Potential Black Hole Seeding of the Spiral Galaxy NGC 4424 via an Infalling Star Cluster

Abstract

Galaxies can grow through their mutual gravitational attraction and subsequent union. While orbiting a regular high-surface-brightness galaxy, the body of a low-mass galaxy can be stripped away. However, the stellar heart of the infalling galaxy, if represented by a tightly-bound nuclear star cluster, is more resilient. From archival Hubble Space Telescope images, we have discovered a red, tidally-stretched star cluster positioned ~5 arcseconds (~400 pc in projection) from, and pointing toward the center of, the post-merger spiral galaxy NGC 4424. The star cluster, which we refer to as `Nikhuli', has a near-infrared luminosity of (6.88+/-1.85)x10^6 L_{solar,F160W} and likely represents the nucleus of a captured/wedded galaxy. Moreover, from our Chandra X-ray Observatory image, Nikhuli is seen to contain a high-energy X-ray point source, with L_{0.5-8 keV} = 6.31^{+7.50}_{-3.77}x10^{38} erg/s (90% confidence). We argue that this is more likely to be an active massive black hole than an X-ray binary. Lacking an outward-pointing comet-like appearance, the stellar structure of Nikhuli favors infall rather than the ejection from a gravitational-wave recoil event. A minor merger with a low-mass early-type galaxy may have sown a massive black hole, aided an X-shaped pseudobulge, and be sewing a small bulge. The stellar mass and the velocity dispersion of NGC 4424 predict a central black hole of (0.6-1.0)x10^5 M_solar, similar to the expected intermediate-mass black hole in Nikhuli, and suggestive of a black hole supply mechanism for bulgeless late-type galaxies. We may potentially be witnessing black hole seeding by capture and sinking, with a nuclear star cluster the delivery vehicle.

To appear in ApJ (accepted 21 September 2021)

References in corpus (60)

• HI4PI: A full-sky HI survey based on EBHIS and GASS
• An Ultraluminous X-ray Source Powered by An Accreting Neutron Star
• The ACS Virgo Cluster Survey. VIII. The Nuclei of Early-Type Galaxies
• An Improved Distance and Mass Estimate for Sgr A* from a Multistar Orbit Analysis
• Does the Fornax dwarf spheroidal have a central cusp or core?
• Rapid growth of seed black holes in the early universe by supra-exponential accretion
• Dynamical friction in constant density cores: a failure of the Chandrasekhar formula
• The Streams of the Gaping Abyss: A population of entangled stellar streams surrounding the Inner Galaxy
• Correlation between the photon index and X-ray luminosity of black hole X-ray binaries and active galactic nuclei: observations and interpretation
• The erratic dynamical life of black hole seeds in high-redshift galaxies
• Gravitational Wave Recoil and the Retention of Intermediate Mass Black Holes
• X-ray Binary Luminosity Function Scaling Relations for Local Galaxies Based on Subgalactic Modeling
• Wandering Black Holes in Bright Disk Galaxy Halos
• A Search for "Dwarf" Seyfert Nuclei. VII. A Catalog of Central Stellar Velocity Dispersions of Nearby Galaxies
• Black Hole Mass Scaling Relations for Early-Type Galaxies: $M_{BH}$-$M_{\ast ,sph}$ and $M_{BH}$-$M_{\ast ,gal}$
• Effects of gravitational-wave recoil on the dynamics and growth of supermassive black holes
• Updated Mass Scaling Relations for Nuclear Star Clusters and a Comparison to Supermassive Black Holes
• The powerful jet of an off-nuclear intermediate-mass black hole in the spiral galaxy NGC 2276
• The Globular Cluster Migratory Origin of Nuclear Star Clusters
• The PAndAS Field of Streams: stellar structures in the Milky Way halo toward Andromeda and Triangulum
• A Low-Mass Stellar-Debris Stream Associated with a Globular Cluster Pair in the Halo
• Orbital Clustering Identifies the Origins of Galactic Stellar Streams
• Hiding in plain sight: An abundance of compact massive spheroids in the local Universe
• Supermassive black holes from primordial black hole seeds
• The Accreted Nuclear Clusters of the Milky Way
• Origins and Demographics of Wandering Black Holes
• Henize 2-10: the ongoing formation of a nuclear star cluster around a massive black hole
• A new, clean catalogue of extragalactic non-nuclear X-ray sources in nearby galaxies
• Kinematics and simulations of the stellar stream in the halo of the Umbrella Galaxy
• Seeds Don't Sink: Even Massive Black Hole "Seeds" Cannot Migrate to Galaxy Centers Efficiently
• Hidden depths in the local Universe: The Stellar Stream Legacy Survey
• Evidence of a dwarf galaxy stream populating the inner Milky Way Halo
• The Origins of Off-Centre Massive Black Holes in Dwarf Galaxies
• Gravitational Wave Recoil Oscillations of Black Holes: Implications for Unified Models of Active Galactic Nuclei
• A Self-Consistent, Time-Dependent Treatment of Dynamical Friction: New Insights regarding Core Stalling and Dynamical Buoyancy
• Distances from Stellar Kinematics for Peculiar Virgo Cluster Spiral Galaxies
• Formation of super-massive black holes in galactic nuclei I: delivering seed intermediate-mass black holes in massive stellar clusters
• X-ray Binary Luminosity Function Scaling Relations in Elliptical Galaxies: Evidence for Globular Cluster Seeding of Low-Mass X-ray Binaries in Galactic Fields
• The hidden past of M92: Detection and characterization of a newly formed 17° long stellar stream using the Canada-France Imaging Survey
• Quantifying the (X/peanut)-shaped Structure of the Milky Way - New Constraints on the Bar Geometry
• Is NGC 5824 the Core of the Progenitor of the Cetus Stream?
• AGN on the move: A search for off-nuclear AGN from recoiling SMBHs and ongoing galaxy mergers with the Zwicky Transient Facility
• The Fifth Candidate for an Intermediate-mass Black Hole in the Galactic Center
• Expected intermediate-mass black holes in the Virgo cluster. I. Early-type galaxies
• Exposing Sgr tidal debris behind the Galactic disk with M giants selected in WISE$\cap$2MASS
• Was the Milky Way Bulge Formed From The Buckling Disk Instability, Hierarchical Collapse, Accretion of Clumps, or All of the Above?
• Galaxy Flybys: Evolution of the Bulge, Disk, and Spiral Arms
• The quest for the largest depleted galaxy core: supermassive black hole binaries and stalled in-falling satellites
• A consistency-test for determining whether ultra-compact dwarf galaxies could be the remnant nuclei of threshed galaxies
• DELVE-ing into the Jet: a thin stellar stream on a retrograde orbit at 30 kpc
• $S^5$: The destruction of a bright dwarf galaxy as revealed by the chemistry of the Indus stellar stream
• Subhalo sinking and off-center massive black holes in dwarf galaxies
• Building the peanut: simulations and observations of peanut-shaped structures and ansae in face-on disk galaxies
• The Age-Metallicity-Specific Orbital Energy Relation for the Milky Way's Globular Cluster System Confirms the Importance of Accretion for Its Formation
• Signatures of tidal disruption in the Milky Way globular cluster NGC 6981 (M72)
• Realistic triaxial density--potential--force profiles for stellar systems and dark matter halos
• 2MASX J00423991+3017515: An offset active galactic nucleus in an interacting system
• Stellar Properties of the Host Galaxy of an Ultraluminous X-ray Source in NGC 5252
• Star cluster survival in dark matter halos: An old cluster in Eridanus II?
• Introduction to Tidal Streams

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• Central X-ray point-sources found to be abundant in low-mass, late-type galaxies predicted to contain an intermediate-mass black hole
• Probing the Low-mass End of the Black Hole Mass Function via a Study of Faint Local Spiral Galaxies
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