Origin of multiple nuclei in ultraluminous infrared galaxies

Abstract

Ultraluminous infrared galaxies (ULIRGs) with multiple ($\ge 3$) nuclei are frequently observed. It has been suggested that these nuclei are produced by multiple major mergers of galaxies. The expected rate of such mergers is, however, too low to reproduce the observed number of ULIRGs with multiple nuclei. We have performed high-resolution simulations of the merging of two gas-rich disk galaxies. We found that extremely massive and compact star clusters form from the strongly disturbed gas disks after the first or second encounter between the galaxies. The mass of such clusters reaches $\sim 10^8{M}_{\odot }$, and their half-mass radii are $20-30\mathrm{pc}$. Since these clusters consist of young stars, they appear to be several bright cores in the galactic central region ($\sim \mathrm{kpc}$). The peak luminosity of these clusters reaches $\sim 10$ of the total luminosity of the merging galaxy. These massive and compact clusters are consistent with the characteristics of the observed multiple nuclei in ULIRGs. Multiple mergers are not necessary to explain multiple nuclei in ULIRGs.

12 pages, 9 figures, accepted for publication in ApJ

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• Halpha imaging survey of Wolf-Rayet galaxies: morphologies and star formation rates
• Discovery of a Molecular Collision Front in Interacting Galaxies NGC 4567/4568 with ALMA
• Gravitational Fragmentation in Galaxy Mergers: A Stability Criteria
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• Merger Criteria of Multiple Massive Black Holes and the Impact on the Host Galaxy
• High Velocity-dispersion Cold Gas in ULIRG Outflows. I: Direct Simulations
• Gas and star kinematics in cloud-cloud collisions
• A pair of UV nuclei or a compact star forming region near the active nucleus in Mrk~766?