Euclid: Early Release Observations -- Unveiling the morphology of two Milky Way globular clusters out to their periphery

Abstract

As part of the Euclid Early Release Observations (ERO) programme, we analyse deep, wide-field imaging from the VIS and NISP instruments of two Milky Way globular clusters (GCs), namely NGC 6254 (M10) and NGC 6397, to look for observational evidence of their dynamical interaction with the Milky Way. We search for such an interaction in the form of structural and morphological features in the clusters' outermost regions, which are suggestive of the development of tidal tails on scales larger than those sampled by the ERO programme. Our multi-band photometric analysis results in deep and well-behaved colour-magnitude diagrams that, in turn, enable an accurate membership selection. The surface brightness profiles built from these samples of member stars are the deepest ever obtained for these two Milky Way GCs, reaching down to $\sim 30.0$ mag~arcsec${}^{-2}$, which is about $1.5$ mag arcsec${}^{-2}$ below the current limit. The investigation of the two-dimensional density map of NGC 6254 reveals an elongated morphology of the cluster peripheries in the direction and with the amplitude predicted by $N$-body simulations of the cluster's dynamical evolution, at high statistical significance. We interpret this as strong evidence for the first detection of tidally induced morphological distortion around this cluster. The density map of NGC 6397 reveals a slightly elliptical morphology, in agreement with previous studies, which requires further investigation on larger scales to be properly interpreted. This ERO project thus demonstrates the power of Euclid in studying the outer regions of GCs at an unprecedented level of detail, thanks to the combination of large field of view, high spatial resolution, and depth enabled by the telescope. Our results highlight the future Euclid survey as the ideal data set to investigate GC tidal tails and stellar streams.

15 pages, 18 figures. Paper accepted as part of the A&A special issue `Euclid on Sky', which contains Euclid key reference papers and first results from the Euclid Early Release Observations

References in corpus (26)

• The Gaia mission
• galpy: A Python Library for Galactic Dynamics
• Euclid. I. Overview of the Euclid mission
• The ACS Survey of Galactic Globular Clusters. I. Overview and Clusters Without Previous HST Photometry
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. I. Overview of the Project and Detection of Multiple Stellar Populations
• Gaia EDR3 view on Galactic globular clusters
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. IX. The Atlas of Multiple Stellar Populations
• Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST and literature data
• Detection of a 63 Degree Cold Stellar Stream in the Sloan Digital Sky Survey
• The updated BaSTI stellar evolution models and isochrones: II. alpha-enhanced calculations
• Euclid. III. The NISP Instrument
• Euclid. II. The VIS Instrument
• Globular cluster number density profiles using Gaia DR2
• Euclid preparation. XVIII. The NISP photometric system
• The Outer Envelopes of Globular Clusters. II. NGC 1851, NGC 5824 and NGC 1261
• The eye of Gaia on globular clusters structure: tidal tails
• The HST Large Programme on NGC6752. II. Multiple populations at the bottom of the main sequence probed in NIR
• Euclid: Early Release Observations -- Programme overview and pipeline for compact- and diffuse-emission photometry
• Stellar envelopes of globular clusters embedded in dark mini-haloes
• Exploring the outskirts of globular clusters: the peculiar kinematics of NGC 3201
• The discovery of tidal tails around the globular cluster NGC 7492 with Pan-STARRS1
• Cluster Ages to Reconstruct the Milky Way Assembly (CARMA) I. The final word on the origin of NGC6388 and NGC6441
• Using Gaia DR2 to detect extratidal structures around the Galactic globular cluster NGC362
• Euclid: Early Release Observations -- A glance at free-floating new-born planets in the sigma Orionis cluster
• Signatures of tidal disruption in the Milky Way globular cluster NGC 6981 (M72)
• Chemical Analysis of Five Red Giants in the Globular Cluster M10 (NGC 6254)

Cited by in corpus (6)

• Euclid: Early Release Observations -- Globular clusters in the Fornax galaxy cluster, from dwarf galaxies to the intracluster field
• Euclid: Early Release Observations -- Overview of the Perseus cluster and analysis of its luminosity and stellar mass functions
• $S^5$: New insights from deep spectroscopic observations of the tidal tails of the globular clusters NGC 1261 and NGC 1904
• Euclid: Early Release Observations of diffuse stellar structures and globular clusters as probes of the mass assembly of galaxies in the Dorado group
• The Nephele ecosystem: stars, globular clusters, and stellar streams associated with the progenitor galaxy of $\omega$ Centauri
• KRIOS: A new basis-expansion $N$-body code for collisional stellar dynamics