Deep Gemini/GMOS imaging of an extremely isolated globular cluster in the Local Group

Abstract

We report on deep imaging of a remote M31 globular cluster, MGC1, obtained with Gemini/GMOS. Our colour-magnitude diagram for this object extends ~5 magnitudes below the tip of the red giant branch and exhibits features consistent with an ancient metal-poor stellar population, including a long, well-populated horizontal branch. The red giant branch locus suggests MGC1 has a metal abundance [M/H] ~ -2.3. We measure the distance to MGC1 and find that it lies ~160 kpc in front of M31 with a distance modulus of 23.95 +/- 0.06. Combined with its large projected separation of 117 kpc from M31 this implies a deprojected radius of Rgc = 200 +/- 20 kpc, rendering it the most isolated known globular cluster in the Local Group by some considerable margin. We construct a radial brightness profile for MGC1 and show that it is both centrally compact and rather luminous, with Mv = -9.2. Remarkably, the cluster profile shows no evidence for a tidal limit and we are able to trace it to a radius of at least 450 pc, and possibly as far as ~900 pc. The profile exhibits a power-law fall-off with exponent -2.5, breaking to -3.5 in its outermost parts. This core-halo structure is broadly consistent with expectations derived from numerical models, and suggests that MGC1 has spent many gigayears in isolation.

Accepted for publication in MNRAS

References in corpus (15)

• The Dartmouth Stellar Evolution Database
• The remnants of galaxy formation from a panoramic survey of the region around M31
• Empirical Color Transformations Between SDSS Photometry and Other Photometric Systems
• 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
• The Metal-Poor Halo of the Andromeda Spiral Galaxy (M31)
• A kinematically selected, metal-poor stellar halo in the outskirts of M31
• 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
• ACS photometry of newly-discovered globular clusters in the outer halo of M31
• Fiducial Stellar Population Sequences for the u'g'r'i'z' System
• Strangers in the night: Discovery of a dwarf spheroidal galaxy on its first Local Group infall
• The Outer Halo Globular Clusters of M31
• Calibration of photometry from the Gemini Multi-Object Spectrograph on Gemini North

Cited by in corpus (38)

• Evidence for an accretion origin for the outer halo globular cluster system of M31
• On the Formation of Multiple Stellar Populations in Globular Clusters
• The outer halo globular cluster system of M31 - I. The final PAndAS catalogue
• The PAndAS view of the Andromeda satellite system - I. A Bayesian search for dwarf galaxies using spatial and color-magnitude information
• The outer halo globular cluster system of M31 - II. Kinematics
• Evidence Against Dark Matter Halos Surrounding the Globular Clusters MGC1 and NGC 2419
• Current velocity data on dwarf galaxy NGC1052-DF2 do not constrain it to lack dark matter
• Outer density profiles of 19 Galactic globular clusters from deep and wide-field imaging
• Kinematics of Outer Halo Globular Clusters in M31
• Exploring the Properties of the M31 Halo Globular Cluster System
• The Outer Envelopes of Globular Clusters. I. NGC 7089 (M2)
• A Keck/DEIMOS spectroscopic survey of the faint M31 satellites And IX, And XI, And XII, and And XIII
• The Detailed Chemical Properties of M31 Star Clusters I. Fe, Alpha and Light Elements
• The outer halo globular cluster system of M31 - III. Relationship to the stellar halo
• Young accreted globular clusters in the outer halo of M31
• Stellar envelopes of globular clusters embedded in dark mini-haloes
• Deep HST/ACS Photometry of the M81 Halo
• Substructure and Tidal Streams in the Andromeda Galaxy and its Satellites
• Newly-Discovered Globular Clusters in NGC 147 and NGC 185 from PAndAS
• The Globular Cluster System of NGC 6822
• Discovery of the most isolated globular cluster in the local universe
• The structure of star clusters in the outer halo of M31
• Ultra-compact dwarfs beyond the centre of the Fornax galaxy cluster: Hints of UCD formation in low-density environments
• More Remote Globular Clusters in the Outer Halo of M31
• A peculiar faint satellite in the remote outer halo of M31
• Age and structure parameters of a remote M31 globular cluster B514 based on HST, 2MASS, GALEX and BATC observations
• A MegaCam Survey of Outer Halo Satellites. VII. A Single Sérsic Index v/s Effective Radius Relation for Milky Way Outer Halo Satellites
• No sign (yet) of intergalactic globular clusters in the Local Group
• Spectroscopic Study of Globular Clusters in the Halo of M31 with Xinglong 2.16m Telescope
• Hubble Space Telescope imaging of the extremely metal-poor globular cluster EXT8 in Messier 31
• A Search for Intergalactic Globular Clusters in the Local Group
• Isothermal distributions in MONDian gravity as a simple unifying explanation for the ubiquitous $\rho \propto r^{-3}$ density profiles in tenuous stellar halos
• Property of Young Massive Clusters in a Galaxy-Galaxy Merger Remnant
• 2MASS photometry and age estimate of globular clusters in the outer halo of M31
• Spectroscopic Study of Globular Clusters in the Halo of M31 with Xinglong 2.16m Telescope II: Dynamics, Metallicity and Age
• On the Ejection of Dark Matter from Globular Clusters
• A search for stellar structures around nine outer halo globular clusters in the Milky Way
• Tidal stripping as a mechanism for placing globular clusters on wide orbits: the case of MGC1 in M31