sky Survey (HIPASS) in the first complete survey of the entire Magellanic Stream and its surroundings. We also present a summary of the reprocessing techniques used to recover large-scale structure in the Stream. The substantial improvement in spatial resolution and angular coverage compared to previous surveys reveals a variety of prominent features, including bifurcation along the main Stream filament; dense, isolated clouds that follow the entire length of the Stream; head-tail structures; and a complex filamentary web at the head of the Stream where gas is being freshly stripped away from the Small Magellanic Cloud and the Bridge. Debris that appears to be of Magellanic origin extends out to 20 from the main Stream filaments. The Magellanic Stream has a velocity gradient of 700 km s À1 from the Clouds to the tail of the Stream, $390 km s À1 greater than that due to Galactic rotation alone, therefore implying a noncircular orbit. The dual filaments comprising the Stream are likely to be relics from gas stripped separately from the Magellanic Bridge and the SMC. This implies that (1) the Bridge is somewhat older than conventionally assumed; and (2) the Clouds have been bound together for at least one or two orbits. The transverse velocity gradient of the Stream also appears to support long-term binary motion of the Clouds. A significant number of the most elongated cataloged Stream clouds (containing $1% of the Stream mass) have position angles aligned along the Stream. This suggests the presence of shearing motions within the Stream, arising from tidal forces or interaction with the tenuous Galactic halo. As previously noted, clouds within one region of the Stream, along the sight line to the less distant half (southern half on the sky) of the Sculptor Group, show anomalous properties. There are more clouds along this sight line than any other part of the Stream, and their velocity distribution significantly deviates from the gradient along the Stream. We argue that this deviation could be due to a combination of halo material, and not to distant Sculptor clouds, based on a spatial and kinematic comparison between the Sculptor Group galaxies and the anomalous clouds and the lack of cloud detection in the northern half of the group. This result has significant implications for the hypothesis that there might exist distant, massive high-velocity clouds within the Local Group. Cataloged clouds within the Magellanic Stream do not have a preferred scale size. Their mass spectrum f ðM H i Þ / M À2:0 H i and column density spectrum f ðN H i Þ / N À2:8 H i are steep compared with Ly absorbers and galaxies, and similar to the anomalous clouds along the Sculptor Group sight line.

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“…Three of the Sgr clusters, namely M54, Ter 8, and Arp 2, are also known to have ages coeval with the rest of the halo globular clusters (Layden & Sarajedini 2000) ; however, these clusters have traditional blue HB types for their metallicities, i.e., they do not display the second-parameter e †ect. Rosenberg et.…”

Section: Comparison With Sgr and Fornax Dsph Cluster Systemsmentioning

confidence: 99%

Orbits of Globular Clusters in the Outer Galaxy: NGC 7006

Dinescu

Majewski

Girard

et al. 2001

The Astronomical Journal

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We present a proper-motion study of the distant globular cluster NGC 7006 based on the measurement of 25 photographic plates spanning a 40 yr interval. The absolute proper motion determined with respect to extragalactic objects is [1.14)^(0.35, 0.40) mas yr~1. The total space96, velocity of NGC 7006 in a Galactocentric rest frame is 279 km s~1, placing the cluster on one of the most energetic orbits kpc) known to date for clusters within 40 kpc from the Galactic center. (R a \ 102 We compare the orbitsÈas determined from full space velocitiesÈof four clusters that have apocentric radii larger than 80 kpc with those of Galactic satellites with well-measured proper motions. These clusters are NGC 5466, 6934, and 7006 and Pal 13, and the satellites are the Sagittarius dwarf spheroidal galaxy (dSph), the Large Magellanic Cloud, the Ursa Minor dSph, and the Sculptor dSph. Only NGC 5466 and 6934 seem to have similar orbital parameters, indicating a possible phase-space association. NGC 7006, Pal 13, and the "" pair ÏÏ NGC 5466 and 6934 do not show any dynamical association with the Galactic satellites considered here. NGC 5466, 6934, and 7006 and Pal 13 have orbits that are highly eccentric and of various inclinations with respect to the Galactic plane. In contrast, the orbits of the Galactic satellites are of low to moderate eccentricity and highly inclined. Based on orbit types, chemical abundances, and cluster parameters, we discuss the properties of the hypothetical host systems of the remote globular clusters in the Searle-Zinn paradigm. It is apparent that clusters such as NGC 5466, 6934, and 7006 formed in systems that more likely resemble the Fornax dSph rather than the Sagittarius dSph. We also discuss plausible causes for the di †erence found so far between the orbit type of outer halo clusters and that of Galactic satellites and for the tentative, yet suggestive, phase-space scatter found among outer halo clusters.

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Photometry of the Globular Cluster M54 and the Sagittarius Dwarf Galaxy: The Age-Metallicity Relation

Cited by 237 publications

References 58 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 Magellanic Stream, High‐Velocity Clouds, and the Sculptor Group

Orbits of Globular Clusters in the Outer Galaxy: NGC 7006

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