HST/ACS colour-magnitude diagrams of M31 globular clusters

Abstract

With the aim of increasing the sample of M31 clusters for which a colour magnitude diagram is available, we searched the HST archive for ACS images containing objects included in the Revised Bologna Catalogue of M31 globular clusters. Sixty-three such objects were found. We used the ACS images to confirm or revise their classification and we obtained useful CMDs for 11 old globular clusters and 6 luminous young clusters. We obtained simultaneous estimates of the distance, reddening, and metallicity of old clusters by comparing their observed field-decontaminated CMDs with a grid of template clusters of the Milky Way. We estimated the age of the young clusters by fitting with theoretical isochrones. For the old clusters, we found metallicities in the range -0.4<=[Fe/H]<=-1.9, that generally agree with existing spectroscopic extimates. At least four of them display a clear blue HB, indicating ages >10 Gyr. All six candidate young clusters are found to have ages <1Gyr. With the present work the total number of M31 GCs with reliable optical CMD increases from 35 to 44 for the old clusters, and from 7 to 11 for the young ones. The old clusters show similar characteristics to those of the MW. We discuss the case of the cluster B407, with a metallicity [Fe/H] ~-0.6 and located at a large projected distance from the centre of M31 and from the galaxy major axis. Metal-rich globulars at large galactocentric distances are rare both in M31 and in the MW. B407, in addition, has a velocity in stark contrast with the rotation pattern shared by the bulk of M31 clusters of similar metallicity. This, along with other empirical evidence, supports the hypothesis that the cluster is physically associated with a substructure in the M31 halo that has been interpreted as the relic of a merging event.

19 pages, 14 figures, 6 tables. Accepted for publication on Astronomy and Astrophysics

References in corpus (14)

• The Haunted Halos of Andromeda and Triangulum: A panorama of galaxy formation in action
• Discovery and analysis of three faint dwarf galaxies and a globular cluster in the outer halo of the Andromeda galaxy
• Star Clusters in M31: I. A Catalog and a Study of the Young Clusters
• Structural parameters for globular clusters in M31 and generalizations for the fundamental plane
• The Nature and Origin of Substructure in the Outskirts of M31. I. Surveying the Stellar Content with HST/ACS
• An updated survey of globular clusters in M31. II Newly discovered bright and remote clusters
• ACS photometry of extended, luminous globular clusters in the outskirts of M31
• Globular clusters in the outer halo of M31: the survey
• An updated survey of globular clusters in M 31. I. Classification and radial velocity for 76 candidate clusters
• Reddening, Colour and Metallicity of the M31 Globular Cluster System
• ACS photometry of newly-discovered globular clusters in the outer halo of M31
• Wide-Field Survey of Globular Clusters in M31. II. Kinematics of the Globular Cluster System
• An HST Survey of the Disk Cluster Population of M31. I. WFPC2 Pointings
• Evidence for metallicity spreads in three massive M31 globular clusters

Cited by in corpus (27)

• Star Clusters in M31: II. Old Cluster Metallicities and Ages from Hectospec Data
• The SLUGGS Survey: Calcium Triplet-based Spectroscopic Metallicities for Over 900 Globular Clusters
• The outer halo globular cluster system of M31 - I. The final PAndAS catalogue
• M31 Satellite Masses Compared to LCDM Subhaloes
• The outer halo globular cluster system of M31 - II. Kinematics
• Gaia DR3: Specific processing and validation of all-sky RR Lyrae and Cepheid stars -- The Cepheid sample
• Clustering of Local Group distances: publication bias or correlated measurements? II. M31 and beyond
• An updated survey of globular clusters in M 31. III. A spectroscopic metallicity scale for the Revised Bologna Catalog
• Star Clusters in M31: VII. Global Kinematics and Metallicity Subpopulations of the Globular Clusters
• UV Properties of Galactic Globular Clusters with GALEX II. Integrated colors
• Detection of a $\sim$100,000 M${}_{\odot }$ black hole in M31's most massive globular cluster: A tidally stripped nucleus
• Yonsei Evolutionary Population Synthesis (YEPS) Model. I. Spectroscopic Evolution of Simple Stellar Populations
• Spectral energy distributions and age estimates of 104 M31 globular clusters
• Red Supergiants in M31 and M33 I. The Complete Sample
• Infrared High-Resolution Integrated Light Spectral Analyses of M31 Globular Clusters from APOGEE
• The Period-Luminosity Relations of Red Supergiants in M33 and M31
• A low surface brightness halo surrounding the globular cluster NGC 5694
• The horizontal branch luminosity vs metallicity in M31 globular clusters
• The LAMOST spectroscopic survey of star clusters in M31. II. Metallicities, ages and masses
• The Next Generation Virgo cluster Survey (NGVS). XXVI. The issues of photometric age and metallicity estimates for globular clusters
• HST/ACS color-magnitude diagrams of candidate intermediate-age M 31 globular clusters. The role of blue horizontal branches
• Nonlinear Color-Metallicity Relations of Globular Clusters. V. Nonlinear Absorption-line Index versus Metallicity Relations and Bimodal Index Distributions of M31 Globular Clusters
• Estimating ages and metallicities of M31 star clusters from LAMOST DR6
• The horizontal branch morphology of M31 globular clusters. Extreme second parameter effect in outer halo clusters
• On Granulation and Irregular Variation of Red Supergiants
• Kinematics of a globular cluster with an extended profile: NGC5694
• The Ages of M31 Star Clusters: Spectral Energy Distribution Versus Color-Magnitude Diagram