On the Origin of Nuclear Star Clusters in Late-Type Spiral Galaxies

A large fraction of bulgeless disk galaxies contain young compact stellar systems at their centers, in spite of the local gravitational stability of these disks. We evaluate two contrasting hypotheses for the origin of the nuclear star clusters in late-type disk galaxies. The clusters could not have migrated from distant eccentric locations in the disk. Instead they must have formed in situ, requiring radial transport of gas toward the center of the disk. This transport could be a consequence of the development of the magnetorotational instability in the differentially rotating warm neutral medium. We evaluate the rate of gas transport into the disk center and find that it is sufficient to support continuous star formation in that location. Enhanced stellar surface brightness in the inner few hundred parsecs and the formation of a compact stellar system in the central few parsecs are unavoidable in dark matter halos with divergent density profiles. We illustrate our conclusions on a model of the nearest late-type disk galaxy M33.

[1]  L. Ho,et al.  A Hubble Space Telescope Census of Nuclear Star Clusters in Late-Type Spiral Galaxies. II. Cluster Sizes and Structural Parameter Correlations , 2003, astro-ph/0309761.

[2]  Woong-Tae Kim,et al.  Magnetorotationally Driven Galactic Turbulence and the Formation of Giant Molecular Clouds , 2003, astro-ph/0309080.

[3]  D. Meier,et al.  Molecular Gas and the Nuclear Star Cluster in IC 342: Sufficient Inflow for Recurring Star Formation Events? , 2003, astro-ph/0305552.

[4]  A. Tielens,et al.  Neutral Atomic Phases of the Interstellar Medium in the Galaxy , 2003 .

[5]  France.,et al.  Simulating observations of dark matter dominated galaxies: towards the optimal halo profile , 2002, astro-ph/0212102.

[6]  T. Boeker,et al.  Searching for Bulges at the End of the Hubble Sequence , 2002, astro-ph/0212078.

[7]  B. Madore,et al.  The Central Mass Distribution in Dwarf and Low Surface Brightness Galaxies , 2002, astro-ph/0210152.

[8]  Andrew W. Stephens,et al.  The Structure and Stellar Content of the Central Region of M33 , 2002, astro-ph/0206344.

[9]  Guillaume Dubus,et al.  Hubble Space Telescope Spectroscopy of the Nucleus of M33 , 2002 .

[10]  L. Matthews,et al.  High-Resolution Optical Rotation Curves of Low-Luminosity Spiral Galaxies , 2002, astro-ph/0203188.

[11]  T. J. Davidge,et al.  Near-Infrared Adaptive Optics Imaging of the Central Regions of Nearby Sc Galaxies. II. NGC 247 and NGC 2403 , 2002, astro-ph/0202526.

[12]  L. Ho,et al.  A Hubble Space Telescope Census of Nuclear Star Clusters in Late-Type Spiral Galaxies. I. Observations and Image Analysis , 2001, astro-ph/0112086.

[13]  D. Merritt,et al.  No Supermassive Black Hole in M33? , 2001, Science.

[14]  T. Lauer,et al.  M33: A Galaxy with No Supermassive Black Hole , 2001, astro-ph/0107135.

[15]  C. Martin,et al.  Star Formation Thresholds in Galactic Disks , 2001, astro-ph/0103181.

[16]  W. Schattke,et al.  Tagungsberichte: The interstellar medium in M31 and M33/High Field and Quantum Transport in Semiconductors/Interacting Electrons in Nanostructures/DPG‐Lehrerfortbildungskurs 2000: Physik und Musik , 2000 .

[17]  L. Matthews.  The Extraordinary “Superthin” Spiral Galaxy UGC 7321. II. The Vertical Disk Structure , 2000, astro-ph/0006412.

[18]  T. Davidge.  Near-Infrared Adaptive Optics Imaging of the Central Regions of Nearby Sc Galaxies. I. M33 , 1999, astro-ph/9910333.

[19]  P. Salucci,et al.  The extended rotation curve and the dark matter halo of M33 , 1999, astro-ph/9909252.

[20]  J. Holtzman,et al.  WFPC2 Observations of Compact Star Cluster Nuclei in Low-Luminosity Spiral Galaxies , 1999, astro-ph/9904205.

[21]  W. Vacca,et al.  CO Band Head Spectroscopy of IC 342: Mass and Age of the Nuclear Star Cluster , 1999, astro-ph/9903457.

[22]  M. M. Hanson,et al.  The Dusty Starburst Nucleus of M33 , 1999, astro-ph/9902043.

[23]  S. White,et al.  Sinking satellites and the heating of galaxy discs , 1998, astro-ph/9809412.

[24]  J. Sellwood,et al.  Differential Rotation and Turbulence in Extended H I Disks , 1998, astro-ph/9806307.

[25]  C. Carollo,et al.  Spiral Galaxies with WFPC2.I.Nuclear Morphology, Bulges, Star Clusters, and Surface Brightness Profiles , 1997 .

[26]  S. White,et al.  A Universal Density Profile from Hierarchical Clustering , 1996, astro-ph/9611107.

[27]  M. Wahde,et al.  DYNAMICAL FRICTION IN DISC GALAXIES WITH NON-ZERO VELOCITY DISPERSION , 1996 .

[28]  Charles F. Gammie,et al.  Local Three-dimensional Magnetohydrodynamic Simulations of Accretion Disks , 1995 .

[29]  O. Blaes,et al.  LOCAL SHEAR INSTABILITIES IN WEAKLY IONIZED, WEAKLY MAGNETIZED DISKS , 1994 .

[30]  K. J. Donner,et al.  Dynamical friction in disc galaxies , 1993 .

[31]  N. Scoville,et al.  The molecular gas content of the nuclear region of M33 , 1989 .

[32]  M. Begelman,et al.  Bars within bars: a mechanism for fuelling active galactic nuclei , 1989, Nature.

[33]  S. Kent.  Surface Photometry of Six Local Group Galaxies , 1987 .

[34]  J. E. Pringle,et al.  A viscosity prescription for a self-gravitating accretion disc⋆ , 1987 .

[35]  P. Quinn,et al.  Sinking satellites of spiral systems , 1986 .

[36]  B. Draine.  Magneto-Hydrodynamic Shock Waves in Molecular Clouds , 1983 .

[37]  J. Silk,et al.  Dissipational galaxy formation - Confrontation with observations , 1981 .

[38]  S. Tremaine,et al.  The excitation of density waves at the Lindblad and corotation resonances by an external potential. , 1979 .

[39]  A. Toomre,et al.  On the gravitational stability of a disk of stars , 1964 .

[40]  Subrahmanyan Chandrasekhar,et al.  Dynamical friction. I. General considerations: the coefficient of dynamical friction , 1943 .

[41]  Accepted for Publication in the Astrophysical Journal Neutral Atomic Phases of the ISM in the Galaxy , 2002 .

[42]  Andrew King,et al.  Accretion Power in Astrophysics: Contents , 2002 .

[43]  P. Armitage.  ApJ Letters, in press Preprint typeset using L ATEX style emulateapj v. 04/03/99 TURBULENCE AND ANGULAR MOMENTUM TRANSPORT IN A GLOBAL ACCRETION DISK SIMULATION , 1998 .

[44]  J. Hawley,et al.  Instability, turbulence, and enhanced transport in accretion disks , 1997 .

[45]  James M. Stone,et al.  Three-dimensional magnetohydrodynamical simulations of vertically stratified accretion disks , 1996 .

[46]  John Kormendy,et al.  The nucleus of M33 , 1993 .

[47]  R. McCray,et al.  Superbubbles in disk galaxies , 1988 .

[48]  Carl Heiles,et al.  The Atomic Component , 1987 .

[49]  D. Raine,et al.  Accretion power in astrophysics , 1985 .