How elevated is the dynamical-to-stellar mass ratio of the ultra-compact dwarf S999?

Abstract

Here we present new Keck ESI high-resolution spectroscopy and deep archival HST/ACS imaging for S999, an ultra-compact dwarf in the vicinity of M87, which was claimed to have an extremely high dynamical-to-stellar mass ratio. Our data increase the total integration times by a factor of 5 and 60 for spectroscopy and imaging, respectively. This allows us to constrain the stellar population parameters for the first time (simple stellar population equivalent age $=7.6_{-1.6}^{+2.0}$ Gyr; $[Z/\text{H}]=-0.95_{-0.10}^{+0.12}$; $[\alpha /\text{Fe}]=0.34_{-0.12}^{+0.10}$). Assuming a Kroupa stellar initial mass function, the stellar population parameters and luminosity ($M_{F814W}=-12.13\pm 0.06$ mag) yield a stellar mass of $M_{\ast }=3.9_{-0.6}^{+0.9}\times 10^6{M}_{\odot }$, which we also find to be consistent with near-infrared data. Via mass modelling, with our new measurements of velocity dispersion (${\sigma }_{ap}=27\pm 2$ km s${}^{-1}$) and size ($R_e=20.9\pm 1.0$ pc), we obtain an elevated dynamical-to-stellar mass ratio $M_{dyn}/M_{\ast }=8.2$ (with a range $5.6\le M_{dyn}/M_{\ast }\le 11.2$). Furthermore, we analyse the surface brightness profile of S999, finding only a small excess of light in the outer parts with respect to the fitted Sérsic profile, and a positive colour gradient. Taken together these observations suggest that S999 is the remnant of a much larger galaxy that has been tidally stripped. If so, the observed elevated mass ratio may be caused by mechanisms related to the stripping process: the existence of an massive central black hole or internal kinematics that are out of equilibrium due to the stripping event. Given the observed dynamical-to-stellar mass ratio we suggest that S999 is an ideal candidate to search for the presence of an overly massive central black hole.

arXiv comment16 pages, 5 figures, accepted for publication in MNRAS

References in corpus (79)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• Measuring Reddening with SDSS Stellar Spectra and Recalibrating SFD
• PARSEC: stellar tracks and isochrones with the PAdova and TRieste Stellar Evolution Code
• Parametric Recovery of Line-of-Sight Velocity Distributions from Absorption-Line Spectra of Galaxies via Penalized Likelihood
• Evolutionary population synthesis: models, analysis of the ingredients and application to high-z galaxies
• Stellar population models of Lick indices with variable element abundance ratios
• Evolutionary Stellar Population Synthesis with MILES. Part I: The Base Models and a New Line Index System
• Old Stellar Populations. VI. Absorption-Line Spectra of Galaxy Nuclei and Globular Clusters
• Accurate masses for dispersion-supported galaxies
• A concise reference to (projected) Sersic R^{1/n} quantities, including Concentration, Profile Slopes, Petrosian indices, and Kron Magnitudes
• A systematic variation of the stellar initial mass function in early-type galaxies
• The ACS Virgo Cluster Survey. VIII. The Nuclei of Early-Type Galaxies
• The ACS Fornax Cluster Survey. V. Measurement and Recalibration of Surface Brightness Fluctuations and a Precise Value of the Fornax--Virgo Relative Distance
• A database of high and medium-resolution stellar spectra
• STELIB: a library of stellar spectra at R~2000
• The Stellar Initial Mass Function in Early-Type Galaxies From Absorption Line Spectroscopy. II. Results
• ESI, a new Keck Observatory echellette spectrograph and imager
• The ACS Virgo Cluster Survey. I. Introduction to the Survey
• The ACS Virgo Cluster Survey. VII. Resolving the Connection Between Globular Clusters and Ultra-Compact Dwarf Galaxies
• A class of compact dwarf galaxies from disruptive processes in galaxy clusters
• A Supermassive Black Hole in an Ultracompact Dwarf Galaxy
• Compact Stellar Systems in the Fornax Cluster: Super-massive Star Clusters or Extremely Compact Dwarf Galaxies?
• The central region of the Fornax cluster -- II. Spectroscopy and radial velocities of member and background galaxies
• Flux-calibrated stellar population models of Lick absorption-line indices with variable element abundance ratios
• The Relationships Among Compact Stellar Systems: A Fresh View of Ultra Compact Dwarfs
• Total Galaxy Magnitudes and Effective Radii from Petrosian Magnitudes and Radii
• The AIMSS Project I: Bridging the Star Cluster - Galaxy Divide
• The SAGES Legacy Unifying Globulars and GalaxieS Survey (SLUGGS): Sample definition, methods, and initial results
• Empirical calibration of the near-IR CaII triplet - IV. The stellar population synthesis models
• Evidence For A Mild Steepening And Bottom-Heavy IMF In Massive Galaxies From Sodium And Titanium-Oxide Indicators
• Internal Dynamics, Structure and Formation of Dwarf Elliptical Galaxies: I. A Keck/HST Study of Six Virgo Cluster Dwarfs
• Galaxy threshing and the formation of ultra-compact dwarf galaxies
• The Colors of Dwarf Elliptical Galaxy Globular Cluster Systems, Nuclei and Stellar Halos
• Wide-Field Precision Kinematics of the M87 Globular Cluster System
• From star clusters to dwarf galaxies: The properties of dynamically hot stellar systems
• The Nature of UCDs: Internal Dynamics from an Expanded Sample and Homogeneous Database
• Internal Properties of Ultra-Compact Dwarf Galaxies in the Virgo Cluster
• The ACS Fornax Cluster Survey. VI. The Nuclei of Early-Type Galaxies in the Fornax Cluster
• A top-heavy stellar initial mass function in starbursts as an explanation for the high mass-to-light ratios of ultra compact dwarf galaxies
• A Library of Integrated Spectra of Galactic Globular Clusters
• Ultra compact dwarf galaxy formation by tidal stripping of nucleated dwarf galaxies
• The ACS Virgo Cluster Survey III. Chandra and HST Observations of Low-Mass X-Ray Binaries and Globular Clusters in M87
• Color and stellar population gradients in galaxies. Correlation with mass
• The Inner Halo of M87: A First Direct View of the Red-Giant Population
• Uniting Old Stellar Systems: From Globular Clusters to Giant Ellipticals
• Spectroscopic metallicities for Fornax UCDs, GCs and dE,Ns
• Ultra Compact Objects in the Fornax Cluster of Galaxies: Globular clusters or dwarf galaxies?
• Dynamical masses of ultra-compact dwarf galaxies in Fornax
• The Sizes and Luminosities of Massive Star Clusters
• On central black holes in ultra-compact dwarf galaxies
• The Next Generation Virgo Cluster Survey - Infrared (NGVS-IR): I. A new Near-UV/Optical/Near-IR Globular Cluster selection tool
• Structural Properties of Ultra-Compact Dwarf Galaxies in the Fornax and Virgo Clusters
• The Densest Galaxy
• Low-mass X-ray binaries indicate a top-heavy stellar initial mass function in ultra compact dwarf galaxies
• The Ubiquity and Dual Nature of Ultra Compact Dwarfs
• The Color-Magnitude Relation for Metal-Poor Globular Clusters in M87: Confirmation From Deep HST/ACS Imaging
• Dynamical versus Stellar Masses of Ultracompact Dwarf Galaxies in the Fornax Cluster
• SDSSJ124155.33+114003.7 -- a Missing Link Between Compact Elliptical and Ultracompact Dwarf Galaxies
• From Galaxy Clusters to Ultra-Faint Dwarf Spheroidals: A Fundamental Curve Connecting Dispersion-supported Galaxies to Their Dark Matter Halos
• The Sizes of Early-type Galaxies
• The halo+cluster system of the Galactic globular cluster NGC1851
• High mass-to-light ratios of UCDs - Evidence for dark matter ?
• Dynamics of the Globular Cluster System Associated with M87 (NGC 4486). I. New CFHT MOS Spectroscopy and the Composite Database
• Ultra-Compact Dwarfs in the Coma Cluster
• Spatially Resolved Kinematics of an Ultra-Compact Dwarf Galaxy
• Being WISE I: Validating Stellar Population Models and M/L ratios at 3.4 and 4.6 microns
• The HST/ACS Coma Cluster Survey: VII - Colour Gradients in Giant and Dwarf Early-Type Galaxies
• The AIMSS Project II: Dynamical-to-Stellar Mass Ratios Across the Star Cluster - Galaxy Divide
• Mass-loss and expansion of ultra compact dwarf galaxies through gas expulsion and stellar evolution for top-heavy stellar initial mass functions
• Red Giant evolution and specific problems
• Nuclei of early-type dwarf galaxies: are they progenitors of UCDs?
• Hubble Space Telescope survey of the Perseus Cluster -IV: Compact stellar systems in the Perseus Cluster core and Ultra Compact Dwarf formation in star forming filaments
• Color Bimodality in M87 Globular Clusters
• Structural Parameters of the M87 Globular Clusters
• Enhanced Mass-to-Light Ratios in UCDs through Tidal Interaction with the Centre of the Host Galaxy
• The Size Difference Between Red And Blue Globular Clusters Is NOT Due To Projection Effects
• High M/L ratios of UCDs: a variation of the IMF?
• The ages, metallicities and element abundance ratios of massive quenched galaxies at z~1.6
• Observational dynamics of low-mass stellar systems

Cited by in corpus (22)

• Very high redshift quasars and the rapid emergence of super-massive black holes
• Detection of Supermassive Black Holes in Two Virgo Ultracompact Dwarf Galaxies
• The Next Generation Virgo Cluster Survey (NGVS). XIII. The Luminosity and Mass Function of Galaxies in the Core of the Virgo Cluster and the Contribution from Disrupted Satellites
• The Black Hole in the Most Massive Ultracompact Dwarf Galaxy M59-UCD3
• The AIMSS Project III: The Stellar Populations of Compact Stellar Systems
• The Next Generation Virgo Cluster Survey. X. Properties of Ultra-Compact Dwarfs in the M87, M49 and M60 Regions
• The formation of UCDs and massive GCs: Quasar-like objects for testing for a variable stellar initial mass function (IMF)
• The impact of stripped Nuclei on the Super-Massive Black Hole number density in the local Universe
• The Next Generation Virgo Cluster Survey. XXXIV. Ultra-Compact Dwarf (UCD) Galaxies in the Virgo Cluster
• Peculiar compact stellar systems in the Fornax cluster
• To the Edge of M87 and Beyond: Spectroscopy of Intracluster Globular Clusters and Ultra Compact Dwarfs in the Virgo Cluster
• On the formation mechanisms of compact elliptical galaxies
• Hiding in plain sight: record-breaking compact stellar systems in the Sloan Digital Sky Survey
• NGC 3628-UCD1: A possible $\omega$ Cen Analog Embedded in a Stellar Stream
• A search for active galactic nuclei in low-mass compact galaxies
• Ultra-compact dwarfs beyond the centre of the Fornax galaxy cluster: Hints of UCD formation in low-density environments
• Low-mass compact elliptical galaxies: spatially-resolved stellar populations and kinematics with the Keck Cosmic Web Imager
• A Comprehensive Archival Chandra Search for X-ray Emission from Ultracompact Dwarf Galaxies
• Keck Cosmic Web Imager (KCWI) Spectra of Globular Clusters and Ultra Compact Dwarfs in the Halo of M87
• M32 Analogs? A Population of Massive Ultra Compact Dwarf and Compact Elliptical Galaxies in intermediate redshift CLASH Clusters
• A search for intermediate-mass black holes in compact stellar systems through optical emissions from tidal disruption events
• The creation of a massive UCD by tidal threshing from NGC 936