Star Clusters in M31. Ii. Old Cluster Metallicities and Ages From Hectospec Data

Caldwell, Nelson; Schiavon, Ricardo P.; Morrison, Heather; Rose, James A.; Harding, Paul

doi:10.1088/0004-6256/141/2/61

Cited by 166 publications

(472 citation statements)

References 81 publications

(154 reference statements)

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“…More recent studies are those by i) Fan et al (2008), based on correlations between optical and infrared colours and metallicity, combined with the use of various reddening-free parameters (as in Barmby et al 2000); ii) Montalto et al (2009), based on a multiwavelength (far UV to IR) photometric study of dust properties; and iii) Caldwell et al (2011), based on 5 Å resolution spectra of target clusters compared to flux-calibrated spectra of reference clusters with similar metallicity that were dereddened using the Barmby et al (2000) values.…”

Section: Reddeningmentioning

confidence: 99%

The horizontal branch luminosity vs. metallicity in M 31 globular clusters

Federici

Cacciari

Bellazzini

et al. 2012

A&A

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Context. Thanks to the outstanding capabilites of the HS T , our current knowledge about the M31 globular clusters (GCs) is similar to our knowledge of the Milky Way GCs in the 1960s-1970s, which set the basis for studying the halo and galaxy formation using these objects as tracers, and established their importance in defining the cosmic distance scale. Aims. We intend to derive a new calibration of the M V (HB)-[Fe/H] relation by exploiting the large photometric database of old GCs in M31 in the HS T archive. Methods. We collected the BVI data for 48 old GCs in M31 and analysed them by applying the same methods and procedures to all objects. We obtained a set of homogeneous colour-magnitude diagrams (CMDs) that were best-fitted with the fiducial CMD ridge lines of selected Milky Way template GCs. Reddening, metallicity, Horizontal Branch (HB) luminosity and distance were determined self-consistently for each cluster. Results. There are three main results of this study: i) the relation M V (HB)=0.25(±0.02)[Fe/H]+0.89(±0.03), which is obtained from the above parameters and is calibrated on the distances of the template Galactic GCs; ii) the distance modulus to M31 of (m-M) 0 =24.42±0.06 mag, obtained by normalising this relation at the reference value of [Fe/H]=-1.5 to a similar relation using V 0 (HB). This is the first determination of the distance to M31 based on the characteristics of its GC system which is calibrated on Galactic GCs; iii) the distance to the Large Magellanic Cloud (LMC), which is estimated to be 18.54±0.07 mag as a consequence of the previous results. These values agree excellently with the most recent estimate based on HS T parallaxes of Galactic Cepheid and RR Lyrae stars, as well as with recent methods.

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Section: Reddeningmentioning

confidence: 99%

The horizontal branch luminosity vs. metallicity in M 31 globular clusters

Federici

Cacciari

Bellazzini

et al. 2012

A&A

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“…It is possible to reach the MSTO luminosity of M 31 clusters, but this requires such a large amount of HST time as to make a systematic study unpractical (Brown et al 2004). -Global metallicity estimates from integrated spectra and/or from the color of the RGB are also available (Galleti et al 2009;Caldwell et al 2011;Perina et al 2009), analogously to the MW GC compilation by Zinn & West (1984).…”

Section: Introductionmentioning

confidence: 99%

The horizontal branch morphology of M 31 globular clusters

Bellazzini

Buzzoni

Cacciari

et al. 2012

A&A

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We use deep, high quality color magnitude diagrams obtained with the Hubble Space Telescope to compute a simplified version of the Mironov index (SMI; B B+R ) to parametrize the horizontal branch (HB) morphology for 23 globular clusters in the M 31 galaxy (Sample A), all located in the outer halo at projected distances between 10 kpc and 100 kpc. This allows us to compare them with their Galactic counterparts, for which we estimated the SMI exactly in the same way, in the SMI vs. [Fe/H] plane. We find that the majority of the considered M 31 clusters lie in a significantly different locus, in this plane, with respect to Galactic clusters lying at any distance from the center of the Milky Way. In particular they have redder HB morphologies at a given metallicity, or, in other words, clusters with the same SMI value are ≈0.4 dex more metal rich in the Milky Way than in M 31. We discuss the possible origin of this difference and we conclude that the most likely explanation is that many globular clusters in the outer halo of M 31 formed ≈1-2 Gyr later than their counterparts in the outer halo of the Milky Way, while differences in the cluster-to-cluster distribution of He abundance of individual stars may also play a role. The analysis of another sample of 25 bright M 31 clusters (eighteen of them with M V ≤ −9.0, Sample B), whose SMI estimates are much more uncertain as they are computed on shallow color magnitude diagrams, suggests that extended blue HB tails can be relatively frequent among the most massive M 31 globular clusters, possibly hinting at the presence of multiple populations.

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“…We also find that the number of the metal-poor and metal-rich groups becomes comparable while the previous works show that the number of metal-poor group is more than that of the metal-rich one. This may be due to many intermedate metallicty metallicity of Caldwell et al (2011) have been merged into our sample for our statistics. The spatial distributions shows that the metal-rich group is more centrally concentrated while the metal-poor group is occupy a more extended halo and the young population is centrally concentrated while the old populaiton is more extended spatially to the outer halo.…”

Section: Discussionmentioning

confidence: 99%

“…Figure 6 shows the relationship between the metallicities and the radial velocities V r which have been corrected for the systemic velocity of the M31 galaxy. The spectroscopic metallicities are from the literature (Huchra et al, 1991;Barmby et al, 2000;Perrett et al, 2002;Galleti et al, 2009;Caldwell et al, 2011), Paper I as well as this work and the radial velocities V r are from the RBC v.4, Paper I and this work. It seems that there is no any relationship between the metallicities versus the radial velocities V r .…”

Section: Nomentioning

confidence: 99%

“…Figure 8 shows the metallicity distributions of the GCs and the HGCs, respectively. In the Left panel, the sample includes all the GCs which have spectroscopic metallicity from the literature (Huchra et al, 1991;Barmby et al, 2000;Perrett et al, 2002;Galleti et al, 2009;Caldwell et al, 2011) and Paper I as well as this work. In total, there are 386 GCs with spectroscopic metallicity in the distribution.…”

Section: Nomentioning

confidence: 99%

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Spectroscopic study of globular clusters in the halo of M31 with the Xinglong 2.16 m telescope II: dynamics, metallicity and age

Zhang¹,

Huang²,

Li³

et al. 2012

Res. Astron. Astrophys.

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In our Paper I, we performed the spectroscopic observations of 11 confirmed GCs in M31 with the Xinglong 2.16m telescope and we mainly focus on the fits method and the metallicity gradient for the M31 GC sample. In this paper, we analyzed and discussed more about the dynamics, metallicity and age, and their distributions as well as the relationships between these parameters. In our work, eight more confirmed GCs in the halo of M31 were observed, most of which lack the spectroscopic information before. These star clusters are located far from the galactic center at a projected radius of ∼ 14 to ∼ 117 kpc, which are more spatially extended than that in the previous work. The Lick absorption-line indices and the radial velocities have been measured primarily. Then the ages, metallicities [Fe/H] and [α/Fe] have been fitted by comparing the observed spectral feature indices and the SSP model of Thomas et al. in the Cassisi and Padova stellar evolutionary tracks, respectively. Our results show that most of the star clusters of our sample are older than 10 Gyr except B290∼ 5.5 Gyr, and most of them are metal-poor with the metallicity [Fe/H] < −1, suggesting that these clusters were born at the early stage of the galaxy's formation. We find that the metallicity gradient for the outer halo clusters with r p > 25 kpc may not exist with a slope of −0.005 ± 0.005 dex kpc −1 and if the outliers G001 and H11 are excluded, the slope dose not change significantly with a value of −0.002 ± 0.003 dex kpc −1 . We also find that the metallicity is not a function of age for the GCs with age < 7 Gyr while for the old GCs with age > 7 Gyr there seems to be a trend that the older ones have lower metallicity. Besides, We plot metallicity distributions with the largest sample of M31 GCs so far and it shows the bimodality is not significant and the number of the metal-poor and metal-rich groups becomes comparable. The spatial distributions shows that the metal-rich group is more centrally concentrated while the metal-poor group is occupy a more extended halo and the young population is centrally concentrated while the old populaiton is more extended spatially to the outer halo.

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Star Clusters in M31. Ii. Old Cluster Metallicities and Ages From Hectospec Data

Cited by 166 publications

References 81 publications

The horizontal branch luminosity vs. metallicity in M 31 globular clusters

The horizontal branch luminosity vs. metallicity in M 31 globular clusters

The horizontal branch morphology of M 31 globular clusters

Spectroscopic study of globular clusters in the halo of M31 with the Xinglong 2.16 m telescope II: dynamics, metallicity and age

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