The ACS Survey of Galactic Globular Clusters: M54 and Young Populations in the Sagittarius Dwarf Spheroidal Galaxy

By M. Siegel, Aaron Dotter, S. Majewski, A. Sarajedini, B. Chaboyer, D. Nidever, Jay Anderson, A. Marín-Franch, A. Rosenberg, L. Bedin and 4 more. 2007

211 citations recorded by the source corpus.

As part of the ACS Survey of Galactic Globular Clusters, we present new Hubble Space Telescope photometry of the massive globular cluster M54 (NGC 6715) and the superposed core of the tidally disrupted Sagittarius (Sgr) dSph galaxy. Our deep (F606W ~ 26.5), high-precision photometry yields an unprecedentedly detailed color-magnitude diagram showing the extended blue horizontal branch and multiple main sequences of the M54+Sgr system. The distance and reddening to M54 are revised using both isochrone and main-sequence fitting to (m - M)0 = 17.27 and E(B - V) = 0.15. Preliminary assessment finds the M54+Sgr field to be dominated by the old metal-poor populations of Sgr and the globular cluster. Multiple turnoffs indicate the presence of at least two intermediate-aged star formation epochs with 4 and 6 Gyr ages and [Fe/H] = -0.4 to -0.6. We also clearly show, for the first time, a prominent, ~2.3 Gyr old Sgr population of near-solar abundance. A trace population of even younger (~0.1-0.8 Gyr old), more metal-rich ([Fe/H] ~ 0.6) stars is also indicated. The Sgr age-metallicity relation is consistent with a closed-box model and multiple (4-5) star formation bursts over the entire life of the satellite, including the time since Sgr began disrupting.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/e3b861793e6282d8036b541c0d7694f8e0828f80

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. Jay Anderson
2. G. Piotto
3. A. Bragaglia
4. A. Milone
5. S. Majewski
6. E. Carretta
7. R. Gratton
8. Aaron Dotter

In Instrumentation

1. A. Bragaglia
2. Jay Anderson
3. E. Carretta
4. R. Gratton
5. S. Majewski
6. D. Law
7. G. Piotto
8. A. Milone

Citations in the corpus

• The Dartmouth Stellar Evolution Database (2008, methodology): “The performance of the synthetic color transformation in the ACS F606W-F814W CMD has been documented by Sarajedini et al. (2007); Dotter et al. (2007); Richer et al. (2007); Siegel et al. (2007).”
• The ACS survey of Galactic globular clusters. XII. Photometric binaries along the main sequence (2011, background): “We also excluded Palomar 2 because of its high differential reddening, and NGC 5139 (ω Centauri), and NGC 6715 because of the multiple main sequences (Siegel et al. 2007, Bellini et al. 2010 and references therein).”
• Multiple populations in globular clusters (2012, background): “…multiple RGBs visible in all visual colourmagnitude diagrams (e.g., Lee 1999; Pancino et al. 2000) or M 54 projected on the Sgr dSph population (e.g., Siegel et al. 2007), generally only subtle effects are expected on the RGB, difficult to disentangle from errors or differential reddening.”
• GLOBULAR CLUSTERS IN THE OUTER GALACTIC HALO: NEW HUBBLE SPACE TELESCOPE/ADVANCED CAMERA FOR SURVEYS IMAGING OF SIX GLOBULAR CLUSTERS AND THE GALACTIC GLOBULAR CLUSTER AGE–METALLICITY RELATION (2011, methodology): “The closed-box model portrayed in the upper-right panel of Figure 10 was taken from the study of the star formation history of M54 and the central field of the Sagittarius (hereafter Sgr) dwarf spheroidal galaxy by Siegel et al. (2007).”
• Nuclear star clusters (2009, background): “The dominant population in this NSC is old and metal-poor ([Fe/H] = −1.5), with a small number of much younger (.2 Gyr) and more metal-rich ([Fe/H] = −0.5) stars (Monaco et al. 2005; Siegel et al. 2007; Mucciarelli et al. 2017; Alfaro-Cuello et al. 2019).”
• Spectroscopic and photometric evidence of two stellar populations in the Galactic globular cluster NGC 6121 (M 4) (2008, background): “In fact, evidence of multiple populations has been found in other GCs, like NGC 1851 (Milone et al. 2008), NGC 6388 (Siegel et al. 2007, Piotto et al. 2008), and M54 (Piotto et al., in preparation) in the form of a split in the SGB.”
• The formation and assembly history of the Milky Way revealed by its globular cluster population (2018, background): “…with Canis Major (both of which have recently been accreted by the Milky Way and possibly correspond to Satellites 2 and 3, see Section 5.1) are consistent with the enrichment histories derived for Satellites 2 and 3 (see e.g. Layden & Sarajedini 2000; Forbes et al. 2004; Siegel et al. 2007).”
• THE ACS SURVEY OF GALACTIC GLOBULAR CLUSTERS. IX. HORIZONTAL BRANCH MORPHOLOGY AND THE SECOND PARAMETER PHENOMENON (2009, unknown): “Siegel et al. (2007) analyzed the M 54 CMD and measured ages for the stellar populations present and also estimated the metallicities of the stellar populations for which no spectroscopic information was available.”
• ASSESSING THE MILKY WAY SATELLITES ASSOCIATED WITH THE SAGITTARIUS DWARF SPHEROIDAL GALAXY (2010, methodology): “As discussed recently by Forbes & Bridges (2010) for a sample of Sgr-candidate clusters drawn from the literature, the clusters describe a relatively well defined age-metallicity relation (AMR), which we note is generally consistent with the closed-box Sgr AMR derived by Siegel et al. (2007).”
• The stellar halo of the Galaxy (2008, background): “On the other hand, some dwarf galaxies have managed to form stars until very recently, such as Fornax (Stetson et al. 1998) or Sagittarius (Siegel et al. 2007).”
• THE NGC 404 NUCLEUS: STAR CLUSTER AND POSSIBLE INTERMEDIATE-MASS BLACK HOLE (2010, methodology): “Previous studies have found significant evidence for multiple stellar populations in nuclear star clusters (Long et al. 2002; Rossa et al. 2006; Walcher et al. 2006; Seth et al. 2006; Siegel et al. 2007).”
• An Abundance Analysis of Bright Giants in the Globular Cluster NGC 1851 (2007, background): “Both q Centauri and M54 possess a large metallicity spread and are the two most massive Galactic globular clusters. q Centauri is widely regarded as the nucleus of an accreted dwarf galaxy (e.g., Smith et al. 2000), and M54 is suspected to be the nucleus of the Sagittarius dwarf spheroidal galaxy (e”
• THE CHEMICAL EVOLUTION OF THE DRACO DWARF SPHEROIDAL GALAXY (2009, unknown): “The globular cluster M54 is at the location of the nucleus of the Sgr dSph galaxy, but Siegel et al (2007) suggest that it is not the nucleus itself, but rather was pulled in very close to it by dynamical friction.”
• Origin of multiple stellar populations in globular clusters and their helium enrichment (2008, background): “Some circumstantial evidence for this now widely entertained scenario is the finding that M54, one of the most massive GCs in the Galaxy, is indeed associated with the Sagittarius dwarf, albeit there is no evidence for multiple populations within this cluster (Siegel et al. 2007).”
• The ACS Survey of Galactic Globular Clusters. III. The Double Subgiant Branch of NGC 1851 (2007, background): “One more cluster, M54, shows a complex color-magnitude diagram (CMD; see, e.g., Layden&Sarajedini 2000), including a bifurcated SGB (Siegel et al. 2007, Paper IV of this series).”
• THE ACS SURVEY OF GALACTIC GLOBULAR CLUSTERS. VII. RELATIVE AGES (2008, background): “For clusters with multiple stellar populations, such as NGC 1851 (Milone et al. 2008a), NGC 2808 (Piotto et al. 2007), M54 (Siegel et al. 2007) and ωCen (Lee et al. 1999; Pancino et al. 2000; Bedin et al. 2004), the mean ridge line fitting procedure fits the dominant population (see Figure 1).”