Hidden in the Haystack: Low-luminosity globular clusters towards the Milky Way bulge

Abstract

Recent wide-area surveys have enabled us to study the Milky Way with unprecedented detail. Its inner regions, hidden behind dust and gas, have been partially unveiled with the arrival of near-IR photometric and spectroscopic datasets. Among recent discoveries, there is a population of low-mass globular clusters, known to be missing, especially towards the Galactic bulge. In this work, five new low-luminosity globular clusters located towards the bulge area are presented. They were discovered by searching for groups in the multi-dimensional space of coordinates, colours, and proper motions from the Gaia EDR3 catalogue and later confirmed with deeper VVV survey near-IR photometry. The clusters show well-defined red-giant branches and, in some cases, horizontal branches with their members forming a dynamically coherent structure in proper motion space. Four of them were confirmed by spectroscopic follow-up with the MUSE instrument on the ESO VLT. Photometric parameters were derived, and when available, metallicities, radial velocities and orbits were determined. The new clusters Gran 1 and 5 are bulge globular clusters, while Gran 2, 3, and 4 present halo-like properties. Preliminary orbits indicate that Gran 1 might be related to the Main Progenitor, or the so-called ''low-energy'' group, while Gran 2, 3 and 5 appear to follow the Gaia-Enceladus-Sausage. This study demonstrates that the Gaia proper motions, combined with the spectroscopic follow-up and colour-magnitude diagrams, are required to confirm the nature of cluster candidates towards the inner Galaxy. High stellar crowding and differential extinction may hide other low-luminosity clusters.

arXiv comment15 pages, 11 figures, appendix: 7 figures, accepted for publication in MNRAS. Updated version with the correct orbit transformation applied. Fig. 11 and one sentence in Abstract, one in Sec. 4 and one in Summary were changed

References in corpus (101)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Array Programming with NumPy
• Astropy: A Community Python Package for Astronomy
• Gaia Data Release 2. Summary of the contents and survey properties
• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• The Gaia mission
• PARSEC: stellar tracks and isochrones with the PAdova and TRieste Stellar Evolution Code
• The SIMBAD astronomical database
• Gaia Data Release 2: The astrometric solution
• The Galaxy in Context: Structural, Kinematic and Integrated Properties
• The VizieR database of Astronomical Catalogues
• galpy: A Python Library for Galactic Dynamics
• The merger that led to the formation of the Milky Way's inner stellar halo and thick disk
• A new generation of PARSEC-COLIBRI stellar isochrones including the TP-AGB phase
• Co-formation of the Galactic disc and the stellar halo
• VISTA Variables in the Via Lactea (VVV): The public ESO near-IR variability survey of the Milky Way
• New catalogue of optically visible open clusters and candidates
• The MUSE second-generation VLT instrument
• Global survey of star clusters in the Milky Way II. The catalogue of basic parameters
• Multiple Stellar Populations in Globular Clusters
• Improving PARSEC models for very low mass stars
• PARSEC evolutionary tracks of massive stars up to $350M_{\odot }$ at metallicities 0.0001$\le Z\le$0.04
• A catalogue of masses, structural parameters and velocity dispersion profiles of 112 Milky Way globular clusters
• Painting a portrait of the Galactic disc with its stellar clusters
• Evidence for Two Early Accretion Events That Built the Milky Way Stellar Halo
• New PARSEC evolutionary tracks of massive stars at low metallicity: testing canonical stellar evolution in nearby star forming dwarf galaxies
• Gaia Data Release 2: first stellar parameters from Apsis
• The Optical to Mid-Infrared Extinction Law Based on the APOGEE, Gaia DR2, Pan-STARRS1, SDSS, APASS, 2MASS and WISE Surveys
• Mean proper motions, space orbits and velocity dispersion profiles of Galactic globular clusters derived from Gaia DR2 data
• Origin of the system of globular clusters in the Milky Way
• Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST and literature data
• The formation and assembly history of the Milky Way revealed by its globular cluster population
• Empirical calibration of the near-IR Ca II triplet - I. The stellar library and index definition
• Clusters and mirages: cataloguing stellar aggregates in the Milky Way
• Proper motions and dynamics of the Milky Way globular cluster system from Gaia DR2
• The RR Lyrae Period-Luminosity Relation. I. Theoretical Calibration
• Galactic Halo substructure in the Sloan Digital Sky Survey: the ancient tidal stream from the Sagittarius dwarf galaxy
• What is a globular cluster? An observational perspective
• Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia DR2 stars brighter than G = 18
• StarHorse: A Bayesian tool for determining stellar masses, ages, distances, and extinctions for field stars
• The Bifurcated Age-Metallicity Relation of Milky Way Globular Clusters and its Implications For the Accretion History of the Galaxy
• Evidence from APOGEE for the presence of a major building block of the halo buried in the inner Galaxy
• Constraining the thermally-pulsing asymptotic giant branch phase with resolved stellar populations in the Small Magellanic Cloud
• The Sausage Globular Clusters
• Comparing the properties of local globular cluster systems: implications for the formation of the Galactic halo
• Chemodynamical history of the Galactic Bulge
• Accreted versus In Situ Milky Way Globular Clusters
• Hunting for open clusters in \textit{Gaia} DR2: $582$ new OCs in the Galactic disc
• Galactic Globular Cluster Metallicity Scale from the Ca II Triplet. I. Catalog
• Resolving stellar populations with crowded field 3D spectroscopy
• Hunting for open clusters in \textit{Gaia} DR2: the Galactic anticentre
• Gaia Data Release 2: Variable stars in the colour-absolute magnitude diagram
• Improving the open cluster census. I. Comparison of clustering algorithms applied to Gaia DR2 data
• Gaia DR2 unravels incompleteness of nearby cluster population: New open clusters in the direction of Perseus
• Systematics in virial mass estimators for pressure-supported systems
• A New Catalog of Globular Clusters in the Milky Way
• Globular clusters in the Galactic bulge
• A Multi-Band Catalog of 10978 Star Clusters, Associations and Candidates in the Milky Way
• Near Infrared properties of 12 Globular Clusters toward the inner Bulge of the Galaxy
• Effects of Helium Enrichment in Globular Clusters I.Theoretical Plane with PGPUC stellar evolution code
• Discovery of VVV CL001. A Low-Mass Globular Cluster Next to UKS~1 in the Direction of the Galactic Bulge
• Finding Forming Globular Clusters at High Redshifts
• Three Galactic globular cluster candidates
• Completeness of the Gaia-verse II: what are the odds that a star is missing from Gaia DR2?
• The Edge of the Milky Way Stellar Disk Revealed Using Clump Giant Stars as Distance Indicators
• New galactic star clusters discovered in the VVV survey. Candidates projected on the inner disk and bulge
• Absolute V-band magnitudes and mass-to-light ratios of Galactic globular clusters
• Proper motions and kinematics of selected bulge globular clusters
• Variable stars in the VVV globular clusters. I. 2MASS-GC02 and Terzan10
• The Bar and Spiral Arms in the Milky Way: Structure and Kinematics
• Microarcsecond Astrometry: Science Highlights from Gaia
• A new class of fossil fragments from the hierarchical assembly of the Galactic bulge
• Spending too much time at the Galactic bar: chaotic fanning of the Ophiuchus stream
• Mapping the outer bulge with RRab stars from the VVV Survey
• Phlegethon, a nearby $75°$-long retrograde stellar stream
• Globular clusters in the inner Galaxy classified from dynamical orbital criteria
• Mapping the stellar age of the Milky Way bulge with the VVV. III. High resolution reddening map
• Analysis of the physical nature of 22 New VVV Survey Globular Cluster candidates in the Milky Way Bulge
• The minimum metallicity of globular clusters and its physical origin -- implications for the galaxy mass-metallicity relation and observations of proto-globular clusters at high redshift
• Mapping the stellar age of the Milky Way bulge with the VVV. I. The method
• Homogeneous metallicities and radial velocities for Galactic globular clusters. II. New CaT metallicities for 28 distant and reddened globular clusters
• Completeness of the Gaia-verse I: when and where were Gaia's eyes on the sky during DR2?
• Strong chemical tagging with APOGEE: 21 candidate star clusters that have dissolved across the Milky Way disc
• Proper motions in the VVV Survey: Results for more than 15 million stars across NGC 6544
• Structural parameters of 11 faint Galactic globular clusters derived with 2MASS
• The [α/Fe]-[Fe/H] relation in the E-MOSAICS simulations: its connection to the birth place of globular clusters and the fraction of globular cluster field stars in the bulge
• The Calcium Triplet metallicity calibration for galactic bulge stars
• Globular cluster candidates in the Galactic bulge: Gaia and VVV view of the latest discoveries
• A Near-Infrared Photometric Study of the Low Latitude Globular Clusters Liller 1, Djorgovski 1, HP 1, and NGC 6528
• A stellar census in globular clusters with MUSE -- Extending the CaT-metallicity relation below the horizontal branch and applying it to multiple populations
• VVVX-Gaia Discovery of a Low Luminosity Globular Cluster in the Milky Way Disk
• AL 3 (BH 261): a new globular cluster in the Galaxy
• The relation between the mass-to-light ratio and the relaxation state of globular clusters
• Completeness of the Gaia-verse III: using hidden states to infer gaps, detection efficiencies and the scanning law from the DR2 light curves
• An enquiry on the origins of N-rich stars in the inner Galaxy basedon APOGEE chemical compositions
• Halo intruders in the Galactic bulge revealed by HST and Gaia: the globular clusters Terzan 10 and Djorgovski 1
• The Age-Metallicity-Specific Orbital Energy Relation for the Milky Way's Globular Cluster System Confirms the Importance of Accretion for Its Formation
• Gemini/Phoenix H-band analysis of the globular cluster AL3
• APOGEE view of the globular cluster NGC 6544
• The Likelihood of Undiscovered Globular Clusters in the Outskirts of the Milky Way
• Dynamical Simulations of the First Globular Clusters

Cited by in corpus (12)

• Improving the open cluster census. III. Using cluster masses, radii, and dynamics to create a cleaned open cluster catalogue
• The Chemo-Dynamical Groups of Galactic Globular Clusters
• The VISTA Variables in the Vía Láctea eXtended (VVVX) ESO public survey: Completion of the observations and legacy
• A census of new globular clusters in the Galactic bulge
• The e-TidalGCs Project: Modeling the extra-tidal features generated by Galactic globular clusters
• Unveiling the nature of 12 new low-luminosity Galactic Globular Cluster Candidates
• Survey for Distant Stellar Aggregates in Galactic Disk: Detecting Two Thousand Star Clusters and Candidates, along with the Dwarf Galaxy IC10
• A new low-luminosity globular cluster discovered in the Milky Way with the VVVX survey
• APOGEE-2S view of the globular cluster Patchick 125 (Gran 3). New metallicity and elemental abundances from high-resolution spectroscopy
• Gaia-IGRINS synergy: Orbits of Newly Identified Milky Way Star Clusters
• Globular clusters in \textsc{OrbIT}: complete dynamical characterisation of the globular cluster population of the Milky Way through updated orbital reconstruction
• Variable stars in the VVV globular clusters. II. NGC6441, NGC6569, NGC6626 (M28), NGC6656 (M22), 2MASS-GC02, and Terzan10